/*
 * Copyright (c) 2023, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2023, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibAccelGfx/GL.h>
#include <LibAccelGfx/Painter.h>
#include <LibGfx/ImmutableBitmap.h>
#include <LibGfx/Painter.h>

namespace AccelGfx {

struct ColorComponents {
    float red;
    float green;
    float blue;
    float alpha;
};

static ColorComponents gfx_color_to_opengl_color(Gfx::Color color)
{
    ColorComponents components;
    components.red = static_cast<float>(color.red()) / 255.0f;
    components.green = static_cast<float>(color.green()) / 255.0f;
    components.blue = static_cast<float>(color.blue()) / 255.0f;
    components.alpha = static_cast<float>(color.alpha()) / 255.0f;
    return components;
}

Gfx::FloatRect Painter::to_clip_space(Gfx::FloatRect const& screen_rect) const
{
    float x = 2.0f * screen_rect.x() / m_target_canvas->size().width() - 1.0f;
    float y = -1.0f + 2.0f * screen_rect.y() / m_target_canvas->size().height();

    float width = 2.0f * screen_rect.width() / m_target_canvas->size().width();
    float height = 2.0f * screen_rect.height() / m_target_canvas->size().height();

    return { x, y, width, height };
}

char const* vertex_shader_source = R"(
#version 330 core
in vec2 aVertexPosition;
void main() {
    gl_Position = vec4(aVertexPosition, 0.0, 1.0);
}
)";

char const* rect_with_rounded_corners_fragment_shader_source = R"(
#version 330 core
uniform vec2 uRectCenter;
uniform vec2 uRectCorner;
uniform vec2 uTopLeftRadius;
uniform vec2 uTopRightRadius;
uniform vec2 uBottomLeftRadius;
uniform vec2 uBottomRightRadius;
uniform vec4 uColor;
out vec4 fragColor;

bool isPointWithinEllipse(vec2 point, vec2 radius) {
    vec2 normalizedPoint = point / radius;
    return dot(normalizedPoint, normalizedPoint) <= 1.0;
}

void main() {
    vec2 p = gl_FragCoord.xy - uRectCenter;
    vec2 cornerRadius = vec2(0.0, 0.0);
    if (p.x < 0.0 && p.y < 0.0) {
        cornerRadius = uTopLeftRadius;
    } else if (p.x > 0.0 && p.y < 0.0) {
        cornerRadius = uTopRightRadius;
    } else if (p.x < 0.0 && p.y > 0.0) {
        cornerRadius = uBottomLeftRadius;
    } else if (p.x > 0.0 && p.y > 0.0) {
        cornerRadius = uBottomRightRadius;
    }
    vec2 q = abs(p) - (uRectCorner - cornerRadius);
    if (q.x < 0 || q.y < 0 || isPointWithinEllipse(q, cornerRadius)) {
        fragColor = uColor;
    } else {
        discard;
    }
}
)";

char const* solid_color_fragment_shader_source = R"(
#version 330 core
uniform vec4 uColor;
out vec4 fragColor;
void main() {
    fragColor = uColor;
}
)";

char const* blit_vertex_shader_source = R"(
#version 330 core
in vec4 aVertexPosition;
out vec2 vTextureCoord;
void main() {
    gl_Position = vec4(aVertexPosition.xy, 0.0, 1.0);
    vTextureCoord = aVertexPosition.zw;
}
)";

char const* blit_fragment_shader_source = R"(
#version 330 core
uniform vec4 uColor;
in vec2 vTextureCoord;
uniform sampler2D uSampler;
out vec4 fragColor;
void main() {
    fragColor = texture(uSampler, vTextureCoord) * uColor;
}
)";

char const* linear_gradient_vertex_shader_source = R"(
#version 330 core
layout (location = 0) in vec2 aVertexPosition;
layout (location = 1) in vec4 aColor;
out vec4 vColor;
void main() {
    gl_Position = vec4(aVertexPosition, 0.0, 1.0);
    vColor = aColor;
}
)";

char const* linear_gradient_fragment_shader_source = R"(
#version 330 core
out vec4 FragColor;
in vec4 vColor;
void main() {
    FragColor = vec4(vColor);
}
)";

char const* blur_fragment_shader_source = R"(
#version 330 core

uniform vec2 uResolution;
uniform int uRadius;
uniform int uHorizontal;
uniform sampler2D uSampler;

in vec2 vTextureCoord;
out vec4 fragColor;

