iphone - uiimageview 上的透明度应该显示图像

Question

可能重复：
如何在 iPhone 上绘制透明笔触（或图像的清晰部分）

我有一个 uiimage 视图，如果我们触摸该透明层，则该透明层存在一个透明层，该透明​​层应该被擦除，并且应该显示其背面的图像..我该怎么做....？提前致谢

Answer 1

据我了解，您想通过触摸来擦除图像的一部分……对吗？

尝试使用此代码通过触摸移动部分图像进行擦除....

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    lastTouch = [touch locationInView:canvasView];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    currentTouch = [touch locationInView:canvasView];

    CGFloat brushSize = 35;
    CGColorRef strokeColor = [UIColor whiteColor].CGColor;

    UIGraphicsBeginImageContext(scratchView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [canvasView.image drawInRect:CGRectMake(0, 0, canvasView.frame.size.width, canvasView.frame.size.height)];
    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, brushSize);
    CGContextSetStrokeColorWithColor(context, strokeColor);
    CGContextSetBlendMode(context, kCGBlendModeClear);
    CGContextBeginPath(context);
    CGContextMoveToPoint(context, lastTouch.x, lastTouch.y);
    CGContextAddLineToPoint(context, currentTouch.x, currentTouch.y);
    CGContextStrokePath(context);
    canvasView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastTouch = [touch locationInView:canvasView];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

}

我希望这能帮到您....