#include <GL/glew.h>

#include "3DScene.hpp"

#include "../../libslic3r/libslic3r.h"
#include "../../libslic3r/ExtrusionEntity.hpp"
#include "../../libslic3r/ExtrusionEntityCollection.hpp"
#include "../../libslic3r/Geometry.hpp"
#include "../../libslic3r/GCode/PreviewData.hpp"
#include "../../libslic3r/Print.hpp"
#include "../../libslic3r/Slicing.hpp"
#include "GCode/Analyzer.hpp"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <utility>
#include <assert.h>

#include <boost/log/trivial.hpp>

#include <tbb/parallel_for.h>
#include <tbb/spin_mutex.h>

#include <wx/bitmap.h>
#include <wx/dcmemory.h>
#include <wx/image.h>
#include <wx/settings.h>

namespace Slic3r {

void GLIndexedVertexArray::load_mesh_flat_shading(const TriangleMesh &mesh)
{
    assert(triangle_indices.empty() && vertices_and_normals_interleaved_size == 0);
    assert(quad_indices.empty() && triangle_indices_size == 0);
    assert(vertices_and_normals_interleaved.size() % 6 == 0 && quad_indices_size == vertices_and_normals_interleaved.size());

    this->vertices_and_normals_interleaved.reserve(this->vertices_and_normals_interleaved.size() + 3 * 3 * 2 * mesh.facets_count());
    
    for (int i = 0; i < mesh.stl.stats.number_of_facets; ++ i) {
        const stl_facet &facet = mesh.stl.facet_start[i];
        for (int j = 0; j < 3; ++ j)
            this->push_geometry(facet.vertex[j].x, facet.vertex[j].y, facet.vertex[j].z, facet.normal.x, facet.normal.y, facet.normal.z);
    }
}

void GLIndexedVertexArray::finalize_geometry(bool use_VBOs)
{
    assert(this->vertices_and_normals_interleaved_VBO_id == 0);
    assert(this->triangle_indices_VBO_id == 0);
    assert(this->quad_indices_VBO_id == 0);

    this->setup_sizes();

    if (use_VBOs) {
        if (! empty()) {
            glGenBuffers(1, &this->vertices_and_normals_interleaved_VBO_id);
            glBindBuffer(GL_ARRAY_BUFFER, this->vertices_and_normals_interleaved_VBO_id);
            glBufferData(GL_ARRAY_BUFFER, this->vertices_and_normals_interleaved.size() * 4, this->vertices_and_normals_interleaved.data(), GL_STATIC_DRAW);
            glBindBuffer(GL_ARRAY_BUFFER, 0);
            this->vertices_and_normals_interleaved.clear();
        }
        if (! this->triangle_indices.empty()) {
            glGenBuffers(1, &this->triangle_indices_VBO_id);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->triangle_indices_VBO_id);
            glBufferData(GL_ELEMENT_ARRAY_BUFFER, this->triangle_indices.size() * 4, this->triangle_indices.data(), GL_STATIC_DRAW);
            this->triangle_indices.clear();
        }
        if (! this->quad_indices.empty()) {
            glGenBuffers(1, &this->quad_indices_VBO_id);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->quad_indices_VBO_id);
            glBufferData(GL_ELEMENT_ARRAY_BUFFER, this->quad_indices.size() * 4, this->quad_indices.data(), GL_STATIC_DRAW);
            this->quad_indices.clear();
        }
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    }
    this->shrink_to_fit();
}

void GLIndexedVertexArray::release_geometry()
{
    if (this->vertices_and_normals_interleaved_VBO_id)
        glDeleteBuffers(1, &this->vertices_and_normals_interleaved_VBO_id);
    if (this->triangle_indices_VBO_id)
        glDeleteBuffers(1, &this->triangle_indices_VBO_id);
    if (this->quad_indices_VBO_id)
        glDeleteBuffers(1, &this->quad_indices_VBO_id);
    this->clear();
    this->shrink_to_fit();
}

void GLIndexedVertexArray::render() const
{
    if (this->vertices_and_normals_interleaved_VBO_id) {
        glBindBuffer(GL_ARRAY_BUFFER, this->vertices_and_normals_interleaved_VBO_id);
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), (const void*)(3 * sizeof(float)));
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), nullptr);
    } else {
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), this->vertices_and_normals_interleaved.data() + 3);
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), this->vertices_and_normals_interleaved.data());
    }
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_NORMAL_ARRAY);

    if (this->indexed()) {
        if (this->vertices_and_normals_interleaved_VBO_id) {
            // Render using the Vertex Buffer Objects.
            if (this->triangle_indices_size > 0) {
                glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->triangle_indices_VBO_id);
                glDrawElements(GL_TRIANGLES, GLsizei(this->triangle_indices_size), GL_UNSIGNED_INT, nullptr);
            }
            if (this->quad_indices_size > 0) {
                glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->quad_indices_VBO_id);
                glDrawElements(GL_QUADS, GLsizei(this->quad_indices_size), GL_UNSIGNED_INT, nullptr);
            }
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
        } else {
            // Render in an immediate mode.
            if (! this->triangle_indices.empty())
                glDrawElements(GL_TRIANGLES, GLsizei(this->triangle_indices_size), GL_UNSIGNED_INT, this->triangle_indices.data());
            if (! this->quad_indices.empty())
                glDrawElements(GL_QUADS, GLsizei(this->quad_indices_size), GL_UNSIGNED_INT, this->quad_indices.data());
        }
    } else
        glDrawArrays(GL_TRIANGLES, 0, GLsizei(this->vertices_and_normals_interleaved_size / 6));

    if (this->vertices_and_normals_interleaved_VBO_id)
        glBindBuffer(GL_ARRAY_BUFFER, 0);
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
}

void GLIndexedVertexArray::render(
    const std::pair<size_t, size_t> &tverts_range,
    const std::pair<size_t, size_t> &qverts_range) const 
{
    assert(this->indexed());
    if (! this->indexed())
        return;

    if (this->vertices_and_normals_interleaved_VBO_id) {
        // Render using the Vertex Buffer Objects.
        glBindBuffer(GL_ARRAY_BUFFER, this->vertices_and_normals_interleaved_VBO_id);
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), (const void*)(3 * sizeof(float)));
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), nullptr);
        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_NORMAL_ARRAY);
        if (this->triangle_indices_size > 0) {
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->triangle_indices_VBO_id);
            glDrawElements(GL_TRIANGLES, GLsizei(std::min(this->triangle_indices_size, tverts_range.second - tverts_range.first)), GL_UNSIGNED_INT, (const void*)(tverts_range.first * 4));
        }
        if (this->quad_indices_size > 0) {
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->quad_indices_VBO_id);
            glDrawElements(GL_QUADS, GLsizei(std::min(this->quad_indices_size, qverts_range.second - qverts_range.first)), GL_UNSIGNED_INT, (const void*)(qverts_range.first * 4));
        }
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    } else {
        // Render in an immediate mode.
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), this->vertices_and_normals_interleaved.data() + 3);
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), this->vertices_and_normals_interleaved.data());
        glEnableClientState(GL_VERTEX_ARRAY);
        glEnableClientState(GL_NORMAL_ARRAY);
        if (! this->triangle_indices.empty())
            glDrawElements(GL_TRIANGLES, GLsizei(std::min(this->triangle_indices_size, tverts_range.second - tverts_range.first)), GL_UNSIGNED_INT, (const void*)(this->triangle_indices.data() + tverts_range.first));
        if (! this->quad_indices.empty())
            glDrawElements(GL_QUADS, GLsizei(std::min(this->quad_indices_size, qverts_range.second - qverts_range.first)), GL_UNSIGNED_INT, (const void*)(this->quad_indices.data() + qverts_range.first));
    }

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
}

void GLVolume::set_range(double min_z, double max_z)
{
    this->qverts_range.first  = 0;
    this->qverts_range.second = this->indexed_vertex_array.quad_indices_size;
    this->tverts_range.first  = 0;
    this->tverts_range.second = this->indexed_vertex_array.triangle_indices_size;
    if (! this->print_zs.empty()) {
        // The Z layer range is specified.
        // First test whether the Z span of this object is not out of (min_z, max_z) completely.
        if (this->print_zs.front() > max_z || this->print_zs.back() < min_z) {
            this->qverts_range.second = 0;
            this->tverts_range.second = 0;
        } else {
            // Then find the lowest layer to be displayed.
            size_t i = 0;
            for (; i < this->print_zs.size() && this->print_zs[i] < min_z; ++ i);
            if (i == this->print_zs.size()) {
                // This shall not happen.
                this->qverts_range.second = 0;
                this->tverts_range.second = 0;
            } else {
                // Remember start of the layer.
                this->qverts_range.first = this->offsets[i * 2];
                this->tverts_range.first = this->offsets[i * 2 + 1];
                // Some layers are above $min_z. Which?
                for (; i < this->print_zs.size() && this->print_zs[i] <= max_z; ++ i);
                if (i < this->print_zs.size()) {
                    this->qverts_range.second = this->offsets[i * 2];
                    this->tverts_range.second = this->offsets[i * 2 + 1];
                }
            }
        }
    }
}

void GLVolume::render() const
{
    if (!is_active)
        return;

    glCullFace(GL_BACK);
    glPushMatrix();
    glTranslated(this->origin.x, this->origin.y, this->origin.z);
    if (this->indexed_vertex_array.indexed())
        this->indexed_vertex_array.render(this->tverts_range, this->qverts_range);
    else
        this->indexed_vertex_array.render();
    glPopMatrix();
}

void GLVolume::generate_layer_height_texture(PrintObject *print_object, bool force)
{
    GLTexture *tex = this->layer_height_texture.get();
	if (tex == nullptr)
		// No layer_height_texture is assigned to this GLVolume, therefore the layer height texture cannot be filled.
		return;

	// Always try to update the layer height profile.
	bool update = print_object->update_layer_height_profile(print_object->model_object()->layer_height_profile) || force;
	// Update if the layer height profile was changed, or when the texture is not valid.
	if (! update && ! tex->data.empty() && tex->cells > 0)
        // Texture is valid, don't update.
        return; 

    if (tex->data.empty()) {
        tex->width  = 1024;
        tex->height = 1024;
        tex->levels = 2;
        tex->data.assign(tex->width * tex->height * 5, 0);
    }

    SlicingParameters slicing_params = print_object->slicing_parameters();
    bool level_of_detail_2nd_level = true;
    tex->cells = Slic3r::generate_layer_height_texture(
        slicing_params, 
        Slic3r::generate_object_layers(slicing_params, print_object->model_object()->layer_height_profile), 
        tex->data.data(), tex->height, tex->width, level_of_detail_2nd_level);
}

// 512x512 bitmaps are supported everywhere, but that may not be sufficent for super large print volumes.
#define LAYER_HEIGHT_TEXTURE_WIDTH  1024
#define LAYER_HEIGHT_TEXTURE_HEIGHT 1024

std::vector<int> GLVolumeCollection::load_object(
    const ModelObject       *model_object, 
    int                      obj_idx,
    const std::vector<int>  &instance_idxs,
    const std::string       &color_by,
    const std::string       &select_by,
    const std::string       &drag_by,
    bool                     use_VBOs)
{
    static float colors[4][4] = {
        { 1.0f, 1.0f, 0.0f, 1.f }, 
        { 1.0f, 0.5f, 0.5f, 1.f },
        { 0.5f, 1.0f, 0.5f, 1.f }, 
        { 0.5f, 0.5f, 1.0f, 1.f }
    };

