demo地址 https://github.com/nullLuli/ImageSizeAfterTransformDemo
方法一：计算图片每个角旋转后坐标，然后计算外围矩形 （原理型）
class func caculateFrame(frame: CGRect, after trans: CGAffineTransform) -> CGRect {
//找出四个frame的四个角坐标
let point1 = CGPoint(x: frame.minX, y: frame.minY)
let point2 = CGPoint(x: frame.maxX, y: frame.minY)
let point3 = CGPoint(x: frame.maxX, y: frame.maxY)
let point4 = CGPoint(x: frame.minX, y: frame.maxY)
//计算出四个角以center为坐标系原点的相对坐标
let point1RP = CGPoint(x: point1.x - frame.midX, y: point1.y - frame.midY)
let point2RP = CGPoint(x: point2.x - frame.midX, y: point2.y - frame.midY)
let point3RP = CGPoint(x: point3.x - frame.midX, y: point3.y - frame.midY)
let point4RP = CGPoint(x: point4.x - frame.midX, y: point4.y - frame.midY)
//旋转相对坐标
let point1RPAfter = __CGPointApplyAffineTransform(point1RP, trans)
let point2RPAfter = __CGPointApplyAffineTransform(point2RP, trans)
let point3RPAfter = __CGPointApplyAffineTransform(point3RP, trans)
let point4RPAfter = __CGPointApplyAffineTransform(point4RP, trans)
//从相对坐标转换成iOS系统的坐标
let point1After = CGPoint(x: point1RPAfter.x + frame.midX, y: point1RPAfter.y + frame.midY)
let point2After = CGPoint(x: point2RPAfter.x + frame.midX, y: point2RPAfter.y + frame.midY)
let point3After = CGPoint(x: point3RPAfter.x + frame.midX, y: point3RPAfter.y + frame.midY)
let point4After = CGPoint(x: point4RPAfter.x + frame.midX, y: point4RPAfter.y + frame.midY)
//遍历找出四个新角
var maxX: CGFloat = point4After.x //随便给个初始值，后面会遍历
var maxY: CGFloat = point4After.y
var minX: CGFloat = point1After.x
var minY: CGFloat = point1After.y
for point in [point1After, point2After, point3After, point4After] {
if point.x > maxX {
maxX = point.x
}
if point.x < minX {
minX = point.x
}
if point.y > maxY {
maxY = point.y
}
if point.y < minY {
minY = point.y
}
}
return CGRect(x: minX, y: minY, width: maxX - minX, height: maxY - minY)
}
方法二：使用UIView的transform让系统帮我们计算
class func caculateFrame2(frame: CGRect, after trans: CGAffineTransform) -> CGRect {
let rotatedImageBox = UIView(frame: frame)
rotatedImageBox.frame = frame
rotatedImageBox.transform = trans
return rotatedImageBox.frame
}
方法三：使用CGRect.applying方法计算
class func caculateFrame3(frame: CGRect, after trans: CGAffineTransform) -> CGRect {
let frameR = CGRect(origin: CGPoint(x: -frame.width / 2, y: -frame.height / 2), size: frame.size)
let frameAfterR = frameR.applying(trans)
let frameAfter = CGRect(origin: CGPoint(x: frameAfterR.origin.x + frame.midX, y: frameAfterR.origin.y + frame.midY), size: frameAfterR.size)
return frameAfter
}
下面是原文
方法一：计算图片每个角旋转后坐标，然后计算外围矩形
假设图片位置（x,y,width,height）
则图片四个角坐标分别是
point1 = （x,y）;
point2 = (x+width, y);
point3 = (x+width, y+height);
point4 =(x,y+height);
旋转中心点为（centerX,centerY）
旋转变换矩阵为trans（iOS中CGAffineTransform，安卓中的Matrix）
旋转后每个角的坐标分别是
point1 = (CGPointApplyAffineTransform(x-centerX, trans) + centerX,CGPointApplyAffineTransform(y-centerY, trans) + centerY);
point2 = (CGPointApplyAffineTransform(x+width-centerX, trans) + centerX,CGPointApplyAffineTransform(y-centerY, trans) + centerY);
point3 = (CGPointApplyAffineTransform(x+width-centerX, trans) + centerX,CGPointApplyAffineTransform(y+height-centerY, trans) + centerY);
point4 = (CGPointApplyAffineTransform(x-centerX, trans) + centerX,CGPointApplyAffineTransform(y+height-centerY, trans) + centerY);
遍历旋转后的点找出x、y方向的最大、最小值
将这些最大、最小值组合成为新的矩形，这个矩形就是我们要找的旋转后的图片大小
方法二：
UIView * rotatedImageBox = [[UIView alloc]initWithFrame:imageFrame];//imageFrame是旋转前的图片位置
CGFloat rotateAnchorX = (-imageFrame.origin.x + rotateCenter.x)/imageFrame.size.width;
CGFloat rotateAnchorY = (-imageFrame.origin.y + rotateCenter.y)/imageFrame.size.height;
rotatedImageBox.layer.anchorPoint = CGPointMake(rotateAnchorX, rotateAnchorY);
rotatedImageBox.frame = imageFrame;
rotatedImageBox.transform = trans;
CGRect timeFrameInPDF = rotatedImageBox.frame;
