High Resolution-Retina display screenshot of OpenGL ES [CAEAGLLayer] content - iphone

Question

I’m using GLPaint example for my Paint app , I needed to take a screenshot of OpenGL ES [CAEAGLLayer] rendered content. I am using function:
-(UIImage *)snapUIImage
{
int s = 2;
const int w = self.frame.size.width;
const int h = self.frame.size.height;
const NSInteger myDataLength = w * h * 4 * s * s;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, w*s, h*s, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
// gl renders "upside down" so swap top to bottom into new array.
// there's gotta be a better way, but this works.
GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
for(int y = 0; y < h*s; y++)
{
memcpy( buffer2 + (h*s - 1 - y) * w * 4 * s, buffer + (y * 4 * w * s), w * 4 * s );
}
free(buffer); // work with the flipped buffer, so get rid of the original one.
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * w * s;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaLast;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(w*s, h*s, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// then make the uiimage from that
UIImage *myImage = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];
CGImageRelease( imageRef );
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpaceRef);
// buffer2 will be destroyed once myImage is autoreleased.
return myImage;
}
-(void)captureToPhotoAlbum {
UIImage *image = [self snapUIImage];
    UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);
}
Above code is working I am getting the image but it is not a high resolution [Retina display] image.Please help.
Thanks in advance.

Answer 1

Working code solution
- (UIImage*) getGLScreenshot
{
int myWidth = self.frame.size.width*2;
int myHeight = self.frame.size.height*2;
int myY = 0;
int myX = 0;
int bufferLength = (myWidth*myHeight*4);
//unsigned char buffer[bufferLength];
unsigned char* buffer =(unsigned char*)malloc(bufferLength);
glReadPixels(myX, myY, myWidth, myHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, buffer, bufferLength, NULL);
CGImageRef iref = CGImageCreate(myWidth,myHeight,8,32,myWidth*4,CGColorSpaceCreateDeviceRGB(),
kCGBitmapByteOrderDefault,ref,NULL, true, kCGRenderingIntentDefault);
uint32_t* pixels = (uint32_t *)malloc(bufferLength);
CGContextRef context = CGBitmapContextCreate(pixels, myWidth, myHeight, 8, myWidth*4, CGImageGetColorSpace(iref),
kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big);
CGContextTranslateCTM(context, 0.0, myHeight);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, CGRectMake(0.0, 0.0, myWidth, myHeight), iref);
CGImageRef outputRef = CGBitmapContextCreateImage(context);
UIImage *image = nil;
if(regardOrientation) {
UIDeviceOrientation deviceOrientation = [UIDevice currentDevice].orientation;
if (deviceOrientation == UIDeviceOrientationPortraitUpsideDown) {
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationDown];
} else if (deviceOrientation == UIDeviceOrientationLandscapeLeft) {
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationLeft];
} else if (deviceOrientation == UIDeviceOrientationLandscapeRight) {
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationRight];
} else {
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationUp];
}
} else {
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationUp];
}
image = [UIImage imageWithCGImage:outputRef scale:1 orientation:UIImageOrientationUp];
CGImageRelease(iref);
CGImageRelease(outputRef);
CGContextRelease(context);
CGDataProviderRelease(ref);
free(buffer);
free(pixels);
UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);
return image;
}