WIP: cogl/clip-stack-gl: Allow writing to two bits of the stencil buffer
The old mask of 0x1 meant that the if (merge)
code paths did not work
because stencil buffer entries would be limited to:
GL_INCR(old value) & 0x1 <= 0x1
So then the GL_DECR
step would always result in every stencil entry
becoming zero. The stencil buffer was left always empty when
merge == TRUE
and didn't stencil anything. The good news is it was
hard to notice this bug because the if (!rect->can_be_scissor)
optimization was causing us to skip the broken code in most cases.
Using a mask of 0x3 is sufficient because we only ever GL_INCR
up to
a maximum value of 2. So now GL_DECR
can actually result in some values
being non-zero.