#define pow2(x) (x * x)
const float pi = atan(1.0) * 4.0;
float gaussian(vec2 i, float sigma) {
    return 1.0 / (2.0 * pi * pow2(sigma)) * exp(-((pow2(i.x) + pow2(i.y)) / (2.0 * pow2(sigma))));
}

void main() {
    vec2 scale = vec2(1.0) / uResolution.xy;
    float sigma = float(uRadius);
    vec4 col = vec4(0.0);
    float accum = 0.0;
    float weight = 0.0;
    for (int i = -uRadius; i <= uRadius; i++) {
        vec2 offset = vec2(i * uHorizontal, i * (1 - uHorizontal));
        weight = gaussian(offset, sigma);
        col += texture(uSampler, vTextureCoord + scale * offset) * weight;
        accum += weight;
    }
    fragColor = col / accum;
}
)";

static void set_blending_mode(Painter::BlendingMode blending_mode)
{
    switch (blending_mode) {
    case Painter::BlendingMode::AlphaAdd:
        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
        break;
    case Painter::BlendingMode::AlphaOverride:
        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::Zero);
        break;
    case Painter::BlendingMode::AlphaPreserve:
        GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::Zero, GL::BlendFactor::One);
        break;
    default:
        VERIFY_NOT_REACHED();
    }
}

HashMap<u32, GL::Texture> s_immutable_bitmap_texture_cache;

NonnullOwnPtr<Painter> Painter::create(Context& context, NonnullRefPtr<Canvas> canvas)
{
    return make<Painter>(context, canvas);
}

Painter::Painter(Context& context, NonnullRefPtr<Canvas> canvas)
    : m_context(context)
    , m_target_canvas(canvas)
    , m_rectangle_program(Program::create(Program::Name::RectangleProgram, vertex_shader_source, solid_color_fragment_shader_source))
    , m_rounded_rectangle_program(Program::create(Program::Name::RoundedRectangleProgram, vertex_shader_source, rect_with_rounded_corners_fragment_shader_source))
    , m_blit_program(Program::create(Program::Name::BlitProgram, blit_vertex_shader_source, blit_fragment_shader_source))
    , m_linear_gradient_program(Program::create(Program::Name::LinearGradientProgram, linear_gradient_vertex_shader_source, linear_gradient_fragment_shader_source))
    , m_blur_program(Program::create(Program::Name::BlurProgram, blit_vertex_shader_source, blur_fragment_shader_source))
{
    m_state_stack.empend(State());
    state().clip_rect = { { 0, 0 }, m_target_canvas->size() };
    bind_target_canvas();
}

Painter::~Painter()
{
}

void Painter::clear(Gfx::Color color)
{
    bind_target_canvas();
    GL::clear_color(color);
}

void Painter::fill_rect(Gfx::IntRect rect, Gfx::Color color)
{
    fill_rect(rect.to_type<float>(), color);
}

static Array<GLfloat, 8> rect_to_vertices(Gfx::FloatRect const& rect)
{
    return {
        rect.left(),
        rect.top(),
        rect.left(),
        rect.bottom(),
        rect.right(),
        rect.bottom(),
        rect.right(),
        rect.top(),
    };
}

void Painter::fill_rect(Gfx::FloatRect rect, Gfx::Color color)
{
    bind_target_canvas();

    // Draw a filled rect (with `color`) using OpenGL after mapping it through the current transform.

    auto vertices = rect_to_vertices(to_clip_space(transform().map(rect)));

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto [red, green, blue, alpha] = gfx_color_to_opengl_color(color);

    m_rectangle_program.use();

    auto position_attribute = m_rectangle_program.get_attribute_location("aVertexPosition");
    auto color_uniform = m_rectangle_program.get_uniform_location("uColor");

    GL::set_uniform(color_uniform, red, green, blue, alpha);
    GL::set_vertex_attribute(position_attribute, 0, 2);
    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
    GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::fill_rect_with_rounded_corners(Gfx::IntRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode blending_mode)
{
    fill_rect_with_rounded_corners(rect.to_type<float>(), color, top_left_radius, top_right_radius, bottom_left_radius, bottom_right_radius, blending_mode);
}

void Painter::fill_rect_with_rounded_corners(Gfx::FloatRect const& rect, Color const& color, CornerRadius const& top_left_radius, CornerRadius const& top_right_radius, CornerRadius const& bottom_left_radius, CornerRadius const& bottom_right_radius, BlendingMode blending_mode)
{
    bind_target_canvas();

    auto transformed_rect = transform().map(rect);
    auto vertices = rect_to_vertices(to_clip_space(transformed_rect));

