Speed up UIImage creation from SpriteSheet

问题

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

回答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!

来源：https://stackoverflow.com/questions/15303053/speed-up-uiimage-creation-from-spritesheet