Andrew Pouliot

Core Animation debug mode

If you're into optimizing scrolling or drawing performance on the iPhone, then you know that blended layers (ie, non-opaque) can really slow things down. Sometimes it's hard to know what is opaque and what is being blended, however.

The good news is that there is a tool for this! You can easily get a visual readout of all of the layers in your app and their blending. Here is an example:

The red areas are being blended, whereas the green areas are totally opaque, giving the best performance.

Here's how to set it up:

##Debug Mode On-Device

Open up the Instruments tool, and select an iPhone or iPod touch as the applicable device, then add a new Core Animation instrument.

You'll then need to show Detail (View > Detail, or the button in the bottom bar). Then there is a checkbox for "Color blended layers." This is what you want.

Your iPhone or iPod Touch should now switch into red-green mode. This setting is persistent, so you can detach your phone and use it now. To disable, attach to Instruments again and uncheck the box or restart the phone.

##Debug Mode in Simulator

Turns out, there is an easier way! You can do all of this fun in the simulator. Just launch it with the CA_COLOR_OPAQUE environment variable set:

`CA_COLOR_OPAQUE=1 /Developer/Platforms/iPhoneSimulator.platform/Developer/Applications/iPhone\\ Simulator`

##Xcode 4.2 Update

If you're running this version of Xcode, you can enable these options directly in the simulator application.

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And, boom! You can now run your apps as usual using Xcode and they'll show up in the simulator with color blended layers enabled. To disable it, just quit and relaunch Simulator.

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