HP Workstation zx2000 HP OpenGL Implementation Guide for HP-UX 11.X (IPF versi - Page 39

programming hints Performance is increased by maximizing the number of vertices per Begin/End pair. If your vertex data in memory is organized in a linear, rather than a random manner, performance is enhanced by taking advantage of vertex pre-fetch. It is most efficient to use 32-bit float data, which avoids the need to convert data. texture downloading performance This section includes some helpful hints for improving the performance of your program when downloading textures. ■ If you are downloading MIPmaps, always begin with the base level (level 0) first. ■ If it is possible, you should use texture objects to store and bind textures. ■ If you are doing dynamic downloading of texture maps, you will get better performance by replacing the current texture with a texture of the same width, height, border size, and format. This should be done instead of deleting the old texture and creating a new one. selection performance To increase the performance of selection (glRenderMode GL_SELECTION) it is recommended that the following capabilities be disabled before entering the selection mode. GL_TEXTURE_* GL_TEXTURE_GEN_* GL_FOG GL_LIGHTING state change OpenGL state setting commands can be classified into two different categories. The first category is vertex-data commands. These are the calls that can occur between a glBegin/glEnd pair: glVertex glColor glIndex glNormal glEdgeFlag glMaterial glTexCoord The processing of these calls is very fast. Restructuring a program to eliminate some vertex data commands will not significantly improve performance. The second category is modal state-setting commands, or sometimes referred to as "mode changes." These are the commands that: ■ turn on/off capabilities ■ change attribute settings for capabilities ■ define lights ■ change matrices OpenGL implementation guide 5-5