UIImage 使用UIGraphicsBeginImageContext做一些簡單操作

UIImage 繪制

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UIGraphicsBeginImageContext

步驟：

1. UIGraphicsBeginImageContext(CGSize size) 或者 UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale)
   • 准備繪圖環境

• CGContextRef __nullable UIGraphicsGetCurrentContext(void)
  • 獲取繪圖的CGContextRef
• 開始繪圖
• UIImage* UIGraphicsGetImageFromCurrentImageContext(void);
  • 獲取當前繪制的圖形
• void UIGraphicsEndImageContext(void);
  • 關閉繪圖環境

簡單應用：

等比縮放 將圖片改為自定義大小

- (UIImage *) scaleImage:(UIImage *)image toScale:(float)scaleSize {
	UIGraphicsBeginImageContext(CGSizeMake(image.size.width * scaleSize, image.size.height * scaleSize);
	[image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height * scaleSize)];
	UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	return scaledImage;
}

將UIView轉為UIImage

-(UIImage*) captureView:(UIView *)theView {
	CGRect rect = theView.frame;
	UIGraphicsBeginImageContext(rect.size);
	CGContextRef context = UIGraphicsGetCurrentContext();
	[theView.layer renderInContext:context];
	UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	return img;
}	

** renderInContext 只會繪制在左上角 **

** 若要將UIView繪制在指定地方可以平移context **
如：

CGContextTranslateCTM(context, 50, 50);
[theView.layer renderInContext:context];
CGContextTranslateCTM(context, -50, -50);

根據給定得圖片，從其指定區域截取一張新得圖片

-(UIImage *)getImageFromImage{
//大圖bigImage
//定義myImageRect，截圖的區域
CGRect myImageRect = CGRectMake(10.0, 10.0, 57.0, 57.0);
UIImage* bigImage= [UIImage imageNamed:@"k00030.jpg"];
CGImageRef imageRef = bigImage.CGImage;
CGImageRef subImageRef =CGImageCreateWithImageInRect(imageRef, myImageRect);
CGSize size;
size.width = 57.0;
size.height = 57.0;
UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, myImageRect, subImageRef);
UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
UIGraphicsEndImageContext();
return smallImage;
}	

合並兩張圖片

-(UIImage *)addImage:(UIImage *)image1 toImage:(UIImage*)image2 {
UIGraphicsBeginImageContext(image1.size);
// Draw image1
[image1 drawInRect:CGRectMake(0, 0, image1.size.width,image1.size.height)];
// Draw image2
[image2 drawInRect:CGRectMake(0, 0, image2.size.width,image2.size.height)];
UIImage *resultingImage =UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resultingImage;
}

截取當前屏幕

CGSize windowSize = behandView.bounds.size;
UIGraphicsBeginImageContextWithOptions(windowSize, YES, 2.0);
CGContextRef context = UIGraphicsGetCurrentContext();
[behandView.window.layer renderInContext:context];
UIImage *snapshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();	

截取scrollview

-(UIImage *)captureScrollView:(UIScrollView *)scrollView{

UIImage* image = nil;
UIGraphicsBeginImageContextWithOptions(scrollView.contentSize, NO, 2.0f);

scrollView.contentOffset = CGPointZero;
scrollView.frame = CGRectMake(0, 0, scrollView.contentSize.width, scrollView.contentSize.height);
[scrollView.layer renderInContext: UIGraphicsGetCurrentContext()];
image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image;

}