CGContextClearRect在touchesMove事件中无法在目标C中顺利运行

debugcn 发表于 Dev

吉山·戈达尼（kishan godhani）

我使用了这段代码，但部分起作用，但是图像无法正确裁剪，如下所示

-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:_img.superview];

UIGraphicsBeginImageContext(self.img.frame.size);
[_img.image drawInRect:CGRectMake(0, 0, _img.frame.size.width, _img.frame.size.height)];

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10);
CGContextBeginPath(UIGraphicsGetCurrentContext());

CGContextClearRect (UIGraphicsGetCurrentContext(), CGRectMake(currentPoint.x, currentPoint.y, 15, 15));
CGContextStrokePath(UIGraphicsGetCurrentContext());
_img.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();   
}

维拉吉·帕萨拉（Viraj Padsala）

我之前遇到过同样的问题，然后尝试了以下代码，这对我来说很有效

UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.img_main];
// NSLog(@"Current ponint : %f,%f",currentPoint.x,currentPoint.y);

self.img_main.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
self.img_main.contentMode = UIViewContentModeScaleAspectFit;

UIGraphicsBeginImageContextWithOptions(self.img_main.bounds.size, NO, 0.0);
[_img_main.image drawInRect:CGRectMake(0,0, self.img_main.bounds.size.width,self.img_main.bounds.size.height)];
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);

//For clearing Size and Mode
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush_Size );
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeDestinationOut);
//For Clearing Opacity        
CGContextSetAlpha(UIGraphicsGetCurrentContext(), brush_opacity);
CGContextStrokePath(UIGraphicsGetCurrentContext());

_img_main.image = UIGraphicsGetImageFromCurrentImageContext();

CGContextFlush(UIGraphicsGetCurrentContext());
UIGraphicsEndImageContext();

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