Previously, SkTextBlob was built on every paint in
DisplayListPlayerSkia::draw_glyph_run(), which meant:
- Repeated work when the same display list is painted multiple times
- Glyph arrays were allocated and populated on each paint
Now the blob is built once during display list recording and cached in
GlyphRun.
Move the visual viewport (pinch-to-zoom) transform from a reserved slot
in DisplayList to the AccumulatedVisualContext tree as a root transform
node. Fixed position elements now correctly inherit from this context.
This requires rebuilding the context tree and display list on each zoom
change, but this overhead will be eliminated by future partial context
tree rebuilds.
Adds pinch event handling that adjusts the VisualViewport scale and
offset. VisualViewport's (offset, scale) is then used to construct a
transformation matrix which is applied before display list execution.
Before this change we would emit PushStackingContext/PopStackingContext
display list items regardless of whether the stacking context had any
transform/opacity/clip effects.
Display list size on https://x.com/ladybirdbrowser is reduced from ~2700
to ~800 items.
