You can see similar problems even without anti-aliasing. If you have three collinear points A B C, drawing a line from A to B and then B to C may hit slightly d

You can see similar problems even without anti-aliasing. If you have three collinear points A B C, drawing a line from A to B and then B to C may hit slightly different pixels compared to just drawing a single line from A to C. If you try to draw a polygonal mesh which has T-junctions (overlapping edges whose endpoints are not identical) you can end up with slight gaps between adjacent polygons. In 3 dimensions, a similar phenomenon causes "Z-fighting". https://en.wikipedia.org/wiki/Z-fighting https://en.wikipedia.org/wiki/Z-fighting