deb9292395
A Xenos RectangleList gives 3 corners of a rectangle; the GPU synthesizes the 4th (v3 = v0 + v2 - v1) and tessellates the quad as two triangles (v0,v1,v2) + (v0,v2,v3). Our expansion emitted only the front triangle, so the movie's fullscreen YUV rect filled half the screen and left a diagonal seam down the frame (absent in canary). expand_rectangles now emits the full 6-index quad. Since v3 has no backing vertex in the guest window, the translated VS synthesizes its attributes: the RectangleList arm maps 6 host verts through [0,1,2, 0,2,3], flags the 4th corner, and emit_vfetch computes that corner's attributes (position and every interpolator) as v0 + v2 - v1 by reading the three real source vertices. Non-rect draws are unaffected (the synth flag is false). Verified: the movie background now fills the whole frame uniformly, no diagonal, matching canary. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>