CGPoint旋转改变从原点

Question

我要旋转CGPoint（红色矩形）周围其他CGPoint（蓝色矩形），但它从原点（蓝色矩形）的距离改变的距离......当我在角度给予270它创建点正好在原点之上，但是当我给出角度值90时，它会降低原点，但更改距离几乎等于三倍......我想保持距离相同并且想要围绕另一个角度旋转CGPoint。请指导任何方法对cgpoints的旋转...

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]]; 

感谢

Answer 1

CGAffineTransform是一个方便的工具，当谈到旋转，平移和缩放。为确保点正确旋转，您必须将其翻译为原点，旋转它，然后将其翻译回原点。

要完成转型，类似于下面的东西应该做的伎俩：

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); 

这里是CGAffineTransform的文档，如果你想进一步审查：http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGAffineTransform/Reference/reference.html

请让如果这不能解决您的问题，我知道您是否需要其他任何东西！