at the moment I am trying to set the point size depending on a zoom level in my OpenGL 3.3 viewer. I found that in my environment there is a difference between using glPontSize in the C++ program and using gl_PointSize in the vertex shader.
When I zoom out the pointsize value gets small, in both cases (I compute the value myself and use the same one in both cases).
In the shader case, the points vanishes at some point due to the small point size I guess (or maybe fading is involved too).
If I set the point size in the main program using glPointSize, the point never vanish completely, I guess it always has a one pixel width.
I wonder what is the reason for this difference. I tried to use multi sampling as well, but in the case of not using the shader I never achieved that the point vanishes completely.
In the OpenGL 3.3 spec in my understanding there is no statement that would indicate that behaviour.
Does anyone has a hint what both cases do internally or can me explain what the difference really is?