18.6 Rendering Images Efficiently

To improve performance when drawing pixel rectangles, follow these guidelines:

• Disable all per-fragment operations.
• Disable texturing and fog.
• Define images in the native hardware format so type conversion is not necessary.
• Know where the bottleneck is.

  Similar to polygon drawing, there can be a pixel-drawing bottleneck due to overload in host bandwidth, processing, or rasterizing. When all modes are off, the path is most likely limited by host bandwidth, and a wise choice of host pixel format and type pays off tremendously. For this reason, using type GL_UNSIGNED_BYTE, for the image components is sometimes faster.

  Zooming up pixels may create a raster bottleneck.

• A big pixel rectangle has a higher throughput (that is, pixels per second) than a small rectangle. Because the imaging pipeline is tuned to trade off a relatively large setup time with a high throughput, a large rectangle amortizes the setup cost over many pixels.