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# 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>
		
	
			
		
			
				
	
	
		
			200 lines
		
	
	
		
			6.1 KiB
		
	
	
	
		
			Rust
		
	
	
	
	
	
			
		
		
	
	
			200 lines
		
	
	
		
			6.1 KiB
		
	
	
	
		
			Rust
		
	
	
	
	
	
| //! A scene showcasing screen space ambient occlusion.
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| 
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| use bevy::{
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|     core_pipeline::experimental::taa::{TemporalAntiAliasBundle, TemporalAntiAliasPlugin},
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|     pbr::{
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|         ScreenSpaceAmbientOcclusionBundle, ScreenSpaceAmbientOcclusionQualityLevel,
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|         ScreenSpaceAmbientOcclusionSettings,
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|     },
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|     prelude::*,
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|     render::camera::TemporalJitter,
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| };
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| use std::f32::consts::PI;
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| 
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| fn main() {
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|     App::new()
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|         .insert_resource(AmbientLight {
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|             brightness: 5.0,
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|             ..default()
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|         })
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|         .add_plugins(DefaultPlugins)
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|         .add_plugin(TemporalAntiAliasPlugin)
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|         .add_systems(Startup, setup)
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|         .add_systems(Update, update)
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|         .run();
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| }
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| 
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| fn setup(
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|     mut commands: Commands,
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|     mut meshes: ResMut<Assets<Mesh>>,
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|     mut materials: ResMut<Assets<StandardMaterial>>,
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|     asset_server: Res<AssetServer>,
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| ) {
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|     commands
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|         .spawn(Camera3dBundle {
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|             camera: Camera {
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|                 hdr: true,
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|                 ..default()
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|             },
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|             transform: Transform::from_xyz(-2.0, 2.0, -2.0).looking_at(Vec3::ZERO, Vec3::Y),
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|             ..default()
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|         })
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|         .insert(ScreenSpaceAmbientOcclusionBundle::default())
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|         .insert(TemporalAntiAliasBundle::default());
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| 
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|     let material = materials.add(StandardMaterial {
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|         base_color: Color::rgb(0.5, 0.5, 0.5),
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|         perceptual_roughness: 1.0,
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|         reflectance: 0.0,
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|         ..default()
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|     });
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|     commands.spawn(PbrBundle {
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|         mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
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|         material: material.clone(),
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|         transform: Transform::from_xyz(0.0, 0.0, 1.0),
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|         ..default()
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|     });
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|     commands.spawn(PbrBundle {
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|         mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
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|         material: material.clone(),
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|         transform: Transform::from_xyz(0.0, -1.0, 0.0),
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|         ..default()
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|     });
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|     commands.spawn(PbrBundle {
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|         mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
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|         material,
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|         transform: Transform::from_xyz(1.0, 0.0, 0.0),
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|         ..default()
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|     });
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|     commands.spawn((
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|         PbrBundle {
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|             mesh: meshes.add(Mesh::from(shape::UVSphere {
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|                 radius: 0.4,
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|                 sectors: 72,
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|                 stacks: 36,
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|             })),
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|             material: materials.add(StandardMaterial {
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|                 base_color: Color::rgb(0.4, 0.4, 0.4),
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|                 perceptual_roughness: 1.0,
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|                 reflectance: 0.0,
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|                 ..default()
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|             }),
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|             ..default()
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|         },
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|         SphereMarker,
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|     ));
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| 
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|     commands.spawn(DirectionalLightBundle {
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|         directional_light: DirectionalLight {
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|             shadows_enabled: true,
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|             ..default()
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|         },
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|         transform: Transform::from_rotation(Quat::from_euler(
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|             EulerRot::ZYX,
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|             0.0,
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|             PI * -0.15,
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|             PI * -0.15,
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|         )),
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|         ..default()
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|     });
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| 
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|     commands.spawn(
