Why is glReadPixels() failing in this code in iOS 6.0? - ios

Question

The following is code I use for reading an image from an OpenGL ES scene:
-(UIImage *)getImage{
GLint width;
GLint height;
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &width);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &height);
NSLog(#"%d %d",width,height);
NSInteger myDataLength = width * height * 4;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *) malloc(myDataLength);
glReadPixels(0, 0, width, height, 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 < height; y++)
{
for(int x = 0; x < width * 4; x++)
{
buffer2[((height - 1) - y) * width * 4 + x] = buffer[y * 4 * width + x];
}
}
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
// then make the uiimage from that
UIImage *myImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpaceRef);
free(buffer);
free(buffer2);
return myImage;
}
This is working in iOS 5.x and lower versions, but on iOS 6.0 this is now returning a black image. Why is glReadPixels() failing on iOS 6.0?

Answer 1

CAEAGLLayer *eaglLayer = (CAEAGLLayer *) self.layer;
eaglLayer.drawableProperties = #{
kEAGLDrawablePropertyRetainedBacking: [NSNumber numberWithBool:YES],
kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8
};
set
kEAGLDrawablePropertyRetainedBacking = YES
(I do not know why this tip is going well..///)

Answer 2

bro try this method to get your screenshot image. The output image is MailImage
- (UIImage*)screenshot
{
// Create a graphics context with the target size
// On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
// On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
CGSize imageSize = [[UIScreen mainScreen] bounds].size;
if (NULL != UIGraphicsBeginImageContextWithOptions)
UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
else
UIGraphicsBeginImageContext(imageSize);
CGContextRef context = UIGraphicsGetCurrentContext();
// Iterate over every window from back to front
for (UIWindow *window in [[UIApplication sharedApplication] windows])
{
if (![window respondsToSelector:#selector(screen)] || [window screen] == [UIScreen mainScreen])
{
// -renderInContext: renders in the coordinate space of the layer,
// so we must first apply the layer's geometry to the graphics context
CGContextSaveGState(context);
// Center the context around the window's anchor point
CGContextTranslateCTM(context, [window center].x, [window center].y);
// Apply the window's transform about the anchor point
CGContextConcatCTM(context, [window transform]);
// Offset by the portion of the bounds left of and above the anchor point
CGContextTranslateCTM(context,
-[window bounds].size.width * [[window layer] anchorPoint].x,
-[window bounds].size.height * [[window layer] anchorPoint].y);
// Render the layer hierarchy to the current context
[[window layer] renderInContext:context];
// Restore the context
CGContextRestoreGState(context);
}
}
// Retrieve the screenshot image
Mailimage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return Mailimage;
}