Drawing round points using modern OpenGL

Question

I know how to draw round points using fixed pipeline. However I need to do the same using modern OpenGL. Is it possible, or should I use point sprites and textures?

Answer 1

• Drawing circle with shader.
• OpenGL ES shader sphere.

Answer 2

One way would be to draw point sprites with a circle-texture and a self-made alpha test in the fragment shader:

uniform sampler2D circle;

void main()
{
    if(texture(circle, gl_PointCoord).r < 0.5)
        discard;
    ...
}

But in fact you don't even need a texture for this, since a circle is a pretty well-defined mathematical concept. So just check the gl_PointCoord only, which says in which part of the [0,1] square representing the whole point your current fragment is:

vec2 coord = gl_PointCoord - vec2(0.5);  //from [0,1] to [-0.5,0.5]
if(length(coord) > 0.5)                  //outside of circle radius?
    discard;