* Replace saveLayer with MaskFilter for drop shadows
Drop shadows now draw directly with MaskFilter.MakeBlur instead of
saveLayer + ImageFilter. Eliminates per-shadow offscreen buffer
allocation, significantly improving render throughput for scenes
with many shadowed nodes.
Text shadows still use saveLayer (MaskFilter can't be applied to
text glyphs individually).
Benchmark: 50 shadow nodes render at 1.55ms/frame (scene change).
* Cache per-node SkPictures for effect rendering
Nodes with visible effects (shadows, blurs) are recorded into
individual SkPictures and replayed on subsequent scene redraws.
Only the modified node re-records; unchanged shadow nodes replay
from cache.
- MaskFilter.MakeBlur for drop shadows instead of saveLayer
- Reusable effectLayerPaint and cached ImageFilters/MaskFilters
- invalidateNodePicture() called on node update
- invalidateAllPictures() on font load; invalidateScenePicture()
preserves node cache for scene-only invalidation
- Shadow benchmark: 50 nodes at 1.47ms/frame (scene change)
* Update changelog with shadow rendering performance improvements
a9a1f9ac1f