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LibWeb: Apply scroll boxes offsets after painting commands recording

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With this change, instead of applying scroll offsets during the
recording of the painting command list, we do the following:
1. Collect all boxes with scrollable overflow into a PaintContext,
   each with an id and the total amount of scrolling offset accumulated
   from ancestor scrollable boxes.
2. During the recording phase assign a corresponding scroll_frame_id to
   each command that paints content within a scrollable box.
3. Before executing the recorded commands, translate each command that
   has a scroll_frame_id by the accumulated scroll offset.

This approach has following advantages:
- Implementing nested scrollables becomes much simpler, as the
  recording phase only requires the correct assignment of the nearest
  scrollable's scroll_frame_id, while the accumulated offset from
  ancestors is applied subsequently.
- The recording of painting commands is not tied to a specific offset
  within scrollable boxes, which means in the future, it will be
  possible to update the scrolling offset and repaint without the need
  to re-record painting commands.
This commit is contained in:
Aliaksandr Kalenik 2023-12-29 06:10:32 +01:00 • committed by Andreas Kling
parent d3025668a4
commit ac6b3c989d
12 changed files with 307 additions and 24 deletions
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11
Userland/Libraries/LibWeb/Painting/PaintContext.h
View file

@ -72,11 +72,14 @@ public:
double device_pixels_per_css_pixel() const { return m_device_pixels_per_css_pixel; }
CSSPixelPoint scroll_offset() const { return m_scroll_offset; }
void translate_scroll_offset_by(CSSPixelPoint offset) { m_scroll_offset.translate_by(offset); }
u32 allocate_corner_clipper_id() { return m_next_corner_clipper_id++; }
struct ScrollFrame {
i32 id { -1 };
CSSPixelPoint offset;
};
HashMap<Painting::PaintableBox const*, ScrollFrame>& scroll_frames() { return m_scroll_frames; }
private:
Painting::RecordingPainter& m_recording_painter;
Palette m_palette;
@ -85,9 +88,9 @@ private:
bool m_should_show_line_box_borders { false };
bool m_should_paint_overlay { true };
bool m_focus { false };
CSSPixelPoint m_scroll_offset;
Gfx::AffineTransform m_svg_transform;
u32 m_next_corner_clipper_id { 0 };
HashMap<Painting::PaintableBox const*, ScrollFrame> m_scroll_frames;
};
}