Skipping the 'CompressResources' build step for Xcode iPhone apps

Question

Is it possible to set an iPhone Xcode project to skip the 'CompressResources' build step?

Specifically, I want to skip the stage where it runs pngcrush on all of my .png files, many of which don't survive the experience in a form which my app can read.

Edit: the version of pngcrush used creates png files which contain a non-standard 'mandatory, private' chunk which explicitly prevents decoding. I've modified my png reader to handle these files, but I'd still like a per-project method of skipping this step. One of the other side effects of pngcrush is that it doesn't save the colour value of transparent pixels, so alpha-ed textures show fringing at smaller mip levels.

The iphone png format is described here: https://web.archive.org/web/20110519164905/http://modmyi.com/wiki/index.php/Iphone_PNG_images. In short,

• Skip the CgBI chunk
• Skip the zlib headers
• Swap BGR to RGB channel order

Edit: It appears it also premultiplies the alpha, so:

• Divide by alpha

Answer 1

You can add "IPHONE_OPTIMIZE_OPTIONS=-skip-PNGs" to your project settings to prevent the png mangling, but be careful with it, you might need to optimize the icon and Default.png separately then.

Answer 2

The iphoneos-optimize script converts PNG files into a nonstandard format that is optimized for display on the iPhone. The script will convert any files with the png extension that it finds inside your app bundle.

I had a similar problem, and solved it by giving my file the extension _png (i.e., prefixed an underscore). iphoneos-optimize ignored it and left it a regular PNG file. If you can deal with it that way, it's probably a lot safer than mucking about with the build scripts.

Answer 3

• Open build settings
• Under "packaging" choose Compress PNG files
• Choose "NO"