如何在 Quartz2d 绘图中对某个点执行擦除功能？

Question

我用这段代码在quartz2d中画了一条线

CGPoint currentPoint = CGPointMake(rascalImage.center.x, rascalImage.center.y);
        currentPoint.y += 10;


        UIGraphicsBeginImageContext(self.view.frame.size);
        [drawingView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
        CGContextBeginPath(UIGraphicsGetCurrentContext());
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        drawingView.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        lastPoint = currentPoint;

现在我将如何为橡皮擦相交的地方制作擦除功能？我知道我必须从线上擦除某个点（橡皮擦接触的地方），我只是不知道该怎么做，所以请帮忙！！

Answer 1

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

        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(),lineWidth);
        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);

        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
        CGContextBeginPath(UIGraphicsGetCurrentContext());  
        CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);

        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint1.x, lastPoint1.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        imgBlankView.image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();

Answer 2

我假设您不是在纯色背景上绘画？如果你是，只需使用相同的函数在对比线条上绘制背景色线条。

但是，由于您很可能有一个复杂的背景：一旦您结束图形上下文，并从您绘制的线条中获取 UIImage，就无法仅擦除线条。如果您正在创建某种复杂的绘图应用程序，我建议您使用图层，并简单地将一个图层“堆叠”在另一个之上以创建绘图环境。

还请查看此帖子： How to erase some portion of a UIImageView's image on iOS?