Account for the framespace offset on perspective fx and fy of each map
point.
This is just a workaround because I could not understand exactly why it
is needed. When no perspective is used, the viewport is set to the size
of the surface, and each map point seems to be used as is, with no
adjustment being needed.
However, when the map is not flat (perspective is used), a more complex
math is used to find the glViewport size. It ends up being bigger, but
there are some offsets used to compensate that, gc->shared->ax/y, which
are added to each vertex before pushing them. Thus, it seems to me that
the framespace offset should not be added to them, but things are weird
if this is not done.
Anyway, I just added those offsets, and it should not impact on gl_x11
since it's not using framespace, and software engines don't seem to
implement perspective anyway, so it all should be fine.
If anyone understands better what's going on here, please make a proper
fix or at least contact me to explain the problem, and maybe I can fix
it by myself.
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