unculled backfaces don't throw shadows

[JulianGro]

When a model had backface culling disabled, that backface doesn't seem to throw a shadow.

[HifiExperiments]

I just tested this quickly with the "Material Data Creator" from the More app. it creates a cube with the material applied and you can toggle the backface culling near the bottom. all three modes seem to cast shadows correctly. also just generally I'd expect this to work. does this still reproduce? perhaps it's related to the texture with opacity specifically?

[SilverfishVR]

I just tested this quickly with the "Material Data Creator" from the More app. it creates a cube with the material applied and you can toggle the backface culling near the bottom. all three modes seem to cast shadows correctly. also just generally I'd expect this to work. does this still reproduce? perhaps it's related to the texture with opacity specifically?

I think that is because it is a cube, so there is always a front face towards the keylight?

With a true quad (not the one from shapes, it's actually a flat cube) it only shows shadows from one side.

Now if I add a material entity to it an set it to CULL_FRONT it is clear that the shadows do not care if front, back, or both are rendered, only if a front face is facing the keylight:

Tested on 2323.11.1 with material entity and GLTF model (quad) set to double sided, same same.

[HifiExperiments]

ah! ok, thank you! I see the problem:

in RenderShadowTask::build we force the state to CULL_BACK:

        auto state = std::make_shared<gpu::State>();
        state->setCullMode(gpu::State::CULL_BACK);
        state->setDepthTest(true, true, gpu::LESS_EQUAL);

        auto fadeEffect = DependencyManager::get<FadeEffect>();
        initZPassPipelines(*shapePlumber, state, fadeEffect->getBatchSetter(), fadeEffect->getItemUniformSetter());

as opposed to initForwardPipelines/initDeferredPipelines which properly set up pipelines for all possible culling modes in addPlumberPipeline