iPhone石英绘图橡皮擦

Question

我试图与擦除iPhone应用程序。我遇到了两个问题，如果你有任何一个解决方案，请回答。我想删除一部分图像。

1）我目前只是清除RECT但它有一个方形的边缘。我希望它是圆的，我以前尝试翻译，但这不起作用。我也需要它翻译/旋转尽可能少的时间来保持相同的性能。

2）此外，我想知道，如果有删除的任何其他方式。当擦除速度很快时，它将擦除1/2英寸。有没有办法打通一条路，清理房子？对不起，如果这很难理解。

CGRect circleRect = CGRectMake([touch CGPointValue].x, [touch CGPointValue].y, 25, 25); 
CGContextClearRect(currentContext,circleRect); 

Answer 1

此代码应该做你要找的内容：

CGContextRef context = UIGraphicsGetCurrentContext(); 
CGContextSetLineCap(context, kCGLineCapRound); 
CGContextSetLineWidth(context, self.strokeWidth); 
CGContextSetBlendMode(context, kCGBlendModeClear); 
CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]); 
CGContextBeginPath(context); 
CGContextMoveToPoint(context, lastPoint.x, lastPoint.y); 
CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y); 
CGContextStrokePath(context);  
CGContextFlush(context); 

的关键点是

1）CGContextSetLineCap(context, kCGLineCapRound)，这使得它圆

2）CGContextSetBlendMode(context, kCGBlendModeClear)清除上下文。

Answer 2

我意识到这是一个老问题，但我想我会扩大埃里克Reids答案，因为我试图用drawRect方法之外他为榜样，不得不修改它让它与我创建了一个环境中工作UIView子类中的'touchesMoved'方法。

我称之为从“touchesMoved”这个方法，并将其传递的CGPoint中，我在绘制视图触摸的。

-(void) processEraseAtPoint:(CGPoint)point 
{ 
    // setup a context with the size of our canvas view (the canvas view is the UIView instance I'm drawing into) 
    UIGraphicsBeginImageContext(self.canvasView.bounds.size); 

    // get a reference to the context we just created 
    CGContextRef context = UIGraphicsGetCurrentContext(); 

    // draw the image we want to edit into this context (this is the image containing the drawing I want to erase part of) 
    [self.canvasView.incrementalImage drawAtPoint:CGPointZero]; 

    // set our context options 
    CGContextSetLineCap(context, kCGLineCapRound); 
    CGContextSetLineWidth(context, self.canvasView.settings.brushDiameter); 
    CGContextSetBlendMode(context, kCGBlendModeClear); 

    // make the color clear since we're erasing 
    CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]); 

    // start our path in this context 
    CGContextBeginPath(context); 

    // set our first point 
    CGContextMoveToPoint(context, lastTouch.x, lastTouch.y); 

    // draw from our last point to this point 
    CGContextAddLineToPoint(context, point.x, point.y); 

    // stroke this path (in this case it's clear so it will erase what's there) 
    CGContextStrokePath(context); 

    // set our incrementalImage in the canvasView with the updated image from this context 
    // Note that in the canvasView 'drawRect' method I am calling 
    // '[self.incrementalImage drawInRect:rect]', so this new image will get drawn 
    // in my canvasView when I call 'setNeedsDisplay' 
    self.canvasView.incrementalImage = UIGraphicsGetImageFromCurrentImageContext(); 

    // cleanup our context 
    CGContextFlush(context); 
    UIGraphicsEndImageContext(); 

    // set our last touch point for the next line segment 
    lastTouch = point; 

    // update our view 
    [self.canvasView setNeedsDisplay]; 

}