Not too happy right now, after rummaging through my code looking for an error I expected to have caused by my own fault, I come across a conversion inaccuracy:

// Note this is already in 2d ortho mode

glPushMatrix();

int x = 500;
int y = 30;

glTranslatef((float)x,(float)y,0.0f);

glBegin(GL_POINTS);
   glVertex2i(0,0);
glEnd();

glPopMatrix();

For some reason, (float)x is getting converted to 499.0f, and in turn, causes the pixel to be drawn at (499,30) instead of (500,30). However, if you change x to something like 300 or so, it gets converted properly, and the pixel gets drawn at (300,30). What can I do to fix this? Is there a better way to get pixel perfect positioning in 2d? Thanks for any help you might provide in advance.

If your card supports either OpenGL1.4 or the GL_ARB_window_pos extension, you can use the glWindowPos command which is pixel-exact but that''s limited for raster position (eg Bitmaps).

Otherwise there is an hint at the OpenGL.org FAQ : How do I draw 2D controls over my 3D rendering?

Thanks vincoof, the hints there helped me with my problem. All is looking alright now.