Rendering issue with tornado in Lunar Silver Star

[hrydgard]

Thanks xMoJox12 for reporting on discord!

Happens on PC, all backends.

1.15:

1.14.4:

Frame dump:

ULUS10482_1.zip

[hrydgard]

This turns out to be fallout from #17032 - was expected we'd run into something eventually...

The game uses the blend mode add: 2.0 * src.a, 1.0 - 2.0 * dst.a which isn't supported by non-PSP GPUs, so we go on the fallback path where we copy the framebuffer and blend in the shader, and we'd really need to copy between every draw here.

I think we can save the optimization in Dante's Inferno by only "preserving" the copied framebuffer if we did the copy because of overlap, and not in case of weird blend modes. Will fix for 1.15.4.