    // Object will have a single common layer height texture for all volumes.
    std::shared_ptr<GLTexture> layer_height_texture = std::make_shared<GLTexture>();
    
    std::vector<int> volumes_idx;
    for (int volume_idx = 0; volume_idx < int(model_object->volumes.size()); ++ volume_idx) {
        const ModelVolume *model_volume = model_object->volumes[volume_idx];
        for (int instance_idx : instance_idxs) {
            const ModelInstance *instance = model_object->instances[instance_idx];
            TriangleMesh mesh = model_volume->mesh;
            instance->transform_mesh(&mesh);
            volumes_idx.push_back(int(this->volumes.size()));
            float color[4];
            memcpy(color, colors[((color_by == "volume") ? volume_idx : obj_idx) % 4], sizeof(float) * 3);
            color[3] = model_volume->modifier ? 0.5f : 1.f;
            this->volumes.emplace_back(new GLVolume(color));
            GLVolume &v = *this->volumes.back();
			v.indexed_vertex_array.load_mesh_flat_shading(mesh);
            // finalize_geometry() clears the vertex arrays, therefore the bounding box has to be computed before finalize_geometry().
            v.bounding_box = v.indexed_vertex_array.bounding_box();
            v.indexed_vertex_array.finalize_geometry(use_VBOs);
            v.composite_id = obj_idx * 1000000 + volume_idx * 1000 + instance_idx;
            if (select_by == "object")
                v.select_group_id = obj_idx * 1000000;
            else if (select_by == "volume")
                v.select_group_id = obj_idx * 1000000 + volume_idx * 1000;
            else if (select_by == "instance")
                v.select_group_id = v.composite_id;
            if (drag_by == "object")
                v.drag_group_id = obj_idx * 1000;
            else if (drag_by == "instance")
                v.drag_group_id = obj_idx * 1000 + instance_idx;
            if (! model_volume->modifier)
                v.layer_height_texture = layer_height_texture;
        }
    }
    
    return volumes_idx; 
}


int GLVolumeCollection::load_wipe_tower_preview(
    int obj_idx, float pos_x, float pos_y, float width, float depth, float height, float rotation_angle, bool use_VBOs)
{
    float color[4] = { 1.0f, 1.0f, 0.0f, 0.5f };
    this->volumes.emplace_back(new GLVolume(color));
    GLVolume &v = *this->volumes.back();
    auto mesh = make_cube(width, depth, height);    
    mesh.translate(-width/2.f,-depth/2.f,0.f);    
    Point origin_of_rotation(0.f,0.f);
    mesh.rotate(rotation_angle,&origin_of_rotation);

	v.indexed_vertex_array.load_mesh_flat_shading(mesh);
	v.origin = Pointf3(pos_x, pos_y, 0.);
    // finalize_geometry() clears the vertex arrays, therefore the bounding box has to be computed before finalize_geometry().
    v.bounding_box = v.indexed_vertex_array.bounding_box();
	v.indexed_vertex_array.finalize_geometry(use_VBOs);
    v.composite_id = obj_idx * 1000000;
    v.select_group_id = obj_idx * 1000000;
    v.drag_group_id = obj_idx * 1000;
    return int(this->volumes.size() - 1);
}

void GLVolumeCollection::render_VBOs() const
{
//    glEnable(GL_BLEND);
//    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glCullFace(GL_BACK);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_NORMAL_ARRAY);
 
    GLint current_program_id;
    glGetIntegerv(GL_CURRENT_PROGRAM, &current_program_id);
    GLint color_id = (current_program_id > 0) ? glGetUniformLocation(current_program_id, "uniform_color") : -1;

    for (GLVolume *volume : this->volumes) {
        if (!volume->is_active)
            continue;

        if (!volume->indexed_vertex_array.vertices_and_normals_interleaved_VBO_id)
            continue;
        GLsizei n_triangles = GLsizei(std::min(volume->indexed_vertex_array.triangle_indices_size, volume->tverts_range.second - volume->tverts_range.first));
        GLsizei n_quads     = GLsizei(std::min(volume->indexed_vertex_array.quad_indices_size,     volume->qverts_range.second - volume->qverts_range.first));
        if (n_triangles + n_quads == 0)
        {
            if (_render_interleaved_only_volumes.enabled)
            {
                ::glDisableClientState(GL_VERTEX_ARRAY);
                ::glDisableClientState(GL_NORMAL_ARRAY);
                ::glEnable(GL_BLEND);
                ::glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

                if (color_id >= 0)
                {
                    float color[4];
                    ::memcpy((void*)color, (const void*)volume->color, 3 * sizeof(float));
                    color[3] = _render_interleaved_only_volumes.alpha;
                    ::glUniform4fv(color_id, 1, (const GLfloat*)color);
                }
                else
                    ::glColor4f(volume->color[0], volume->color[1], volume->color[2], _render_interleaved_only_volumes.alpha);

                volume->render();

                ::glDisable(GL_BLEND);
                ::glEnableClientState(GL_VERTEX_ARRAY);
                ::glEnableClientState(GL_NORMAL_ARRAY);
            }
            continue;
        }
        if (color_id >= 0)
            glUniform4fv(color_id, 1, (const GLfloat*)volume->color);
        else
            glColor4f(volume->color[0], volume->color[1], volume->color[2], volume->color[3]);            
        glBindBuffer(GL_ARRAY_BUFFER, volume->indexed_vertex_array.vertices_and_normals_interleaved_VBO_id);
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), (const void*)(3 * sizeof(float)));
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), nullptr);
        if (n_triangles > 0) {
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, volume->indexed_vertex_array.triangle_indices_VBO_id);
            glDrawElements(GL_TRIANGLES, n_triangles, GL_UNSIGNED_INT, (const void*)(volume->tverts_range.first * 4));
        }
        if (n_quads > 0) {
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, volume->indexed_vertex_array.quad_indices_VBO_id);
            glDrawElements(GL_QUADS, n_quads, GL_UNSIGNED_INT, (const void*)(volume->qverts_range.first * 4));
        }
    }

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
//    glDisable(GL_BLEND);
}

void GLVolumeCollection::render_legacy() const
{
    glCullFace(GL_BACK);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_NORMAL_ARRAY);
 
    for (GLVolume *volume : this->volumes) {
        assert(! volume->indexed_vertex_array.vertices_and_normals_interleaved_VBO_id);
        if (!volume->is_active)
            continue;

        GLsizei n_triangles = GLsizei(std::min(volume->indexed_vertex_array.triangle_indices_size, volume->tverts_range.second - volume->tverts_range.first));
        GLsizei n_quads     = GLsizei(std::min(volume->indexed_vertex_array.quad_indices_size,     volume->qverts_range.second - volume->qverts_range.first));
        if (n_triangles + n_quads == 0)
        {
            if (_render_interleaved_only_volumes.enabled)
            {
                ::glDisableClientState(GL_VERTEX_ARRAY);
                ::glDisableClientState(GL_NORMAL_ARRAY);
                ::glEnable(GL_BLEND);
                ::glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

                ::glColor4f(volume->color[0], volume->color[1], volume->color[2], _render_interleaved_only_volumes.alpha);
                volume->render();

                ::glDisable(GL_BLEND);
                ::glEnableClientState(GL_VERTEX_ARRAY);
                ::glEnableClientState(GL_NORMAL_ARRAY);
            }
            continue;
        }
        glColor4f(volume->color[0], volume->color[1], volume->color[2], volume->color[3]);
        glVertexPointer(3, GL_FLOAT, 6 * sizeof(float), volume->indexed_vertex_array.vertices_and_normals_interleaved.data() + 3);
        glNormalPointer(GL_FLOAT, 6 * sizeof(float), volume->indexed_vertex_array.vertices_and_normals_interleaved.data());
        bool has_offset = volume->origin.x != 0 || volume->origin.y != 0 || volume->origin.z != 0;
        if (has_offset) {
            glPushMatrix();
            glTranslated(volume->origin.x, volume->origin.y, volume->origin.z);
        }
        if (n_triangles > 0)
            glDrawElements(GL_TRIANGLES, n_triangles, GL_UNSIGNED_INT, volume->indexed_vertex_array.triangle_indices.data() + volume->tverts_range.first);
        if (n_quads > 0)
            glDrawElements(GL_QUADS, n_quads, GL_UNSIGNED_INT, volume->indexed_vertex_array.quad_indices.data() + volume->qverts_range.first);
        if (has_offset)
            glPushMatrix();
    }

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
}

// caller is responsible for supplying NO lines with zero length
static void thick_lines_to_indexed_vertex_array(
    const Lines                 &lines, 
    const std::vector<double>   &widths,
    const std::vector<double>   &heights, 
    bool                         closed,
    double                       top_z,
    GLIndexedVertexArray        &volume)
{
    assert(! lines.empty());
    if (lines.empty())
        return;

#define LEFT    0
#define RIGHT   1
#define TOP     2
#define BOTTOM  3

    Line prev_line;
    // right, left, top, bottom
    int     idx_prev[4]      = { -1, -1, -1, -1 };
    double  bottom_z_prev    = 0.;
    Pointf  b1_prev;
    Pointf  b2_prev;
    Vectorf v_prev;
    int     idx_initial[4]   = { -1, -1, -1, -1 };
    double  width_initial    = 0.;

    // loop once more in case of closed loops
    size_t lines_end = closed ? (lines.size() + 1) : lines.size();
    for (size_t ii = 0; ii < lines_end; ++ ii) {
        size_t i = (ii == lines.size()) ? 0 : ii;
        const Line &line = lines[i];
        double len = unscale(line.length());
        double bottom_z = top_z - heights[i];
        double middle_z = (top_z + bottom_z) / 2.;
        double width = widths[i];
        
        Vectorf v = Vectorf::new_unscale(line.vector());
        v.scale(1. / len);
        
        Pointf a = Pointf::new_unscale(line.a);
        Pointf b = Pointf::new_unscale(line.b);
        Pointf a1 = a;
        Pointf a2 = a;
        Pointf b1 = b;
        Pointf b2 = b;
        {
            double dist = width / 2.;  // scaled
            a1.translate(+dist*v.y, -dist*v.x);
            a2.translate(-dist*v.y, +dist*v.x);
            b1.translate(+dist*v.y, -dist*v.x);
            b2.translate(-dist*v.y, +dist*v.x);
        }

        // calculate new XY normals
        Vector n = line.normal();
        Vectorf3 xy_right_normal = Vectorf3::new_unscale(n.x, n.y, 0);
        xy_right_normal.scale(1.f / len);

        int idx_a[4];
        int idx_b[4];
        int idx_last = int(volume.vertices_and_normals_interleaved.size() / 6);

        bool bottom_z_different = bottom_z_prev != bottom_z;
        bottom_z_prev = bottom_z;

        // Share top / bottom vertices if possible.
        if (ii == 0) {
            idx_a[TOP] = idx_last ++;
            volume.push_geometry(a.x, a.y, top_z   , 0., 0.,  1.); 
        } else {
            idx_a[TOP] = idx_prev[TOP];
        }
        if (ii == 0 || bottom_z_different) {
            // Start of the 1st line segment or a change of the layer thickness while maintaining the print_z.
            idx_a[BOTTOM] = idx_last ++;
            volume.push_geometry(a.x, a.y, bottom_z, 0., 0., -1.);
            idx_a[LEFT ] = idx_last ++;
            volume.push_geometry(a2.x, a2.y, middle_z, -xy_right_normal.x, -xy_right_normal.y, -xy_right_normal.z);
            idx_a[RIGHT] = idx_last ++;
            volume.push_geometry(a1.x, a1.y, middle_z, xy_right_normal.x, xy_right_normal.y, xy_right_normal.z);
        } else {
            idx_a[BOTTOM] = idx_prev[BOTTOM];
        }

