Well, glPointSize() won't change anything because you have a call to glPointParameter().
// Do even more strange stuff I don't quite understand glPointParameterfARB( GL_POINT_FADE_THRESHOLD_SIZE_ARB, 60.0f ); glPointParameterfARB( GL_POINT_SIZE_MIN_ARB, 5.0f ); glPointParameterfARB( GL_POINT_SIZE_MAX_ARB, maxSize ); glTexEnvf( GL_POINT_SPRITE_ARB, GL_COORD_REPLACE_ARB, GL_TRUE ); glEnable( GL_POINT_SPRITE_ARB );
You *need* to research this stuff in order to understand what your doing here. I'll try to explain it a bit, but to be honest, I've never used this before, so this is all comming out of the book "Beginning OpenGL Game Program" (which is an excellent read, and explains this pretty nicely). The extension that you are using simply makes point's sizes affected by distance from the camera (like any other object).
The first parameter to glPointParameterARB() defines what is being changed. GL_POINT_FADE_THRESHOLD_SIZE_ARB determines how small a point can get before OpenGL makes it transparent (not sure if it will actually be transparent without enabling blending first). GL_POINT_SIZE_MIN determines the minimum size that a point can be, you can figure out GL_POINT_SIZE_MAX, then.
GL_POINT_DISTANCE_ATTENUATION is a little more interesting. It determines the formula used to calculate the size of points. It is, 1/(a + b*d + c *d^2), where a b and c are the values in the parameters you pass it (in this case, 'quadratic').
So, to change the point size, you need to change GL_POINT_SIZE_MAX and MIN. Looks like you've already got a global or something which is used for MAX.
Hope that helps.