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LibWeb: Add simple canvas path clipper

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This adds CanvasPathClipper and ScopedCanvasPathClip. These allow
clipping the canvas by some arbitrary path.

This initial implementation is fairly naive, with a good few
allocations, though this can probably be improved in future.
This commit is contained in:
MacDue 2023-04-06 20:52:19 +01:00 • committed by Linus Groh
parent ef58062f71
commit 92d9b6edb8
3 changed files with 112 additions and 0 deletions
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46
Userland/Libraries/LibWeb/HTML/Canvas/CanvasPathClipper.cpp Normal file
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/*
* Copyright (c) 2023, MacDue <macdue@dueutil.tech>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibGfx/AntiAliasingPainter.h>
#include <LibWeb/HTML/Canvas/CanvasPathClipper.h>
namespace Web::HTML {
// FIXME: This pretty naive, we should be able to cut down the allocations here
// (especially for the paint style which is a bit sad).
ErrorOr<CanvasPathClipper> CanvasPathClipper::create(Gfx::Painter& painter, CanvasClip const& canvas_clip)
{
auto bounding_box = enclosing_int_rect(canvas_clip.path.bounding_box());
Gfx::IntRect actual_save_rect {};
auto maybe_bitmap = painter.get_region_bitmap(bounding_box, Gfx::BitmapFormat::BGRA8888, actual_save_rect);
RefPtr<Gfx::Bitmap> saved_clip_region;
if (!maybe_bitmap.is_error()) {
saved_clip_region = maybe_bitmap.release_value();
} else if (actual_save_rect.is_empty()) {
// This is okay, no need to report an error.
} else {
return maybe_bitmap.release_error();
}
painter.save();
painter.add_clip_rect(bounding_box);
return CanvasPathClipper(move(saved_clip_region), bounding_box, canvas_clip);
}
ErrorOr<void> CanvasPathClipper::apply_clip(Gfx::Painter& painter)
{
painter.restore();
if (!m_saved_clip_region)
return {};
Gfx::IntRect actual_save_rect {};
auto clip_area = TRY(painter.get_region_bitmap(m_bounding_box, Gfx::BitmapFormat::BGRA8888, actual_save_rect));
painter.blit(actual_save_rect.location(), *m_saved_clip_region, m_saved_clip_region->rect(), 1.0f, false);
Gfx::AntiAliasingPainter aa_painter { painter };
auto fill_offset = m_bounding_box.location() - actual_save_rect.location();
aa_painter.fill_path(m_canvas_clip.path, TRY(Gfx::BitmapPaintStyle::create(clip_area, fill_offset)), m_canvas_clip.winding_rule);
return {};
}
}