I couldn’t find any examples of using a mask on a CALayer, so I’m posting one.
Just create a custom view and put this code in it to see how they work.

Or download the sample project I created and posted on my blog.

http://allusions.sourceforge.net/cocoamondo/?p=3

– MatthieuCormier

• (void)awakeFromNib {
  [self maskTest]; }

• (CGImageRef)createMaskImage { [[NSColor colorWithCalibratedWhite:1.0 alpha:1.0] set];

  float minX = 0; float minY = 0; float maxX = 100; float maxY = 100;

  NSBezierPath* path = [NSBezierPath bezierPath]; NSPoint topLeft = NSMakePoint (minX, maxY); NSPoint topRight = NSMakePoint (maxX, maxY); NSPoint bottomRight = NSMakePoint (maxX, minY); NSPoint bottomLeft = NSMakePoint (minX, minY);

  NSPoint centerPoint = NSMakePoint((maxX - minX) * 0.5, (maxY - minY) * 0.5);

  [path moveToPoint:topLeft]; [path lineToPoint:topRight];
  [path curveToPoint:centerPoint controlPoint1:NSMakePoint((maxX - minX) * 0.5, maxY) controlPoint2:centerPoint];
  [path curveToPoint:bottomRight controlPoint1:NSMakePoint((maxX - minX) * 0.5, minY) controlPoint2:bottomRight]; [path lineToPoint:bottomLeft];

  NSImage* maskImage = [[NSImage alloc] initWithSize:NSMakeSize(100, 100)]; [maskImage lockFocus]; { [[NSColor colorWithCalibratedWhite:1.0 alpha:1.0] set]; [path fill]; [path stroke]; } [maskImage unlockFocus];

  CGImageSourceRef source;

  source = CGImageSourceCreateWithData((CFDataRef)[maskImage TIFFRepresentation], NULL); CGImageRef maskRef = CGImageSourceCreateImageAtIndex(source, 0, NULL);

  [maskImage release]; return maskRef;

}

• (void)maskTest { CGRect viewFrame = NSRectToCGRect( self.frame ); viewFrame.origin.y = 0;

  // create a layer and match its frame to the view’s frame self.wantsLayer = YES; CALayer* mainLayer = self.layer; mainLayer.name = @”mainLayer”; mainLayer.frame = viewFrame; mainLayer.delegate = self;

  // causes the layer content to be drawn in -drawRect: [mainLayer setNeedsDisplay];

  CGFloat midX = CGRectGetMidX( mainLayer.frame ); CGFloat midY = CGRectGetMidY( mainLayer.frame );

  // create a “container” layer for all content layers. // same frame as the view’s master layer, automatically // resizes as necessary.
  CALayer* contentContainer = [CALayer layer];
  contentContainer.bounds = mainLayer.bounds; contentContainer.delegate = self; contentContainer.anchorPoint = CGPointMake(0.5,0.5); contentContainer.position = CGPointMake( midX, midY ); contentContainer.autoresizingMask = kCALayerWidthSizable | kCALayerHeightSizable;

  contentContainer.borderWidth = 2.0; contentContainer.borderColor = SFWhiteColor;

  [self.layer addSublayer:contentContainer];

  CALayer* boxLayer = [CALayer layer];
  boxLayer.frame = CGRectMake(0, 0, 100, 100); boxLayer.backgroundColor = CGColorCreateGenericRGB(0.0f,0.0f,0.0f,1.0f); boxLayer.position = CGPointMake(110, 10); boxLayer.anchorPoint = CGPointMake(0,0);

  CALayer* maskLayer = [CALayer layer];
  maskLayer.frame = CGRectMake(0, 0, 100, 100); maskLayer.position = CGPointMake(0, 0); maskLayer.anchorPoint = CGPointMake(0,0);

  CGImageRef maskImage = [self createMaskImage]; [maskLayer setContents:(id)maskImage];

  [boxLayer setMask:maskLayer];

  [contentContainer addSublayer:boxLayer];

  [contentContainer layoutSublayers]; [contentContainer layoutIfNeeded]; }