Performance Hints for Silicon Graphics' Implementation of OpenGL on Windows

The following performance hints are of special importance for the OpenGL implementation on Windows. Note that this information may change as more highly tuned versions become available in the future.

• "The Compiled Vertex Arrays Extension" lets you lock down objects that share vertices between adjacent primitives. This reduces per-vertex calculations.

• "The Object Space Vertex Culling Extension" lets you improve performance for datasets with culled vertices. The extension culls vertices based on the vertex normal, allowing vertices to be culled early, before other vertex processing.

• Triangle strips and quad strips are fastest under OpenGL on Windows.

• Use textures to replace complex geometry. This can greatly simplify geometry, resulting in a net speed increase and an improved picture (as long as it does not cause the program to become fill limited).

• When using textures, consider using the subtexture functionality available in OpenGL 1.1 (see "Updating Textures Quickly With Subtextures" or "The Paletted Texture Extension") to make downloading textures more efficient. The paletted texture extension allows texture compression.

• Consider the choice between color index rendering and RGB rendering carefully.

  If OpenGL is rendered in software only, color index rendering may be faster. For example, color index lighting is faster than RGB lighting if lighting is not hardware-accelerated, but the functionality is more limited in color index mode. Also, smaller pixel formats (8-bit color index) are faster in software implementations.

• For fastest RGB texturing performance, set the texture environment to GL_REPLACE, disable dithering, and set the texture filter to GL_NEAREST. With these settings, RGB texturing will run as fast as color index texturing.

• If possible, use interleaved arrays to define primitives. The N3F_V3F and T2F_N3F_V3F formats are fastest.

• Avoid per-fragment operations, if possible. For example, draw large background polygons first without depth buffering, then enable depth buffering for polygons.

• Avoid these expensive modes:

  • alpha test

  • alpha blending, stencil, and logic op

  • fog and anti-aliasing

  • wide lines or points

  • stipple

  • polygon offset

  • texture filters other than GL_NEAREST

  • mipmapping, texture borders

  • glColorMask() other than (0,0,0,0) and (1,1,1,1)