CGPoint旋轉改變從原點

Question

我要旋轉CGPoint（紅色矩形）周圍其他CGPoint（藍色矩形），但它從原點（藍色矩形）的距離改變的距離......當我在角度給予270它創建點正好在原點之上，但是當我給出角度值90時，它會降低原點，但更改距離幾乎等於三倍......我想保持距離相同並且想要圍繞另一個角度旋轉CGPoint。請指導任何方法對cgpoints的旋轉...

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]]; 

感謝

Answer 1

CGAffineTransform是一個方便的工具，當談到旋轉，平移和縮放。爲確保點正確旋轉，您必須將其翻譯爲原點，旋轉它，然後將其翻譯回原點。

要完成轉型，類似於下面的東西應該做的伎倆：

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); 

這裏是CGAffineTransform的文檔，如果你想進一步審查：http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGAffineTransform/Reference/reference.html

請讓如果這不能解決您的問題，我知道您是否需要其他任何東西！