        if (ii == 0) {
            // Start of the 1st line segment.
            width_initial    = width;
            memcpy(idx_initial, idx_a, sizeof(int) * 4);
        } else {
            // Continuing a previous segment.
            // Share left / right vertices if possible.
			double v_dot    = dot(v_prev, v);
            bool   sharp    = v_dot < 0.707; // sin(45 degrees)
            if (sharp) {
                // Allocate new left / right points for the start of this segment as these points will receive their own normals to indicate a sharp turn.
                idx_a[RIGHT] = idx_last ++;
                volume.push_geometry(a1.x, a1.y, middle_z, xy_right_normal.x, xy_right_normal.y, xy_right_normal.z);
                idx_a[LEFT ] = idx_last ++;
                volume.push_geometry(a2.x, a2.y, middle_z, -xy_right_normal.x, -xy_right_normal.y, -xy_right_normal.z);
            }
            if (v_dot > 0.9) {
                // The two successive segments are nearly collinear.
                idx_a[LEFT ] = idx_prev[LEFT];
                idx_a[RIGHT] = idx_prev[RIGHT];
            } else if (! sharp) {
                // Create a sharp corner with an overshot and average the left / right normals.
                // At the crease angle of 45 degrees, the overshot at the corner will be less than (1-1/cos(PI/8)) = 8.2% over an arc.
                Pointf intersection;
                Geometry::ray_ray_intersection(b1_prev, v_prev, a1, v, intersection);
                a1 = intersection;
                a2 = 2. * a - intersection;
                assert(length(a1.vector_to(a)) < width);
                assert(length(a2.vector_to(a)) < width);
                float *n_left_prev  = volume.vertices_and_normals_interleaved.data() + idx_prev[LEFT ] * 6;
                float *p_left_prev  = n_left_prev  + 3;
                float *n_right_prev = volume.vertices_and_normals_interleaved.data() + idx_prev[RIGHT] * 6;
                float *p_right_prev = n_right_prev + 3;
                p_left_prev [0] = float(a2.x);
                p_left_prev [1] = float(a2.y);
                p_right_prev[0] = float(a1.x);
                p_right_prev[1] = float(a1.y);
                xy_right_normal.x += n_right_prev[0];
                xy_right_normal.y += n_right_prev[1];
                xy_right_normal.scale(1. / length(xy_right_normal));
                n_left_prev [0] = float(-xy_right_normal.x);
                n_left_prev [1] = float(-xy_right_normal.y);
                n_right_prev[0] = float( xy_right_normal.x);
                n_right_prev[1] = float( xy_right_normal.y);
                idx_a[LEFT ] = idx_prev[LEFT ];
                idx_a[RIGHT] = idx_prev[RIGHT];
            } else if (cross(v_prev, v) > 0.) {
                // Right turn. Fill in the right turn wedge.
                volume.push_triangle(idx_prev[RIGHT], idx_a   [RIGHT],  idx_prev[TOP]   );
                volume.push_triangle(idx_prev[RIGHT], idx_prev[BOTTOM], idx_a   [RIGHT] );
            } else {
                // Left turn. Fill in the left turn wedge.
                volume.push_triangle(idx_prev[LEFT],  idx_prev[TOP],    idx_a   [LEFT]  );
                volume.push_triangle(idx_prev[LEFT],  idx_a   [LEFT],   idx_prev[BOTTOM]);
            }
            if (ii == lines.size()) {
                if (! sharp) {
                    // Closing a loop with smooth transition. Unify the closing left / right vertices.
                    memcpy(volume.vertices_and_normals_interleaved.data() + idx_initial[LEFT ] * 6, volume.vertices_and_normals_interleaved.data() + idx_prev[LEFT ] * 6, sizeof(float) * 6);
                    memcpy(volume.vertices_and_normals_interleaved.data() + idx_initial[RIGHT] * 6, volume.vertices_and_normals_interleaved.data() + idx_prev[RIGHT] * 6, sizeof(float) * 6);
                    volume.vertices_and_normals_interleaved.erase(volume.vertices_and_normals_interleaved.end() - 12, volume.vertices_and_normals_interleaved.end());
                    // Replace the left / right vertex indices to point to the start of the loop. 
                    for (size_t u = volume.quad_indices.size() - 16; u < volume.quad_indices.size(); ++ u) {
                        if (volume.quad_indices[u] == idx_prev[LEFT])
                            volume.quad_indices[u] = idx_initial[LEFT];
                        else if (volume.quad_indices[u] == idx_prev[RIGHT])
                            volume.quad_indices[u] = idx_initial[RIGHT];
                    }
                }
                // This is the last iteration, only required to solve the transition.
                break;
            }
        }

        // Only new allocate top / bottom vertices, if not closing a loop.
        if (closed && ii + 1 == lines.size()) {
            idx_b[TOP] = idx_initial[TOP];
        } else {
            idx_b[TOP] = idx_last ++;
            volume.push_geometry(b.x, b.y, top_z   , 0., 0.,  1.);
        }
        if (closed && ii + 1 == lines.size() && width == width_initial) {
            idx_b[BOTTOM] = idx_initial[BOTTOM];
        } else {
            idx_b[BOTTOM] = idx_last ++;
            volume.push_geometry(b.x, b.y, bottom_z, 0., 0., -1.);
        }
        // Generate new vertices for the end of this line segment.
        idx_b[LEFT  ] = idx_last ++;
        volume.push_geometry(b2.x, b2.y, middle_z, -xy_right_normal.x, -xy_right_normal.y, -xy_right_normal.z);
        idx_b[RIGHT ] = idx_last ++;
        volume.push_geometry(b1.x, b1.y, middle_z, xy_right_normal.x, xy_right_normal.y, xy_right_normal.z);

        prev_line = line;
        memcpy(idx_prev, idx_b, 4 * sizeof(int));
        bottom_z_prev = bottom_z;
        b1_prev = b1;
        b2_prev = b2;
        v_prev  = v;

        if (! closed) {
            // Terminate open paths with caps.
            if (i == 0)
                volume.push_quad(idx_a[BOTTOM], idx_a[RIGHT], idx_a[TOP], idx_a[LEFT]);
            // We don't use 'else' because both cases are true if we have only one line.
            if (i + 1 == lines.size())
                volume.push_quad(idx_b[BOTTOM], idx_b[LEFT], idx_b[TOP], idx_b[RIGHT]);
        }
        
        // Add quads for a straight hollow tube-like segment.
        // bottom-right face
        volume.push_quad(idx_a[BOTTOM], idx_b[BOTTOM], idx_b[RIGHT], idx_a[RIGHT]);
        // top-right face
        volume.push_quad(idx_a[RIGHT], idx_b[RIGHT], idx_b[TOP], idx_a[TOP]);
        // top-left face
        volume.push_quad(idx_a[TOP], idx_b[TOP], idx_b[LEFT], idx_a[LEFT]);
        // bottom-left face
        volume.push_quad(idx_a[LEFT], idx_b[LEFT], idx_b[BOTTOM], idx_a[BOTTOM]);
    }

#undef LEFT
#undef RIGHT
#undef TOP
#undef BOTTOM
}

// caller is responsible for supplying NO lines with zero length
static void thick_lines_to_indexed_vertex_array(const Lines3& lines,
    const std::vector<double>& widths,
    const std::vector<double>& heights,
    bool closed,
    GLIndexedVertexArray& volume)
{
    assert(!lines.empty());
    if (lines.empty())
        return;

#define LEFT    0
#define RIGHT   1
#define TOP     2
#define BOTTOM  3

    // left, right, top, bottom
    int      idx_initial[4] = { -1, -1, -1, -1 };
    int      idx_prev[4] = { -1, -1, -1, -1 };
    double   z_prev = 0.0;
    Vectorf3 n_right_prev;
    Vectorf3 n_top_prev;
    Vectorf3 unit_v_prev;
    double   width_initial = 0.0;

    // new vertices around the line endpoints
    // left, right, top, bottom
    Pointf3 a[4];
    Pointf3 b[4];

    // loop once more in case of closed loops
    size_t lines_end = closed ? (lines.size() + 1) : lines.size();
    for (size_t ii = 0; ii < lines_end; ++ii)
    {
        size_t i = (ii == lines.size()) ? 0 : ii;

        const Line3& line = lines[i];
        double height = heights[i];
        double width = widths[i];

        Vectorf3 unit_v = normalize(Vectorf3::new_unscale(line.vector()));

        Vectorf3 n_top;
        Vectorf3 n_right;
        Vectorf3 unit_positive_z(0.0, 0.0, 1.0);

        if ((line.a.x == line.b.x) && (line.a.y == line.b.y))
        {
            // vertical segment
            n_right = (line.a.z < line.b.z) ? Vectorf3(-1.0, 0.0, 0.0) : Vectorf3(1.0, 0.0, 0.0);
            n_top = Vectorf3(0.0, 1.0, 0.0);
        }
        else
        {
            // generic segment
            n_right = normalize(cross(unit_v, unit_positive_z));
            n_top = normalize(cross(n_right, unit_v));
        }

        Vectorf3 rl_displacement = 0.5 * width * n_right;
        Vectorf3 tb_displacement = 0.5 * height * n_top;
        Pointf3 l_a = Pointf3::new_unscale(line.a);
        Pointf3 l_b = Pointf3::new_unscale(line.b);

        a[RIGHT] = l_a + rl_displacement;
        a[LEFT] = l_a - rl_displacement;
        a[TOP] = l_a + tb_displacement;
        a[BOTTOM] = l_a - tb_displacement;
        b[RIGHT] = l_b + rl_displacement;
        b[LEFT] = l_b - rl_displacement;
        b[TOP] = l_b + tb_displacement;
        b[BOTTOM] = l_b - tb_displacement;

        Vectorf3 n_bottom = -n_top;
        Vectorf3 n_left = -n_right;

        int idx_a[4];
        int idx_b[4];
        int idx_last = int(volume.vertices_and_normals_interleaved.size() / 6);

        bool z_different = (z_prev != l_a.z);
        z_prev = l_b.z;

        // Share top / bottom vertices if possible.
        if (ii == 0)
        {
            idx_a[TOP] = idx_last++;
            volume.push_geometry(a[TOP], n_top);
        }
        else
            idx_a[TOP] = idx_prev[TOP];

        if ((ii == 0) || z_different)
        {
            // Start of the 1st line segment or a change of the layer thickness while maintaining the print_z.
            idx_a[BOTTOM] = idx_last++;
            volume.push_geometry(a[BOTTOM], n_bottom);
            idx_a[LEFT] = idx_last++;
            volume.push_geometry(a[LEFT], n_left);
            idx_a[RIGHT] = idx_last++;
            volume.push_geometry(a[RIGHT], n_right);
        }
        else
            idx_a[BOTTOM] = idx_prev[BOTTOM];

        if (ii == 0)
        {
            // Start of the 1st line segment.
            width_initial = width;
            ::memcpy(idx_initial, idx_a, sizeof(int) * 4);
        }
        else
        {
            // Continuing a previous segment.
            // Share left / right vertices if possible.
            double v_dot = dot(unit_v_prev, unit_v);
            bool is_sharp = v_dot < 0.707; // sin(45 degrees)
            bool is_right_turn = dot(n_top_prev, cross(unit_v_prev, unit_v)) > 0.0;

            if (is_sharp)
            {
                // Allocate new left / right points for the start of this segment as these points will receive their own normals to indicate a sharp turn.
                idx_a[RIGHT] = idx_last++;
                volume.push_geometry(a[RIGHT], n_right);
                idx_a[LEFT] = idx_last++;
                volume.push_geometry(a[LEFT], n_left);
            }

            if (v_dot > 0.9)
            {
                // The two successive segments are nearly collinear.
                idx_a[LEFT] = idx_prev[LEFT];
                idx_a[RIGHT] = idx_prev[RIGHT];
            }
            else if (!is_sharp)
            {
                // Create a sharp corner with an overshot and average the left / right normals.
                // At the crease angle of 45 degrees, the overshot at the corner will be less than (1-1/cos(PI/8)) = 8.2% over an arc.

