How to Save CCSprite as PNG [closed] - ios4

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Closed 11 years ago.
I created CCSprite and add it to the main view.
Then I want to see the sprite image, so I saved it to PNG
But lots of them doesn't saved correctly.
Only show white background.
I can't know the reason, and also found some articles via Google, but they didn't help me at all.
How can I solve this?
CCSprite *sprite = [[CCSprite spriteWithFile:[NSString stringWithUTF8String:name] rect:CGRectMake(startx, starty, w, h)] retain];
float drawX = x, drawY = y;
CGSize size = [sprite contentSize];
int nWidth = size.width;
int nHeight = size.height;
nWidth *= scale;
nHeight *= scale;
drawX = drawX + nWidth/2;
drawY = drawY - nHeight/2;
ConvertCoordf(&drawX, &drawY);
drawY -= nHeight;
[sprite setScale:scale];
[sprite setPosition:ccp(drawX, drawY)];
[_mainLayer addChild:sprite];
CCRenderTexture* render = [CCRenderTexture renderTextureWithWidth:sprite.contentSize.width height:sprite.contentSize.height];
[render begin];
[sprite visit];
[render end];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *pngPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"new%d.png",i]];
i++;
[render saveBuffer:pngPath format:kCCImageFormatPNG];
[sprite release];