Getting screenshot on iOS OpenGL ES

screenshot.mm

- (UIImage*) takePicture {
    int s = 1;
    UIScreen* screen = [UIScreen mainScreen];
    if ([screen respondsToSelector:@selector(scale)]) {
        s = (int) [screen scale];
    }
    
    GLint viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);

    
    int width = viewport[2];
    int height = viewport[3];
    
    int myDataLength = width * height * 4;
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    for(int y1 = 0; y1 < height; y1++) {
        for(int x1 = 0; x1 <width * 4; x1++) {
            buffer2[(height - 1 - y1) * width * 4 + x1] = buffer[y1 * 4 * width + x1];
        }
    }
    free(buffer);
    
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, releaseData);
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * width;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);
    UIImage *image = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];
    return image;
}

this does not work, i just got black image

@sakrist: Thank You so Much.. This above code worked so well for me... I would love to thank u once again because I passed 2 days for getting UIImage from GlImage

@notedit It could because you need another settings for CGDataProvider or in glReadPixels, or even something else. Debug and check each setting/parameter. For @vikram123456 it works and for me too, so look in your code.

For ios 7+ one can use the following snippet:
UIGraphicsBeginImageContext(self.view.frame.size);
[self.view drawViewHierarchyInRect:self.view.frame afterScreenUpdates:YES];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

I also got a black image because glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer) fills buffer with zeroes

@namiazad Were you able to solve the issue? Even I am getting empty buffer

This works great.