Lighting Tips

Since lights add a per-vertex cost to each rendered frame, you can achieve significant performance improvements by being careful about how you use them in your application. Most of the following tips derive from the maxim, "the fastest code is code that is never called."

• Use as few lights as possible. If you just need to bring up the overall level of lighting, use the ambient light instead of adding a new light. (It's much cheaper.)
• Directional lights are cheaper than point lights or spotlights. For directional lights, the direction to the light is fixed and doesn't need to be calculated on a per-vertex basis.
• Spotlights can be cheaper than point lights, because the area outside of the cone of light is calculated quickly. Whether or not they are cheaper depends on how much of your scene is lit by the spotlight.
• Use the range parameter to limit your lights to only the parts of the scene you need to illuminate. All the light types exit fairly early when they are out of range.
• Specular highlights almost double the cost of a light—use them only when you must. Use the D3DLIGHT_NO_SPECULAR flag in the D3DLIGHT2 structure as often as reasonable. When defining materials you must set the specular power value to zero to turn off specular highlights for that material—simply setting the specular color to 0,0,0 is not enough.