使用UIBezierPath（IOS）绘制带有2个CGPoint的Ray

Question

UIBezierPath *myPath = [[UIBezierPath bezierPath];
[myPath moveToPoint: firstPoint];
[myPath addLineToPoint: secondPoint];
myPath.lineWidth = 10;
[[UIColor yellowColor]setStroke];
[myPath stroke];

当我运行此代码时，它会自然地绘制一个段（从1点到另一点）。我试图找到一种绘制光线的方法。我的意思是从“firstPoint”到“secondPoint”直到屏幕结束。我不介意光点是否永远持续（我猜）。

这就是它的样子。

谢谢。

（如果需要，屏幕尺寸为736x414像素）

Answer 1

您可以使用公式m =（y2-y1）/（x2-x1）使用两个点计算线的斜率。然后通过设置x并基于斜率计算y来计算第三个点。确保检查除以0。

y3 = m（x3-x2）+ y2

将x3作为屏幕宽度，在您的情况下为414。 y1是firstPoint.y，x2是secondPoint.x，依此类推。

示例代码

CGPoint firstPoint = CGPointMake(50, 150);
CGPoint secondPoint = CGPointMake(100, 250);
CGPoint screenMax = CGPointMake(414,736);
CGPoint lastPoint = CGPointZero;
CGFloat slope = 1.0;
if (secondPoint.x != firstPoint.x) {
    slope = (secondPoint.y - firstPoint.y) / (secondPoint.x - firstPoint.x);
    lastPoint = CGPointMake(screenMax.x, slope * (screenMax.x-secondPoint.x)+secondPoint.y);
} else {
    slope = 0;
    lastPoint.x = secondPoint.x;
    lastPoint.y = screenMax.y;
}
UIBezierPath *myPath = [UIBezierPath bezierPath];
[myPath moveToPoint: firstPoint];
[myPath addLineToPoint: secondPoint];
myPath.lineWidth = 10;
[[UIColor yellowColor]setStroke];
[myPath stroke];

//this is the extension from the second point to the end of the screen
[myPath addLineToPoint: lastPoint];
[myPath stroke];

Answer 2

从第二个点中减去第一个点以获得光线的方向向量：

CGPoint direction = CGPointMake(secondPoint.x - firstPoint.x, secondPoint.y - firstPoint.y);

计算方向向量的大小：

CGFloat magnitude = hypot(direction.x, direction.y);

使用幅度将方向矢量缩放为足够大的长度;让我们说4000点：

if (magnitude == 0) {
    magnitude = 1;
}
CGFloat factor = 4000 / magnitude;
direction.x *= factor;
direction.y *= factor;

将缩放的方向向量添加到第一个点以获得沿光线的远点：

CGPoint farPoint = CGPointMake(firstPoint.x + direction.x, firstPoint.y + direction.y);

使用第一个点和远点绘制光线：

UIBezierPath *myPath = [[UIBezierPath bezierPath];
[myPath moveToPoint:firstPoint];
[myPath addLineToPoint:farPoint];
myPath.lineWidth = 10;
[[UIColor yellowColor] setStroke];
[myPath stroke];