Low-End Specific Extensions

Low-End Specific Extensions

For Indy and Indigo2 XL systems, an extension has been developed that increases fill rate by drawing pixels as N x N rectangles (effectively lowering the window resolution). This "framezoom" extension, SGIX_framezoom, is available as a separate patch under both IRIX 5.3 and IRIX 6.2.

Caution: This extension is experimental. The interface and supported systems may change in the future. When using the extension, consider the following performance tips:

The extension works best when texturing is enabled. When pixels are zoomed up by N, you can expect the fill rate to go up by about N2/2. This number is an estimate; a speed-up of this magnitude occurs only if texturing performance has been optimized as explained in the last bullet of "Getting the Optimum Fill Rates".
When texturing is not enabled, performance, although faster than the texture map case, is relatively slow compared to the non-framezoomed case. Actually, a framezoom value of 2 is slower than if framezoom was not enabled. The reason is that the graphics hardware in low-end systems is optimized for flat or interpolated spans, and not for cases where the color changes from pixel to pixel (as with texturing). When pixels are bigger (as with the framezoom extension), this benefit cannot be used.
The framezoom factor can be changed on a frame-to-frame basis, so you can render with framezoom set to a larger value when you're moving around a scene, and lower the value, or turn framezoom off, when there are no changes in the scene.

For more detailed information, see the reference page for glFrameZoomSGIX() for those systems that have the patch installed.