iPhone 3D Programming

Chapter 9. Optimizing

Act, and you shall have dinner; wait, and you shall be dinner.

—Klingon proverb

One reason you might be reading this book in the first place is that you don’t just want pretty graphics; you want fast graphics. Since OpenGL ES gives you the lowest possible level of access to Apple’s graphics hardware, it’s the ideal API when speed is your primary concern. Many speed-hungry developers use OpenGL even for 2D games for this reason.

Until this point in this book, we’ve been focusing mostly on the fundamentals of OpenGL or showing how to use it to achieve cool effects. We’ve mentioned a few performance tips along the way, but we haven’t dealt with performance head-on.

Instruments

Of all the performance metrics, your frame rate (number of presentRenderbuffer calls per second) is the metric that you’ll want to measure most often. We presented one way of determining frame rate in Chapter 7, where we rendered an FPS counter on top of the scene. This was convenient and simple, but Apple’s Instruments tool (Figure 9-1) can accomplish the same thing, and much more—without requiring you to modify your application! The best part is that it’s included in the SDK that you already have.

Warning

As with any performance analysis tool, beware of the Heisenberg effect. In this context, I’m referring to the fact that measuring performance can, in itself, affect performance. This has never been problematic for me, and it’s certainly not as bothersome as a Heisenbug (a bug that seems to vanish ...