Creating a UIButton in shape of the image given - ios

Question

how can i create a UIButton in shape of the image given.
i am able to create something close to it,but the image seems to be not fitting in the button.
my requirement is the image given below.i.e;semicircle
the code i used to create the button is given below.
what changes should i make on the following image to get this button.
ps-add subview done in another class..
btnStartGame =[UIButton buttonWithType:UIButtonTypeCustom];
[btnStartGame setFrame:CGRectMake(60, 200, 200, 200)];
btnStartGame.titleLabel.font=[UIFont fontWithName:#"Helvetica-Bold" size:30];
[btnStartGame setImage:
[UIImage imageNamed:#"Draw button.png"] forState:UIControlStateNormal];
btnStartGame.titleLabel.textColor=[UIColor redColor];
btnStartGame.clipsToBounds = YES;
btnStartGame.layer.cornerRadius = 50;//half of the width
btnStartGame.layer.borderColor=[UIColor redColor].CGColor;
btnStartGame.layer.borderWidth=2.0f;
btnStartGame.tag=20;
btnStartGame.highlighted=NO;

Answer 1

There is a really great tutorial here with downloadable source code:
http://iphonedevelopment.blogspot.co.uk/2010/03/irregularly-shaped-uibuttons.html
In essence you need to create a category on UIImage, which checks whether the point you have touched is transparent image or not. This means you can use it to check hit tests on irregular shapes.
You then subclass UIButton and over-ride the hitTest:withEvent:
Hope this helps

Answer 2

Although the solution by Jeff Lamarche linked by the other answer works fine, it uses a lot of memory, and/or does a lot of work:
If you create NSData once in the initializer, you end up holding a relatively large block of memory for the lifetime of each button
If you make it transient, the way it is done in the answer, then you end up converting the entire image each time you hit test your button - processing thousands of pixels and throwing away the result after fetching a single byte!
It turns out that you can do this much more efficiently, both in terms of memory use and CPU consumption, by following the approach outlined in this answer.
Subclass UIButton, and override its pointInside:withEvent: method like this:
-(BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event {
if (![super pointInside:point withEvent:event]) {
return NO;
}
unsigned char pixel[1] = { 0 };
CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 1, NULL, (CGBitmapInfo)kCGImageAlphaOnly);
UIGraphicsPushContext(context);
UIImage *image = [self backgroundImageForState:UIControlStateNormal] ;
[image drawAtPoint:CGPointMake(-point.x, -point.y)];
UIGraphicsPopContext();
CGContextRelease(context);
return pixel[0] != 0;
}
The code above takes alpha from the background image of the button. If your button uses another image, change the line that initializes image variable above.