I'm looking an easy and reliable way to know if vertices hits the final framebuffer.
I'm not looking for the exact count, but if something actually hits the buffer. I'm trying to debug a shadow map. All my tools told me I'm drawing something, but on the final result, I don't see anything, even if I convert all in a regular framebuffer. So I want to know from the API "I'm putting a vertex on the buffer right now" to be sure and to don't waste time on a faulty framebuffer.