如何擦除子视图中的行 [英] How to erase lines in a subview

问题描述

我正在开发一款可以在照片上画线的照片应用。
背景是照片，通过画画我在子视图上绘制线条。

I'm working on an photo app where you can draw lines on an photo. The background is the photo, and via drawrect I draw lines on a subview.

每件事情都有效但是如何擦除子视图上的线条（如橡皮擦），我尝试使用clearColor作为setStroke。

Every thing works but how can I erase lines on a subview (like an eraser), I tried with clearColor as setStroke.

是否可以删除这样的行。

Is it possible to erase the lines like this.

推荐答案

@omz给出的响应的实现可能是：

（假设 imgBlank 是 UIImageView 放置在viewcontroller的主视图之上）

An implementation of the response given by @omz could be:
(assuming imgBlank is a UIImageView placed on top of the main view of the viewcontroller)

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.imgBlank];
    NSValue *valCurrPoint=[NSValue valueWithCGPoint:CGPointMake(currentPoint.x, currentPoint.y)];
    [self.dots addObject:valCurrPoint];
    [self performSelector:@selector(draw:) withObject:valCurrPoint afterDelay:0];
}

-(void)draw:(NSValue*)pointz{
    CGPoint point=[pointz CGPointValue];
    UIGraphicsBeginImageContextWithOptions(self.imgBlank.frame.size,NO,0);
    [self.imgBlank.image drawInRect:CGRectMake(0, 0, self.imgBlank.frame.size.width, self.imgBlank.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(),tickness);//set the tickness here
    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0f, 1.0f, 1.0f, 1.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());  
    CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), _lastPoint.x, _lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), point.x, point.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    self.imgBlank.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    _lastPoint = point;
}

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