Quartz转换实现的原理，Quartz把绘图分成两个部分，
用户空间，即和设备无关，
设备空间；
用户空间和设备空间中间存在一个转换矩阵：CTM
Quartz提供三大功能
移动、旋转、缩放
void CGContextDrawImage ( CGContextRef c, CGRect rect, CGImageRef image );
移动函数CGContextTranslateCTM (myContext, 100, 50);
旋转函数
include <math.h> static inline double radians (double degrees) {return degrees * M_PI/180;}
CGContextRotateCTM (myContext, radians(–45.));
缩放CGContextScaleCTM (myContext, .5, .75);
翻转， 两种转换合成后的效果，先把图片移动到右上角，然后旋转180度
CGContextTranslateCTM (myContext, w,h); CGContextRotateCTM (myContext, radians(-180.));
//***************************************************************************************************************************************************//
组合几个动作
CGContextTranslateCTM (myContext, w/4, 0);CGContextScaleCTM (myContext, .25, .5);CGContextRotateCTM (myContext, radians ( 22.));
CGContextRotateCTM (myContext, radians ( 22.));CGContextScaleCTM (myContext, .25, .5);CGContextTranslateCTM (myContext, w/4, 0);
上面是通过直接修改当前的ctm实现3大效果，下面是通过创建Affine Transforms，然后连接ctm实现同样的3种效果这样做的好处是可以重用这个Affine Transforms应用Affine Transforms 到ctm的函数void CGContextConcatCTM (CGContextRef c, CGAffineTransform transform );Creating Affine Transforms移动效果CGAffineTransform CGAffineTransformMakeTranslation (CGFloat tx, CGFloat ty );CGAffineTransform CGAffineTransformTranslate (CGAffineTransform t, CGFloat tx, CGFloat ty );旋转效果CGAffineTransform CGAffineTransformMakeRotation (CGFloat angle );CGAffineTransform CGAffineTransformRotate (CGAffineTransform t, CGFloat angle );缩放效果CGAffineTransform CGAffineTransformMakeScale ( CGFloat sx, CGFloat sy );CGAffineTransform CGAffineTransformScale (CGAffineTransform t, CGFloat sx, CGFloat sy );反转效果CGAffineTransform CGAffineTransformInvert (CGAffineTransform t );只对局部产生效果CGRect CGRectApplyAffineTransform (CGRect rect, CGAffineTransform t );判断两个AffineTrans是否相等bool CGAffineTransformEqualToTransform (CGAffineTransform t1, CGAffineTransform t2 );获得Affine TransformCGAffineTransform CGContextGetUserSpaceToDeviceSpaceTransform ( CGContextRef c );下面的函数只起到查看的效果，比如看一下这个用户空间的点，转换到设备空间去坐标是多少CGPoint CGContextConvertPointToDeviceSpace (CGContextRef c, CGPoint point );CGPoint CGContextConvertPointToUserSpace (CGContextRef c, CGPoint point );CGSize CGContextConvertSizeToDeviceSpace (CGContextRef c, CGSize size );CGSize CGContextConvertSizeToUserSpace (CGContextRef c, CGSize size );CGRect CGContextConvertRectToDeviceSpace ( CGContextRef c, CGRect rect );CGRect CGContextConvertRectToUserSpace ( CGContextRef c, CGRect rect );
CGContextRef context = CGBitmapContextCreate(NULL, pageSize.width, pageSize.height,
8,/* bits per component*/ pageSize.width *4, /* bytes
per row */ colorSpace, kCGImageAlphaPremultipliedLast|kCGBitmapByteOrder32Big); //创建上下文
CGAffineTransform scale = CGAffineTransformMakeScale(scaleFactor, scaleFactor);
CGRect scaledInnerRect = CGRectApplyAffineTransform(innerRect, scale);
CGAffineTransformtranslation = CGAffineTransformMakeTranslation((outerRect.size.width -
scaledInnerRect.size.width) / 2 - scaledInnerRect.origin.x,
(outerRect.size.height - scaledInnerRect.size.height)
/ 2 - scaledInnerRect.origin.y);
CGAffineTransformtransform = CGAffineTransformConcat(scale, translation); //连接两个
CGAffineTransform
CGContextConcatCTM(context,transform);
CGContextDrawPDFPage(context,_pageRef);
CGImageRef image =CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGPDFPageRef page = CGPDFDocumentGetPage(cgPdfRef,number+1);
UIGraphicsBeginImageContext(CGSizeMake(156, 208)); //创建上下文
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBFillColor( context, 1.0, 1.0, 1.0, 1.0 );
CGContextFillRect( context, CGContextGetClipBoundingBox(context));
CGContextTranslateCTM(context, 0.0, 208);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextSaveGState(context);
CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFCropBox,CGRectMake(0.0f, 0.0f, 156.0f, 208.0f), 0, true);
CGContextConcatCTM(context, pdfTransform);
CGContextDrawPDFPage(context, page);
CGContextRestoreGState(context);
UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();