How come IKImageBrowserView can resize images so much faster than I can?

Question

This is my image resize code:

CALayer *newCALayer = [[CALayer layer] retain];
NSImage* image = [[NSImage alloc] initWithData:[NSData  dataWithContentsOfFile:path]];
CGImageRef newCGImageFullResolution = [image CGImageForProposedRect:nil context:nil hints:nil];
CGContextRef context = CGBitmapContextCreate(NULL, drawRect.size.width, drawRect.size.height,
                                             CGImageGetBitsPerComponent(newCGImageFullResolution),
                                             CGImageGetBytesPerRow(newCGImageFullResolution),
                                             CGImageGetColorSpace(newCGImageFullResolution),
                                             CGImageGetAlphaInfo(newCGImageFullResolution));
CGContextDrawImage(context, CGRectMake(0, 0, drawRect.size.width, drawRect.size.height), newCGImageFullResolution);
CGImageRef scaledImage = CGBitmapContextCreateImage(context);
newCALayer.contents = (id)scaledImage;
CGImageRelease(scaledImage);
newCALayer.contentsGravity = kCAGravityResizeAspect;
newCALayer.opacity = 0.0;
newCALayer.anchorPoint = CGPointMake(0.0f,0.0f);
newCALayer.frame = CGRectMake( 0.0, 
          0.0, 
          [Singleton sharedSingleton].fullscreenRect.size.width,
          [Singleton sharedSingleton].fullscreenRect.size.height);
[newCALayer setAutoresizingMask:kCALayerWidthSizable | kCALayerHeightSizable];
//CGImageRelease(cgImageFullResolution); (bonus points if you can explain why I can't release this! I mean, I can release the scaled image ok??)
CGContextRelease(context);
[image release];

I am doing all of this from a background thread in order to preload pictures so my GUI feels snappy. It took some work getting synchronization and what not set up so the CALayers ends up in view.

But I believe the term for describing how fast this is would be "it's a dog".

Comparing to IKImageView - that thing flings up thumbnails of images faster than I can scroll.

Does anybody have some suggestions for how to handle this better than I am doing it now?

In other words, my problem is that I want to have a super-fast UX. I believe the way to accomplish this is by preloading things to CALayers (this may be wrong? I tried NSImageView and some IK-stuff, but at least CALayer is better than that).

Answer 1

ImageKit is probably using CGImageSourceCreateThumbnailAtIndex() to quickly get an image appropriate to the destination, rather than reading in the entire image file.

Answer 2

Here:

NSImage *image = [[[NSImage alloc] initWithContentsOfFile:path] autorelease];
[image setScalesWhenResized:YES]; // *
[image setDataRetained:YES]; // *
[image setSize:desiredNewSize];

Then use the image as it is.

As for why your app is slow, run it under Instruments. That will tell you specifically where you are spending the majority of the processor time you use—it may not be in your scaling code after all.

*Since 10.6, these messages do nothing useful and are deprecated, so you can omit them if you are requiring Snow Leopard or later.