mirror of
https://github.com/RGBCube/serenity
synced 2025-05-27 19:05:08 +00:00
469491906f
This implements support for painting linear-gradients in a spec correct way :^). Right now it supports: - Multi-stop gradients - Color stop fixups - Using pre-multiplied alpha mixing when required - Painting gradients at arbitrary angles It still needs to support: - Transition hints - Double position color stops However what is implemented now seems to be accurate to other browsers, and covers the most common use cases.
198 lines
8 KiB
C++
198 lines
8 KiB
C++
/*
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* Copyright (c) 2022, MacDue <macdue@dueutil.tech>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Checked.h>
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#include <AK/Math.h>
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#include <LibGfx/Gamma.h>
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#include <LibGfx/Line.h>
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#include <LibWeb/Painting/GradientPainting.h>
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namespace Web::Painting {
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static float normalized_gradient_angle_radians(float gradient_angle)
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{
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// Adjust angle so 0 degrees is bottom
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float real_angle = 90 - gradient_angle;
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return real_angle * (AK::Pi<float> / 180);
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}
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static float calulate_gradient_length(Gfx::IntRect const& gradient_rect, float sin_angle, float cos_angle)
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{
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return AK::fabs(gradient_rect.height() * sin_angle) + AK::fabs(gradient_rect.width() * cos_angle);
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}
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static float calulate_gradient_length(Gfx::IntRect const& gradient_rect, float gradient_angle)
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{
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float angle = normalized_gradient_angle_radians(gradient_angle);
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float sin_angle, cos_angle;
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AK::sincos(angle, sin_angle, cos_angle);
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return calulate_gradient_length(gradient_rect, sin_angle, cos_angle);
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}
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LinearGradientData resolve_linear_gradient_data(Layout::Node const& node, Gfx::FloatRect const& gradient_rect, CSS::LinearGradientStyleValue const& linear_gradient)
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{
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auto& color_stop_list = linear_gradient.color_stop_list();
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VERIFY(color_stop_list.size() >= 2);
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ColorStopList resolved_color_stops;
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resolved_color_stops.ensure_capacity(color_stop_list.size());
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for (auto& stop : color_stop_list)
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resolved_color_stops.append(ColorStop { .color = stop.color_stop.color });
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auto gradient_angle = linear_gradient.angle_degrees(gradient_rect);
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auto gradient_length_px = calulate_gradient_length(gradient_rect.to_rounded<int>(), gradient_angle);
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auto gradient_length = CSS::Length::make_px(gradient_length_px);
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// 1. If the first color stop does not have a position, set its position to 0%.
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auto& first_stop = color_stop_list.first().color_stop;
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resolved_color_stops.first().position = first_stop.length.has_value()
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? first_stop.length->resolved(node, gradient_length).to_px(node)
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: 0;
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// If the last color stop does not have a position, set its position to 100%
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auto& last_stop = color_stop_list.last().color_stop;
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resolved_color_stops.last().position = last_stop.length.has_value()
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? last_stop.length->resolved(node, gradient_length).to_px(node)
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: gradient_length_px;
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// FIXME: Handle transition hints
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// 2. If a color stop or transition hint has a position that is less than the
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// specified position of any color stop or transition hint before it in the list,
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// set its position to be equal to the largest specified position of any color stop
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// or transition hint before it.
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auto max_previous_color_stop = resolved_color_stops[0].position;
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for (size_t i = 1; i < color_stop_list.size(); i++) {
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auto& stop = color_stop_list[i];
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if (stop.color_stop.length.has_value()) {
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float value = stop.color_stop.length->resolved(node, gradient_length).to_px(node);
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value = max(value, max_previous_color_stop);
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resolved_color_stops[i].position = value;
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max_previous_color_stop = value;
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}
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}
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// 3. If any color stop still does not have a position, then, for each run of adjacent color stops
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// without positions, set their positions so that they are evenly spaced between the preceding
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// and following color stops with positions.
