Graphics Reference
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equivalent FPS value onscreen, but an in-app FPS display cannot ever be completely
accurate when measuring Core Animation performance because it only measures the frame
rate inside the app. We know that a lot of the animation happens outside the app (in the
render server process), so while an in-app FPS counter can be a useful tool for certain types
of performance issues, once you've identified a problem area, you will need to get some
more accurate and detailed metrics to narrow down the cause. Apple provides the powerful
Instruments toolset to help us with this.
Instruments
Instruments is an underutilized feature of the Xcode suite. Many iOS developers have either
never used Instruments, or have only made use of the Leaks tool to check for retain cycles.
But there are many other Instruments tools, including ones that are specifically designed to
help us to tune our animation performance.
You can invoke Instruments by selecting the Profile option in the Product menu. (Before
you do this, remember to target an actual iOS device, not the simulator.) This will present
the screen shown in Figure 12.1. (If you don't see all of these options, you might be testing
on the simulator by mistake.)
Figure 12.1 The Instruments tool selection window
 
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