Qual è il codice corretto per salvare un CGLayer come file PNG?

Question

Si prega di notare che questa domanda è circa CGLayer (che in genere si usa per disegnare fuori dallo schermo), non si tratta di CALayer.

In iOS, qual è il codice corretto per salvare un CGLayer come file PNG? Grazie!

Ancora, questo è CGLayer, non CALayer.

Si noti che è NON PUO uso UIGraphicsGetImageFromCurrentImageContext.

(Dalla documentazione, "Si può chiamare UIGraphicsGetImageFromCurrentImageContext solo quando un contesto grafico bitmap-based è il contesto grafico corrente.")

Si noti che è NON PUO uso renderInContext :. renderInContext: è strettamente per CALayers. I CGLayer sono completamente diversi.

Quindi, come è possibile convertire un CGLayer in un'immagine PNG? O in effetti, come eseguire il rendering di un CGLayer in una bitmap in qualche modo (ovviamente puoi salvarlo facilmente come immagine).

---

Più tardi ... Ken ha risposto a questa difficile domanda. Inserirò un codice di esempio lungo che può aiutare le persone. Grazie ancora Ken! Stupefacente!

-(void)drawingExperimentation 
{ 
// this code uses the ASTOUNDING solution by KENNYTM -- Oct/Nov2010 
// 
// create a CGLayer for offscreen drawing 
// note. for "yourContext", ideally it should be a context from your screen, ie the 
// context you "normally get" in one of your drawRect routines associated with 
// drawing to the screen normally. 
// UIGraphicsGetCurrentContext() also normally works but you could have colorspace woes 

// so create the CGLayer called notepad... 

CGLayerRef notepad = CGLayerCreateWithContext(yourContext,CGSizeMake(1500,1500), NULL); 
CGContextRef notepadContext = CGLayerGetContext(notepad); 

// you can for example write an image in to notepad 
CGImageRef imageExamp = [[UIImage imageWithContentsOfFile: 
    [[NSBundle mainBundle] pathForResource:@"smallTestImage" ofType:@"png"] ] CGImage]; 
CGContextDrawImage(notepadContext, CGRectMake(100,100, 50,50), imageExamp); 

// setting the colorspace may or may not be relevant to you 
CGContextSetFillColorSpace(notepadContext, CGColorSpaceCreateDeviceRGB()); 

// you can draw to notepad as much as you like in the normal way 
// don't forget to push it's context on and off your work space so you can draw to it 

UIGraphicsPushContext(notepadContext); 

// set the colors 
CGContextSetRGBFillColor(notepadContext, 0.15,0.25,0.35, 0.45); 
// draw rects 
UIRectFill(CGRectMake(x,y,w,h)); 
// draw ovals, filled stroked or whatever you wish 
UIBezierPath* d = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(x,y,w,h)]; 
[d fill]; 
// draw cubic and other curves 
UIBezierPath *longPath; 
longPath.lineWidth = 42; 
longPath.lineCapStyle = kCGLineCapRound; 
longPath.lineJoinStyle = kCGLineJoinRound; 
[longPath moveToPoint:p]; 
[longPath addCurveToPoint:q controlPoint1:r controlPoint2:s]; 
[longPath addCurveToPoint:a controlPoint1:b controlPoint2:c]; 
[longPath addCurveToPoint:m controlPoint1:n controlPoint2:o]; 
[longPath closePath]; 
[longPath stroke]; 

UIGraphicsPopContext(); 

// so now you have a nice CGLayer. 

// how to save it to a file? 

// you can save it to a file using the amazing KENNY-TM-METHOD !!! 

UIGraphicsBeginImageContext(CGLayerGetSize(notepad)); 
CGContextRef rr = UIGraphicsGetCurrentContext(); 
CGContextDrawLayerAtPoint(rr, CGPointZero, notepad); 
UIImage* ii = UIGraphicsGetImageFromCurrentImageContext(); 
NSData* pp = UIImagePNGRepresentation(ii); 
[pp writeToFile:@"foo.png" atomically:YES]; 
UIGraphicsEndImageContext(); 

// you may prefer to look at it like this: 

UIGraphicsBeginImageContext(CGLayerGetSize(notepad)); 
CGContextDrawLayerAtPoint(UIGraphicsGetCurrentContext(), CGPointZero, notepad); 
[UIImagePNGRepresentation(UIGraphicsGetImageFromCurrentImageContext()) writeToFile:@"foo.png" atomically:YES]; 
UIGraphicsEndImageContext(); 

// there are three clever steps in the KENNY-TM-METHOD: 
// - start a new UIGraphics image context 
// - CGContextDrawLayerAtPoint which can, in fact, draw a CGLayer 
// - just use the usual UIImagePNGRepresentation to convert to a png 

// done! a miracle 

// if you are testing on your mac-simulator, you'll find the file 
// simply in the main drive directory 
return; 
} 

Answer 1

per iPhone OS, dovrebbe essere possibile tracciare un CGLayer su un CGContext e poi convertire in un UIImage, che possono poi essere codificato in formato PNG e salvato.

CGSize size = CGLayerGetSize(layer); 
UIGraphicsBeginImageContext(size); 
CGContextRef ctx = UIGraphicsGetCurrentContext(); 
CGContextDrawLayerAtPoint(ctx, CGPointZero, layer); 
UIImage* image = UIGraphicsGetImageFromCurrentImageContext(); 
NSData* pngData = UIImagePNGRepresentation(image); 
[pngData writeToFile:... atomically:YES]; 
UIGraphicsEndImageContext(); 

(non testato)