MAMEWorld Forums - Programming - Dumping images on every frame

Hi.

I have a question about mame source code from mame.net.

Im trying to save graphic elements mame is drawing every frame.
So far I've modifed the source to call my function on every frame.
I have modified draw_video_contents()
function in "src\windows\window.c" to call my function from .dll,
im doing this by passing window handle to it, so im able to save each frame to
.bmp file using window HDC.
Now i'm looking for something more complicated.

How to distinguish images that are drawn in current frame?
For example, character sprites or background images.
Can it be done with 'render_primitive_list' member of 'win_window_info'
structure and how ?

Thanks in advance