CGPoint旋转会改变到原点的距离

Question

我想围绕另一个CGPoint（蓝色矩形）旋转一个CGPoint（红色矩形），但它会改变到原点的距离（蓝色矩形）...当我将角度设置为270时，它会创建位于原点正上方的点，但当我将角度值设置为90时，它会下降到原点但同时距离也几乎增加了三倍...我想保持距离不变，并围绕另一个CGPoint旋转。请指导任何旋转cgpoints的方法...

distance = 100;
angle = 270*M_PI/180;    
rotatedPoint.x = initialPoint.x+distance*cos(angle);
rotatedPoint.y = initialPoint.y+distance*sin(angle);
    //rotatedPoint.x = initialPoint.x+tan(angle);

[test setCenter:rotatedPoint];   
[test setBackgroundColor:[UIColor redColor]];

谢谢

- Dani

Answer 1

CGAffineTransform是一个方便的工具，用于旋转、平移和缩放。为了确保点正确旋转，必须将其平移到原点，旋转它，然后再平移到原来的位置。

要完成变换，可以使用类似以下代码：

CGPoint pointToRotate = CGPointMake(30, 30);
float angleInRadians = DEGREES_TO_RADIANS(90);
CGPoint distanceFromOrigin = CGPointMake(0 - pointToRotate.x, 0 - pointToRotate.y);

CGAffineTransform translateToOrigin = CGAffineTransformMakeTranslation(distanceFromOrigin.x, distanceFromOrigin.y);
CGAffineTransform rotationTransform = CGAffineTransformMakeRotation(angleInRadians);
CGAffineTransform translateBackFromOrigin = CGAffineTransformInvert(translateToOrigin);

CGAffineTransform totalTransform = CGAffineTransformConcat(translateToOrigin, rotationTransform);
totalTransform = CGAffineTransformConcat(totalTransform, translateBackFromOrigin);

pointToRotate = CGPointApplyAffineTransform(pointToRotate, totalTransform);

如果您需要进一步了解CGAffineTransform的文档，请参考以下链接：http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGAffineTransform/Reference/reference.html

如果这不能解决您的问题，请告诉我您还需要什么帮助！

- WendiKidd