Saving a 32 bit RGBA buffer into a .png file (Cocoa OSX)

Question

I need to save the contents of a pixel editor application into a .png file but I am having trouble finding the best way to accomplish this. The pixel data is stored in a 32 bit RGBA buffer. Can anyone suggest any good tools I could use to accomplish this?

EDIT: Unfortunately, CGImage and representationUsingType: are not supported by cocotron and I need to be able to target my app for PC release as well, can anyone suggest a third way of accomplishing this task?

Answer 1

NSBitmapImageRep should get you what you need. Load the data up into the NSBitmapImageRep and then use representationUsingType:properties: to get it out as a PNG. A quick example:

NSBitmapImageRep *imageRep = 
    [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:imageBuffer
                                            pixelsWide:imageWidth
                                            pixelsHigh:imageHeight
                                         bitsPerSample:8
                                       samplesPerPixel:4
                                              hasAlpha:YES
                                              isPlanar:NO
                                        colorSpaceName:NSDeviceRGBColorSpace
                                          bitmapFormat:NSAlphaFirstBitmapFormat
                                           bytesPerRow:imageWidth * 4
                                          bitsPerPixel:32];
NSData *pngData = [imageRep representationUsingType:NSPNGFileType 
                                         properties:propertyDictionary];

If you can't use these Cocoa methods, check out libpng.

Answer 2

Create a CGImage from the pixel data and feed it to a CGImageDestination.

Don't forget to finalize the destination before releasing it. That step is mandatory, and very easy to forget.