iOS CGAffineTransform 仿射变换

CGAffineTransform

介绍：

CGAffineTransformIdentity ：单位矩阵变换，一般用于仿射变换的初始化或者还原。

CGAffineTransformEqualToTransform(CGAffineTransform t1, CGAffineTransform t2) ：判断两个变换矩阵是否相等

CGAffineTransformConcat(CGAffineTransform t1, CGAffineTransform t2) ：得到两个矩阵相加后得到的最终矩阵

CGPoint CGPointApplyAffineTransform(CGPoint point, CGAffineTransform t) ：某点通过矩阵变换之后的点

CGSize CGSizeApplyAffineTransform(CGSize size, CGAffineTransform t) ：某个size通过矩阵变换之后的size

CGRect CGRectApplyAffineTransform(CGRect rect, CGAffineTransform t) ：某个Rect通过矩阵变换之后的区域

矩阵的加减乘 http://www.ruanyifeng.com/blog/2015/09/matrix-multiplication.html

一、2D仿射变换

UIView的transform属性是一个CGAffineTransform类型，用于在二维空间做旋转，缩放和平移。

CGAffineTransform是一个可以和二维空间向量（例如CGPoint）做乘法的3X2的矩阵:

矩阵平移（如下图）：

CGAffineTransform transform = CGAffineTransformMakeTranslation(10, 10);
结果： (CGAffineTransform) transform = (a = 1, b = 0, c = 0, d = 1, tx = 10, ty = 10)

矩阵缩放（如下图）：

CGAffineTransform transform = CGAffineTransformMakeScale(0.8, 0.8);
结果： (CGAffineTransform) transform = (a = 0.80000000000000004, b = 0, c = 0, d = 0.80000000000000004, tx = 0, ty = 0)

矩阵旋转（如下图）：

CGAffineTransform transform = CGAffineTransformMakeRotation(M_PI_4);

结果 :
(CGAffineTransform) transform = 
(a = 0.70710678118654757, b = 0.70710678118654746, 
c = -0.70710678118654746, d = 0.70710678118654757,
 tx = 0, ty = 0)

修改仿射变换矩阵

CGAffineTransformRotate(CGAffineTransform t, CGFloat angle) // 在矩阵t上添加旋转效果 
CGAffineTransformScale(CGAffineTransform t, CGFloat sx, CGFloat sy) // 在矩阵t上添加缩放效果
CGAffineTransformTranslate(CGAffineTransform t, CGFloat tx, CGFloat ty) // 在矩阵t上添加平移效果

//create a new transform
CGAffineTransform transform = CGAffineTransformIdentity;

//scale by 50%
transform = CGAffineTransformScale(transform, 0.5, 0.5);

//rotate by 30 degrees
transform = CGAffineTransformRotate(transform, M_PI / 180.0 * 30.0);

//translate by 200 points
transform = CGAffineTransformTranslate(transform, 200, 0);

//apply transform to layer
self.layerView.layer.affineTransform = transform;

参考资料：

https://zsisme.gitbooks.io/ios-/content/chapter5/affine-fransforms.html

二、3D变换：

CG的前缀告诉我们，CGAffineTransform类型属于Core Graphics框架，Core Graphics实际上是一个严格意义上的2D绘图API，并且CGAffineTransform仅仅对2D变换有效。

zPosition属性，可以用来让图层靠近或者远离相机（用户视角），transform属性（CATransform3D类型）可以真正做到这点，即让图层在3D空间内移动或者旋转。

和CGAffineTransform类似，CATransform3D也是一个矩阵，但是和3x2的矩阵不同，CATransform3D是一个可以在3维空间内做变换的4x4的矩阵。

CATransform3DMakeRotation(CGFloat angle, CGFloat x, CGFloat y, CGFloat z)
CATransform3DMakeScale(CGFloat sx, CGFloat sy, CGFloat sz) 
CATransform3DMakeTranslation(Gloat tx, CGFloat ty, CGFloat tz)

 if ([key isEqualToString:@"rotationY"]) {//绕Y旋转
        CATransform3D transform = CATransform3DMakeRotation(M_PI_4, 0, 1, 0);
        exampleVC.myImageView.layer.transform = transform;
    }
    else if ([key isEqualToString:@"rotationY_and_m34"])  {//绕Y旋转_透视投影
        //create a new transform
        CATransform3D transform = CATransform3DIdentity;
        //apply perspective
        transform.m34 = - 1.0 / 500.0;
        //rotate by 45 degrees along the Y axis
        transform = CATransform3DRotate(transform, M_PI_4, 0, 1, 0);
        //apply to layer
         exampleVC.myImageView.layer.transform = transform;
    }
    else if ([key isEqualToString:@"sublayerTransform"]) {//共享m34
        /** CALayer有一个属性叫做sublayerTransform。它也是CATransform3D类型，但和对一个图层的变换不同，它影响到所有的子图层。
    　　　　 这意味着你可以一次性对包含这些图层的容器做变换，于是所有的子图层都自动继承了这个变换方法。 **/
        CATransform3D perspective = CATransform3DIdentity;
        perspective.m34 = - 1.0 / 500.0;
        exampleVC.containerView.layer.sublayerTransform = perspective;
        
        //rotate layerView1 by 45 degrees along the Y axis
        CATransform3D transform1 = CATransform3DMakeRotation(M_PI_4, 0, 1, 0);
        exampleVC.layerView1.layer.transform = transform1;
        
        //rotate layerView2 by 45 degrees along the Y axis
        CATransform3D transform2 = CATransform3DMakeRotation(-M_PI_4, 0, 1, 0);
        exampleVC.layerView2.layer.transform = transform2;
        
    }else if ([key isEqualToString:@"background"]) {//背面
       
        CATransform3D transform = CATransform3DMakeRotation(M_PI, 0, 1, 0);
        exampleVC.myImageView.layer.transform = transform;
        
        //背面不绘制 默认yes
        exampleVC.myImageView.layer.doubleSided = NO;//不绘制就看不到了
        
    }else if ([key isEqualToString:@"outer_inner"]) {// 扁平化图层
        CATransform3D outer = CATransform3DMakeRotation(0, 0, 0, 1);
        exampleVC.layerView1.layer.transform = outer;
        
        CATransform3D inner = CATransform3DMakeRotation(-0, 0, 0, 1);
        exampleVC.layerView2.layer.transform = inner;

    }

参考资料:
https://zsisme.gitbooks.io/ios-/content/chapter5/3d-transform.html
https://tech.imdada.cn/2016/06/21/ios-core-animation/