                // averages normals
                Vectorf3 average_n_right = normalize(0.5 * (n_right + n_right_prev));
                Vectorf3 average_n_left = -average_n_right;
                Vectorf3 average_rl_displacement = 0.5 * width * average_n_right;

                // updates vertices around a
                a[RIGHT] = l_a + average_rl_displacement;
                a[LEFT] = l_a - average_rl_displacement;

                // updates previous line normals
                float* normal_left_prev = volume.vertices_and_normals_interleaved.data() + idx_prev[LEFT] * 6;
                normal_left_prev[0] = float(average_n_left.x);
                normal_left_prev[1] = float(average_n_left.y);
                normal_left_prev[2] = float(average_n_left.z);

                float* normal_right_prev = volume.vertices_and_normals_interleaved.data() + idx_prev[RIGHT] * 6;
                normal_right_prev[0] = float(average_n_right.x);
                normal_right_prev[1] = float(average_n_right.y);
                normal_right_prev[2] = float(average_n_right.z);

                // updates previous line's vertices around b
                float* b_left_prev = normal_left_prev + 3;
                b_left_prev[0] = float(a[LEFT].x);
                b_left_prev[1] = float(a[LEFT].y);
                b_left_prev[2] = float(a[LEFT].z);

                float* b_right_prev = normal_right_prev + 3;
                b_right_prev[0] = float(a[RIGHT].x);
                b_right_prev[1] = float(a[RIGHT].y);
                b_right_prev[2] = float(a[RIGHT].z);

                idx_a[LEFT] = idx_prev[LEFT];
                idx_a[RIGHT] = idx_prev[RIGHT];
            }
            else if (is_right_turn)
            {
                // Right turn. Fill in the right turn wedge.
                volume.push_triangle(idx_prev[RIGHT], idx_a[RIGHT], idx_prev[TOP]);
                volume.push_triangle(idx_prev[RIGHT], idx_prev[BOTTOM], idx_a[RIGHT]);
            }
            else
            {
                // Left turn. Fill in the left turn wedge.
                volume.push_triangle(idx_prev[LEFT], idx_prev[TOP], idx_a[LEFT]);
                volume.push_triangle(idx_prev[LEFT], idx_a[LEFT], idx_prev[BOTTOM]);
            }

            if (ii == lines.size())
            {
                if (!is_sharp)
                {
                    // Closing a loop with smooth transition. Unify the closing left / right vertices.
                    ::memcpy(volume.vertices_and_normals_interleaved.data() + idx_initial[LEFT] * 6, volume.vertices_and_normals_interleaved.data() + idx_prev[LEFT] * 6, sizeof(float) * 6);
                    ::memcpy(volume.vertices_and_normals_interleaved.data() + idx_initial[RIGHT] * 6, volume.vertices_and_normals_interleaved.data() + idx_prev[RIGHT] * 6, sizeof(float) * 6);
                    volume.vertices_and_normals_interleaved.erase(volume.vertices_and_normals_interleaved.end() - 12, volume.vertices_and_normals_interleaved.end());
                    // Replace the left / right vertex indices to point to the start of the loop. 
                    for (size_t u = volume.quad_indices.size() - 16; u < volume.quad_indices.size(); ++u)
                    {
                        if (volume.quad_indices[u] == idx_prev[LEFT])
                            volume.quad_indices[u] = idx_initial[LEFT];
                        else if (volume.quad_indices[u] == idx_prev[RIGHT])
                            volume.quad_indices[u] = idx_initial[RIGHT];
                    }
                }

                // This is the last iteration, only required to solve the transition.
                break;
            }
        }

        // Only new allocate top / bottom vertices, if not closing a loop.
        if (closed && (ii + 1 == lines.size()))
            idx_b[TOP] = idx_initial[TOP];
        else
        {
            idx_b[TOP] = idx_last++;
            volume.push_geometry(b[TOP], n_top);
        }

        if (closed && (ii + 1 == lines.size()) && (width == width_initial))
            idx_b[BOTTOM] = idx_initial[BOTTOM];
        else
        {
            idx_b[BOTTOM] = idx_last++;
            volume.push_geometry(b[BOTTOM], n_bottom);
        }

        // Generate new vertices for the end of this line segment.
        idx_b[LEFT] = idx_last++;
        volume.push_geometry(b[LEFT], n_left);
        idx_b[RIGHT] = idx_last++;
        volume.push_geometry(b[RIGHT], n_right);

        ::memcpy(idx_prev, idx_b, 4 * sizeof(int));
        n_right_prev = n_right;
        n_top_prev = n_top;
        unit_v_prev = unit_v;

        if (!closed)
        {
            // Terminate open paths with caps.
            if (i == 0)
                volume.push_quad(idx_a[BOTTOM], idx_a[RIGHT], idx_a[TOP], idx_a[LEFT]);

            // We don't use 'else' because both cases are true if we have only one line.
            if (i + 1 == lines.size())
                volume.push_quad(idx_b[BOTTOM], idx_b[LEFT], idx_b[TOP], idx_b[RIGHT]);
        }

        // Add quads for a straight hollow tube-like segment.
        // bottom-right face
        volume.push_quad(idx_a[BOTTOM], idx_b[BOTTOM], idx_b[RIGHT], idx_a[RIGHT]);
        // top-right face
        volume.push_quad(idx_a[RIGHT], idx_b[RIGHT], idx_b[TOP], idx_a[TOP]);
        // top-left face
        volume.push_quad(idx_a[TOP], idx_b[TOP], idx_b[LEFT], idx_a[LEFT]);
        // bottom-left face
        volume.push_quad(idx_a[LEFT], idx_b[LEFT], idx_b[BOTTOM], idx_a[BOTTOM]);
    }

#undef LEFT
#undef RIGHT
#undef TOP
#undef BOTTOM
}

static void point_to_indexed_vertex_array(const Point3& point,
    double width,
    double height,
    GLIndexedVertexArray& volume)
{
    // builds a double piramid, with vertices on the local axes, around the point

    Pointf3 center = Pointf3::new_unscale(point);

    double scale_factor = 1.0;
    double w = scale_factor * width;
    double h = scale_factor * height;

    // new vertices ids
    int idx_last = int(volume.vertices_and_normals_interleaved.size() / 6);
    int idxs[6];
    for (int i = 0; i < 6; ++i)
    {
        idxs[i] = idx_last + i;
    }

    Vectorf3 displacement_x(w, 0.0, 0.0);
    Vectorf3 displacement_y(0.0, w, 0.0);
    Vectorf3 displacement_z(0.0, 0.0, h);

    Vectorf3 unit_x(1.0, 0.0, 0.0);
    Vectorf3 unit_y(0.0, 1.0, 0.0);
    Vectorf3 unit_z(0.0, 0.0, 1.0);

    // vertices
    volume.push_geometry(center - displacement_x, -unit_x); // idxs[0]
    volume.push_geometry(center + displacement_x, unit_x);  // idxs[1]
    volume.push_geometry(center - displacement_y, -unit_y); // idxs[2]
    volume.push_geometry(center + displacement_y, unit_y);  // idxs[3]
    volume.push_geometry(center - displacement_z, -unit_z); // idxs[4]
    volume.push_geometry(center + displacement_z, unit_z);  // idxs[5]

    // top piramid faces
    volume.push_triangle(idxs[0], idxs[2], idxs[5]);
    volume.push_triangle(idxs[2], idxs[1], idxs[5]);
    volume.push_triangle(idxs[1], idxs[3], idxs[5]);
    volume.push_triangle(idxs[3], idxs[0], idxs[5]);

    // bottom piramid faces
    volume.push_triangle(idxs[2], idxs[0], idxs[4]);
    volume.push_triangle(idxs[1], idxs[2], idxs[4]);
    volume.push_triangle(idxs[3], idxs[1], idxs[4]);
    volume.push_triangle(idxs[0], idxs[3], idxs[4]);
}

static void thick_lines_to_verts(
    const Lines                 &lines, 
    const std::vector<double>   &widths,
    const std::vector<double>   &heights, 
    bool                         closed,
    double                       top_z,
    GLVolume                    &volume)
{
    thick_lines_to_indexed_vertex_array(lines, widths, heights, closed, top_z, volume.indexed_vertex_array);
}

static void thick_lines_to_verts(const Lines3& lines,
    const std::vector<double>& widths,
    const std::vector<double>& heights,
    bool closed,
    GLVolume& volume)
{
    thick_lines_to_indexed_vertex_array(lines, widths, heights, closed, volume.indexed_vertex_array);
}

static void thick_point_to_verts(const Point3& point,
    double width,
    double height,
    GLVolume& volume)
{
    point_to_indexed_vertex_array(point, width, height, volume.indexed_vertex_array);
}

// Fill in the qverts and tverts with quads and triangles for the extrusion_path.
static inline void extrusionentity_to_verts(const ExtrusionPath &extrusion_path, float print_z, GLVolume &volume)
{
    Lines               lines = extrusion_path.polyline.lines();
    std::vector<double> widths(lines.size(), extrusion_path.width);
    std::vector<double> heights(lines.size(), extrusion_path.height);
    thick_lines_to_verts(lines, widths, heights, false, print_z, volume);
}

// Fill in the qverts and tverts with quads and triangles for the extrusion_path.
static inline void extrusionentity_to_verts(const ExtrusionPath &extrusion_path, float print_z, const Point &copy, GLVolume &volume)
{
    Polyline            polyline = extrusion_path.polyline;
    polyline.remove_duplicate_points();
    polyline.translate(copy);
    Lines               lines = polyline.lines();
    std::vector<double> widths(lines.size(), extrusion_path.width);
    std::vector<double> heights(lines.size(), extrusion_path.height);
    thick_lines_to_verts(lines, widths, heights, false, print_z, volume);
}

// Fill in the qverts and tverts with quads and triangles for the extrusion_loop.
static inline void extrusionentity_to_verts(const ExtrusionLoop &extrusion_loop, float print_z, const Point &copy, GLVolume &volume)
{
    Lines               lines;
    std::vector<double> widths;
    std::vector<double> heights;
    for (const ExtrusionPath &extrusion_path : extrusion_loop.paths) {
        Polyline            polyline = extrusion_path.polyline;
        polyline.remove_duplicate_points();
        polyline.translate(copy);
        Lines lines_this = polyline.lines();
        append(lines, lines_this);
        widths.insert(widths.end(), lines_this.size(), extrusion_path.width);
        heights.insert(heights.end(), lines_this.size(), extrusion_path.height);
    }
    thick_lines_to_verts(lines, widths, heights, true, print_z, volume);
}

// Fill in the qverts and tverts with quads and triangles for the extrusion_multi_path.
static inline void extrusionentity_to_verts(const ExtrusionMultiPath &extrusion_multi_path, float print_z, const Point &copy, GLVolume &volume)
{
    Lines               lines;
    std::vector<double> widths;
    std::vector<double> heights;
    for (const ExtrusionPath &extrusion_path : extrusion_multi_path.paths) {
        Polyline            polyline = extrusion_path.polyline;
        polyline.remove_duplicate_points();
        polyline.translate(copy);
        Lines lines_this = polyline.lines();
        append(lines, lines_this);
        widths.insert(widths.end(), lines_this.size(), extrusion_path.width);
        heights.insert(heights.end(), lines_this.size(), extrusion_path.height);
    }
    thick_lines_to_verts(lines, widths, heights, false, print_z, volume);
}

static void extrusionentity_to_verts(const ExtrusionEntity *extrusion_entity, float print_z, const Point &copy, GLVolume &volume);

static inline void extrusionentity_to_verts(const ExtrusionEntityCollection &extrusion_entity_collection, float print_z, const Point &copy, GLVolume &volume)
{
    for (const ExtrusionEntity *extrusion_entity : extrusion_entity_collection.entities)
        extrusionentity_to_verts(extrusion_entity, print_z, copy, volume);
}

static void extrusionentity_to_verts(const ExtrusionEntity *extrusion_entity, float print_z, const Point &copy, GLVolume &volume)
{
    if (extrusion_entity != nullptr) {
        auto *extrusion_path = dynamic_cast<const ExtrusionPath*>(extrusion_entity);
        if (extrusion_path != nullptr)
            extrusionentity_to_verts(*extrusion_path, print_z, copy, volume);
        else {
            auto *extrusion_loop = dynamic_cast<const ExtrusionLoop*>(extrusion_entity);
            if (extrusion_loop != nullptr)
                extrusionentity_to_verts(*extrusion_loop, print_z, copy, volume);
            else {
                auto *extrusion_multi_path = dynamic_cast<const ExtrusionMultiPath*>(extrusion_entity);
                if (extrusion_multi_path != nullptr)
                    extrusionentity_to_verts(*extrusion_multi_path, print_z, copy, volume);
                else {
                    auto *extrusion_entity_collection = dynamic_cast<const ExtrusionEntityCollection*>(extrusion_entity);
                    if (extrusion_entity_collection != nullptr)
                        extrusionentity_to_verts(*extrusion_entity_collection, print_z, copy, volume);
                    else {
                        CONFESS("Unexpected extrusion_entity type in to_verts()");
                    }
                }
            }
        }
    }
}

static void polyline3_to_verts(const Polyline3& polyline, double width, double height, GLVolume& volume)
{
    Lines3 lines = polyline.lines();
    std::vector<double> widths(lines.size(), width);
    std::vector<double> heights(lines.size(), height);
    thick_lines_to_verts(lines, widths, heights, false, volume);
}

static void point3_to_verts(const Point3& point, double width, double height, GLVolume& volume)
{
    thick_point_to_verts(point, width, height, volume);
}

