Is there any way to determine whether any pixels passed the z-test, say between the last glBegin() / glEnd() pair? My instinct says no, but it would be extremely useful to my final year thesis, so I thought I’d ask.



Feedback does not do this. Feedback does surprisingly little.

  • Matt

It would be a nice thing to have more control on the end of the graphic pipeline…
Modifying local variable (that can be accessed by vertex programs?) according to Z, stencil, etc… tests would be really usefull sometimes.

Even with vertex programs and pixel shaders, the end of the OpenGL pipeline still looks so fixed and unflexible.

PS: to give a short answer to your question: I have no idea

Unfortunately, feedback only returns information on vertices, as far as I can tell - i.e. feedback is performed before rasterization which is not what I need.

I’m trying, as part of a university project, to develop a very quick (but not necessarily quick enough for real time), approximate visibility approach based on the cheapness of very fast commodity hardware (essentially farming out approximate visibility computations to a bunch of cheap machines, based on drawing everything front to back until there is complete coverage).

So I need to know when fragments stop writing to the framebuffer. Any ideas?