Replace layer+MultiEffect mask with GPU-native clipping for rounded
corners. The previous approach created offscreen textures for every
clickable element with rounded corners (used in 34+ files across the
UI), adding 100-300MB VRAM on NVIDIA GPUs.
The new approach uses clip: true on a Rectangle with the corner
radius, which is handled natively by the GPU without creating
intermediate textures.
Visual impact: Minimal - the ripple effect works identically.
The only theoretical difference is slightly less smooth edges on
rounded corners during the ripple animation, which is not noticeable
at 10% opacity during the quick animation.
VRAM improvement: Tested on NVIDIA, ~100-300MB reduction.
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