_3DScene::GCodePreviewVolumeIndex _3DScene::s_gcode_preview_volume_index;
_3DScene::LegendTexture _3DScene::s_legend_texture;

const unsigned char _3DScene::LegendTexture::Squares_Border_Color[3] = { 64, 64, 64 };
const unsigned char _3DScene::LegendTexture::Background_Color[3] = { 9, 91, 134 };
const unsigned char _3DScene::LegendTexture::Opacity = 255;

// Generate a texture data, but don't load it into the GPU yet, as the GPU context may not yet be valid.
bool _3DScene::LegendTexture::generate(const GCodePreviewData& preview_data, const std::vector<float>& tool_colors)
{
    // Mark the texture as released, but don't release the texture from the GPU yet.
    m_tex_width = m_tex_height = 0;
    m_data.clear();

    // collects items to render
    const std::string& title = preview_data.get_legend_title();
    const GCodePreviewData::LegendItemsList& items = preview_data.get_legend_items(tool_colors);

    unsigned int items_count = (unsigned int)items.size();
    if (items_count == 0)
        // nothing to render, return
        return false;

    wxMemoryDC memDC;
    // select default font
    memDC.SetFont(wxSystemSettings::GetFont(wxSYS_DEFAULT_GUI_FONT));

    // calculates texture size
    wxCoord w, h;
    memDC.GetTextExtent(title, &w, &h);
    unsigned int title_width = (unsigned int)w;
    unsigned int title_height = (unsigned int)h;

    unsigned int max_text_width = 0;
    unsigned int max_text_height = 0;
    for (const GCodePreviewData::LegendItem& item : items)
    {
        memDC.GetTextExtent(item.text, &w, &h);
        max_text_width = std::max(max_text_width, (unsigned int)w);
        max_text_height = std::max(max_text_height, (unsigned int)h);
    }

    m_tex_width = std::max(2 * Px_Border + title_width, 2 * (Px_Border + Px_Square_Contour) + Px_Square + Px_Text_Offset + max_text_width);
    m_tex_height = 2 * (Px_Border + Px_Square_Contour) + title_height + Px_Title_Offset + items_count * Px_Square;
    if (items_count > 1)
        m_tex_height += (items_count - 1) * Px_Square_Contour;

    // generates bitmap
    wxBitmap bitmap(m_tex_width, m_tex_height);

#if defined(__APPLE__) || defined(_MSC_VER)
    bitmap.UseAlpha();
#endif

    memDC.SelectObject(bitmap);
    memDC.SetBackground(wxBrush(wxColour(Background_Color[0], Background_Color[1], Background_Color[2])));
    memDC.Clear();

    memDC.SetTextForeground(*wxWHITE);

    // draw title
    unsigned int title_x = Px_Border;
    unsigned int title_y = Px_Border;
    memDC.DrawText(title, title_x, title_y);

    // draw icons contours as background
    unsigned int squares_contour_x = Px_Border;
    unsigned int squares_contour_y = Px_Border + title_height + Px_Title_Offset;
    unsigned int squares_contour_width = Px_Square + 2 * Px_Square_Contour;
    unsigned int squares_contour_height = items_count * Px_Square + 2 * Px_Square_Contour;
    if (items_count > 1)
        squares_contour_height += (items_count - 1) * Px_Square_Contour;

    wxColour color(Squares_Border_Color[0], Squares_Border_Color[1], Squares_Border_Color[2]);
    wxPen pen(color);
    wxBrush brush(color);
    memDC.SetPen(pen);
    memDC.SetBrush(brush);
    memDC.DrawRectangle(wxRect(squares_contour_x, squares_contour_y, squares_contour_width, squares_contour_height));

    // draw items (colored icon + text)
    unsigned int icon_x = squares_contour_x + Px_Square_Contour;
    unsigned int icon_x_inner = icon_x + 1;
    unsigned int icon_y = squares_contour_y + Px_Square_Contour;
    unsigned int icon_y_step = Px_Square + Px_Square_Contour;

    unsigned int text_x = icon_x + Px_Square + Px_Text_Offset;
    unsigned int text_y_offset = (Px_Square - max_text_height) / 2;

    unsigned int px_inner_square = Px_Square - 2;

    for (const GCodePreviewData::LegendItem& item : items)
    {
        // draw darker icon perimeter
        const std::vector<unsigned char>& item_color_bytes = item.color.as_bytes();
        wxImage::HSVValue dark_hsv = wxImage::RGBtoHSV(wxImage::RGBValue(item_color_bytes[0], item_color_bytes[1], item_color_bytes[2]));
        dark_hsv.value *= 0.75;
        wxImage::RGBValue dark_rgb = wxImage::HSVtoRGB(dark_hsv);
        color.Set(dark_rgb.red, dark_rgb.green, dark_rgb.blue, item_color_bytes[3]);
        pen.SetColour(color);
        brush.SetColour(color);
        memDC.SetPen(pen);
        memDC.SetBrush(brush);
        memDC.DrawRectangle(wxRect(icon_x, icon_y, Px_Square, Px_Square));

        // draw icon interior
        color.Set(item_color_bytes[0], item_color_bytes[1], item_color_bytes[2], item_color_bytes[3]);
        pen.SetColour(color);
        brush.SetColour(color);
        memDC.SetPen(pen);
        memDC.SetBrush(brush);
        memDC.DrawRectangle(wxRect(icon_x_inner, icon_y + 1, px_inner_square, px_inner_square));

        // draw text
        memDC.DrawText(item.text, text_x, icon_y + text_y_offset);

        // update y
        icon_y += icon_y_step;
    }

    memDC.SelectObject(wxNullBitmap);

    // Convert the bitmap into a linear data ready to be loaded into the GPU.
    {
        wxImage image = bitmap.ConvertToImage();
        image.SetMaskColour(Background_Color[0], Background_Color[1], Background_Color[2]);

        // prepare buffer
        m_data.assign(4 * m_tex_width * m_tex_height, 0);
        for (unsigned int h = 0; h < m_tex_height; ++h)
        {
            unsigned int hh = h * m_tex_width;
            unsigned char* px_ptr = m_data.data() + 4 * hh;
            for (unsigned int w = 0; w < m_tex_width; ++w)
            {
                *px_ptr++ = image.GetRed(w, h);
                *px_ptr++ = image.GetGreen(w, h);
                *px_ptr++ = image.GetBlue(w, h);
                *px_ptr++ = image.IsTransparent(w, h) ? 0 : Opacity;
            }
        }
    }
    return true;
}

unsigned int _3DScene::LegendTexture::finalize()
{
    if (! m_data.empty()) {
        // sends buffer to gpu
        ::glGenTextures(1, &m_tex_id);
        ::glBindTexture(GL_TEXTURE_2D, m_tex_id);
        ::glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, (GLsizei)m_tex_width, (GLsizei)m_tex_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, (const GLvoid*)m_data.data());
        ::glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        ::glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        ::glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 1);
        ::glBindTexture(GL_TEXTURE_2D, 0);
        m_data.clear();
    }
    return (m_tex_width > 0 && m_tex_height > 0) ? m_tex_id : 0;
}

void _3DScene::LegendTexture::_destroy_texture()
{
    if (m_tex_id > 0)
    {
        ::glDeleteTextures(1, &m_tex_id);
        m_tex_id = 0;
        m_tex_height = 0;
        m_tex_width = 0;
    }
    m_data.clear();
}

void _3DScene::_glew_init()
{ 
    glewInit();
}

static inline int hex_digit_to_int(const char c)
{
    return 
        (c >= '0' && c <= '9') ? int(c - '0') : 
        (c >= 'A' && c <= 'F') ? int(c - 'A') + 10 :
		(c >= 'a' && c <= 'f') ? int(c - 'a') + 10 : -1;
}

static inline std::vector<float> parse_colors(const std::vector<std::string> &scolors)
{
    std::vector<float> output(scolors.size() * 4, 1.f);
    for (size_t i = 0; i < scolors.size(); ++ i) {
        const std::string &scolor = scolors[i];
        const char        *c      = scolor.data() + 1;
        if (scolor.size() == 7 && scolor.front() == '#') {
			for (size_t j = 0; j < 3; ++j) {
                int digit1 = hex_digit_to_int(*c ++);
                int digit2 = hex_digit_to_int(*c ++);
                if (digit1 == -1 || digit2 == -1)
                    break;
                output[i * 4 + j] = float(digit1 * 16 + digit2) / 255.f;
            }
        }
    }
    return output;
}

void _3DScene::load_gcode_preview(const Print* print, const GCodePreviewData* preview_data, GLVolumeCollection* volumes, const std::vector<std::string>& str_tool_colors, bool use_VBOs)
{
    if ((preview_data == nullptr) || (volumes == nullptr))
        return;

    if (volumes->empty())
    {
        std::vector<float> tool_colors = parse_colors(str_tool_colors);

        s_gcode_preview_volume_index.reset();

        _load_gcode_extrusion_paths(*preview_data, *volumes, tool_colors, use_VBOs);
        _load_gcode_travel_paths(*preview_data, *volumes, tool_colors, use_VBOs);
        _load_gcode_retractions(*preview_data, *volumes, use_VBOs);
        _load_gcode_unretractions(*preview_data, *volumes, use_VBOs);

        if (volumes->empty())
        {
            reset_legend_texture();
            volumes->set_render_interleaved_only_volumes(GLVolumeCollection::RenderInterleavedOnlyVolumes(false, 0.0f));
        }
        else
        {
            _generate_legend_texture(*preview_data, tool_colors);

            _load_shells(*print, *volumes, use_VBOs);
            volumes->set_render_interleaved_only_volumes(GLVolumeCollection::RenderInterleavedOnlyVolumes(true, 0.25f));
        }
    }

    _update_gcode_volumes_visibility(*preview_data, *volumes);
}

unsigned int _3DScene::get_legend_texture_id()
{
    return s_legend_texture.get_texture_id();
}

unsigned int _3DScene::get_legend_texture_width()
{
    return s_legend_texture.get_texture_width();
}

unsigned int _3DScene::get_legend_texture_height()
{
    return s_legend_texture.get_texture_height();
}

void _3DScene::reset_legend_texture()
{
    s_legend_texture.reset_texture();
}

// Create 3D thick extrusion lines for a skirt and brim.
// Adds a new Slic3r::GUI::3DScene::Volume to volumes.
void _3DScene::_load_print_toolpaths(
    const Print                     *print, 
    GLVolumeCollection              *volumes,
    const std::vector<std::string>  &tool_colors,
    bool                             use_VBOs)
{
    if (!print->has_skirt() && print->config.brim_width.value == 0)
        return;
    
    const float color[] = { 0.5f, 1.0f, 0.5f, 1.f }; // greenish

    // number of skirt layers
    size_t total_layer_count = 0;
    for (const PrintObject *print_object : print->objects)
        total_layer_count = std::max(total_layer_count, print_object->total_layer_count());
    size_t skirt_height = print->has_infinite_skirt() ? 
        total_layer_count :
        std::min<size_t>(print->config.skirt_height.value, total_layer_count);
    if (skirt_height == 0 && print->config.brim_width.value > 0)
        skirt_height = 1;

