带圆圈的CGContextClearRect [英] CGContextClearRect with circle

问题描述

我正在创建一个应用程序，我试图清除 UIImageView 的 rect 。我用 CGContextClearRect 实现了这一点，但问题是它正在清除方形中的 rect 并且我想要实现这个效果是圆形的。

I am creating an app in which i am trying to clear the rect of UIImageView. I have achieved this with CGContextClearRect, but the problem is that it is clearing rect in square shape and i want to achieve this effect in round shape.

到目前为止我尝试了什么：

What i have tried so far:

UITouch *touch2 = [touches anyObject];
CGPoint point = [touch2 locationInView:img];

UIGraphicsBeginImageContextWithOptions(img.bounds.size, NO, 0.0f);
[img.image drawInRect:CGRectMake(0, 0, img.frame.size.width, img.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
CGContextRef context = UIGraphicsGetCurrentContext();

CGRect cirleRect = CGRectMake(point.x, point.y, 40, 40);
CGContextAddArc(context, 50, 50, 50, 0.0, 2*M_PI, 0);
CGContextClip(context);
CGContextClearRect(context,cirleRect);
//CGContextClearRect(context, CGRectMake(point.x, point.y, 30, 30));
img.image =UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

推荐答案

我不确定你到底在做什么，但您的剪裁弧未正确创建。你是在一个固定的位置创建它，这就是为什么它不能真正起作用 - 除非你点击左上角。

I'm not sure exactly what you are doing, but your clipping arc isn't being created correctly. You are creating it at a fixed position which is why it doesn't really work - except it does, if you click in the top left corner.

如果你想要看到它工作试试这个：

If you want to see it working try this:

- (IBAction)clearCircle:(UITapGestureRecognizer *)sender {
    UIImageView *imageView = self.imageView;
    UIImage *currentImage = imageView.image;
    CGSize imageViewSize = imageView.bounds.size;

    CGFloat rectWidth = 40.0f;
    CGFloat rectHeight = 40.0f;

    CGPoint touchPoint = [sender locationInView:imageView];

    UIGraphicsBeginImageContextWithOptions(imageViewSize, YES, 0.0f);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    [currentImage drawAtPoint:CGPointZero];

    CGRect clippingEllipseRect = CGRectMake(touchPoint.x - rectWidth / 2, touchPoint.y - rectHeight / 2, rectWidth, rectHeight);
    CGContextAddEllipseInRect(ctx, clippingEllipseRect);

    CGContextClip(ctx);

    CGContextClearRect(ctx, clippingEllipseRect);

    imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

}

创建剪裁椭圆（在本例中为圆形）在以触摸点为中心的矩形40 x 40中。

Which creates a clipping ellipse (in this case a circle) in the rect 40 x 40 centred at the touch point.

您可以在 Bitbucket ，你可以为自己下载尝试

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