adding white border along a circle UIImage - iphone

Question

I have generated a circle UIImage using a mask as following (where masked_circle is a black circle):
CGContextRef context = UIGraphicsGetCurrentContext();
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
UIImage *maskImage = [UIImage imageNamed:#"masked_circle.png"];
CGImageRef maskImageRef = [maskImage CGImage];
// create a bitmap graphics context the size of the image
CGContextRef mainViewContentContext = CGBitmapContextCreate (NULL, maskImage.size.width, maskImage.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
CGFloat ratio = 0;
ratio = maskImage.size.width/ self.image_.size.width;
if(ratio * self.image_.size.height < maskImage.size.height) {
ratio = maskImage.size.height/ self.image_.size.height;
}
CGRect rect1 = {{0, 0}, {maskImage.size.width, maskImage.size.height}};
CGRect rect2 = {{-((self.image_.size.width*ratio)-maskImage.size.width)/2 , -((self.image_.size.height*ratio)-maskImage.size.height)/2}, {self.image_.size.width*ratio, self.image_.size.height*ratio}};
CGContextClipToMask(mainViewContentContext, rect1, maskImageRef);
CGContextDrawImage(mainViewContentContext, rect2, self.image_.CGImage);
CGImageRef newImage = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
UIImage *theImage = [UIImage imageWithCGImage:newImage];
Now after this I wanted to add a 1px white border around the circle image, how can I do so?

Answer 1

Here's a much simpler solution to turn any view, but specifically a UIImageView into a circle with a border of varying size and color. This of course assumes you're dealing with a square image like an icon.
#import <UIKit/UIKit.h>
#interface UIView (Shapes)
- (void)makeCircle;
- (void)makeCircleWithBorderColor:(UIColor *) color Width:(CGFloat) width;
#end
#implementation UIView (Shapes)
- (void)makeCircle {
CALayer *lyr = self.layer;
lyr.masksToBounds = YES;
lyr.cornerRadius = self.bounds.size.width / 2; // assumes image is a square
}
- (void)makeCircleWithBorderColor:(UIColor *) color Width:(CGFloat) width {
[self makeCircle];
CALayer *lyr = self.layer;
lyr.borderWidth = width;
lyr.borderColor = [color CGColor];
}
#end

Answer 2

Here's some code that draws a border around a frame with a corner radius. Make that radius equal to half size and you've got a circle!
CGFloat strokeWidth =1.0;
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, strokeWidth);
CGContextSetStrokeColorWithColor(context, [UIColor grayColor].CGColor);
CGFloat radius = 7.0;
CGRect rrect = self.bounds;
rrect.size.width = rrect.size.width - strokeWidth*2;
rrect.size.height = rrect.size.height - strokeWidth*2;
rrect.origin.x = rrect.origin.x + (strokeWidth / 2);
rrect.origin.y = rrect.origin.y + (strokeWidth / 2);
CGFloat width = CGRectGetWidth(rrect);
CGFloat height = CGRectGetHeight(rrect);
if (radius > width/2.0)
radius = width/2.0;
if (radius > height/2.0)
radius = height/2.0;
CGFloat minx = CGRectGetMinX(rrect);
CGFloat midx = CGRectGetMidX(rrect);
CGFloat maxx = CGRectGetMaxX(rrect);
CGFloat miny = CGRectGetMinY(rrect);
CGFloat midy = CGRectGetMidY(rrect);
CGFloat maxy = CGRectGetMaxY(rrect);
CGContextMoveToPoint(context, minx, midy);
CGContextAddArcToPoint(context, minx, miny, midx, miny, radius);
CGContextAddArcToPoint(context, maxx, miny, maxx, midy, radius);
CGContextAddArcToPoint(context, maxx, maxy, midx, maxy, radius);
CGContextAddArcToPoint(context, minx, maxy, minx, midy, radius);
CGContextClosePath(context);
CGContextDrawPath(context, kCGPathFillStroke);