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size_t i = 1;
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auto find_run_end = [&] {
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while (i < color_stop_list.size() - 1 && !color_stop_list[i].color_stop.length.has_value()) {
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i++;
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}
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return i;
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};
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while (i < color_stop_list.size() - 1) {
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auto& stop = color_stop_list[i];
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if (!stop.color_stop.length.has_value()) {
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auto run_start = i - 1;
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auto run_end = find_run_end();
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auto start_position = resolved_color_stops[run_start].position;
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auto end_position = resolved_color_stops[run_end].position;
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auto spacing = (end_position - start_position) / (run_end - run_start);
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for (auto j = run_start + 1; j < run_end; j++) {
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resolved_color_stops[j].position = start_position + (j - run_start) * spacing;
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}
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}
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i++;
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}
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return { gradient_angle, resolved_color_stops };
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}
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static float mix(float x, float y, float a)
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{
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return x * (1 - a) + y * a;
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}
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// Note: Gfx::gamma_accurate_blend() is NOT correct for linear gradients!
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static Gfx::Color color_mix(Gfx::Color x, Gfx::Color y, float a)
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{
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if (x.alpha() == y.alpha() || x.with_alpha(0) == y.with_alpha(0)) {
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return Gfx::Color {
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round_to<u8>(mix(x.red(), y.red(), a)),
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round_to<u8>(mix(x.green(), y.green(), a)),
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round_to<u8>(mix(x.blue(), y.blue(), a)),
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round_to<u8>(mix(x.alpha(), y.alpha(), a)),
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};
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}
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// Use slower but more visually pleasing premultiplied alpha mixing if both the color and alpha differ.
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// https://drafts.csswg.org/css-images/#coloring-gradient-line
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auto mixed_alpha = mix(x.alpha(), y.alpha(), a);
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auto premultiplied_mix_channel = [&](float channel_x, float channel_y, float a) {
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return round_to<u8>(mix(channel_x * (x.alpha() / 255.0f), channel_y * (y.alpha() / 255.0f), a) / (mixed_alpha / 255.0f));
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};
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return Gfx::Color {
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premultiplied_mix_channel(x.red(), y.red(), a),
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premultiplied_mix_channel(x.green(), y.green(), a),
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premultiplied_mix_channel(x.blue(), y.blue(), a),
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round_to<u8>(mixed_alpha),
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};
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}
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void paint_linear_gradient(PaintContext& context, Gfx::IntRect const& gradient_rect, LinearGradientData const& data)
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{
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float angle = normalized_gradient_angle_radians(data.gradient_angle);
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float sin_angle, cos_angle;
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AK::sincos(angle, sin_angle, cos_angle);
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auto length = calulate_gradient_length(gradient_rect, sin_angle, cos_angle);
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Gfx::FloatPoint offset { cos_angle * (length / 2), sin_angle * (length / 2) };
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auto center = gradient_rect.translated(-gradient_rect.location()).center();
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auto start_point = center.to_type<float>() - offset;
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// Rotate gradient line to be horizontal
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auto rotated_start_point_x = start_point.x() * cos_angle - start_point.y() * -sin_angle;
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// FIXME: Handle transition hint interpolation
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auto linear_step = [](float min, float max, float value) -> float {
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if (value < min)
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return 0.;
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if (value > max)
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return 1.;
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return (value - min) / (max - min);
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};
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Vector<Gfx::Color, 1024> gradient_line_colors;
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auto int_length = round_to<int>(length);
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gradient_line_colors.resize(int_length);
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auto& color_stops = data.color_stops;
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for (int loc = 0; loc < int_length; loc++) {
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Gfx::Color gradient_color = color_mix(
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color_stops[0].color,
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color_stops[1].color,
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linear_step(
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color_stops[0].position,
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color_stops[1].position,
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loc));
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for (size_t i = 1; i < color_stops.size() - 1; i++) {
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gradient_color = color_mix(
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gradient_color,
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color_stops[i + 1].color,
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linear_step(
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color_stops[i].position,
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color_stops[i + 1].position,
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loc));
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}
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gradient_line_colors[loc] = gradient_color;
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}
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auto lookup_color = [&](int loc) {
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return gradient_line_colors[clamp(loc, 0, int_length - 1)];
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};
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for (int y = 0; y < gradient_rect.height(); y++) {
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for (int x = 0; x < gradient_rect.width(); x++) {
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auto loc = (x * cos_angle - (gradient_rect.height() - y) * -sin_angle) - rotated_start_point_x;
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// Blend between the two neighbouring colors (this fixes some nasty aliasing issues at small angles)
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auto blend = loc - static_cast<int>(loc);
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auto gradient_color = color_mix(lookup_color(loc - 1), lookup_color(loc), blend);
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context.painter().set_pixel(gradient_rect.x() + x, gradient_rect.y() + y, gradient_color, gradient_color.alpha() < 255);
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}
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}
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}
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}
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