GPU clipping: rounded containers render on the device too

The GPU renderer learns to clip. A rounded-rectangle clip - the overflow-hidden-with-a-border-radius that rounds off a card, an avatar, a thumbnail - now renders its contents on the GPU and masks them to the rounded shape on the device, matching the software clip within a rounding level. The renderer became recursive to do it: a clip draws its sub-content to its own transparent GPU layer and composites it back through the mask, and clips inside clips compose. This was the first of the container primitives - clips, transforms, filters - to move off the software-fallback path, and it is the most common one on real pages. The GPU aspect moves 31 to 34. Polygon clip-paths and elliptical corners stay on software. The overall holds at 57.