Creating a UIImage from a CGLayer ,通過CGLayer穿件UIImage

http://www.gotow.net/creative/wordpress/?p=33

 

 

CGLayers are great for drawing - especially when things need to be drawn over and over again. Converting a CGLayer to a UIImage is another story, though. NetSketch uses CGLayers for the drawing canvas, but converts them to UIImages when you go to upload your drawing or email it to a friend. The code below shows how it’s done. The CGLayer is drawn into a bitmap CGContext of the same size, and then a CGImage is created around the CGContext. The CGImage can be turned into a UIImage, and you’re done!

Be sure to leave a comment if you find this function useful!

1. UIImage* UIImageFromLayer(CGLayerRef layer)  
2. {  
3.     // Create the bitmap context  
4.     CGContextRef    bitmapContext = NULL;  
5.     void *          bitmapData;  
6.     int             bitmapByteCount;  
7.     int             bitmapBytesPerRow;  
8.     CGSize          size = CGLayerGetSize(layer);  
9.   
10.     // Declare the number of bytes per row. Each pixel in the bitmap in this  
11.     // example is represented by 4 bytes; 8 bits each of red, green, blue, and  
12.     // alpha.  
13.     bitmapBytesPerRow   = (size.width * 4);  
14.     bitmapByteCount     = (bitmapBytesPerRow * size.height);  
15.   
16.     // Allocate memory for image data. This is the destination in memory  
17.     // where any drawing to the bitmap context will be rendered.  
18.     bitmapData = malloc( bitmapByteCount );  
19.     if (bitmapData == NULL)  
20.     {  
21.         return nil;  
22.     }  
23.   
24.     // Create the bitmap context. We want pre-multiplied ARGB, 8-bits  
25.     // per component. Regardless of what the source image format is  
26.     // (CMYK, Grayscale, and so on) it will be converted over to the format  
27.     // specified here by CGBitmapContextCreate.  
28.     bitmapContext = CGBitmapContextCreate (bitmapData, size.width, size.height,8,bitmapBytesPerRow,  
29.                                         CGColorSpaceCreateDeviceRGB(),kCGImageAlphaNoneSkipFirst);  
30.   
31.     if (bitmapContext == NULL)  
32.         // error creating context  
33.         return nil;  
34.   
35.     CGContextScaleCTM(bitmapContext, 1, -1);  
36.     CGContextTranslateCTM(bitmapContext, 0, -size.height);  
37.   
38.     // Draw the image to the bitmap context. Once we draw, the memory  
39.     // allocated for the context for rendering will then contain the  
40.     // raw image data in the specified color space.  
41.     CGContextDrawLayerAtPoint(bitmapContext, CGPointZero, layer);  
42.     CGImageRef   img = CGBitmapContextCreateImage(bitmapContext);  
43.     UIImage*     ui_img = [UIImage imageWithCGImage: img];  
44.   
45.     CGImageRelease(img);  
46.     CGContextRelease(bitmapContext);  
47.     free(bitmapData);  
48.   
49.     return ui_img;  
50.   
51. }  

總體意思是：把CGLayer畫在建立的CGContext上，然後再轉換為UIImage。我的方法會更簡單。

 

UIImage* UIImageFromLayer(CGLayerRef layer)<br />{<br /> CGContextRef ctx = CGLayerGetContext(layer);<br /> CGImageRef img = CGBitmapContextCreateImage(bitmapContext);<br /> UIImage* ui_img = [UIImage imageWithCGImage: img];<br />}