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JMS55 af9c945f40
Screen Space Ambient Occlusion (SSAO) MVP (#7402) 
![image](https://github.com/bevyengine/bevy/assets/47158642/dbb62645-f639-4f2b-b84b-26fd915c186d)

# Objective

- Add Screen space ambient occlusion (SSAO). SSAO approximates
small-scale, local occlusion of _indirect_ diffuse light between
objects. SSAO does not apply to direct lighting, such as point or
directional lights.
- This darkens creases, e.g. on staircases, and gives nice contact
shadows where objects meet, giving entities a more "grounded" feel.
- Closes https://github.com/bevyengine/bevy/issues/3632.

## Solution

- Implement the GTAO algorithm.
-
https://www.activision.com/cdn/research/Practical_Real_Time_Strategies_for_Accurate_Indirect_Occlusion_NEW%20VERSION_COLOR.pdf
-
https://blog.selfshadow.com/publications/s2016-shading-course/activision/s2016_pbs_activision_occlusion.pdf
- Source code heavily based on [Intel's
XeGTAO](0d177ce06b/Source/Rendering/Shaders/XeGTAO.hlsli).
- Add an SSAO bevy example.

## Algorithm Overview
* Run a depth and normal prepass
* Create downscaled mips of the depth texture (preprocess_depths pass)
* GTAO pass - for each pixel, take several random samples from the
depth+normal buffers, reconstruct world position, raytrace in screen
space to estimate occlusion. Rather then doing completely random samples
on a hemisphere, you choose random _slices_ of the hemisphere, and then
can analytically compute the full occlusion of that slice. Also compute
edges based on depth differences here.
* Spatial denoise pass - bilateral blur, using edge detection to not
blur over edges. This is the final SSAO result.
* Main pass - if SSAO exists, sample the SSAO texture, and set occlusion
to be the minimum of ssao/material occlusion. This then feeds into the
rest of the PBR shader as normal.

---

## Future Improvements
- Maybe remove the low quality preset for now (too noisy)
- WebGPU fallback (see below)
- Faster depth->world position (see reverted code)
- Bent normals 
- Try interleaved gradient noise or spatiotemporal blue noise
- Replace the spatial denoiser with a combined spatial+temporal denoiser
- Render at half resolution and use a bilateral upsample
- Better multibounce approximation
(https://drive.google.com/file/d/1SyagcEVplIm2KkRD3WQYSO9O0Iyi1hfy/view)

## Far-Future Performance Improvements
- F16 math (missing naga-wgsl support
https://github.com/gfx-rs/naga/issues/1884)
- Faster coordinate space conversion for normals
- Faster depth mipchain creation
(https://github.com/GPUOpen-Effects/FidelityFX-SPD) (wgpu/naga does not
currently support subgroup ops)
- Deinterleaved SSAO for better cache efficiency
(https://developer.nvidia.com/sites/default/files/akamai/gameworks/samples/DeinterleavedTexturing.pdf)

## Other Interesting Papers
- Visibility bitmask
(https://link.springer.com/article/10.1007/s00371-022-02703-y,
https://cdrinmatane.github.io/posts/cgspotlight-slides/)
- Screen space diffuse lighting
(https://github.com/Patapom/GodComplex/blob/master/Tests/TestHBIL/2018%20Mayaux%20-%20Horizon-Based%20Indirect%20Lighting%20(HBIL).pdf)

## Platform Support
* SSAO currently does not work on DirectX12 due to issues with wgpu and
naga:
  * https://github.com/gfx-rs/wgpu/pull/3798
  * https://github.com/gfx-rs/naga/pull/2353
* SSAO currently does not work on WebGPU because r16float is not a valid
storage texture format
https://gpuweb.github.io/gpuweb/wgsl/#storage-texel-formats. We can fix
this with a fallback to r32float.

---

## Changelog

- Added ScreenSpaceAmbientOcclusionSettings,
ScreenSpaceAmbientOcclusionQualityLevel, and
ScreenSpaceAmbientOcclusionBundle

---------

Co-authored-by: IceSentry <c.giguere42@gmail.com>
Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
Co-authored-by: Daniel Chia <danstryder@gmail.com>
Co-authored-by: Elabajaba <Elabajaba@users.noreply.github.com>
Co-authored-by: Robert Swain <robert.swain@gmail.com>
Co-authored-by: robtfm <50659922+robtfm@users.noreply.github.com>
Co-authored-by: Brandon Dyer <brandondyer64@gmail.com>
Co-authored-by: Edgar Geier <geieredgar@gmail.com>
Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2023-06-18 21:05:55 +00:00
..
3d_gizmos.rs Instanced line rendering for gizmos based on bevy_polyline (#8427) 2023-06-13 06:49:47 +00:00
3d_scene.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
3d_shapes.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
anti_aliasing.rs standardize instructions in examples (#8478) 2023-04-26 19:52:31 +00:00
atmospheric_fog.rs standardize instructions in examples (#8478) 2023-04-26 19:52:31 +00:00
blend_modes.rs fix new clippy lints before they reach stable (#8700) 2023-05-29 07:23:50 +00:00
bloom_3d.rs standardize instructions in examples (#8478) 2023-04-26 19:52:31 +00:00
fog.rs Rename keys like LAlt to AltLeft (#8792) 2023-06-15 01:37:04 +00:00
lighting.rs standardize instructions in examples (#8478) 2023-04-26 19:52:31 +00:00
lines.rs reflect: stable type path v2 (#7184) 2023-06-05 20:31:20 +00:00
load_gltf.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
orthographic.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
parallax_mapping.rs fix new clippy lints before they reach stable (#8700) 2023-05-29 07:23:50 +00:00
parenting.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
pbr.rs add a default font (#8445) 2023-04-21 22:30:18 +00:00
render_to_texture.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
shadow_biases.rs Rename keys like LAlt to AltLeft (#8792) 2023-06-15 01:37:04 +00:00
shadow_caster_receiver.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
skybox.rs Rename keys like LAlt to AltLeft (#8792) 2023-06-15 01:37:04 +00:00
spherical_area_lights.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
split_screen.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
spotlight.rs fix new clippy lints before they reach stable (#8700) 2023-05-29 07:23:50 +00:00
ssao.rs Screen Space Ambient Occlusion (SSAO) MVP (#7402) 2023-06-18 21:05:55 +00:00
texture.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
tonemapping.rs reflect: stable type path v2 (#7184) 2023-06-05 20:31:20 +00:00
transparency_3d.rs Fixed several missing links in docs. (#8117) 2023-04-23 17:28:36 +00:00
two_passes.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
update_gltf_scene.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
vertex_colors.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00
wireframe.rs Schedule-First: the new and improved add_systems (#8079) 2023-03-18 01:45:34 +00:00