Wednesday, June 5, 2013

UIBezierPath addClip example in Objective C (iOS).

UIBezierPath addClip

Intersects the area enclosed by the receiver’s path with the clipping path of the current graphics context and makes the resulting shape the current clipping path.

- (void)addClip

Discussion of [UIBezierPath addClip]
This method modifies the visible drawing area of the current graphics context. After calling it, subsequent drawing operations result in rendered content only if they occur within the fill area of the specified path.

Important: If you need to remove the clipping region to perform subsequent drawing operations, you must save the current graphics state (using the CGContextSaveGState function) before calling this method. When you no longer need the clipping region, you can then restore the previous drawing properties and clipping region using the CGContextRestoreGState function.[UIBezierPath addClip]
The usesEvenOddFillRule property is used to determine whether the even-odd or non-zero rule is used to determine the area enclosed by the path.

UIBezierPath addClip example.
UIBezierPath *clipPath = [UIBezierPath bezierPathWithRect:CGRectInfinite];
[clipPath appendPath:smallMaskPath];
clipPath.usesEvenOddFillRule = YES;

CGContextSaveGState(UIGraphicsGetCurrentContext()); {
    [clipPath addClip];
    [[UIColor orangeColor] setFill];
    [bigMaskPath fill];
} CGContextRestoreGState(UIGraphicsGetCurrentContext());

Example of [UIBezierPath addClip].
- (void)drawRect:(CGRect)rect
    // This assumes the clippingPath and image are in the same coordinate space, and scales both to fill the view bounds.
    if ([self image])
        CGSize imageSize = [[self image] size];
        CGRect bounds = [self bounds];

        CGContextRef context = UIGraphicsGetCurrentContext();
        CGContextScaleCTM(context, bounds.size.width/imageSize.width, bounds.size.height/imageSize.height);

        [[self clippingPath] addClip];
        [[self image] drawAtPoint:CGPointZero];

UIBezierPath addClip example.
- (UIImage *)maskImage:(UIImage *)originalImage toPath:(UIBezierPath *)path {
    UIGraphicsBeginImageContextWithOptions(originalImage.size, NO, 0);
    [path addClip];
    [originalImage drawAtPoint:CGPointZero];
    UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
    return maskedImage;

End of UIBezierPath addClip example article.