iphone 使用Core Graphics 合成图片

//底图

UIImage *oriPic=[UIImage imageNamed:@"1.png"];

//将要画在底图上的图片

UIImage *subImage=[UIImage imageNamed:@"diy4.png"];

//创建绘图上下文

UIGraphicsBeginImageContext(oriPic.size);

CGContextRef thisctx=UIGraphicsGetCurrentContext();

//图像坐标变换

CGContextRotateCTM(thisctx, M_PI);

CGContextTranslateCTM(thisctx, -oriPic.size.width, -oriPic.size.height);

//绘制底图

CGContextDrawImage(thisctx, CGRectMake(0, 0, oriPic.size.width, oriPic.size.height), [oriPic CGImage]);

//在底图上绘制图片

CGContextDrawImage(thisctx, CGRectMake(5, 5, 30, 30), [subImage CGImage]);

//得到所绘制的图片

UIImage *newImage=UIGraphicsGetImageFromCurrentImageContext();

//关闭上下文

UIGraphicsEndImageContext();

UIImageView *imageView=[[UIImageView alloc] initWithImage:newImage];

imageView.frame=CGRectMake(160,240, 40, 40);

[self.view addSubview:imageView];