UIView drawRect() : fill everything except polygon - objective-c

Question

I need to fill my UIView in drawRect() method with 'reverted polygon' - everything in view is filled with some color except polygon itself.
I've got this code to draw a simple polygon:
CGContextBeginPath(context);
for(int i = 0; i < corners.count; ++i)
{
CGPoint cur = [self cornerAt:i], next = [self cornerAt:(i + 1) % corners.count];
if(i == 0)
CGContextMoveToPoint(context, cur.x, cur.y);
CGContextAddLineToPoint(context, next.x, next.y);
}
CGContextClosePath(context);
CGContextFillPath(context);
I found a similar question, but in C#, not Obj-C : c# fill everything but GraphicsPath

Answer 1

Probably the fastest way is to set a clip:
// create your path as posted
// but don't fill it (remove the last line)
CGContextAddRect(context, self.bounds);
CGContextEOClip(context);
CGContextSetRGBFillColor(context, 1, 1, 0, 1);
CGContextFillRect(context, self.bounds);
Both the other answers suggest to first fill a rect, then draw the shape with clear color on top. Both omit the necessary blend mode. Here's a working version:
CGContextSetRGBFillColor(context, 1, 1, 0, 1);
CGContextFillRect(context, self.bounds);
CGContextSetBlendMode(context, kCGBlendModeClear);
// create and fill your path as posted
Edit: Both approaches require the backgroundColor to be the clearColor and opaque to be set to NO.
Second Edit: The original question was about Core Graphics. Of course there are other ways of masking part of a view. Most notably CALayer's mask property.
You can set this property to an instance of a CAPathLayer that contains your clip path to create a stencil effect.

Answer 2

in drawRect u can set the background color of ur view with the color u want
self.backgroundColor = [UIcolor redColor]; //set ur color
and then draw a polygon the way u r doing.
CGContextBeginPath(context);
for(int i = 0; i < corners.count; ++i)
{
CGPoint cur = [self cornerAt:i], next = [self cornerAt:(i + 1) % corners.count];
if(i == 0)
CGContextMoveToPoint(context, cur.x, cur.y);
CGContextAddLineToPoint(context, next.x, next.y);
}
CGContextClosePath(context);
CGContextFillPath(context);
hope it helps.. happy coding :)

Answer 3

Create a new CGLayer, fill it with your outside color, then draw your polygon using a clear color.
layer1 = CGLayerCreateWithContext(context, self.bounds.size, NULL);
context1 = CGLayerGetContext(layer1);
[... fill entire layer ...]
CGContextSetFillColorWithColor(self.context1, [[UIColor clearColor] CGColor]);
[... draw your polygon ...]
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawLayerAtPoint(context, CGPointZero, layer1);