Change of speed but no change of size after OpenGL Perspective Projection I am new to OpenGL and I am trying to code un optic flow with dots appearing from the background and moving towards the viewer. As a consequence of a perspective projection, the dots are faster and bigger when they move towards the viewer, but they are smaller and slower when they are farther away from the viewer. 

As a result of OpenGL perspective projection, I got the dots moving faster when approaching the viewer, but their size does not change with the distance. Isn't the change of size a consequence of the projection -- just as the change of speed? If not, shall I compute it separately?

Thanks in advance for your help]1
When you draw a point with GL_POINTS, it's not a 3D object with a size in world-space: its size is a fixed number of pixels. Because of that, the size of the point is independent of the distance from the camera.

If you want to draw dots whose size depends on distance, you either need to compute the perspective yourself and change the point size for each point (not recommended, because state changes like that are expensive); or use another method to draw them. For instance, you might draw a quad and use the fragment shader to make it a circle (e.g. by discarding the fragment if the world co-ordinate was more than a particular distance from the centre of the quad, or by using a transparent texture with a circle in it).