iphone stroke path used for clipping UIImage - iphone

Question

I'm very new to CoreGraphics (although I've been doing iphone programming for a while)
Question, I have this snippet that scales proportionally and clips an UIImage to a circle:
-(UIImage *)counterpartImageForSchedule:(Schedule *)counterpartSchedule inSize:(CGSize)size
{
// This function returns a newImage, based on image, that has been:
// - scaled to fit in (CGRect) rect
// - and cropped within a circle of radius: rectWidth/2
UIImage *image=[UIImage imageNamed:#"fakeuser1.png"];
// when kendy sends hash, check that this image is not on the cache, otherwise download, clip & stylized
UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.height), NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
//Get the width and heights
CGFloat imageWidth = image.size.width;
CGFloat imageHeight = image.size.height;
CGFloat rectWidth = size.width;
CGFloat rectHeight = size.height;
//Calculate the scale factor
CGFloat scaleFactorX = rectWidth/imageWidth;
CGFloat scaleFactorY = rectHeight/imageHeight;
if (scaleFactorX>scaleFactorY) {
scaleFactorY=scaleFactorX;
} else
{
scaleFactorX=scaleFactorY;
}
//Calculate the centre of the circle
CGFloat imageCentreX = rectWidth/2;
CGFloat imageCentreY = rectHeight/2;
// Create and CLIP to a CIRCULAR Path
// (This could be replaced with any closed path if you want a different shaped clip)
CGFloat radius = rectWidth/2;
CGContextBeginPath (context);
CGContextAddArc (context, imageCentreX, imageCentreY, radius, 0, 2*M_PI, 0);
CGContextClosePath (context);
CGContextClip (context);
//Set the SCALE factor for the graphics context
//All future draw calls will be scaled by this factor
CGContextScaleCTM (context, scaleFactorX, scaleFactorY);
// the stroke
// Draw the IMAGE
CGRect myRect = CGRectMake(0, 0, imageWidth, imageHeight);
[image drawInRect:myRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
Question is, how can I stroke the path I'm using to clip the image (say, 4 pixels with black or white color)? do i need to draw a new one?
any help is much appreciated!

Answer 1

A path can be an object like any other - in this case, a CGPath (CGPathRef). Before using the path for anything, encapsulate it as a CGPath (in this case, probably a CGMutablePathRef, or perhaps you can call CGContextCopyPath before using the path to clip to). Now you can reuse that path.
Here's an example from one of my apps where I form a path, then stroke it, and then clip to the same path (c is the graphics context):
CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, nil, CGRectGetMaxX(r) - radius, ins);
CGPathAddArc(path, nil,
radius+ins, radius+ins, radius, -M_PI/2.0, M_PI/2.0, true);
CGPathAddArc(path, nil,
CGRectGetMaxX(r) - radius, radius+ins, radius, M_PI/2.0, -M_PI/2.0, true);
CGPathCloseSubpath(path);
CGContextAddPath(c, path);
CGContextSetLineWidth(c, 2);
CGContextStrokePath(c);
CGContextAddPath(c, path);
CGContextClip(c);
CGPathRelease(path);
Another possibility is to use UIBezierPath - a full-fledged Objective-C object, instead of CGContext functions. It encapsulates a CGPath and you can reuse that path - clip to it, then stroke it. Or the other way round.