Speed up UIImage creation from SpriteSheet - ios

Question

I'm not really sure I got the title exactly right, but I'm not sure where my problem is exactly.
I need to load an array of UIImages from an spritesheet, which I'll then use as animations in a UIImageView.
The spritesheet is generated with TexturePacker, which generates the huge atlas (2048x2048) and a json with the sprites descriptions.
Until now, I've had it working without issues, even loading 100 frames in just 0.5-0.8 secs which I was really happy with.
The problem is now I need to load the spritesheets from the Documents folder (they are downloaded, so can't be integrated in the app), so I have to use UIImage imageWithContentsOfFile instead of UIImage imagenamed.
This makes my loading time increase by 5-15 seconds depending the number of frames in the animation.
I'm guessing the problem is that because the image isn't being cached, is loading it for every frame, but I don't see why
This is the code:
// With this line, perfect
//UIImage *atlas = [UIImage imageNamed:#"media/spritesheets/default-pro7#2x.png"];
// But with this one, incredibly looooong loading times
UIImage *atlas = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"media/spritesheets/default-pro7#2x" ofType:#"png"]];
CGImageRef atlasCGI = [atlas CGImage];
for( NSDictionary* dict in frames) {
NSDictionary *frame = [dict objectForKey:#"frame"];
int x = [[frame objectForKey:#"x"] intValue];
int y = [[frame objectForKey:#"y"] intValue];
int width = [[frame objectForKey:#"w"] intValue];
int height = [[frame objectForKey:#"h"] intValue];
NSDictionary *spriteSize = [dict objectForKey:#"spriteSourceSize"];
int realx = [[spriteSize objectForKey:#"x"] intValue];
NSDictionary *size = [dict objectForKey:#"sourceSize"];
int realWidth = [[size objectForKey:#"w"] intValue];
int realHeight = [[size objectForKey:#"h"] intValue];
//Initialize the canvas size!
canvasSize = CGSizeMake(realWidth, realHeight);
bitmapBytesPerRow = (canvasSize.width * 4);
bitmapByteCount = (bitmapBytesPerRow * canvasSize.height);
bitmapData = malloc( bitmapByteCount );
//Create the context
context = CGBitmapContextCreate(bitmapData, canvasSize.width, canvasSize.height, 8, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast);
// Clear background
CGContextClearRect(context,CGRectMake(0.0f,0.0f,canvasSize.width,canvasSize.height));
// Get spriteRect
CGRect cropRect = CGRectMake(x, y, width, height);
CGImageRef imageRef = CGImageCreateWithImageInRect(atlasCGI, cropRect);
//Draw the image into the bitmap context
CGContextDrawImage(context, CGRectMake(realx, 0, width, height), imageRef);
//Get the result image
resultImage = CGBitmapContextCreateImage(context);
UIImage *result = result = [UIImage imageWithCGImage:resultImage];
[images addObject:result];
//Cleanup
free(bitmapData);
CGImageRelease(resultImage);
CGImageRelease(imageRef);
}
I can even try an upload system profiler sessions which show where is taking so much time loading

Answer 1

Well, I finally figured out where the problem was. After looking more carefully with Instruments Time profiler, I noticed a lot of time was spent in copyImageBlockSetPNG , which was what made me believe first that I was loading the image from disk for every frame. turn out, somebody already had this problem Does CGContextDrawImage decompress PNG on the fly?, and it ended being true that I was loading the memory each frame, but not from disk, instead it was being uncompressed from memory in png format for every frame.
In that post theres a solution, which consists in writing the image to a context and getting from it an uncompressed copy of the image.
That works, but I found other way which I believe It's a little bit more efficient
NSDictionary *dict = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES]
forKey:(id)kCGImageSourceShouldCache];
NSData *imageData = [NSData dataWithContentsOfFile:#"path/to/image.png"]];
CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)(imageData), NULL);
CGImageRef atlasCGI = CGImageSourceCreateImageAtIndex(source, 0, (__bridge CFDictionaryRef)dict);
CFRelease(source);
Hope it helps!