HighSpeedImageDownloadDemo

I am learning this example design provided on the nioswikihome, but I am a little confused. Can the author or someone who are familiar with this design provided more introduction about it?

For example, I am puzzled with "image_download_demo.c", who can tell me the function of it?

If it's function is controlling the VGA, I don't know how the variable "uncached_buffer" or "main_frame_buffer" is related to the VGA.

Thanks very much.