iPhone绘图总结

1.绘图总结:  
绘图前设置:  
CGContextSetRGBFillColor/CGContextSetFillColorWithColor          //填充色  
CGContextSetRGBStrokeColor/CGContextSetStrokeColorWithColor           //笔颜色  
CGContextSetLineWidth                           //线宽度  
绘图后设置:  
注:  画完图后,必须  
先用CGContextStrokePath来描线,即形状  
后用CGContextFillPath来填充形状内的颜色.  
2.常见图形绘制:  
CGContextFillRect/CGContextFillRects  
CGContextFillEllipseInRect  
CGContextAddRect/CGContextAddRects  
CGContextAddEllipseInRect  
CGContextAddLines  
CGContextMoveToPoint  
CGContextAddLineToPoint  
3.常见控制方法:  
CGContextSaveGState ->  将当前的graphics的状态加到context栈中 
CGContextRestoreGState ->  就是恢复最近保存的graphics的状态 
4.创建内存图像context:  
CGBitmapContextCreate       <-----CGContextRlease释放  
CGColorSpaceCreateWithName    (KCGColorSpaceGenericRGB)  
CGColorSpaceRlease  
CGBitmapContextCreateImage()   <-----CGImageRlease 释放.  
eg:  
CGContextRefMyCreateBitmapContext(intpixelsWide,intpixelsHigh)  
{  
CGContextRef    context=NULL;  
CGColorSpaceRefcolorSpace;  
void*          bitmapData;  
int             bitmapByteCount;  
int             bitmapBytesPerRow;  
bitmapBytesPerRow   =(pixelsWide*4);  
bitmapByteCount     =(bitmapBytesPerRow*pixelsHigh);  
colorSpace=CGColorSpaceCreateDeviceRGB();  
bitmapData=malloc(bitmapByteCount);  
if(bitmapData==NULL)  
{  
fprintf(stderr,"Memorynotallocated!");  
returnNULL;  
}  
context=CGBitmapContextCreate(bitmapData,    pixelsWide,    pixelsHigh,    8,    bitmapBytesPerRow,    colorSpace,    kCGImageAlphaPremultipliedLast);  
if(context==NULL)  
{  
free(bitmapData);  
fprintf(stderr,"Contextnotcreated!");  
returnNULL;  
}  
CGColorSpaceRelease(colorSpace);  
returncontext;  
}  
5.图形的变换:  
CGContextTranslateCTM -> 移动context 
CGContextRotateCTM -> 旋转context 
CGContextScaleCTM -> 缩放context 
   6.常用函数:  
 CGRectContainsPoint();  
CGRectContainsRect();  
CGRectIntersectsRect();  
CGRectIntersection();  
CGPointEqualToPoint();  
CGSizeEqualToSize();  
  7.从原图片中取小图.  
CGImageCreateWithImageInRect  
8.屏幕快照:  
#import "QuartzCore/QuartzCore.h"  

UIGraphicsBeginImageContext(yourView.frame.size);  
[[yourView layer] renderInContext:UIGraphicsGetCurrentContext()];  
UIImage*screenshot =UIGraphicsGetImageFromCurrentImageContext();  
UIGraphicsEndImageContext();  
from:http://www.cppblog.com/zhangyuntaoshe/articles/123066.html  

合并两张bit图到一张image的方法  
To graphically merge two images into a new image, you do something like this:  
UIImage *result = nil;  
unsignedchar *data = calloc(1,size.width*size.height*kBytesPerPixel);  
if (data != NULL) {  
// kCGImageAlphaPremultipliedLast 为预记录的#define value  
// 设置context上下文  
CGContextRef context = CGBitmapContextCreate(  
data, size.width, size.height, 8, size.width*kBytesPerPixel,  
CGColorSpaceCreateDeviceRGB(), kCGImageAlphaPremultipliedLast);  
if (context != NULL) {  
UIGraphicsPushContext(context);  
//  Image 为下载的背景图片,用于比较context  
CGContextTranslateCTM(context, 0, size.height);  
CGContextScaleCTM(context, 1, -1);  
[image drawInRect:imageRect];  
[image2 drawInRect:image2Rect];  
UIGraphicsPopContext();  
CGImageRef imageRef = CGBitmapContextCreateImage(context);  
if (imageRef != NULL) {  
result = [UIImageimageWithCGImage:imageRef];  
CGImageRelease(imageRef);  
}  
CGContextRelease(context);  
}  
free(data);  
}  
return result;  

关键方法：  CGContextRef context = CGBitmapContextCreate();  
CGContextTranslateCTM();  
CGContextScaleCTM();  
CGImageRef imageRef = CGBitmapContextCreateImage(context);  
CGImageRelease(imageRef);