glDrawArrays gives vertical lines when using GL_POINTS

Question

I'm drawing a points using glDrawArrays with GL_POINTS. On my Intel 82945G Express Chipset Family everything is working fine. But on ATI Radeon Mobility 5730 vertical lines appear randomly when resizing the window.

Here is the code that renders the picture:

glMatrixMode(GL_MODELVIEW);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glColorPointer(color_p_v,GL_FLOAT,offset,color_array);
glDrawArrays(GL_POINTS,0,N);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_COLOR_ARRAY);

I have omitted the array initialization here.

I have checked with gDEBugger that lines are rendered into back buffer after the glDrawArrays function is executed.

I saw similar questions here but people are having similar problems when rendering a texture. My case is a bit simpler.

Also there are advice not to use GL_POINTS but this sounds strange to me.

I want to understand what is going on under the hood.

IMHO there is band implementation in particular driver but what is really going on?

Answer 1

It seems that i have found the problem. When specifying coordinates as in float like (5,6) for instance on ATI i get vertical lines. When specifying (5+0.5f,6+0.5f) everything is fine on all systems. This related how driver interprets the coordinates and pixel position. Integer coordinates values are lying between pixels not in the center of them.

I would like to read more about that issue but failed to find any good article on that.