创建CGPathRef的垂直线

Question

我正在使用SKShapeNodes通过在用户触摸屏幕时更新路径属性来动态绘制线条。 一旦线完成，我想在路径的末尾附加一条新的固定长度垂直线。

我已经调查了CGAffineTransform以根据路径的终点旋转新行，但到目前为止还没有任何运气。 任何提示或见解将非常感激。

我目前的一些参考代码如下：

        - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
    {
        UITouch* touch = [touches anyObject];
        CGPoint positionInScene = [touch locationInNode:self];

        //add a line to the new coordinates the user moved to
        CGPathAddLineToPoint(pathToDraw, NULL, positionInScene.x, positionInScene.y);
    }


-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
//create local copy of path
CGPathRef myPath_ = pathToDraw;

CGPoint myPoint = CGPathGetCurrentPoint(pathToDraw);

//create rectangle to append to end of line        
CGRect newRect = CGRectMake(myPoint.x, myPoint.y, 25, 3);
CGPathRef newPath = CGPathCreateWithRect(newRect, NULL);

//add new line to the end of the path
CGPathAddPath(newPath, NULL, myPath_);

//set shape node path to drawn path        
lineNode.path = myPath_;
}

Answer 1

要获得垂直，您可以将向量指向最后一个线段的方向，然后交换x和y，并反转其中一个。 像这样的东西：

CGPoint v = { currentPoint.x - lastPoint.x, currentPoint.y - lastPoint.y };
CGPoint perp;
if (v.x == 0)
{
    perp.x = -v.y;
    perp.y = v.x;
}
else
{
    perp.x = v.y;
    perp.y = -v.x;
}

现在你可以在perp方向画一条线，从当前点开始，如下所示：

CGPathMoveToPoint (somePath, currentPoint);
CGPathAddLineToPoint (somePath, NULL, currentPoint.x + perp.x * length, currentPoint.y + perp.y * length);

其中length是您要绘制的线段的长度。

并且不要忘记将lastPoint设置为currentPoint以便下一次正确：

lastPoint = currentPoint;