A new display list item type named PaintScrollBar is introduced. Having
a dedicated type for scroll bars allows the thumb position to be updated
without rebuilding a display list. This was not possible with
FillRectWithRoundedCorners that does not allow to tell whether it
belongs to scroll thumb.
While introducing clip and scroll frame trees, I made a mistake by
assuming that the paintable tree includes boxes from nested navigables.
Therefore, this comment in the code was incorrect, and clip/scroll
frames were simply not assigned for iframes:
// NOTE: We only need to refresh the scroll state for traversables
// because they are responsible for tracking the state of all
// nested navigables.
As a result, anything with "overflow: scroll" is currently not
scrollable inside an iframe
This change fixes that by ensuring clip and scroll frames are assigned
and refreshed for each navigable. To achieve this, I had to modify the
display list building process to record a separate display list for each
navigable. This is necessary because scroll frame ids are local to a
navigable, making it impossible to call
`DisplayList::apply_scroll_offsets()` on a display list that contains
ids from multiple navigables.
Instead of carrying the display list for a mask in each command that
might potentially be affected by "background-clip: text", this change
introduces a new AddMask command that is applied once for all
background layers within one box.
The new AddMask command includes a rectangle for the mask destination
that is translated by the corresponding scroll offset.
Fixes https://github.com/LadybirdBrowser/ladybird/issues/857
Contrary to LibGfx, where corner clipping was implemented by sampling
and blitting pixels under corners into a temporary bitmap, Skia allows
us to simply apply a mask. As a result, we no longer need the
BlitCornerClipping command, which has become a no-op.
- SampleUnderCorners is renamed to AddRoundedRectClip
- The optimization that skipped unnecessary blit and sample commands has
been removed. However, this should not result in a performance
regression because Skia seems to perform mask rasterization lazily.
Before this change, "background-clip: text" was implemented by saving a
Vector<Gfx::Path> of all glyphs needed to paint a mask for the
background. The issue with this approach was that once glyphs were
extracted into vector paths, the glyph rasterization cache could no
longer be utilized.
With this change, all text required for mask painting is saved in a
nested display list and rasterized as a regular text.
With this change display list player will be able to recurse into
executing another display list, without having to construct new display
list player. It is going to be useful in the upcoming changes to paint
a mask from a display list owned by a command.
CommandResult was needed by LibGfx display list player that could have
failed to allocate a temporary bitmap for painting a stacking context
with CSS transforms. This is no longer an issue with Skia painter, so
we can delete CommandResult::SkipStackingContext handling path.
With this change, instead of recording a display list item for each
instance of a repeated background, a new DrawRepeatedImmutableBitmap
type is used. This allows the painter to use optimized repeated image
painting and, when the GPU backend is used, avoid re-uploading the image
texture for each repetition.
Some screenshot tests are affected, but there are no visible
regressions.
https://null.com/games/chainstaff works a lof faster with this change.
Skia now uses GPU-accelerated painting on Linux if Vulkan is available.
Most of the performance gain is currently negated by reading the GPU
backend back into RAM to pass it to the Browser process. In the future,
this could be improved by sharing GPU-allocated memory across the
Browser and WebContent processes.
If Metal context and IOSurface are available, Skia painter will use
Ganesh GPU backend on macOS, which is noticeably faster than the default
CPU backend.
Painting pipeline:
1. (WebContent) Allocate IOSurface for backing store
2. (WebContent) Allocate MTLTexture that wraps IOSurface
3. (WebContent) Paint into MTLTexture using Skia
4. (Browser) Wrap IOSurface into Gfx::Painter and use
QPainter/CoreGraphics to blit backing store into viewport.
Things we should improve in the future:
1. Upload textures for images in advance instead of doing that before
every repaint.
2. Teach AppKit client to read directly from IOSurface instead of
copying.