    // get first skirt_height layers (maybe this should be moved to a PrintObject method?)
    const PrintObject *object0 = print->objects.front();
    std::vector<float> print_zs;
    print_zs.reserve(skirt_height * 2);
    for (size_t i = 0; i < std::min(skirt_height, object0->layers.size()); ++ i)
        print_zs.push_back(float(object0->layers[i]->print_z));
    //FIXME why there are support layers?
    for (size_t i = 0; i < std::min(skirt_height, object0->support_layers.size()); ++ i)
        print_zs.push_back(float(object0->support_layers[i]->print_z));
    sort_remove_duplicates(print_zs);
    if (print_zs.size() > skirt_height)
        print_zs.erase(print_zs.begin() + skirt_height, print_zs.end());
    
    volumes->volumes.emplace_back(new GLVolume(color));
    GLVolume &volume = *volumes->volumes.back();
    for (size_t i = 0; i < skirt_height; ++ i) {
        volume.print_zs.push_back(print_zs[i]);
        volume.offsets.push_back(volume.indexed_vertex_array.quad_indices.size());
        volume.offsets.push_back(volume.indexed_vertex_array.triangle_indices.size());
        if (i == 0)
            extrusionentity_to_verts(print->brim, print_zs[i], Point(0, 0), volume);
        extrusionentity_to_verts(print->skirt, print_zs[i], Point(0, 0), volume);
    }
    volume.bounding_box = volume.indexed_vertex_array.bounding_box();
    volume.indexed_vertex_array.finalize_geometry(use_VBOs);
}

// Create 3D thick extrusion lines for object forming extrusions.
// Adds a new Slic3r::GUI::3DScene::Volume to $self->volumes,
// one for perimeters, one for infill and one for supports.
void _3DScene::_load_print_object_toolpaths(
    const PrintObject              *print_object,
    GLVolumeCollection             *volumes,
    const std::vector<std::string> &tool_colors_str,
    bool                            use_VBOs)
{
    std::vector<float> tool_colors = parse_colors(tool_colors_str);

    struct Ctxt
    {
        const Points                *shifted_copies;
        std::vector<const Layer*>    layers;
        bool                         has_perimeters;
        bool                         has_infill;
        bool                         has_support;
        const std::vector<float>*    tool_colors;

        // Number of vertices (each vertex is 6x4=24 bytes long)
        static const size_t          alloc_size_max    () { return 131072; } // 3.15MB
//        static const size_t          alloc_size_max    () { return 65536; } // 1.57MB 
//        static const size_t          alloc_size_max    () { return 32768; } // 786kB
        static const size_t          alloc_size_reserve() { return alloc_size_max() * 2; }

        static const float*          color_perimeters  () { static float color[4] = { 1.0f, 1.0f, 0.0f, 1.f }; return color; } // yellow
        static const float*          color_infill      () { static float color[4] = { 1.0f, 0.5f, 0.5f, 1.f }; return color; } // redish
        static const float*          color_support     () { static float color[4] = { 0.5f, 1.0f, 0.5f, 1.f }; return color; } // greenish

        // For cloring by a tool, return a parsed color.
        bool                         color_by_tool() const { return tool_colors != nullptr; }
        size_t                       number_tools()  const { return this->color_by_tool() ? tool_colors->size() / 4 : 0; }
        const float*                 color_tool(size_t tool) const { return tool_colors->data() + tool * 4; }
        int                          volume_idx(int extruder, int feature) const 
            { return this->color_by_tool() ? std::min<int>(this->number_tools() - 1, std::max<int>(extruder - 1, 0)) : feature; }
    } ctxt;

    ctxt.shifted_copies = &print_object->_shifted_copies;

    // order layers by print_z
    ctxt.layers.reserve(print_object->layers.size() + print_object->support_layers.size());
    for (const Layer *layer : print_object->layers)
        ctxt.layers.push_back(layer);
    for (const Layer *layer : print_object->support_layers)
        ctxt.layers.push_back(layer);
    std::sort(ctxt.layers.begin(), ctxt.layers.end(), [](const Layer *l1, const Layer *l2) { return l1->print_z < l2->print_z; });

    // Maximum size of an allocation block: 32MB / sizeof(float)
    ctxt.has_perimeters = print_object->state.is_done(posPerimeters);
    ctxt.has_infill     = print_object->state.is_done(posInfill);
    ctxt.has_support    = print_object->state.is_done(posSupportMaterial);
    ctxt.tool_colors    = tool_colors.empty() ? nullptr : &tool_colors;
    
    BOOST_LOG_TRIVIAL(debug) << "Loading print object toolpaths in parallel - start";

    //FIXME Improve the heuristics for a grain size.
    size_t          grain_size = std::max(ctxt.layers.size() / 16, size_t(1));
    tbb::spin_mutex new_volume_mutex;
    auto            new_volume = [volumes, &new_volume_mutex](const float *color) -> GLVolume* {
        auto *volume = new GLVolume(color);
        new_volume_mutex.lock();
        volumes->volumes.emplace_back(volume);
        new_volume_mutex.unlock();
        return volume;
    };
    const size_t   volumes_cnt_initial = volumes->volumes.size();
    std::vector<GLVolumeCollection> volumes_per_thread(ctxt.layers.size());
    tbb::parallel_for(
        tbb::blocked_range<size_t>(0, ctxt.layers.size(), grain_size),
        [&ctxt, &new_volume](const tbb::blocked_range<size_t>& range) {
            std::vector<GLVolume*> vols;
            if (ctxt.color_by_tool()) {
                for (size_t i = 0; i < ctxt.number_tools(); ++ i)
                    vols.emplace_back(new_volume(ctxt.color_tool(i)));
            } else
                vols = { new_volume(ctxt.color_perimeters()), new_volume(ctxt.color_infill()), new_volume(ctxt.color_support()) };
            for (GLVolume *vol : vols)
                vol->indexed_vertex_array.reserve(ctxt.alloc_size_reserve());
            for (size_t idx_layer = range.begin(); idx_layer < range.end(); ++ idx_layer) {
                const Layer *layer = ctxt.layers[idx_layer];
                for (size_t i = 0; i < vols.size(); ++ i) {
                    GLVolume &vol = *vols[i];
                    if (vol.print_zs.empty() || vol.print_zs.back() != layer->print_z) {
                        vol.print_zs.push_back(layer->print_z);
                        vol.offsets.push_back(vol.indexed_vertex_array.quad_indices.size());
                        vol.offsets.push_back(vol.indexed_vertex_array.triangle_indices.size());
                    }
                }
                for (const Point &copy: *ctxt.shifted_copies) {
                    for (const LayerRegion *layerm : layer->regions) {
                        if (ctxt.has_perimeters)
                            extrusionentity_to_verts(layerm->perimeters, float(layer->print_z), copy, 
                                *vols[ctxt.volume_idx(layerm->region()->config.perimeter_extruder.value, 0)]);
                        if (ctxt.has_infill) {
                            for (const ExtrusionEntity *ee : layerm->fills.entities) {
                                // fill represents infill extrusions of a single island.
                                const auto *fill = dynamic_cast<const ExtrusionEntityCollection*>(ee);
                                if (! fill->entities.empty())
                                    extrusionentity_to_verts(*fill, float(layer->print_z), copy, 
                                        *vols[ctxt.volume_idx(
                                            is_solid_infill(fill->entities.front()->role()) ? 
                                                layerm->region()->config.solid_infill_extruder : 
                                                layerm->region()->config.infill_extruder,
                                        1)]);
                            }
                        }
                    }
                    if (ctxt.has_support) {
                        const SupportLayer *support_layer = dynamic_cast<const SupportLayer*>(layer);
                        if (support_layer) {
                            for (const ExtrusionEntity *extrusion_entity : support_layer->support_fills.entities)
                                extrusionentity_to_verts(extrusion_entity, float(layer->print_z), copy, 
                                    *vols[ctxt.volume_idx(
                                            (extrusion_entity->role() == erSupportMaterial) ? 
                                                support_layer->object()->config.support_material_extruder : 
                                                support_layer->object()->config.support_material_interface_extruder,
                                            2)]);
                        }
                    }
                }
                for (size_t i = 0; i < vols.size(); ++ i) {
                    GLVolume &vol = *vols[i];
                    if (vol.indexed_vertex_array.vertices_and_normals_interleaved.size() / 6 > ctxt.alloc_size_max()) {
                        // Store the vertex arrays and restart their containers, 
                        vols[i] = new_volume(vol.color);
                        GLVolume &vol_new = *vols[i];
                        // Assign the large pre-allocated buffers to the new GLVolume.
                        vol_new.indexed_vertex_array = std::move(vol.indexed_vertex_array);
                        // Copy the content back to the old GLVolume.
                        vol.indexed_vertex_array = vol_new.indexed_vertex_array;
                        // Finalize a bounding box of the old GLVolume.
                        vol.bounding_box = vol.indexed_vertex_array.bounding_box();
                        // Clear the buffers, but keep them pre-allocated.
                        vol_new.indexed_vertex_array.clear();
                        // Just make sure that clear did not clear the reserved memory.
                        vol_new.indexed_vertex_array.reserve(ctxt.alloc_size_reserve());
                    }
                }
            }
            for (GLVolume *vol : vols) {
                vol->bounding_box = vol->indexed_vertex_array.bounding_box();
                vol->indexed_vertex_array.shrink_to_fit();
            }
        });

    BOOST_LOG_TRIVIAL(debug) << "Loading print object toolpaths in parallel - finalizing results";
    // Remove empty volumes from the newly added volumes.
    volumes->volumes.erase(
        std::remove_if(volumes->volumes.begin() + volumes_cnt_initial, volumes->volumes.end(), 
            [](const GLVolume *volume) { return volume->empty(); }),
        volumes->volumes.end());
    for (size_t i = volumes_cnt_initial; i < volumes->volumes.size(); ++ i)
        volumes->volumes[i]->indexed_vertex_array.finalize_geometry(use_VBOs);
  
    BOOST_LOG_TRIVIAL(debug) << "Loading print object toolpaths in parallel - end"; 
}

void _3DScene::_load_wipe_tower_toolpaths(
    const Print                    *print,
    GLVolumeCollection             *volumes,
    const std::vector<std::string> &tool_colors_str,
    bool                            use_VBOs)
{
    if (print->m_wipe_tower_tool_changes.empty())
        return;

    std::vector<float> tool_colors = parse_colors(tool_colors_str);

    struct Ctxt
    {
        const Print                 *print;
        const std::vector<float>    *tool_colors;

        // Number of vertices (each vertex is 6x4=24 bytes long)
        static const size_t          alloc_size_max    () { return 131072; } // 3.15MB
        static const size_t          alloc_size_reserve() { return alloc_size_max() * 2; }

        static const float*          color_support     () { static float color[4] = { 0.5f, 1.0f, 0.5f, 1.f }; return color; } // greenish

        // For cloring by a tool, return a parsed color.
        bool                         color_by_tool() const { return tool_colors != nullptr; }
        size_t                       number_tools()  const { return this->color_by_tool() ? tool_colors->size() / 4 : 0; }
        const float*                 color_tool(size_t tool) const { return tool_colors->data() + tool * 4; }
        int                          volume_idx(int tool, int feature) const 
            { return this->color_by_tool() ? std::min<int>(this->number_tools() - 1, std::max<int>(tool, 0)) : feature; }

        const std::vector<WipeTower::ToolChangeResult>& tool_change(size_t idx) { 
            return priming.empty() ? 
                ((idx == print->m_wipe_tower_tool_changes.size()) ? final : print->m_wipe_tower_tool_changes[idx]) :
                ((idx == 0) ? priming : (idx == print->m_wipe_tower_tool_changes.size() + 1) ? final : print->m_wipe_tower_tool_changes[idx - 1]);
        }
        std::vector<WipeTower::ToolChangeResult> priming;
        std::vector<WipeTower::ToolChangeResult> final;
    } ctxt;

    ctxt.print          = print;
    ctxt.tool_colors    = tool_colors.empty() ? nullptr : &tool_colors;
	if (print->m_wipe_tower_priming)
		ctxt.priming.emplace_back(*print->m_wipe_tower_priming.get());
	if (print->m_wipe_tower_final_purge)
		ctxt.final.emplace_back(*print->m_wipe_tower_final_purge.get());
    
