Hi, I just started using openGL and am having a little trouble. At certain x positions my program is just displaying black verticle lines. Here's a picture of the problem imageshack

And here's the display code.

Code :
void draw(){
	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_POINTS);
	for(int y=-100;y<100;y++){
		for(int x=-400;x<400;x++){
			glVertex2i(x,y);
		}
	}
	glEnd();
	glFlush();
}

Does anyone know why this is happening?

Thanks.