ImGuiIntegration: glUseProgram(0) called anywhere in drawEvent causes imgui to not render about magnum-integration HOT 5 CLOSED

I understand now, I was just a bit confused by the automated project management stuff. Thank you.

And good luck with vulkan!

from magnum-integration.

Hi!

This is not related to ImGui, but rather to the way how Magnum tracks OpenGL state in general -- in order to avoid redundant OpenGL calls, Magnum remembers what buffers / VAOs / textures ... are bound and what shaders are used. Doing it like this leads to significant perf improvements where the cost of GL API calls is high, especially Emscripten and shitter mobile drivers.

But of course this breaks when you (or some 3rd party lib) accesses GL directly, and in that case Magnum gets confused and assumes a particular state is set while it isn't. To fix that, you need to inform Magnum's state tracker before and after the direct GL access is happening. Docs: https://doc.magnum.graphics/magnum/opengl-wrapping.html#opengl-state-tracking

Hope this helps! :)

from magnum-integration.

Yes, thank you!

Is this on the milestone to do better state tracking? or automatic state tracking? or something else?

from magnum-integration.

I just realize you may not have wanted me to close this

from magnum-integration.

How do you mean, better? :) There's not really a way to handle this automatically and still be performant enough -- the "safe bet" which works with 3rd party GL code would be that every API assumes no state is set to desired values and always bind / use / set ... everything needed upfront, and then reset all that back so 3rd party GL code isn't affected by what magnum did. That's what I was doing originally back in ~2010 but that made the driver waste a lot of time compared to what it does now. So there's not really much to do now (except for adding similar state tracking for a bunch of features that don't have it yet).

In comparison, with Vulkan (that's on the roadmap) this whole global driver state is gone and this is not a problem there anymore.

Hope that explains it :)

from magnum-integration.