使用CGPoint (IOS)用2 CGPoint绘制光线

Question

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

当我运行这段代码时，它会自然地绘制一个段(从1点到另一点)。我正在设法画一条射线。我的意思是从"firstPoint“到"secondPoint”直到屏幕的末尾。我不介意光线点是否会永远持续下去(我猜)。

这里会是什么样子。

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谢谢。

(如果需要，屏幕大小为736x414像素)

Answer 1

您可以使用公式m= (y2-y1)/(x2-x1)使用这两个点计算直线的斜率。然后通过设置x和根据斜率计算y来计算第三个点。请确保检查是否除以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是第二点，依此类推。

样本代码

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

从第二个点减去第一个点，得到射线的方向矢量：

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);

使用震级来缩放方向矢量，使其长度足够大；比如说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，以便沿光线得到一个很远的点：

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

使用第一点和远点绘制光线：

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