CGImageCreateWithMask with an image as a mask
- by Peyman
Hi
I am trying to use an image (painted as Core Graphics) to create a mask. What I am doing is this
1. creating a Core Graphics path
CGContextSaveGState(context);
CGContextBeginPath(context);
CGContextMoveToPoint(context,circleCenter.x,circleCenter.y);
//CGContextSetAllowsAntialiasing(myBitmapContext, YES);
CGContextAddArc(context,circleCenter.x, circleCenter.y,circleRadius,startingAngle, endingAngle, 0); // 0 is counterclockwise
CGContextClosePath(context);
CGContextSetRGBStrokeColor(context,1.0,0.0,0.0,1.0);
CGContextSetRGBFillColor(context,1.0,0.0,0.0,0.2);
CGContextDrawPath(context, kCGPathFillStroke);
2. then I'm saving the context that has the path just painted
CGImageRef pacmanImage = CGBitmapContextCreateImage (context);
3. restoring the context
CGContextRestoreGState(context);
CGContextSaveGState(context);
4. creating a 1 bit mask (which will provide the black-white mask)
bitsPerComponent = 1;
bitsPerPixel = bitsPerComponent * 1 ;
bytesPerRow = (CGImageGetWidth(imgToMaskRef) * bitsPerPixel);
mask = CGImageCreate(CGImageGetWidth(imgToMaskRef),
CGImageGetHeight(imgToMaskRef),
bitsPerComponent,
bitsPerPixel,
bytesPerRow,
greyColorSpace,
kCGImageAlphaNone,
CGImageGetDataProvider(pacmanImage),
NULL, //decode
YES, //shouldInterpolate
kCGRenderingIntentDefault);
5. masking the imgToMaskRef (which is a CGImageRef imgToMaskRef =imgToMask.CGImage;) with the mask just created
imageMaskedWithImage = CGImageCreateWithMask(imgToMaskRef, mask);
CGContextDrawImage(context,imgRectBox, imageMaskedWithImage);
CGImageRef maskedImageFinal = CGBitmapContextCreateImage (context);
returning the maskedImageFinal to the caller of this method (as wheelChoiceMadeState, which is a CGImageRef) who then updates the CALayer contents property with the image
theLayer.contents = (id) wheelChoiceMadeState;
the problem I am seeing is that the mask does not work properly and looks very strange indeed. I get strange patterns across the path painted by the Core Graphics. My hunch is there is something with CGImageGetDataProvider() but I am not sure.
Any help would be appreciated
thank you