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto [red, green, blue, alpha] = gfx_color_to_opengl_color(color);

    m_rounded_rectangle_program.use();

    auto position_attribute = m_rounded_rectangle_program.get_attribute_location("aVertexPosition");
    GL::set_vertex_attribute(position_attribute, 0, 2);

    auto color_uniform = m_rounded_rectangle_program.get_uniform_location("uColor");
    GL::set_uniform(color_uniform, red, green, blue, alpha);

    auto rect_center_uniform = m_rounded_rectangle_program.get_uniform_location("uRectCenter");
    GL::set_uniform(rect_center_uniform, transformed_rect.center().x(), transformed_rect.center().y());
    auto rect_corner_uniform = m_rounded_rectangle_program.get_uniform_location("uRectCorner");
    GL::set_uniform(rect_corner_uniform, rect.width() / 2, rect.height() / 2);
    auto top_left_corner_radius_uniform = m_rounded_rectangle_program.get_uniform_location("uTopLeftRadius");
    GL::set_uniform(top_left_corner_radius_uniform, top_left_radius.horizontal_radius, top_left_radius.vertical_radius);
    auto top_right_corner_radius_uniform = m_rounded_rectangle_program.get_uniform_location("uTopRightRadius");
    GL::set_uniform(top_right_corner_radius_uniform, top_right_radius.horizontal_radius, top_right_radius.vertical_radius);
    auto bottom_left_corner_radius_uniform = m_rounded_rectangle_program.get_uniform_location("uBottomLeftRadius");
    GL::set_uniform(bottom_left_corner_radius_uniform, bottom_left_radius.horizontal_radius, bottom_left_radius.vertical_radius);
    auto bottom_right_corner_radius_uniform = m_rounded_rectangle_program.get_uniform_location("uBottomRightRadius");
    GL::set_uniform(bottom_right_corner_radius_uniform, bottom_right_radius.horizontal_radius, bottom_right_radius.vertical_radius);

    set_blending_mode(blending_mode);

    GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::draw_line(Gfx::IntPoint a, Gfx::IntPoint b, float thickness, Gfx::Color color)
{
    draw_line(a.to_type<float>(), b.to_type<float>(), thickness, color);
}

void Painter::draw_line(Gfx::FloatPoint a, Gfx::FloatPoint b, float thickness, Color color)
{
    bind_target_canvas();

    auto midpoint = (a + b) / 2.0f;
    auto length = a.distance_from(b);
    auto angle = AK::atan2(b.y() - a.y(), b.x() - a.x());
    auto offset = Gfx::FloatPoint {
        (length / 2) * AK::cos(angle) - (thickness / 2) * AK::sin(angle),
        (length / 2) * AK::sin(angle) + (thickness / 2) * AK::cos(angle),
    };
    auto rect = Gfx::FloatRect(midpoint - offset, { length, thickness });

    auto vertices = rect_to_vertices(to_clip_space(transform().map(rect)));

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto [red, green, blue, alpha] = gfx_color_to_opengl_color(color);

    m_rectangle_program.use();

    auto position_attribute = m_rectangle_program.get_attribute_location("aVertexPosition");
    auto color_uniform = m_rectangle_program.get_uniform_location("uColor");

    GL::set_uniform(color_uniform, red, green, blue, alpha);
    GL::set_vertex_attribute(position_attribute, 0, 2);
    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
    GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::draw_scaled_bitmap(Gfx::IntRect const& dest_rect, Gfx::Bitmap const& bitmap, Gfx::IntRect const& src_rect, ScalingMode scaling_mode)
{
    draw_scaled_bitmap(dest_rect.to_type<float>(), bitmap, src_rect.to_type<float>(), scaling_mode);
}

void Painter::draw_scaled_immutable_bitmap(Gfx::IntRect const& dst_rect, Gfx::ImmutableBitmap const& immutable_bitmap, Gfx::IntRect const& src_rect, ScalingMode scaling_mode)
{
    draw_scaled_immutable_bitmap(dst_rect.to_type<float>(), immutable_bitmap, src_rect.to_type<float>(), scaling_mode);
}

