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我想允许用户以这样一种方式绘制曲线，即没有一条线可以穿过另一条线，甚至是它自己。绘制曲线是没有问题的，我什至发现我可以通过向前和向后跟踪线的节点然后关闭路径来创建一个封闭的并且仍然很像线的路径。

不幸的是，iOS 只提供了一个点是否包含在封闭路径中的测试（containsPoint: 和 CGPathContainsPoint）。不幸的是，用户可以很容易地将手指移动得足够快，以至于触摸点落在现有路径的两侧，而实际上并没有被该路径包含，因此测试触摸点毫无意义。

我找不到路径方法的任何“交叉点”。

关于如何完成此任务的任何其他想法？

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2 回答 2

6

好吧，我确实想出了一个方法来做到这一点。它是不完美的，但我认为其他人可能希望看到该技术，因为这个问题被多次投票。我使用的技术将所有要测试的项目绘制到位图上下文中，然后将进度线的新段绘制到另一个位图上下文中。使用按位运算符比较这些上下文中的数据，如果发现任何重叠，则声明命中。

这种技术背后的想法是针对所有先前绘制的线，甚至针对同一条线的较早部分，测试新绘制的线的每一段。换句话说，这种技术将检测一条线何时与另一条线相交以及何时与自身相交。

提供了演示该技术的示例应用程序：LineSample.zip。

命中测试的核心是在我的 LineView 对象中完成的。这里有两个关键方法：

- (CGContextRef)newBitmapContext {

    // creating b&w bitmaps to do hit testing
    // based on: http://robnapier.net/blog/clipping-cgrect-cgpath-531
    // see "Supported Pixel Formats" in Quartz 2D Programming Guide
    CGContextRef bitmapContext =
    CGBitmapContextCreate(NULL, // data automatically allocated
                          self.bounds.size.width,
                          self.bounds.size.height,
                          8, 
                          self.bounds.size.width,
                          NULL,
                          kCGImageAlphaOnly);
    CGContextSetShouldAntialias(bitmapContext, NO);
    // use CGBitmapContextGetData to get at this data

    return bitmapContext;
}


- (BOOL)line:(Line *)line canExtendToPoint:(CGPoint) newPoint {

    //  Lines are made up of segments that go from node to node. If we want to test for self-crossing, then we can't just test the whole in progress line against the completed line, we actually have to test each segment since one segment of the in progress line may cross another segment of the same line (think of a loop in the line). We also have to avoid checking the first point of the new segment against the last point of the previous segment (which is the same point). Luckily, a line cannot curve back on itself in just one segment (think about it, it takes at least two segments to reach yourself again). This means that we can both test progressive segments and avoid false hits by NOT drawing the last segment of the line into the test! So we will put everything up to the  last segment into the hitProgressLayer, we will put the new segment into the segmentLayer, and then we will test for overlap among those two and the hitTestLayer. Any point that is in all three layers will indicate a hit, otherwise we are OK.

    if (line.failed) {
        // shortcut in case a failed line is retested
        return NO;
    }
    BOOL ok = YES; // thinking positively

    // set up a context to hold the new segment and stroke it in
    CGContextRef segmentContext = [self newBitmapContext];
    CGContextSetLineWidth(segmentContext, 2); // bit thicker to facilitate hits
    CGPoint lastPoint = [[[line nodes] lastObject] point];
    CGContextMoveToPoint(segmentContext, lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(segmentContext, newPoint.x, newPoint.y);
    CGContextStrokePath(segmentContext);

    // now we actually test
    // based on code from benzado: http://stackoverflow.com/questions/6515885/how-to-do-comparisons-of-bitmaps-in-ios/6515999#6515999
    unsigned char *completedData = CGBitmapContextGetData(hitCompletedContext);
    unsigned char *progressData = CGBitmapContextGetData(hitProgressContext);
    unsigned char *segmentData = CGBitmapContextGetData(segmentContext);

    size_t bytesPerRow = CGBitmapContextGetBytesPerRow(segmentContext);
    size_t height = CGBitmapContextGetHeight(segmentContext);
    size_t len = bytesPerRow * height;

    for (int i = 0; i < len; i++) {
        if ((completedData[i] | progressData[i]) & segmentData[i]) { 
            ok = NO; 
            break; 
        }
    }

    CGContextRelease(segmentContext);

    if (ok) {
        // now that we know we are good to go, 
        // we will add the last segment onto the hitProgressLayer
        int numberOfSegments = [[line nodes] count] - 1;
        if (numberOfSegments > 0) {
            // but only if there is a segment there!
            CGPoint secondToLastPoint = [[[line nodes] objectAtIndex:numberOfSegments-1] point];
            CGContextSetLineWidth(hitProgressContext, 1); // but thinner
            CGContextMoveToPoint(hitProgressContext, secondToLastPoint.x, secondToLastPoint.y);
            CGContextAddLineToPoint(hitProgressContext, lastPoint.x, lastPoint.y);
            CGContextStrokePath(hitProgressContext);
        }
    } else {
        line.failed = YES;
        [linesFailed addObject:line];
    }
    return ok;
}

我很想听听建议或看到改进。一方面，只检查新段的边界矩形而不是整个视图会快得多。

于 2011-06-29T20:29:38.430 回答
1

Swift 4，答案基于CGPath Hit Testing - Ole Begemann (2012)

来自 Ole Begemann 博客：

contains(point: CGPoint)

如果您想在路径覆盖的整个区域上进行测试，此功能很有帮助。因此，contains(point: CGPoint)不适用于未闭合路径，因为这些路径没有可以填充的内部。

copy(strokingWithWidth lineWidth: CGFloat, lineCap: CGLineCap, lineJoin: CGLineJoin, miterLimit: CGFloat, transform: CGAffineTransform = default) -> CGPath

此函数创建一个镜像点击目标对象，该对象仅覆盖路径的描边区域。当用户点击屏幕时，我们会遍历点击目标而不是实际形状。


我的代码解决方案

我使用链接到函数 tap() 的 UITapGestureRecognizer：

var bezierPaths = [UIBezierPath]()   // containing all lines already drawn
var tappedPaths = [CAShapeLayer]()

@IBAction func tap(_ sender: UITapGestureRecognizer) {        
    let point = sender.location(in: imageView)

    for path in bezierPaths {
        // create tapTarget for path
        if let target = tapTarget(for: path) {
            if target.contains(point) {
                tappedPaths.append(layer)
            }
        }
    }
}

fileprivate func tapTarget(for path: UIBezierPath) -> UIBezierPath {

    let targetPath = path.copy(strokingWithWidth: path.lineWidth, lineCap: path..lineCapStyle, lineJoin: path..lineJoinStyle, miterLimit: path.miterLimit)

    return UIBezierPath.init(cgPath: targetPath)
}
于 2018-12-29T09:40:04.473 回答