Creating a UIImage from a CGLayer, using CGLayer to wear 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 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 );
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 );
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. }
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 );
31. If (bitmapContext = NULL)
32. // Error creating context
33. Return nil;
35. CGContextScaleCTM (bitmapContext, 1,-1 );
36. CGContextTranslateCTM (bitmapContext, 0,-size. height );
38. // Draw the image to the bitmap context. Once we draw, the memory
39. // Allocated for the context for rendering will then contain
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];
45. CGImageRelease (img );
46. CGContextRelease (bitmapContext );
47. Free (bitmapData );
49. Return ui_img;
51. }

In general, CGLayer is painted on the newly created CGContext and then converted to UIImage. My method will be simpler.

 

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