I’m working in an older fixed-function codebase and this is causing points that are intended to be square to appear circular if GL_MULTISAMPLE is enabled (when rendering to an MSAA back buffer). Point rasterization produces a fragment for each framebuffer pixel with one or more sample points that intersect the region lying within the circle having diameter equal to the current point width and centered at the point’s (Xw,Yw)” “If MULTISAMPLE_ARB is enabled, and SAMPLE_BUFFERS_ARB is a value of one, then points are rasterized using the following algorithm, regardless of whether point antialiasing (POINT_SMOOTH) is enabled or disabled.
I learned somewhat recently about this behavior described in the GL_ARB_multisample spec:
