OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Points

Points are represented by a single vertex. The vertex represents a point in four-dimensional homogeneous coordinates. As such, a point really has no area, and so in OpenGL it is really an analogue for a square region of the display (or draw buffer). When rendering points, OpenGL determines which pixels are covered by the point using a set of rules called rasterization rules. The rules for rasterizing a point in OpenGL are quite straightforward—a sample is considered covered by a point if it falls within a square centered on the point’s location in window coordinates. The side length of the square is equal to the point’s size, which is fixed state (set with glPointSize()), or the value written to the gl_PointSize built-in variable in the ...