On the 3DS, for some cores, the screen will flicker if OSD is enabled,
and sometimes when going in and out of the menu.
As far as I can tell, this happens when a frame is dup'd, and we send
0x0 as the frame to the gfx driver. When that happens, we still draw
the OSD, using a vertex shader to transform and render it at the right
size.
When the frame is 0x0, though, the vertex shader uniforms are never
_reset_ to redraw the previous frame, so it's drawn with different
params, and gets drawn the wrong size. It will draw as the correct
size when the correct vertex shader uniforms are set, and the
incorrect size when the incorrect uniforms are set, causing
flickering.
At least, that's what I think is happening. Forcing the vertex shader
to be set regardless of whether the frame data is set fixes it, at
least during some light testing with PCSX.
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