First time a viewport of a unique size uses the render engine, the texture is ... odd. I can't identify exactly what's failing / miscalculating. It's not 100% guaranteed and is immediately fixed by resizing the viewport by any amount.
Fixed - source render texture was packed as RGB in shared memory. glTexImage2D was expecting word-aligned data so it was skipping bytes (which also was causing the occasional access violation crash)
First time a viewport of a unique size uses the render engine, the texture is ... odd. I can't identify exactly what's failing / miscalculating. It's not 100% guaranteed and is immediately fixed by resizing the viewport by any amount.