OpenGL Programming Guide

Appendix HProgramming Tips

OpenGL Performance Tips

• Use glColorMaterial() when only a single material property is being varied rapidly (at each vertex, for example). Use glMaterial() for infrequent changes, or when more than a single material property is being varied rapidly.
  
  

• Use glLoadIdentity() to initialize a matrix, rather than loading your own copy of the identity matrix.
  
  

• Use specific matrix calls such as glRotate*(), glTranslate*(), and glScale*(), rather than composing your own rotation, translation, and scale matrices and calling glMultMatrix().
  
  

• Use glPushAttrib() and glPopAttrib() to save and restore state values. Use query functions only when your application requires the state values for its own computations.
  
  

• Use display lists to encapsulate potentially expensive state changes. For example, place all the glTexImage*() calls required to completely specify a texture, and perhaps the associated glTexParameter*(), glPixelStore*(), and glPixelTransfer*() calls as well, into a single display list. Call this display list to select the texture.
  
  

• Use display lists to encapsulate the rendering calls of rigid objects that will be drawn repeatedly.
  
  

• Use evaluators even for simple surface tessellations to minimize network bandwidth in client-server environments.
  
  

• Provide unit-length normals if it's possible to do so, and avoid the overhead of GL_NORMALIZE. Avoid using glScale*() when doing lighting because it almost always requies that GL_NORMALIZE be enabled.
  
  

• Set glShadeModel() to GL_FLAT if smooth shading isn't required.
  
  

• Use a single glClear() call per frame if possible. Do not use glClear() to clear small subregions of the buffers; use it only for complete or near-complete clears.
  
  

• Use a single call to glBegin(GL_TRIANGLES) to draw multiple independent triangles, rather than calling glBegin(GL_TRIANGLES) multiple times, or calling glBegin(GL_POLYGON). Even if only a single triangle is to be drawn, use GL_TRIANGLES rather than GL_POLYGON. Use a single call to glBegin(GL_QUADS) in the same manner, rather than calling glBegin(GL_POLYGON) repeatedly. Likewise, use a single call to glBegin(GL_LINES) to draw multiple independent line segments, rather than calling glBegin(GL_LINES) multiple times.
  
  

• In general, use the vector forms of commands to pass precomputed data, and use the scalar forms of commands to pass values that are computed near call time.
  
  

• Avoid making redundant mode changes, such as setting the color to the same value between each vertex of a flat-shaded polygon.
  
  

• Be sure to disable expensive rasterization and per-fragment operations when drawing or copying images. OpenGL will apply textures to pixel images if asked to!

OpenGL Programming Guide