Pro OpenGL ES for iOS

298 CHAPTER 9: Performance ’n’ Stuff^

The images that work best when compressed are those with color palettes that rely

heavily on one or two parts of the spectrum. The more varied your colors, the harder it

will be minimize the artifacting. The image of Hedly works better than the earth’s texture

map, because the former is largely grays and greens, while the latter is composed of

greens, browns, grays (for the polar regions), and blue.

Figure 9-5. Texture (from left ot right): 32 bit, RGB565, RGBA5551, and RGBA:4444

Other Tips to Remember

The following are some useful tips to keep in mind:

„ Even though multisample antialiasing can be very useful in smoothing

out your images, it means sudden death in the performance

department, cutting frame rates by 30 percent or more. So, you must

really, really need to use it.

„ Avoid using GL_ALPHA_TEST. This was never covered, but it can also kill

performance as much as MSAA.

„ When going to background, make sure to stop the animation and

delete any easily re-created resources.

„ Minimize the use of any calls that return information from the system,

such as the glGet* family of methods, especially glGetError(). Many

of these will force any previous commands to execute before state

information can be retrieved.

„ Use as few lights as possible. Going down to only a single light (the

sun), by turning off the fill and the ambient lights, increased frame

rates by as much as 30 percent on my iPad 2.