Sub pixel drawing with opengl

Question

I am drawing lots of small black rectangles to the white screen and as they move about and zoom it doesn't look very graceful.

How can I draw them so if the edge lies between pixels, the pixels will be grey rather than black?

Answer 1

Sub-pixel rendering is actually more complicated than regular anti-aliasing. If you're using a display with pixels in RGB format, then a gray shape ending halfway through a pixel might be rendered as yellow or as cyan, depending on which side of the pixel the shape lies. This can look strange when the resulting image is not drawn in native resolution or on a display with a different layout than expected, but otherwise it can look quite nice.

Here is a sample of sub-pixel rendering applied to text; the left panel is color, the center panel is the displayed version of the color, and the right panel is the perceived brightness. Notice that accuracy in hue is exchanged for accuracy in brightness.

One approach might be to render each channel separately, each slightly offset in rendering space by the appropriate amount, so that the combined image is in full color. Each of the channels must be the same resolution as the resulting image; each channel is rendered with anti-aliasing the same way as the original would have been, except the other colors are ignored. Once the channels are created, they can be combined with simple addition. I don't know of a "pure" solution like the glEnable/glHint versions available for normal anti-aliasing, but it may exist or may in the future.

Answer 2

What you are effectively asking for is anti-aliasing ,and there are numerous ways of doing it. One way is summarized in this gamedev topic: http://www.gamedev.net/topic/107637-glenablegl_polygon_smooth/ .

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

glHint(GL_POINT_SMOOTH, GL_NICEST);
glHint(GL_LINE_SMOOTH, GL_NICEST);
glHint(GL_POLYGON_SMOOTH, GL_NICEST);

glEnable(GL_POINT_SMOOTH);
glEnable(GL_LINE_SMOOTH);
glEnable(GL_POLYGON_SMOOTH);

Answer 3

glEnable(GL_SMOOTH); should do it.