The fragment shaders converted gl_FragCoord.y to the bottom-left based
system of the rectangle uniforms unconditionally, which only holds for
Vulkan, Metal and D3D, where gl_FragCoord.y counts from the top. On
OpenGL it counts from the bottom, so the media viewer and PiP fades,
the content rounding and the incoming call shadow came out mirrored
there. The conversion is now driven by a fragCoordYUp uniform, kept at
offset 8 in every block that needs it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>