Marco Buono 4465f256eb Add MAY_DISCARD shader def, enabling early depth tests for most cases (#6697) ... # Objective - Right now we can't really benefit from [early depth testing](https://www.khronos.org/opengl/wiki/Early_Fragment_Test) in our PBR shader because it includes codepaths with `discard`, even for situations where they are not necessary. ## Solution - This PR introduces a new `MeshPipelineKey` and shader def, `MAY_DISCARD`; - All possible material/mesh options that that may result in `discard`s being needed must set `MAY_DISCARD` ahead of time: - Right now, this is only `AlphaMode::Mask(f32)`, but in the future might include other options/effects; (e.g. one effect I'm personally interested in is bayer dither pseudo-transparency for LOD transitions of opaque meshes) - Shader codepaths that can `discard` are guarded by an `#ifdef MAY_DISCARD` preprocessor directive: - Right now, this is just one branch in `alpha_discard()`; - If `MAY_DISCARD` is _not_ set, the `@early_depth_test` attribute is added to the PBR fragment shader. This is a not yet documented, possibly non-standard WGSL extension I found browsing Naga's source code. [I opened a PR to document it there](https://github.com/gfx-rs/naga/pull/2132). My understanding is that for backends where this attribute is supported, it will force an explicit opt-in to early depth test. (e.g. via `layout(early_fragment_tests) in;` in GLSL) ## Caveats - I included `@early_depth_test` for the sake of us being explicit, and avoiding the need for the driver to be “smart” about enabling this feature. That way, if we make a mistake and include a `discard` unguarded by `MAY_DISCARD`, it will either produce errors or noticeable visual artifacts so that we'll catch early, instead of causing a performance regression. - I'm not sure explicit early depth test is supported on the naga Metal backend, which is what I'm currently using, so I can't really test the explicit early depth test enable, I would like others with Vulkan/GL hardware to test it if possible; - I would like some guidance on how to measure/verify the performance benefits of this; - If I understand it correctly, this, or _something like this_ is needed to fully reap the performance gains enabled by #6284; - This will _most definitely_ conflict with #6284 and #6644. I can fix the conflicts as needed, depending on whether/the order they end up being merging in. --- ## Changelog ### Changed - Early depth tests are now enabled whenever possible for meshes using `StandardMaterial`, reducing the number of fragments evaluated for scenes with lots of occlusions.		2023-05-29 15:15:01 +00:00
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src	Add MAY_DISCARD shader def, enabling early depth tests for most cases (#6697)	2023-05-29 15:15:01 +00:00
Cargo.toml	chore: Release (#7920)	2023-03-06 05:13:36 +00:00