Why is there no circle or ellipse primitive in OpenGL?

Question

Circles are one of the basics geometric entities. Yet there is no primitives defined in OpenGL for this, like lines or polygons. Why so? It\'s a little annoying to include custo

Answer 1

Because graphic cards operate on 3-dimensional points, lines and triangles. A circle requires curves or splines. It cannot be perfectly represented by a "normal" 3D primitive, only approximated as an N-gon (so it will look like a circle at a certain distance). If you want a circle, write the routine yourself (it isn't hard to do). Either draw it as an N-gon, or make a square (2 triangles) and cut a circle out of it it using fragment shader (you can get a perfect circle this way).