How to tile the contents of a CALayer?

Question

I would like to tile a CGImage across a CALayer, but it seems to only want to stretch it.

The example code:

 self.background = [UIImage imageNamed: @"Background.png"];
 [documentDisplay.layer setContents: self.background.CGImage];

I would like to avoid subclassing if I could.

Answer 1

You can create a color with a pattern image and set that as the background color of the layer.

To do that you need wrap your CGImage in a CGPattern and make a CGColor from it.

// callback for CreateImagePattern.
static void drawPatternImage (void *info, CGContextRef ctx)
{
    CGImageRef image = (CGImageRef) info;
    CGContextDrawImage(ctx, 
                       CGRectMake(0,0, CGImageGetWidth(image),CGImageGetHeight(image)),
                       image);
}

// callback for CreateImagePattern.
static void releasePatternImage( void *info )
{
    CGImageRelease((CGImageRef)info);
}

//assume image is the CGImage you want to assign as the layer background
int width = CGImageGetWidth(image);
int height = CGImageGetHeight(image);
static const CGPatternCallbacks callbacks = {0, &drawPatternImage, &releasePatternImage};
CGPatternRef pattern = CGPatternCreate (image,
                        CGRectMake (0, 0, width, height),
                        CGAffineTransformMake (1, 0, 0, 1, 0, 0),
                        width,
                        height,
                        kCGPatternTilingConstantSpacing,
                        true,
                        &callbacks);
CGColorSpaceRef space = CGColorSpaceCreatePattern(NULL);
CGFloat components[1] = {1.0};
CGColorRef color = CGColorCreateWithPattern(space, pattern, components);
CGColorSpaceRelease(space);
CGPatternRelease(pattern);
yourLayer.backgroundColor = color; //set your layer's background to the image
CGColorRelease(color);

This code is modified from the GeekGameBoard sample code.

Answer 2

The simplest code to accomplish this is:

CALayer *layer = [CALayer layer];
layer.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"background_tile"]].CGColor;