"The bounding shape of the output window is clipped in that case, and the way in which we swap buffers should have nothing to do with it."
No, that's incorrect. Buffer swapping is a hardware operation that always swaps the whole screen (all outputs), unconditionally. It does not do clipping of any sort. It's a GLX function, not GL.
"The bounding shape of the output window is clipped in that case, and the way in which we swap buffers should have nothing to do with it."
No, that's incorrect. Buffer swapping is a hardware operation that always swaps the whole screen (all outputs), unconditionally. It does not do clipping of any sort. It's a GLX function, not GL.