iphone - 将 CGLayer 保存为 PNG 文件的正确代码是什么？

Question

请注意，这个问题是关于CGLayer(您通常用它来在屏幕外绘制)，而不是关于CALayer。

在 iOS 中，将 CGLayer 保存为 PNG 文件的正确代码是什么？谢谢!

再说一遍，那是 CGLayer，而不是 CALayer。

请注意，您不能使用 UIGraphicsGetImageFromCurrentImageContext。

(根据文档，“仅当基于位图的图形上下文是当前图形上下文时，您才能调用 UIGraphicsGetImageFromCurrentImageContext。”)

请注意，您不能使用 renderInContext:。 renderInContext:严格适用于 CALayers。 CGLayers 完全不同。

那么，如何将 CGLayer 实际转换为 PNG 图像呢？或者实际上，如何以某种方式将 CGLayer 渲染为位图(当然，您可以轻松保存为图像)。

<小时/>

后来...... Ken回答了这个难题。我将粘贴一个可能对人们有帮助的长示例代码。再次感谢肯!太棒了!

-(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

对于 iPhone 操作系统，应该可以在 CGContext 上绘制 CGLayer，然后转换为 UIImage，然后可以将其编码为 PNG 并保存。

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();

(未测试)