void Painter::draw_scaled_immutable_bitmap(Gfx::FloatRect const& dst_rect, Gfx::ImmutableBitmap const& immutable_bitmap, Gfx::FloatRect const& src_rect, ScalingMode scaling_mode)
{
    auto texture = s_immutable_bitmap_texture_cache.get(immutable_bitmap.id());
    VERIFY(texture.has_value());
    blit_scaled_texture(dst_rect, texture.value(), src_rect, scaling_mode);
}

static Gfx::FloatRect to_texture_space(Gfx::FloatRect rect, Gfx::IntSize image_size)
{
    auto x = rect.x() / image_size.width();
    auto y = rect.y() / image_size.height();
    auto width = rect.width() / image_size.width();
    auto height = rect.height() / image_size.height();

    return { x, y, width, height };
}

static GL::ScalingMode to_gl_scaling_mode(Painter::ScalingMode scaling_mode)
{
    switch (scaling_mode) {
    case Painter::ScalingMode::NearestNeighbor:
        return GL::ScalingMode::Nearest;
    case Painter::ScalingMode::Bilinear:
        return GL::ScalingMode::Linear;
    default:
        VERIFY_NOT_REACHED();
    }
}

void Painter::draw_scaled_bitmap(Gfx::FloatRect const& dst_rect, Gfx::Bitmap const& bitmap, Gfx::FloatRect const& src_rect, ScalingMode scaling_mode)
{
    // FIXME: We should reuse textures across repaints if possible.
    auto texture = GL::create_texture();
    GL::upload_texture_data(texture, bitmap);
    blit_scaled_texture(dst_rect, texture, src_rect, scaling_mode);
    GL::delete_texture(texture);
}

void Painter::draw_glyph_run(Span<Gfx::DrawGlyphOrEmoji const> glyph_run, Color const& color)
{
    bind_target_canvas();

    Vector<GLfloat> vertices;
    vertices.ensure_capacity(glyph_run.size() * 24);

    auto const& glyph_atlas = GlyphAtlas::the();

    for (auto const& glyph_or_emoji : glyph_run) {
        if (glyph_or_emoji.has<Gfx::DrawGlyph>()) {
            auto const& glyph = glyph_or_emoji.get<Gfx::DrawGlyph>();

            auto const& font = *glyph.font;
            auto code_point = glyph.code_point;
            auto point = glyph.position;

            auto maybe_texture_rect = glyph_atlas.get_glyph_rect(&font, code_point);
            if (!maybe_texture_rect.has_value()) {
                continue;
            }

            auto texture_rect = to_texture_space(maybe_texture_rect.value().to_type<float>(), *glyph_atlas.texture().size);

            auto glyph_position = point + Gfx::FloatPoint(font.glyph_left_bearing(code_point), 0);
            auto glyph_size = maybe_texture_rect->size().to_type<float>();
            auto glyph_rect = transform().map(Gfx::FloatRect { glyph_position, glyph_size });
            auto rect_in_clip_space = to_clip_space(glyph_rect);

            // p0 --- p1
            // | \     |
            // |   \   |
            // |     \ |
            // p2 --- p3

            auto p0 = rect_in_clip_space.top_left();
            auto p1 = rect_in_clip_space.top_right();
            auto p2 = rect_in_clip_space.bottom_left();
            auto p3 = rect_in_clip_space.bottom_right();

            auto s0 = texture_rect.top_left();
            auto s1 = texture_rect.top_right();
            auto s2 = texture_rect.bottom_left();
            auto s3 = texture_rect.bottom_right();

            auto add_triangle = [&](auto& p1, auto& p2, auto& p3, auto& s1, auto& s2, auto& s3) {
                vertices.unchecked_append(p1.x());
                vertices.unchecked_append(p1.y());
                vertices.unchecked_append(s1.x());
                vertices.unchecked_append(s1.y());

                vertices.unchecked_append(p2.x());
                vertices.unchecked_append(p2.y());
                vertices.unchecked_append(s2.x());
                vertices.unchecked_append(s2.y());

                vertices.unchecked_append(p3.x());
                vertices.unchecked_append(p3.y());
                vertices.unchecked_append(s3.x());
                vertices.unchecked_append(s3.y());
            };

            add_triangle(p0, p1, p3, s0, s1, s3);
            add_triangle(p0, p3, p2, s0, s3, s2);
        }
    }