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|         TextBundle::from_section(
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|             "",
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|             TextStyle {
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|                 font: asset_server.load("fonts/FiraMono-Medium.ttf"),
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|                 font_size: 26.0,
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|                 color: Color::BLACK,
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|             },
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|         )
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|         .with_style(Style {
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|             position_type: PositionType::Absolute,
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|             bottom: Val::Px(10.0),
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|             left: Val::Px(10.0),
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|             ..default()
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|         }),
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|     );
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| }
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| 
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| fn update(
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|     camera: Query<
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|         (
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|             Entity,
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|             Option<&ScreenSpaceAmbientOcclusionSettings>,
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|             Option<&TemporalJitter>,
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|         ),
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|         With<Camera>,
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|     >,
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|     mut text: Query<&mut Text>,
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|     mut sphere: Query<&mut Transform, With<SphereMarker>>,
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|     mut commands: Commands,
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|     keycode: Res<Input<KeyCode>>,
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|     time: Res<Time>,
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| ) {
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|     let mut sphere = sphere.single_mut();
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|     sphere.translation.y = (time.elapsed_seconds() / 1.7).sin() * 0.7;
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| 
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|     let (camera_entity, ssao_settings, temporal_jitter) = camera.single();
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| 
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|     let mut commands = commands.entity(camera_entity);
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|     if keycode.just_pressed(KeyCode::Key1) {
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|         commands.remove::<ScreenSpaceAmbientOcclusionSettings>();
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|     }
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|     if keycode.just_pressed(KeyCode::Key2) {
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|         commands.insert(ScreenSpaceAmbientOcclusionSettings {
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|             quality_level: ScreenSpaceAmbientOcclusionQualityLevel::Low,
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|         });
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|     }
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|     if keycode.just_pressed(KeyCode::Key3) {
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|         commands.insert(ScreenSpaceAmbientOcclusionSettings {
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|             quality_level: ScreenSpaceAmbientOcclusionQualityLevel::Medium,
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|         });
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|     }
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|     if keycode.just_pressed(KeyCode::Key4) {
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|         commands.insert(ScreenSpaceAmbientOcclusionSettings {
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|             quality_level: ScreenSpaceAmbientOcclusionQualityLevel::High,
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|         });
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|     }
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|     if keycode.just_pressed(KeyCode::Key5) {
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|         commands.insert(ScreenSpaceAmbientOcclusionSettings {
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|             quality_level: ScreenSpaceAmbientOcclusionQualityLevel::Ultra,
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|         });
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|     }
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|     if keycode.just_pressed(KeyCode::Space) {
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|         if temporal_jitter.is_some() {
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|             commands.remove::<TemporalJitter>();
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|         } else {
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|             commands.insert(TemporalJitter::default());
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|         }
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|     }
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| 
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|     let mut text = text.single_mut();
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|     let text = &mut text.sections[0].value;
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|     text.clear();
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| 
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|     let (o, l, m, h, u) = match ssao_settings.map(|s| s.quality_level) {
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|         None => ("*", "", "", "", ""),
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|         Some(ScreenSpaceAmbientOcclusionQualityLevel::Low) => ("", "*", "", "", ""),
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|         Some(ScreenSpaceAmbientOcclusionQualityLevel::Medium) => ("", "", "*", "", ""),
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|         Some(ScreenSpaceAmbientOcclusionQualityLevel::High) => ("", "", "", "*", ""),
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|         Some(ScreenSpaceAmbientOcclusionQualityLevel::Ultra) => ("", "", "", "", "*"),
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|         _ => unreachable!(),
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|     };
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| 
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|     text.push_str("SSAO Quality:\n");
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|     text.push_str(&format!("(1) {o}Off{o}\n"));
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|     text.push_str(&format!("(2) {l}Low{l}\n"));
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|     text.push_str(&format!("(3) {m}Medium{m}\n"));
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|     text.push_str(&format!("(4) {h}High{h}\n"));
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|     text.push_str(&format!("(5) {u}Ultra{u}\n\n"));
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| 
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|     text.push_str("Temporal Antialiasing:\n");
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|     text.push_str(match temporal_jitter {
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|         Some(_) => "(Space) Enabled",
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|         None => "(Space) Disabled",
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|     });
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| }
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| 
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| #[derive(Component)]
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| struct SphereMarker;
 |