【深入iOS开发】iOS仿射变换和3D变换

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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:

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Paste_Image.png
当对UIView应用变换矩阵，UIView图层矩形内的每一个点都被相应地做变换，从而形成一个新的四边形的形状。CGAffineTransform中的“仿射”的意思是无论变换矩阵用什么值，图层中平行的两条线在变换之后任然保持平行.

单位矩阵

CGAffineTransformIdentity

CGAffineTransform transform = CGAffineTransformIdentity;

结果:
(CGAffineTransform) transform = (a = 1, b = 0, c = 0, d = 1, tx = 0, ty = 0)
创建仿射变换矩阵

CGAffineTransformMakeRotation(CGFloat angle)  // 旋转
CGAffineTransformMakeScale(CGFloat sx, CGFloat sy) // 缩放
CGAffineTransformMakeTranslation(CGFloat tx, CGFloat ty)  // 平移
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)
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)
CGAffineTransform transform = CGAffineTransformMakeTranslation(10, 10);

结果：
(CGAffineTransform) transform = (a = 1, b = 0, c = 0, d = 1, tx = 10, ty = 10)
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Paste_Image.png

图中，灰色为旧图，蓝色为变化后的新图.
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