我如何在 Xcode 中为这条线创建橡皮擦？

发布于 2024-12-20 16:44:47 字数 1198 浏览 1 评论 0原文

怎么样，我有这个代码。当触摸移动时，视图会添加一条线。现在，如果我想为这条线创建一个橡皮擦，我该怎么做？请早点回答我！

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

    UITouch *touch = [touches anyObject];   
    CGPoint currentPoint = [touch locationInView:drawView];

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

    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brushDimension);

    const CGFloat *components = CGColorGetComponents([brushColor CGColor]);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], components[3]);

    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    drawView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;   
}

原文

How, i've this code. When the touch moved, the view adds a line.
Now, if i want to create an eraser for this line, how can i do?
Please, answer me early!

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

    UITouch *touch = [touches anyObject];   
    CGPoint currentPoint = [touch locationInView:drawView];

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

    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brushDimension);

    const CGFloat *components = CGColorGetComponents([brushColor CGColor]);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], components[3]);

    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    drawView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;   
}

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单身情人 2024-12-27 16:44:47

如果您正在寻找一种擦除功能，用户可以使用触摸来擦除该行的一部分，而不是 RickyTheCoder 提供的撤消功能，那么您有 2 个选择。

第一个选项是使用具有相同背景颜色的画笔
背景视图，因此它认为线条被擦除了
实际上只是用与背景相同的颜色进行绘制。

第二个选项是使用清晰颜色的画笔并设置
混合模式清除，因此它会擦除线条并且背景视图仍然存在
可见。

if (isErase)
{

CGContextSetLineWidth(currentContext, 10);

CGContextSetStrokeColorWithColor(currentContext, [UIColor clearColor].CGColor);

CGContextSetFillColorWithColor(currentContext, [UIColor clearColor].CGColor);

CGContextSetBlendMode(currentContext, kCGBlendModeClear);

CGContextDrawPath(currentContext, kCGPathStroke);

}

If you are looking for an erase function that the user can use touches to erase portion of the line instead of undo provide by RickyTheCoder, you have 2 options.

The first option is use the brush that has the same background color of
the background view so it perceive as line got erased while it
actually just got paint over with the color that is same as the background.

The second option is to use the brush with clear color and set the
blend mode to clear so it erase the line and the background view is still
visible.

if (isErase)
{

CGContextSetLineWidth(currentContext, 10);

CGContextSetStrokeColorWithColor(currentContext, [UIColor clearColor].CGColor);

CGContextSetFillColorWithColor(currentContext, [UIColor clearColor].CGColor);

CGContextSetBlendMode(currentContext, kCGBlendModeClear);

CGContextDrawPath(currentContext, kCGPathStroke);

}

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