What's wrong with this code? Help please!

Question

I have been trying to write an image on a layer using Quartz but all I see is totally empty images... this is the code

CGContextRef context = UIGraphicsGetCurrentContext();

CGRect backRect  = CGRectMake (0, 0, image.size.width, image.size.height);

CGLayerRef backLayer = CGLayerCreateWithContext (context, image.size, NULL);
CGContextRef backContext = CGLayerGetContext (backLayer);

CGContextDrawImage(backContext, backRect, image.CGImage);

can you guys please tell me what is wrong with this code?

image is a UIImage taken with the camera.

Yes, the image is there. If I replace the above code with

UIGraphicsBeginImageContext(image.size);  
[image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];

I see the image. But I have to have it in a layer, as it is a sprite.

Answer 1

• Are you sure that the images were found in the right place?
• Is the image format and color numbers supported by this iphone?
• The images are not overdrawn by other drawing calls?
• In the worst case an undetected memory leak caused the images to be overwritten in memory

Answer 2

You're not really doing anything with the layer you created. You should add it to the current context using CGContextDrawLayerAtPoint() or CGContextDrawLayerInRect() or ...

You could add the following:

CGContextDrawLayerInRect(context, backRect, backLayer);

or

CGContextDrawLayerAtPoint(context,CGPointZero,backLayer);

Answer 3

Be aware that a CGLayer is different than a CALayer. A CALayer is what can be animated around by Core Animation, where a CGLayer is just a convenience for pulling together a static 2-D Core Graphics drawing. Because you are referring to this as a sprite, I'm assuming you'll want to animate this around, so CALayer would be the better choice.

I recommend reading the Core Animation Programming Guide, particularly the section on providing layer content. CALayers will give you very good performance when it comes to animation, because they are GPU-accelerated and don't need to be redrawn every frame. Core Graphics will not give you anywhere near acceptable performance for animation, because redraws are expensive operations.