    BOOST_LOG_TRIVIAL(debug) << "Loading wipe tower toolpaths in parallel - start";

    //FIXME Improve the heuristics for a grain size.
    size_t          n_items    = print->m_wipe_tower_tool_changes.size() + (ctxt.priming.empty() ? 0 : 1);
    size_t          grain_size = std::max(n_items / 128, size_t(1));
    tbb::spin_mutex new_volume_mutex;
    auto            new_volume = [volumes, &new_volume_mutex](const float *color) -> GLVolume* {
        auto *volume = new GLVolume(color);
        new_volume_mutex.lock();
        volumes->volumes.emplace_back(volume);
        new_volume_mutex.unlock();
        return volume;
    };
    const size_t   volumes_cnt_initial = volumes->volumes.size();
    std::vector<GLVolumeCollection> volumes_per_thread(n_items);
    tbb::parallel_for(
        tbb::blocked_range<size_t>(0, n_items, grain_size),
        [&ctxt, &new_volume](const tbb::blocked_range<size_t>& range) {
            // Bounding box of this slab of a wipe tower.
            std::vector<GLVolume*> vols;
            if (ctxt.color_by_tool()) {
                for (size_t i = 0; i < ctxt.number_tools(); ++ i)
                    vols.emplace_back(new_volume(ctxt.color_tool(i)));
            } else
                vols = { new_volume(ctxt.color_support()) };
            for (GLVolume *volume : vols)
                volume->indexed_vertex_array.reserve(ctxt.alloc_size_reserve());
            for (size_t idx_layer = range.begin(); idx_layer < range.end(); ++ idx_layer) {
                const std::vector<WipeTower::ToolChangeResult> &layer = ctxt.tool_change(idx_layer);
                for (size_t i = 0; i < vols.size(); ++ i) {
                    GLVolume &vol = *vols[i];
                    if (vol.print_zs.empty() || vol.print_zs.back() != layer.front().print_z) {
                        vol.print_zs.push_back(layer.front().print_z);
                        vol.offsets.push_back(vol.indexed_vertex_array.quad_indices.size());
                        vol.offsets.push_back(vol.indexed_vertex_array.triangle_indices.size());
                    }
                }
                for (const WipeTower::ToolChangeResult &extrusions : layer) {
                    for (size_t i = 1; i < extrusions.extrusions.size();) {
                        const WipeTower::Extrusion &e = extrusions.extrusions[i];
                        if (e.width == 0.) {
                            ++ i;
                            continue;
                        }
                        size_t j = i + 1;
                        if (ctxt.color_by_tool())
                            for (; j < extrusions.extrusions.size() && extrusions.extrusions[j].tool == e.tool && extrusions.extrusions[j].width > 0.f; ++ j) ;
                        else
                            for (; j < extrusions.extrusions.size() && extrusions.extrusions[j].width > 0.f; ++ j) ;
                        size_t              n_lines = j - i;
                        Lines               lines;
                        std::vector<double> widths;
                        std::vector<double> heights;
                        lines.reserve(n_lines);
                        widths.reserve(n_lines);
                        heights.assign(n_lines, extrusions.layer_height);
                        for (; i < j; ++ i) {
                            const WipeTower::Extrusion &e = extrusions.extrusions[i];
                            assert(e.width > 0.f);
                            const WipeTower::Extrusion &e_prev = *(&e - 1);
                            lines.emplace_back(Point::new_scale(e_prev.pos.x, e_prev.pos.y), Point::new_scale(e.pos.x, e.pos.y));
                            widths.emplace_back(e.width);
                        }
                        thick_lines_to_verts(lines, widths, heights, lines.front().a == lines.back().b, extrusions.print_z, 
                            *vols[ctxt.volume_idx(e.tool, 0)]);
                    }
                }
            }
            for (size_t i = 0; i < vols.size(); ++ i) {
                GLVolume &vol = *vols[i];
                if (vol.indexed_vertex_array.vertices_and_normals_interleaved.size() / 6 > ctxt.alloc_size_max()) {
                    // Store the vertex arrays and restart their containers, 
                    vols[i] = new_volume(vol.color);
                    GLVolume &vol_new = *vols[i];
                    // Assign the large pre-allocated buffers to the new GLVolume.
                    vol_new.indexed_vertex_array = std::move(vol.indexed_vertex_array);
                    // Copy the content back to the old GLVolume.
                    vol.indexed_vertex_array = vol_new.indexed_vertex_array;
                    // Finalize a bounding box of the old GLVolume.
                    vol.bounding_box = vol.indexed_vertex_array.bounding_box();
                    // Clear the buffers, but keep them pre-allocated.
                    vol_new.indexed_vertex_array.clear();
                    // Just make sure that clear did not clear the reserved memory.
                    vol_new.indexed_vertex_array.reserve(ctxt.alloc_size_reserve());
                }
            }
            for (GLVolume *vol : vols) {
                vol->bounding_box = vol->indexed_vertex_array.bounding_box();
                vol->indexed_vertex_array.shrink_to_fit();
            }
        });

    BOOST_LOG_TRIVIAL(debug) << "Loading wipe tower toolpaths in parallel - finalizing results";
    // Remove empty volumes from the newly added volumes.
    volumes->volumes.erase(
        std::remove_if(volumes->volumes.begin() + volumes_cnt_initial, volumes->volumes.end(), 
            [](const GLVolume *volume) { return volume->empty(); }),
        volumes->volumes.end());
    for (size_t i = volumes_cnt_initial; i < volumes->volumes.size(); ++ i)
        volumes->volumes[i]->indexed_vertex_array.finalize_geometry(use_VBOs);
  
    BOOST_LOG_TRIVIAL(debug) << "Loading wipe tower toolpaths in parallel - end"; 
}

void _3DScene::_load_gcode_extrusion_paths(const GCodePreviewData& preview_data, GLVolumeCollection& volumes, const std::vector<float>& tool_colors, bool use_VBOs)
{
    // helper functions to select data in dependence of the extrusion view type
    struct Helper
    {
        static float path_filter(GCodePreviewData::Extrusion::EViewType type, const ExtrusionPath& path)
        {
            switch (type)
            {
            case GCodePreviewData::Extrusion::FeatureType:
                return (float)path.role();
            case GCodePreviewData::Extrusion::Height:
                return path.height;
            case GCodePreviewData::Extrusion::Width:
                return path.width;
            case GCodePreviewData::Extrusion::Feedrate:
                return path.feedrate;
            case GCodePreviewData::Extrusion::Tool:
                return (float)path.extruder_id;
            }

            return 0.0f;
        }

        static const GCodePreviewData::Color& path_color(const GCodePreviewData& data, const std::vector<float>& tool_colors, float value)
        {
            switch (data.extrusion.view_type)
            {
            case GCodePreviewData::Extrusion::FeatureType:
                return data.get_extrusion_role_color((ExtrusionRole)(int)value);
            case GCodePreviewData::Extrusion::Height:
                return data.get_extrusion_height_color(value);
            case GCodePreviewData::Extrusion::Width:
                return data.get_extrusion_width_color(value);
            case GCodePreviewData::Extrusion::Feedrate:
                return data.get_extrusion_feedrate_color(value);
            case GCodePreviewData::Extrusion::Tool:
                {
                    static GCodePreviewData::Color color;
                    ::memcpy((void*)color.rgba, (const void*)(tool_colors.data() + (unsigned int)value * 4), 4 * sizeof(float));
                    return color;
                }
            }

            return GCodePreviewData::Color::Dummy;
        }
    };

    // Helper structure for filters
    struct Filter
    {
        float value;
        ExtrusionRole role;
        GLVolume* volume;

        Filter(float value, ExtrusionRole role)
            : value(value)
            , role(role)
            , volume(nullptr)
        {
        }

        bool operator == (const Filter& other) const
        {
            if (value != other.value)
                return false;

            if (role != other.role)
                return false;

            return true;
        }
    };

    typedef std::vector<Filter> FiltersList;

    size_t initial_volumes_count = volumes.volumes.size();

    // detects filters
    FiltersList filters;
    for (const GCodePreviewData::Extrusion::Layer& layer : preview_data.extrusion.layers)
    {
        for (const ExtrusionPath& path : layer.paths)
        {
            ExtrusionRole role = path.role();
            float path_filter = Helper::path_filter(preview_data.extrusion.view_type, path);
            if (std::find(filters.begin(), filters.end(), Filter(path_filter, role)) == filters.end())
                filters.emplace_back(path_filter, role);
        }
    }

    // nothing to render, return
    if (filters.empty())
        return;

    // creates a new volume for each filter
    for (Filter& filter : filters)
    {
        s_gcode_preview_volume_index.first_volumes.emplace_back(GCodePreviewVolumeIndex::Extrusion, (unsigned int)filter.role, (unsigned int)volumes.volumes.size());

        GLVolume* volume = new GLVolume(Helper::path_color(preview_data, tool_colors, filter.value).rgba);
        if (volume != nullptr)
        {
            filter.volume = volume;
            volumes.volumes.emplace_back(volume);
        }
        else
        {
            // an error occourred - restore to previous state and return
            s_gcode_preview_volume_index.first_volumes.pop_back();
            if (initial_volumes_count != volumes.volumes.size())
            {
                std::vector<GLVolume*>::iterator begin = volumes.volumes.begin() + initial_volumes_count;
                std::vector<GLVolume*>::iterator end = volumes.volumes.end();
                for (std::vector<GLVolume*>::iterator it = begin; it < end; ++it)
                {
                    GLVolume* volume = *it;
                    delete volume;
                }
                volumes.volumes.erase(begin, end);
                return;
            }
        }
    }

    // populates volumes
    for (const GCodePreviewData::Extrusion::Layer& layer : preview_data.extrusion.layers)
    {
        for (const ExtrusionPath& path : layer.paths)
        {
            float path_filter = Helper::path_filter(preview_data.extrusion.view_type, path);
            FiltersList::iterator filter = std::find(filters.begin(), filters.end(), Filter(path_filter, path.role()));
            if (filter != filters.end())
            {
                filter->volume->print_zs.push_back(layer.z);
                filter->volume->offsets.push_back(filter->volume->indexed_vertex_array.quad_indices.size());
                filter->volume->offsets.push_back(filter->volume->indexed_vertex_array.triangle_indices.size());

                extrusionentity_to_verts(path, layer.z, *filter->volume);
            }
        }
    }

    // finalize volumes and sends geometry to gpu
    if (volumes.volumes.size() > initial_volumes_count)
    {
        for (size_t i = initial_volumes_count; i < volumes.volumes.size(); ++i)
        {
            GLVolume* volume = volumes.volumes[i];
            volume->bounding_box = volume->indexed_vertex_array.bounding_box();
            volume->indexed_vertex_array.finalize_geometry(use_VBOs);
        }
    }
}

void _3DScene::_load_gcode_travel_paths(const GCodePreviewData& preview_data, GLVolumeCollection& volumes, const std::vector<float>& tool_colors, bool use_VBOs)
{
    size_t initial_volumes_count = volumes.volumes.size();
    s_gcode_preview_volume_index.first_volumes.emplace_back(GCodePreviewVolumeIndex::Travel, 0, (unsigned int)initial_volumes_count);

    bool res = true;
    switch (preview_data.extrusion.view_type)
    {
    case GCodePreviewData::Extrusion::Feedrate:
        {
            res = _travel_paths_by_feedrate(preview_data, volumes);
            break;
        }
    case GCodePreviewData::Extrusion::Tool:
        {
            res = _travel_paths_by_tool(preview_data, volumes, tool_colors);
            break;
        }
    default:
        {
            res = _travel_paths_by_type(preview_data, volumes);
            break;
        }
    }

    if (!res)
    {
        // an error occourred - restore to previous state and return
        if (initial_volumes_count != volumes.volumes.size())
        {
            std::vector<GLVolume*>::iterator begin = volumes.volumes.begin() + initial_volumes_count;
            std::vector<GLVolume*>::iterator end = volumes.volumes.end();
            for (std::vector<GLVolume*>::iterator it = begin; it < end; ++it)
            {
                GLVolume* volume = *it;
                delete volume;
            }
            volumes.volumes.erase(begin, end);
        }

        return;
    }

    // finalize volumes and sends geometry to gpu
    if (volumes.volumes.size() > initial_volumes_count)
    {
        for (size_t i = initial_volumes_count; i < volumes.volumes.size(); ++i)
        {
            GLVolume* volume = volumes.volumes[i];
            volume->bounding_box = volume->indexed_vertex_array.bounding_box();
            volume->indexed_vertex_array.finalize_geometry(use_VBOs);
        }
    }
}

bool _3DScene::_travel_paths_by_type(const GCodePreviewData& preview_data, GLVolumeCollection& volumes)
{
    // Helper structure for types
    struct Type
    {
        GCodePreviewData::Travel::EType value;
        GLVolume* volume;

        explicit Type(GCodePreviewData::Travel::EType value)
            : value(value)
            , volume(nullptr)
        {
        }

        bool operator == (const Type& other) const
        {
            return value == other.value;
        }
    };

    typedef std::vector<Type> TypesList;

