Changing line width of CGContext while changing the image colour? - ios

Question

I am trying to change the width and color of a rectangle that is drawn using CG. In the following function I am masking the image with a different color, but how do I change the width?
- (void)colorImage:(UIImage *)origImage withColor:(UIColor *)color withWidth:(float) width
{
UIImage *image = origImage;
NSLog(#"%f", width);
CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, width);
CGContextClipToMask(context, rect, image.CGImage);
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImage *flippedImage = [UIImage imageWithCGImage:img.CGImage
scale:1.0 orientation: UIImageOrientationDownMirrored];
self.image = flippedImage;
}

Answer 1

You set the line width with CGContextSetLineWidth(context, width).
The reason why you're seeing no effect from this is because you aren't stroking anything. Line width applies to the line painted by stroking. You're filling, not stroking, and a fill has no line to give width to.
If you want to put a border around the rectangle, you need to stroke it. That's what draws a line all the way around the perimeter of some shape.
You have three options:
Call CGContextSetLineWidth, then CGContextStrokeRect.
Call CGContextStrokeRectWithWidth.
Call CGContextSetLineWidth, then CGContextAddRect (to add the rectangle to the current path), then CGContextDrawPath with kCGPathFillStroke. (Or call AddRect before SetLineWidth if you prefer—they only need to both happen before DrawPath.)
Note that a stroke is centered on the path outline, so half of it will be inside the path/rectangle and half of it will be outside. If your line is 1 pixel wide, this will appear as the line being halfway transparent (because there's no other way to represent “half a pixel”). If your line is some even number of pixels wide, and you stroke the entire bounds of the context (or view), you'll only see the half of the line that's inside.
You also should decide whether you really meant to fill at all, or whether stroke alone is what you wanted.