Question

我正在使用route-me的框架来处理位置。在此代码中，两个标记（点）之间的路径将绘制为一条线。

我的问题：“如果我想在线条的中间（或顶部）添加箭头，我应该添加什么代码，以便它指向”

由于



- (void)drawInContext:(CGContextRef)theContext
{
    renderedScale = [contents metersPerPixel];

    float scale = 1.0f / [contents metersPerPixel];

    float scaledLineWidth = lineWidth;
    if(!scaleLineWidth) {
        scaledLineWidth *= renderedScale;
    }
    //NSLog(@"line width = %f, content scale = %f", scaledLineWidth, renderedScale);

    CGContextScaleCTM(theContext, scale, scale);

    CGContextBeginPath(theContext);
    CGContextAddPath(theContext, path);

    CGContextSetLineWidth(theContext, scaledLineWidth);
    CGContextSetStrokeColorWithColor(theContext, [lineColor CGColor]);
    CGContextSetFillColorWithColor(theContext, [fillColor CGColor]);

    // according to Apple's documentation, DrawPath closes the path if it's a filled style, so a call to ClosePath isn't necessary
    CGContextDrawPath(theContext, drawingMode);
}

Answer 1

- (void) drawLine: (CGContextRef) context from: (CGPoint) from to: (CGPoint) to 
{
    double slopy, cosy, siny;
    // Arrow size
    double length = 10.0;  
    double width = 5.0;

    slopy = atan2((from.y - to.y), (from.x - to.x));
    cosy = cos(slopy);
    siny = sin(slopy);

    //draw a line between the 2 endpoint
    CGContextMoveToPoint(context, from.x - length * cosy, from.y - length * siny );
    CGContextAddLineToPoint(context, to.x + length * cosy, to.y + length * siny);
    //paints a line along the current path
    CGContextStrokePath(context);

    //here is the tough part - actually drawing the arrows
    //a total of 6 lines drawn to make the arrow shape
    CGContextMoveToPoint(context, from.x, from.y);
    CGContextAddLineToPoint(context,
                        from.x + ( - length * cosy - ( width / 2.0 * siny )),
                        from.y + ( - length * siny + ( width / 2.0 * cosy )));
    CGContextAddLineToPoint(context,
                        from.x + (- length * cosy + ( width / 2.0 * siny )),
                        from.y - (width / 2.0 * cosy + length * siny ) );
    CGContextClosePath(context);
    CGContextStrokePath(context);

    /*/-------------similarly the the other end-------------/*/
    CGContextMoveToPoint(context, to.x, to.y);
    CGContextAddLineToPoint(context,
                        to.x +  (length * cosy - ( width / 2.0 * siny )),
                        to.y +  (length * siny + ( width / 2.0 * cosy )) );
    CGContextAddLineToPoint(context,
                        to.x +  (length * cosy + width / 2.0 * siny),
                        to.y -  (width / 2.0 * cosy - length * siny) );
    CGContextClosePath(context);
    CGContextStrokePath(context);
}

Answer 2

如果路径上有两个点，则实际三角形/箭头的绘制很容易。

CGContextMoveToPoint( context , ax , ay );
CGContextAddLineToPoint( context , bx , by );
CGContextAddLineToPoint( context , cx , cy );
CGContextClosePath( context ); // for triangle

获得积分有点棘手。你说路径是一条线，而不是一条曲线或一系列曲线。这样会更容易。

使用CGPathApply在路径上选择两个点。可能这是最后两点，其中一个可能是kCGPathElementMoveToPoint，另一个是kCGPathElementAddLineToPoint。设mx，我是第一个点，nx，ny是第二个，所以箭头将从m指向n。

假设您希望箭头位于线的顶端，bx，从上方开始将等于线上的nx，ny。选择mx，my和nx，ny之间的点dx，dy来计算其他点。

现在计算ax，ay和cx，cy，使得它们与dx，dy和路径等距离在一条直线上。以下内容应该很接近，尽管我可能有一些错误的迹象：

r = atan2( ny - my , nx - mx );
bx = nx;
by = ny;
dx = bx + sin( r ) * length;
dy = by + cos( r ) * length;
r += M_PI_2; // perpendicular to path
ax = dx + sin( r ) * width;
ay = dy + cos( r ) * width;
cx = dx - sin( r ) * width;
cy = dy - cos( r ) * width;

长度是从箭头尖端到底座的距离，宽度是从轴到倒钩的距离，或箭头宽度的一半。

如果path是曲线，那么它不是找到mx，而是作为前一个点或移动，它将是最终曲线的最终控制点。每个控制点位于与曲线相切并穿过相邻点的直线上。

Answer 3

我发现这个问题，因为我有同样的问题。我采用了drawonward的例子并且它如此接近......但是随着cos和罪恶的翻转，我能够让它发挥作用：

r = atan2( ny - my , nx - mx );
r += M_PI;
bx = nx;
by = ny;
dx = bx + cos( r ) * length;
dy = by + sin( r ) * length;
r += M_PI_2; // perpendicular to path
ax = dx + cos( r ) * width;
ay = dy + sin( r ) * width;
cx = dx - cos( r ) * width;
cy = dy - sin( r ) * width;

一旦我这样做，我的箭就指向了错误的方向。所以我添加了第二行（r += M_PI;）

谢谢你抽奖！

Answer 4

这是 FriedhelmBrügge 的 Swift 4 + 版本：（我将其绘制在图像上）

func drawArrow(image: UIImage, ptSrc: CGPoint, ptDest: CGPoint) {

        // create context with image size
        UIGraphicsBeginImageContext(image.size)
        let context = UIGraphicsGetCurrentContext()

        // draw current image to the context
        image.draw(in: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))

        var slopY: CGFloat, cosY: CGFloat, sinY: CGFloat;
        // Arrow size
        let length: CGFloat = 35.0;
        let width: CGFloat = 35.0;

        slopY = atan2((ptSrc.y - ptDest.y), (ptSrc.x - ptDest.x));
        cosY = cos(slopY);
        sinY = sin(slopY);

        //here is the tough part - actually drawing the arrows
        //a total of 6 lines drawn to make the arrow shape
        context?.setFillColor(UIColor.white.cgColor)
        context?.move(to: CGPoint(x: ptSrc.x, y: ptSrc.y))
        context?.addLine(to: CGPoint(x: ptSrc.x + ( -length * cosY - ( width / 2.0 * sinY )), y: ptSrc.y + ( -length * sinY + ( width / 2.0 * cosY ))))
        context?.addLine(to: CGPoint(x: ptSrc.x + (-length * cosY + ( width / 2.0 * sinY )), y: ptSrc.y - (width / 2.0 * cosY + length * sinY )))
        context?.closePath()
        context?.fillPath()

        context?.move(to: CGPoint(x: ptSrc.x, y: ptSrc.y))
        context?.addLine(to: CGPoint(x: ptDest.x +  (length * cosY - ( width / 2.0 * sinY )), y: ptDest.y +  (length * sinY + ( width / 2.0 * cosY ))))
        context?.addLine(to: CGPoint(x: ptDest.x +  (length * cosY + width / 2.0 * sinY), y: ptDest.y -  (width / 2.0 * cosY - length * sinY)))
        context?.closePath()
        context?.fillPath()

        // draw current context to image view
        imgView.image = UIGraphicsGetImageFromCurrentImageContext()

        //close context
        UIGraphicsEndImageContext()
    }

使用CGContext在一条线上绘制三角形/箭头

4 个答案: