Question

我想围绕另一个CGPoint（蓝色矩形）旋转一个CGPoint（红色矩形），但它改变了与原点的距离（蓝色矩形）......当我给出270°的角度时，它会在原点正上方创建点，但是当我给出了90作为角度值它降低了原点但是改变距离几乎是三倍....我想保持距离相同并且想要围绕另一个旋转CGPoint。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]];

由于

Answer 1

CGAffineTransform在旋转，平移和缩放方面是一个方便的工具。要确保正确旋转点，必须将其平移到原点，旋转它，然后将其平移。

要完成转换，请执行以下操作：

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);

以下是CGAffineTransform的文档，如果您想进一步查看：http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CGAffineTransform/Reference/reference.html

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CGPoint旋转改变距离原点的距离

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