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto [red, green, blue, alpha] = gfx_color_to_opengl_color(color);

    m_blit_program.use();

    GL::bind_texture(glyph_atlas.texture());
    GL::set_texture_scale_mode(GL::ScalingMode::Nearest);

    auto position_attribute = m_blit_program.get_attribute_location("aVertexPosition");
    auto color_uniform = m_blit_program.get_uniform_location("uColor");

    GL::set_uniform(color_uniform, red, green, blue, alpha);
    GL::set_vertex_attribute(position_attribute, 0, 4);
    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
    GL::draw_arrays(GL::DrawPrimitive::Triangles, vertices.size() / 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::fill_rect_with_linear_gradient(Gfx::IntRect const& rect, ReadonlySpan<Gfx::ColorStop> stops, float angle, Optional<float> repeat_length)
{
    fill_rect_with_linear_gradient(rect.to_type<float>(), stops, angle, repeat_length);
}

void Painter::fill_rect_with_linear_gradient(Gfx::FloatRect const& rect, ReadonlySpan<Gfx::ColorStop> stops, float angle, Optional<float> repeat_length)
{
    bind_target_canvas();

    // FIXME: Implement support for angle and repeat_length
    (void)angle;
    (void)repeat_length;

    Vector<GLfloat> vertices;
    Vector<GLfloat> colors;
    for (size_t stop_index = 0; stop_index < stops.size() - 1; stop_index++) {
        auto const& stop_start = stops[stop_index];
        auto const& stop_end = stops[stop_index + 1];

        // The gradient is divided into segments that represent linear gradients between adjacent pairs of stops.
        auto segment_rect_location = rect.location();
        segment_rect_location.set_x(segment_rect_location.x() + stop_start.position * rect.width());
        auto segment_rect_width = (stop_end.position - stop_start.position) * rect.width();
        auto segment_rect_height = rect.height();
        auto segment_rect = transform().map(Gfx::FloatRect { segment_rect_location.x(), segment_rect_location.y(), segment_rect_width, segment_rect_height });

        auto rect_in_clip_space = to_clip_space(segment_rect);

        // p0 --- p1
        // | \     |
        // |   \   |
        // |     \ |
        // p2 --- p3

        auto p0 = rect_in_clip_space.top_left();
        auto p1 = rect_in_clip_space.top_right();
        auto p2 = rect_in_clip_space.bottom_left();
        auto p3 = rect_in_clip_space.bottom_right();

        auto c0 = gfx_color_to_opengl_color(stop_start.color);
        auto c1 = gfx_color_to_opengl_color(stop_end.color);
        auto c2 = gfx_color_to_opengl_color(stop_start.color);
        auto c3 = gfx_color_to_opengl_color(stop_end.color);

        auto add_triangle = [&](auto& p1, auto& p2, auto& p3, auto& c1, auto& c2, auto& c3) {
            vertices.append(p1.x());
            vertices.append(p1.y());
            colors.append(c1.red * c1.alpha);
            colors.append(c1.green * c1.alpha);
            colors.append(c1.blue * c1.alpha);
            colors.append(c1.alpha);

            vertices.append(p2.x());
            vertices.append(p2.y());
            colors.append(c2.red * c2.alpha);
            colors.append(c2.green * c2.alpha);
            colors.append(c2.blue * c2.alpha);
            colors.append(c2.alpha);

            vertices.append(p3.x());
            vertices.append(p3.y());
            colors.append(c3.red * c3.alpha);
            colors.append(c3.green * c3.alpha);
            colors.append(c3.blue * c3.alpha);
            colors.append(c3.alpha);
        };

        add_triangle(p0, p1, p3, c0, c1, c3);
        add_triangle(p0, p3, p2, c0, c3, c2);
    }

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);

    auto vbo_vertices = GL::create_buffer();
    GL::upload_to_buffer(vbo_vertices, vertices);

    auto vbo_colors = GL::create_buffer();
    GL::upload_to_buffer(vbo_colors, colors);

    m_linear_gradient_program.use();
    auto position_attribute = m_linear_gradient_program.get_attribute_location("aVertexPosition");
    auto color_attribute = m_linear_gradient_program.get_attribute_location("aColor");

    GL::bind_buffer(vbo_vertices);
    GL::set_vertex_attribute(position_attribute, 0, 2);

    GL::bind_buffer(vbo_colors);
    GL::set_vertex_attribute(color_attribute, 0, 4);

