CGContextClip - Fill intersection - ios

Question

I am trying out a simple fill, two intersecting circles with same radius and to fill the intersection alone.Below is what I tried
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 1.0);
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextSetStrokeColorWithColor(context, [UIColor yellowColor].CGColor);
// Draw first circle
CGContextAddArc(context, 150, 150, 50, 0, 2 * M_PI, 1);
CGContextStrokePath(context);
// Draw second circle
CGContextAddArc(context, 200, 150, 50, 0, 2 * M_PI, 1);
CGContextEOClip(context);
CGContextFillPath(context);
}
My code doesn't even render second circle in context. I have gone through lot of question related to CGContextClip here in forum but most of them uses CGPath in their sample. Only CGpaths can be clipped? Any suggestions or ideas are appreciated.
Thank you

Answer 1

The functions CGContextStrokePath(), CGContextEOClip() and CGContextFillPath()
all clear the current path. Therefore the final CGContextFillPath() has no path to fill.
The following code should now work to draw the intersection of the circles:
// Use first circle as clipping path:
CGContextAddArc(context, 150, 150, 50, 0, 2 * M_PI, 1);
CGContextClip(context);
// Draw second circle:
CGContextAddArc(context, 200, 150, 50, 0, 2 * M_PI, 1);
CGContextFillPath(context);
Update: The following code fills and strokes the intersection:
CGContextSaveGState(context);
CGContextAddArc(context, 150, 150, 50, 0, 2 * M_PI, 1);
CGContextClip(context);
CGContextAddArc(context, 200, 150, 50, 0, 2 * M_PI, 1);
CGContextDrawPath(context, kCGPathFillStroke);
CGContextRestoreGState(context);
CGContextAddArc(context, 200, 150, 50, 0, 2 * M_PI, 1);
CGContextClip(context);
CGContextAddArc(context, 150, 150, 50, 0, 2 * M_PI, 1);
CGContextDrawPath(context, kCGPathStroke);
(Original code which does not work:)
To fill and stroke a path, use CGContextDrawPath():
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 1.0);
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextSetStrokeColorWithColor(context, [UIColor yellowColor].CGColor);
CGContextAddArc(context, 150, 150, 50, 0, 2 * M_PI, 1);
CGContextAddArc(context, 200, 150, 50, 0, 2 * M_PI, 1);
CGContextDrawPath(context, kCGPathEOFillStroke);

Answer 2

Did you tried this
- (UIImage *)colorImage:(UIImage *)origImage withColor:(UIColor *)color
{
UIGraphicsBeginImageContextWithOptions(origImage.size, YES, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, (CGRect){ {0,0}, origImage.size} );
CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, origImage.size.height);
CGContextConcatCTM(context, flipVertical);
CGContextDrawImage(context, (CGRect){ pt, origImage.size }, [origImage CGImage]);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
and you can also try Flood Fill