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

ios, ios6, opengl-es

Solution

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..///)

Problem

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?

Original source