    // colors travels by travel type

    // detects types
    TypesList types;
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        if (std::find(types.begin(), types.end(), Type(polyline.type)) == types.end())
            types.emplace_back(polyline.type);
    }

    // nothing to render, return
    if (types.empty())
        return true;

    // creates a new volume for each type
    for (Type& type : types)
    {
        GLVolume* volume = new GLVolume(preview_data.travel.type_colors[type.value].rgba);
        if (volume == nullptr)
            return false;
        else
        {
            type.volume = volume;
            volumes.volumes.emplace_back(volume);
        }
    }

    // populates volumes
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        TypesList::iterator type = std::find(types.begin(), types.end(), Type(polyline.type));
        if (type != types.end())
        {
            type->volume->print_zs.push_back(unscale(polyline.polyline.bounding_box().max.z));
            type->volume->offsets.push_back(type->volume->indexed_vertex_array.quad_indices.size());
            type->volume->offsets.push_back(type->volume->indexed_vertex_array.triangle_indices.size());

            polyline3_to_verts(polyline.polyline, preview_data.travel.width, preview_data.travel.height, *type->volume);
        }
    }

    return true;
}

bool _3DScene::_travel_paths_by_feedrate(const GCodePreviewData& preview_data, GLVolumeCollection& volumes)
{
    // Helper structure for feedrate
    struct Feedrate
    {
        float value;
        GLVolume* volume;

        explicit Feedrate(float value)
            : value(value)
            , volume(nullptr)
        {
        }

        bool operator == (const Feedrate& other) const
        {
            return value == other.value;
        }
    };

    typedef std::vector<Feedrate> FeedratesList;

    // colors travels by feedrate

    // detects feedrates
    FeedratesList feedrates;
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        if (std::find(feedrates.begin(), feedrates.end(), Feedrate(polyline.feedrate)) == feedrates.end())
            feedrates.emplace_back(polyline.feedrate);
    }

    // nothing to render, return
    if (feedrates.empty())
        return true;

    // creates a new volume for each feedrate
    for (Feedrate& feedrate : feedrates)
    {
        GLVolume* volume = new GLVolume(preview_data.get_extrusion_feedrate_color(feedrate.value).rgba);
        if (volume == nullptr)
            return false;
        else
        {
            feedrate.volume = volume;
            volumes.volumes.emplace_back(volume);
        }
    }

    // populates volumes
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        FeedratesList::iterator feedrate = std::find(feedrates.begin(), feedrates.end(), Feedrate(polyline.feedrate));
        if (feedrate != feedrates.end())
        {
            feedrate->volume->print_zs.push_back(unscale(polyline.polyline.bounding_box().max.z));
            feedrate->volume->offsets.push_back(feedrate->volume->indexed_vertex_array.quad_indices.size());
            feedrate->volume->offsets.push_back(feedrate->volume->indexed_vertex_array.triangle_indices.size());

            polyline3_to_verts(polyline.polyline, preview_data.travel.width, preview_data.travel.height, *feedrate->volume);
        }
    }

    return true;
}

bool _3DScene::_travel_paths_by_tool(const GCodePreviewData& preview_data, GLVolumeCollection& volumes, const std::vector<float>& tool_colors)
{
    // Helper structure for tool
    struct Tool
    {
        unsigned int value;
        GLVolume* volume;

        explicit Tool(unsigned int value)
            : value(value)
            , volume(nullptr)
        {
        }

        bool operator == (const Tool& other) const
        {
            return value == other.value;
        }
    };

    typedef std::vector<Tool> ToolsList;

    // colors travels by tool

    // detects tools
    ToolsList tools;
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        if (std::find(tools.begin(), tools.end(), Tool(polyline.extruder_id)) == tools.end())
            tools.emplace_back(polyline.extruder_id);
    }

    // nothing to render, return
    if (tools.empty())
        return true;

    // creates a new volume for each tool
    for (Tool& tool : tools)
    {
        GLVolume* volume = new GLVolume(tool_colors.data() + tool.value * 4);
        if (volume == nullptr)
            return false;
        else
        {
            tool.volume = volume;
            volumes.volumes.emplace_back(volume);
        }
    }

    // populates volumes
    for (const GCodePreviewData::Travel::Polyline& polyline : preview_data.travel.polylines)
    {
        ToolsList::iterator tool = std::find(tools.begin(), tools.end(), Tool(polyline.extruder_id));
        if (tool != tools.end())
        {
            tool->volume->print_zs.push_back(unscale(polyline.polyline.bounding_box().max.z));
            tool->volume->offsets.push_back(tool->volume->indexed_vertex_array.quad_indices.size());
            tool->volume->offsets.push_back(tool->volume->indexed_vertex_array.triangle_indices.size());

            polyline3_to_verts(polyline.polyline, preview_data.travel.width, preview_data.travel.height, *tool->volume);
        }
    }

    return true;
}

void _3DScene::_load_gcode_retractions(const GCodePreviewData& preview_data, GLVolumeCollection& volumes, bool use_VBOs)
{
    s_gcode_preview_volume_index.first_volumes.emplace_back(GCodePreviewVolumeIndex::Retraction, 0, (unsigned int)volumes.volumes.size());

    // nothing to render, return
    if (preview_data.retraction.positions.empty())
        return;

    GLVolume* volume = new GLVolume(preview_data.retraction.color.rgba);
    if (volume != nullptr)
    {
        volumes.volumes.emplace_back(volume);

        for (const GCodePreviewData::Retraction::Position& position : preview_data.retraction.positions)
        {
            volume->print_zs.push_back(unscale(position.position.z));
            volume->offsets.push_back(volume->indexed_vertex_array.quad_indices.size());
            volume->offsets.push_back(volume->indexed_vertex_array.triangle_indices.size());

            point3_to_verts(position.position, position.width, position.height, *volume);
        }

        // finalize volumes and sends geometry to gpu
        volume->bounding_box = volume->indexed_vertex_array.bounding_box();
        volume->indexed_vertex_array.finalize_geometry(use_VBOs);
    }
}

void _3DScene::_load_gcode_unretractions(const GCodePreviewData& preview_data, GLVolumeCollection& volumes, bool use_VBOs)
{
    s_gcode_preview_volume_index.first_volumes.emplace_back(GCodePreviewVolumeIndex::Unretraction, 0, (unsigned int)volumes.volumes.size());

    // nothing to render, return
    if (preview_data.unretraction.positions.empty())
        return;

    GLVolume* volume = new GLVolume(preview_data.unretraction.color.rgba);
    if (volume != nullptr)
    {
        volumes.volumes.emplace_back(volume);

        for (const GCodePreviewData::Retraction::Position& position : preview_data.unretraction.positions)
        {
            volume->print_zs.push_back(unscale(position.position.z));
            volume->offsets.push_back(volume->indexed_vertex_array.quad_indices.size());
            volume->offsets.push_back(volume->indexed_vertex_array.triangle_indices.size());

            point3_to_verts(position.position, position.width, position.height, *volume);
        }

        // finalize volumes and sends geometry to gpu
        volume->bounding_box = volume->indexed_vertex_array.bounding_box();
        volume->indexed_vertex_array.finalize_geometry(use_VBOs);
    }
}

void _3DScene::_update_gcode_volumes_visibility(const GCodePreviewData& preview_data, GLVolumeCollection& volumes)
{
    unsigned int size = (unsigned int)s_gcode_preview_volume_index.first_volumes.size();
    for (unsigned int i = 0; i < size; ++i)
    {
        std::vector<GLVolume*>::iterator begin = volumes.volumes.begin() + s_gcode_preview_volume_index.first_volumes[i].id;
        std::vector<GLVolume*>::iterator end = (i + 1 < size) ? volumes.volumes.begin() + s_gcode_preview_volume_index.first_volumes[i + 1].id : volumes.volumes.end();

        for (std::vector<GLVolume*>::iterator it = begin; it != end; ++it)
        {
            GLVolume* volume = *it;

            switch (s_gcode_preview_volume_index.first_volumes[i].type)
            {
            case GCodePreviewVolumeIndex::Extrusion:
                {
                    volume->is_active = preview_data.extrusion.is_role_flag_set((ExtrusionRole)s_gcode_preview_volume_index.first_volumes[i].flag);
                    break;
                }
            case GCodePreviewVolumeIndex::Travel:
                {
                    volume->is_active = preview_data.travel.is_visible;
                    volume->zoom_to_volumes = false;
                    break;
                }
            case GCodePreviewVolumeIndex::Retraction:
                {
                    volume->is_active = preview_data.retraction.is_visible;
                    volume->zoom_to_volumes = false;
                    break;
                }
            case GCodePreviewVolumeIndex::Unretraction:
                {
                    volume->is_active = preview_data.unretraction.is_visible;
                    volume->zoom_to_volumes = false;
                    break;
                }
            case GCodePreviewVolumeIndex::Shell:
                {
                    volume->is_active = preview_data.shell.is_visible;
                    volume->zoom_to_volumes = false;
                    break;
                }
            default:
                {
                    volume->is_active = false;
                    volume->zoom_to_volumes = false;
                    break;
                }
            }
        }
    }
}

void _3DScene::_generate_legend_texture(const GCodePreviewData& preview_data, const std::vector<float>& tool_colors)
{
    s_legend_texture.generate(preview_data, tool_colors);
}

unsigned int _3DScene::finalize_legend_texture()
{
    return s_legend_texture.finalize();
}

void _3DScene::_load_shells(const Print& print, GLVolumeCollection& volumes, bool use_VBOs)
{
    size_t initial_volumes_count = volumes.volumes.size();
    s_gcode_preview_volume_index.first_volumes.emplace_back(GCodePreviewVolumeIndex::Shell, 0, (unsigned int)initial_volumes_count);

    if (print.objects.empty())
        // nothing to render, return
        return;

    // adds objects' volumes 
    unsigned int object_id = 0;
    for (PrintObject* obj : print.objects)
    {
        ModelObject* model_obj = obj->model_object();

        std::vector<int> instance_ids(model_obj->instances.size());
        for (int i = 0; i < model_obj->instances.size(); ++i)
        {
            instance_ids[i] = i;
        }

        for (ModelInstance* instance : model_obj->instances)
        {
            volumes.load_object(model_obj, object_id, instance_ids, "object", "object", "object", use_VBOs);
        }

        ++object_id;
    }

    // adds wipe tower's volume
    coordf_t max_z = print.objects[0]->model_object()->get_model()->bounding_box().max.z;
    const PrintConfig& config = print.config;
    unsigned int extruders_count = config.nozzle_diameter.size();
    if ((extruders_count > 1) && config.single_extruder_multi_material && config.wipe_tower && !config.complete_objects)
        volumes.load_wipe_tower_preview(1000, config.wipe_tower_x, config.wipe_tower_y, config.wipe_tower_width, config.wipe_tower_per_color_wipe * (extruders_count - 1), max_z, use_VBOs);
}

}
