ANGif is a small class library that can be used to encode Graphics Interchange Format files using a simple interface. It could easily be ported to platforms other than Cocoa (e.g. UIKit/CocoaTouch). The ANGifEncoder class is the root of all GIF encoding, and can be used as follows:
ANGifEncoder * encoder = [[ANGifEncoder alloc] initWithOutputFile:@"myFile.gif" size:CGSizeMake(100, 100) globalColorTable:nil];
[encoder addApplicationExtension:[[ANGifNetscapeAppExtension alloc] init]];
[encoder addImageFrame:anImageFrame];
[encoder addImageFrame:anotherImageFrame];
[encoder closeFile];
The addImageFrame: method takes an instance of ANGifImageFrame, a basic class for enclosing images. The class itself can be instantiated using the initWithPixelSource:colorTable:delayTime: method. As of November 4th, 2011, the best color table to use is ANCutColorTable.
The ANGifImageFramePixelSource protocol is essential to the functionality of ANGif. It is suggested that you make a class that wraps a native image class such as NSBitmapImageRep, and implements all of the required methods.
The Xcode project included with this repository is GifPro, a Mac OS X demo of what ANGif is capable of. The project includes ANNSImageGifPixelSource, an NSBitmapImageRep wrapper that conforms to the ANGifImageFramePixelSource protocol. The ANExportWindow class includes most of the code that directly interfaces the ANGif library.
The GIF format works in a way such that files may only have 256 colors per image. This being said, algorithms exist to accurately calculate the best possible choices of colors for the 256-entry color table. The ANGif library is easily extendable to accomedate any color table algorithm that may be designed in the future.
If you are looking to implement a color table for ANGif, it is suggested that you have a look at the code for the ANColorTable base class. If you are still uncertain of exactly what you need to do to implement a color table, maybe have a look at ANCutColorTable. This was the first color table to be implemented for ANGif, and therefore should be a role model for those that follow.