ios - 测量在 iPhone 屏幕上绘制的线的距离

Question

我正在尝试创建一个应用程序，允许用户在屏幕上画一条线并测量所画线的距离。我已经能够成功地画出线，但我不知道如何测量它。这条线也不必完全笔直。它基本上是一个波浪线。如果有人可以给我指出正确的方向或帮助指导我，那将是非常棒的。我正在使用 Xcode 5.1.1 和 objective-c。今年夏天我才刚刚开始涉足这门语言。

编辑:我希望以英寸或厘米为单位测量距离。我希望测量是整条线，沿着线的曲线。距离不是位移。

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    mouseSwipe = YES; //swipe declared in header

    UITouch *touch = [touches anyObject];
    currentPoint = [touch locationInView:self.view]; //tracking finger movement on screen

    UIGraphicsBeginImageContext(CGSizeMake(320, 568)); // 568 iphone 5, 480 is iphone 4 (320,525)
    [drawImage.image drawInRect:CGRectMake(0, 0, 320, 568)]; // 0,0 centered in corner
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); //round line end
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0); // width of line

    CGContextSetStrokeColorWithColor(UIGraphicsGetCurrentContext(), [[UIColor redColor] CGColor]); //sets color to red (change red to any color for that color)

    //CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0,1,0,1); //green color
    CGContextBeginPath(UIGraphicsGetCurrentContext()); //start of when drawn path
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    [drawImage setFrame:CGRectMake(0, 0, 320, 568)]; //(320, 568)
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext(); //importnant
    UIGraphicsEndImageContext(); //finished drawing for time period
    lastPoint = currentPoint;

    [self.view addSubview:drawImage]; //adds to page
}

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

    UITouch *touch = [[event allTouches] anyObject]; //touch fires of touch

    location = [touch locationInView:touch.view];
    lastClick = [NSDate date];

    lastPoint = [touch locationInView:self.view]; //stops connecting to previous line
    lastPoint.y -= 0;

    [super touchesEnded:touches withEvent: event];
}

Answer 1

首先添加一个累积路径长度的属性。

@property(nonatomic, assign) CGFloat pathLength;

当用户开始绘制路径时，将其初始化为 0.0。也许在 touchesBegan 中执行此操作，或者在您意识到开始绘制的代码中的其他地方执行此操作。添加一个计算点之间笛卡尔距离的方法:

- (CGFloat)distanceFrom:(CGPoint)p1 to:(CGPoint)p2 {
    CGFloat x = (p2.x - p1.x);
    CGFloat y = (p2.y - p1.y);
    return sqrt(x*x + y*y);
}

当您移动触摸时，您已经在处理当前和最后触摸位置。您现在要做的就是累积连续点之间的距离:

// in touches moved, after you have lastPoint and currentPoint
self.pathLength += [self distanceFrom:currentPoint to:lastPoint];

这里和其他地方有相当多的引用将这些点转换为英寸或厘米。据我所知，所有这些都充满了无法在运行时从 SDK 获取设备分辨率的问题。如果你愿意在代码中添加一个(危险的)常量，你可以 get PPI here ，并将其除以上面计算的 pathLength。