    GL::enable_blending(GL::BlendFactor::One, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
    GL::draw_arrays(GL::DrawPrimitive::Triangles, vertices.size() / 2);

    GL::delete_buffer(vbo_vertices);
    GL::delete_buffer(vbo_colors);
    GL::delete_vertex_array(vao);
}

void Painter::save()
{
    m_state_stack.append(state());
}

void Painter::restore()
{
    VERIFY(!m_state_stack.is_empty());
    m_state_stack.take_last();
}

void Painter::set_clip_rect(Gfx::IntRect rect)
{
    state().clip_rect = transform().map(rect);
    GL::enable_scissor_test(transform().map(rect));
}

void Painter::clear_clip_rect()
{
    state().clip_rect = { { 0, 0 }, m_target_canvas->size() };
    GL::disable_scissor_test();
}

void Painter::bind_target_canvas()
{
    m_target_canvas->bind();
    GL::set_viewport({ 0, 0, m_target_canvas->size().width(), m_target_canvas->size().height() });
    GL::enable_scissor_test(state().clip_rect);
}

void Painter::flush(Gfx::Bitmap& bitmap)
{
    m_target_canvas->bind();
    GL::read_pixels({ 0, 0, bitmap.width(), bitmap.height() }, bitmap);
}

void Painter::blit_canvas(Gfx::IntRect const& dst_rect, Canvas const& canvas, float opacity, Optional<Gfx::AffineTransform> affine_transform)
{
    blit_canvas(dst_rect.to_type<float>(), canvas, opacity, move(affine_transform));
}

void Painter::blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const& canvas, float opacity, Optional<Gfx::AffineTransform> affine_transform)
{
    auto texture = GL::Texture(canvas.framebuffer().texture);
    blit_scaled_texture(dst_rect, texture, { { 0, 0 }, canvas.size() }, Painter::ScalingMode::NearestNeighbor, opacity, move(affine_transform));
}

void Painter::blit_canvas(Gfx::FloatRect const& dst_rect, Canvas const& canvas, Gfx::FloatRect const& src_rect, float opacity, Optional<Gfx::AffineTransform> affine_transform, BlendingMode blending_mode)
{
    auto texture = GL::Texture(canvas.framebuffer().texture);
    blit_scaled_texture(dst_rect, texture, src_rect, Painter::ScalingMode::NearestNeighbor, opacity, move(affine_transform), blending_mode);
}

void Painter::blit_scaled_texture(Gfx::FloatRect const& dst_rect, GL::Texture const& texture, Gfx::FloatRect const& src_rect, ScalingMode scaling_mode, float opacity, Optional<Gfx::AffineTransform> affine_transform, BlendingMode blending_mode)
{
    bind_target_canvas();

    m_blit_program.use();

    auto dst_rect_rotated = dst_rect;
    Array<Gfx::FloatPoint, 4> dst_rect_vertices = {
        dst_rect_rotated.top_left(),
        dst_rect_rotated.bottom_left(),
        dst_rect_rotated.bottom_right(),
        dst_rect_rotated.top_right(),
    };

    if (affine_transform.has_value()) {
        for (auto& point : dst_rect_vertices)
            point = affine_transform->map(point);
    }

    auto const viewport_width = static_cast<float>(m_target_canvas->size().width());
    auto const viewport_height = static_cast<float>(m_target_canvas->size().height());
    for (auto& point : dst_rect_vertices) {
        point = transform().map(point);
        point.set_x(2.0f * point.x() / viewport_width - 1.0f);
        point.set_y(-1.0f + 2.0f * point.y() / viewport_height);
    }

    auto src_rect_in_texture_space = to_texture_space(src_rect, *texture.size);

    Vector<GLfloat> vertices;
    vertices.ensure_capacity(16);

    auto add_vertex = [&](auto const& p, auto const& s) {
        vertices.append(p.x());
        vertices.append(p.y());
        vertices.append(s.x());
        vertices.append(s.y());
    };

    add_vertex(dst_rect_vertices[0], src_rect_in_texture_space.top_left());
    add_vertex(dst_rect_vertices[1], src_rect_in_texture_space.bottom_left());
    add_vertex(dst_rect_vertices[2], src_rect_in_texture_space.bottom_right());
    add_vertex(dst_rect_vertices[3], src_rect_in_texture_space.top_right());

