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LibWeb/CSS: Improved implementation of background-blend-mode

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This is a improved version of a73cd88f0c
The old commit was reverted in 552dd18696

The new version only paints an element into a new layer if background
blend modes other than normal are used. The rasterization performance
of most websites should therefore not suffer.

Co-Authored-By: Alexander Kalenik <kalenik.aliaksandr@gmail.com>
This commit is contained in:
Glenn Skrzypczak 2025-03-29 23:44:25 +01:00 • committed by Alexander Kalenik
commit 9973b01848
Notes: github-actions[bot] 2025-04-01 11:39:02 +00:00
16 changed files with 311 additions and 198 deletions
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29
Libraries/LibWeb/Painting/BackgroundPainting.cpp
View file

@ -11,6 +11,7 @@
#include <LibWeb/Layout/TextNode.h>
#include <LibWeb/Layout/Viewport.h>
#include <LibWeb/Painting/BackgroundPainting.h>
#include <LibWeb/Painting/Blending.h>
#include <LibWeb/Painting/DisplayListRecorder.h>
#include <LibWeb/Painting/PaintableBox.h>
@ -77,6 +78,18 @@ void paint_background(PaintContext& context, PaintableBox const& paintable_box,
{
auto& display_list_recorder = context.display_list_recorder();
// https://drafts.fxtf.org/compositing/#background-blend-mode
// Background layers must not blend with the content that is behind the element,
// instead they must act as if they are rendered into an isolated group.
// OPTIMIZATION: It is only required to render the element into an isolated group,
// if a background blend mode other than normal are used.
auto paint_into_isolated_group = any_of(resolved_background.layers, [](auto const& layer) {
return layer.blend_mode != CSS::MixBlendMode::Normal;
});
if (paint_into_isolated_group) {
display_list_recorder.save_layer();
}
DisplayListRecorderStateSaver state { display_list_recorder };
if (resolved_background.needs_text_clip) {
auto display_list = compute_text_clip_paths(context, paintable_box, resolved_background.background_rect.location());
@ -267,6 +280,11 @@ void paint_background(PaintContext& context, PaintableBox const& paintable_box,
}
};
Gfx::CompositingAndBlendingOperator compositing_and_blending_operator = mix_blend_mode_to_compositing_and_blending_operator(layer.blend_mode);
if (compositing_and_blending_operator != Gfx::CompositingAndBlendingOperator::Normal) {
display_list_recorder.apply_compositing_and_blending_operator(compositing_and_blending_operator);
}
if (auto color = image.color_if_single_pixel_bitmap(); color.has_value()) {
// OPTIMIZATION: If the image is a single pixel, we can just fill the whole area with it.
// However, we must first figure out the real coverage area, taking repeat etc into account.
@ -289,6 +307,14 @@ void paint_background(PaintContext& context, PaintableBox const& paintable_box,
image.paint(context, image_device_rect, image_rendering);
});
}
if (compositing_and_blending_operator != Gfx::CompositingAndBlendingOperator::Normal) {
display_list_recorder.restore();
}
}
if (paint_into_isolated_group) {
display_list_recorder.restore();
}
}
@ -404,7 +430,8 @@ ResolvedBackground resolve_background_layers(Vector<CSS::BackgroundLayerData> co
.background_positioning_area = background_positioning_area,
.image_rect = image_rect,
.repeat_x = layer.repeat_x,
.repeat_y = layer.repeat_y });
.repeat_y = layer.repeat_y,
.blend_mode = layer.blend_mode });
}
return ResolvedBackground {