iphone - Saving imageRef from GLPaint creates completely black image

Question

Hi I am trying out drawing app and have a problem when it comes to saving the image that is drawn. Right now I'm very early in learning this but I have added code from: How to get UIImage from EAGLView? to save the image that was drawn.

I have created a new app, then displayed a viewController that I created. In IB I have added a view which is the PaintingView, and an imageView lies behind it.

The only modification I have done to the PaintingView so far is to change the background to clear and set the background to clear so that I can display an image behind it. The drawing works great, my only problem is saving.

- (void)saveImageFromGLView:(UIView *)glView {

    if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES)
        {
            /// This IS being activated with code 0
            NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES));
    }


    int s = 1;
    UIScreen* screen = [ UIScreen mainScreen ];
    if ( [ screen respondsToSelector:@selector(scale) ] )
        s = (int) [ screen scale ];

    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;
    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 ];
    UIImageWriteToSavedPhotosAlbum( myImage, nil, nil, nil );
    CGImageRelease( imageRef );
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    free(buffer2);    

}

Adding the above code to the Sample app works fine, the problem is doing it in my new app. The only difference I can tell is that I have not included PaintingWindow - would that be the problem?

It's as if the saveImage method isn't seeing the data for drawings.

Answer 1

The save method should be called within the scope of the OpenGL context. To solve this you can move your method within the same rendering .m file and call this function from outside.

Also you need to consider OpenGL clear color.

(detail explanation in comments, lol)