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto vertex_position_attribute = m_blit_program.get_attribute_location("aVertexPosition");
    GL::set_vertex_attribute(vertex_position_attribute, 0, 4);

    auto color_uniform = m_blit_program.get_uniform_location("uColor");
    GL::set_uniform(color_uniform, 1, 1, 1, opacity);

    GL::bind_texture(texture);

    auto scaling_mode_gl = to_gl_scaling_mode(scaling_mode);
    GL::set_texture_scale_mode(scaling_mode_gl);

    set_blending_mode(blending_mode);

    GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::blit_blurred_texture(Gfx::FloatRect const& dst_rect, GL::Texture const& texture, Gfx::FloatRect const& src_rect, int radius, BlurDirection direction, ScalingMode scaling_mode)
{
    bind_target_canvas();

    m_blur_program.use();

    auto dst_rect_in_clip_space = to_clip_space(transform().map(dst_rect));
    auto src_rect_in_texture_space = to_texture_space(src_rect, *texture.size);

    Vector<GLfloat> vertices;
    vertices.ensure_capacity(16);

    auto add_vertex = [&](auto const& p, auto const& s) {
        vertices.append(p.x());
        vertices.append(p.y());
        vertices.append(s.x());
        vertices.append(s.y());
    };

    add_vertex(dst_rect_in_clip_space.top_left(), src_rect_in_texture_space.top_left());
    add_vertex(dst_rect_in_clip_space.bottom_left(), src_rect_in_texture_space.bottom_left());
    add_vertex(dst_rect_in_clip_space.bottom_right(), src_rect_in_texture_space.bottom_right());
    add_vertex(dst_rect_in_clip_space.top_right(), src_rect_in_texture_space.top_right());

    auto vbo = GL::create_buffer();
    GL::upload_to_buffer(vbo, vertices);

    auto vao = GL::create_vertex_array();
    GL::bind_vertex_array(vao);
    GL::bind_buffer(vbo);

    auto vertex_position_attribute = m_blur_program.get_attribute_location("aVertexPosition");
    GL::set_vertex_attribute(vertex_position_attribute, 0, 4);

    auto resolution_uniform = m_blur_program.get_uniform_location("uResolution");
    GL::set_uniform(resolution_uniform, dst_rect.width(), dst_rect.height());

    auto radius_uniform = m_blur_program.get_uniform_location("uRadius");
    GL::set_uniform(radius_uniform, radius);

    auto direction_uniform = m_blur_program.get_uniform_location("uHorizontal");
    GL::set_uniform(direction_uniform, direction == BlurDirection::Horizontal ? 1 : 0);

    GL::bind_texture(texture);

    auto scaling_mode_gl = to_gl_scaling_mode(scaling_mode);
    GL::set_texture_scale_mode(scaling_mode_gl);
    GL::enable_blending(GL::BlendFactor::SrcAlpha, GL::BlendFactor::OneMinusSrcAlpha, GL::BlendFactor::One, GL::BlendFactor::One);
    GL::draw_arrays(GL::DrawPrimitive::TriangleFan, 4);

    GL::delete_buffer(vbo);
    GL::delete_vertex_array(vao);
}

void Painter::blit_blurred_canvas(Gfx::FloatRect const& dst_rect, Canvas const& canvas, int radius, BlurDirection direction, ScalingMode scaling_mode)
{
    blit_blurred_texture(dst_rect, canvas.framebuffer().texture, { { 0, 0 }, canvas.size() }, radius, direction, scaling_mode);
}

void Painter::update_immutable_bitmap_texture_cache(HashMap<u32, Gfx::ImmutableBitmap const*>& immutable_bitmaps)
{
    for (auto immutable_bitmap_id : s_immutable_bitmap_texture_cache.keys()) {
        if (!immutable_bitmaps.contains(immutable_bitmap_id)) {
            auto texture = s_immutable_bitmap_texture_cache.get(immutable_bitmap_id).value();
            GL::delete_texture(texture);
            s_immutable_bitmap_texture_cache.remove(immutable_bitmap_id);
        }
    }

    for (auto const& [id, immutable_bitmap] : immutable_bitmaps) {
        if (s_immutable_bitmap_texture_cache.contains(id))
            continue;
        auto texture = GL::create_texture();
        GL::upload_texture_data(texture, immutable_bitmap->bitmap());
        s_immutable_bitmap_texture_cache.set(id, texture);
    }
}

}