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
CGContextRestoreGState
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
CGContextRotateCTM
CGContextScaleCTM
   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);

9.图片变小

- (UIImage *)transformToSize(CGSize)newSize{
UIGraphicsBeginImageContext(newSize);
[self drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}