The intent of this use of glBitmap is to move the raster position
without drawing anything. However, it may be required to use None
instead of the empty bytes object for this. I couldn't quite verify
this as I don't have an affected system.
The final argument is the 'bitmap' argument. The use of a NULL bitmap
together with nonzero xmove/ymove parameters is explicitly
documented as a valid way to move the raster position
(including to offscreen positions); doing it with a zero byte bitmap
is apparently unsupported in some OpenGL implementation even if the
width×height of the bitmap is 0 pixels.
https://docs.gl/gl3/glBitmap specifically documents that negative width
and height are errors, but doesn't document that a height or width of 0
is invalid.
Jeff Epler
a86ac40e4a