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*_PREPASS Shader Def Cleanup (bevyengine#10136)
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# Objective

- This PR aims to make the various `*_PREPASS` shader defs we have
(`NORMAL_PREPASS`, `DEPTH_PREPASS`, `MOTION_VECTORS_PREPASS` AND
`DEFERRED_PREPASS`) easier to use and understand:
- So that their meaning is now consistent across all contexts; (“prepass
X is enabled for the current view”)
  - So that they're also consistently set across all contexts.
- It also aims to enable us to (with a follow up PR) to conditionally
gate the `BindGroupEntry` and `BindGroupLayoutEntry` items associated
with these prepasses, saving us up to 4 texture slots in WebGL
(currently globally limited to 16 per shader, regardless of bind groups)

## Solution

- We now consistently set these from `PrepassPipeline`, the
`MeshPipeline` and the `DeferredLightingPipeline`, we also set their
`MeshPipelineKey`s;
- We introduce `PREPASS_PIPELINE`, `MESH_PIPELINE` and
`DEFERRED_LIGHTING_PIPELINE` that can be used to detect where the code
is running, without overloading the meanings of the prepass shader defs;
- We also gate the WGSL functions in `bevy_pbr::prepass_utils` with
`#ifdef`s for their respective shader defs, so that shader code can
provide a fallback whenever they're not available.
- This allows us to conditionally include the bindings for these prepass
textures (My next PR, which will hopefully unblock bevyengine#8015)
- @robtfm mentioned [these were being used to prevent accessing the same
binding as read/write in the
prepass](https://discord.com/channels/691052431525675048/743663924229963868/1163270458393759814),
however even after reversing the `#ifndef`s I had no issues running the
code, so perhaps the compiler is already smart enough even without tree
shaking to know they're not being used, thanks to `#ifdef
PREPASS_PIPELINE`?

## Comparison

### Before

| Shader Def | `PrepassPipeline` | `MeshPipeline` |
`DeferredLightingPipeline` |
| ------------------------ | ----------------- | -------------- |
-------------------------- |
| `NORMAL_PREPASS` | Yes | No | No |
| `DEPTH_PREPASS` | Yes | No | No |
| `MOTION_VECTORS_PREPASS` | Yes | No | No |
| `DEFERRED_PREPASS` | Yes | No | No |

| View Key | `PrepassPipeline` | `MeshPipeline` |
`DeferredLightingPipeline` |
| ------------------------ | ----------------- | -------------- |
-------------------------- |
| `NORMAL_PREPASS` | Yes | Yes | No |
| `DEPTH_PREPASS` | Yes | No | No |
| `MOTION_VECTORS_PREPASS` | Yes | No | No |
| `DEFERRED_PREPASS` | Yes | Yes\* | No |

\* Accidentally was being set twice, once with only
`deferred_prepass.is_some()` as a condition,
and once with `deferred_p repass.is_some() && !forward` as a condition.

### After

| Shader Def | `PrepassPipeline` | `MeshPipeline` |
`DeferredLightingPipeline` |
| ---------------------------- | ----------------- | --------------- |
-------------------------- |
| `NORMAL_PREPASS` | Yes | Yes | Yes |
| `DEPTH_PREPASS` | Yes | Yes | Yes |
| `MOTION_VECTORS_PREPASS` | Yes | Yes | Yes |
| `DEFERRED_PREPASS` | Yes | Yes | Unconditionally |
| `PREPASS_PIPELINE` | Unconditionally | No | No |
| `MESH_PIPELINE` | No | Unconditionally | No |
| `DEFERRED_LIGHTING_PIPELINE` | No | No | Unconditionally |

| View Key | `PrepassPipeline` | `MeshPipeline` |
`DeferredLightingPipeline` |
| ------------------------ | ----------------- | -------------- |
-------------------------- |
| `NORMAL_PREPASS` | Yes | Yes | Yes |
| `DEPTH_PREPASS` | Yes | Yes | Yes |
| `MOTION_VECTORS_PREPASS` | Yes | Yes | Yes |
| `DEFERRED_PREPASS` | Yes | Yes | Unconditionally |

---

## Changelog

- Cleaned up WGSL `*_PREPASS` shader defs so they're now consistently
used everywhere;
- Introduced `PREPASS_PIPELINE`, `MESH_PIPELINE` and
`DEFERRED_LIGHTING_PIPELINE` WGSL shader defs for conditionally
compiling logic based the current pipeline;
- WGSL functions from `bevy_pbr::prepass_utils` are now guarded with
`#ifdef` based on the currently enabled prepasses;

## Migration Guide

- When using functions from `bevy_pbr::prepass_utils`
(`prepass_depth()`, `prepass_normal()`, `prepass_motion_vector()`) in
contexts where these prepasses might be disabled, you should now wrap
your calls with the appropriate `#ifdef` guards, (`#ifdef
DEPTH_PREPASS`, `#ifdef NORMAL_PREPASS`, `#ifdef MOTION_VECTOR_PREPASS`)
providing fallback logic where applicable.

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
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3 people authored and Ray Redondo committed Jan 9, 2024
1 parent 85b98f9 commit 3ead570
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Showing 7 changed files with 104 additions and 23 deletions.
2 changes: 2 additions & 0 deletions crates/bevy_pbr/src/deferred/deferred_lighting.wgsl
Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,9 @@ fn fragment(in: FullscreenVertexOutput) -> @location(0) vec4<f32> {
#ifdef WEBGL2
frag_coord.z = deferred_types::unpack_unorm3x4_plus_unorm_20_(deferred_data.b).w;
#else
#ifdef DEPTH_PREPASS
frag_coord.z = bevy_pbr::prepass_utils::prepass_depth(in.position, 0u);
#endif
#endif

var pbr_input = pbr_input_from_deferred_gbuffer(frag_coord, deferred_data);
Expand Down
52 changes: 50 additions & 2 deletions crates/bevy_pbr/src/deferred/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use bevy_core_pipeline::{
copy_lighting_id::DeferredLightingIdDepthTexture, DEFERRED_LIGHTING_PASS_ID_DEPTH_FORMAT,
},
prelude::{Camera3d, ClearColor},
prepass::DeferredPrepass,
prepass::{DeferredPrepass, DepthPrepass, MotionVectorPrepass, NormalPrepass},
tonemapping::{DebandDither, Tonemapping},
};
use bevy_ecs::{prelude::*, query::QueryItem};
Expand Down Expand Up @@ -258,6 +258,9 @@ impl SpecializedRenderPipeline for DeferredLightingLayout {
fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor {
let mut shader_defs = Vec::new();

// Let the shader code know that it's running in a deferred pipeline.
shader_defs.push("DEFERRED_LIGHTING_PIPELINE".into());

#[cfg(all(feature = "webgl", target_arch = "wasm32"))]
shader_defs.push("WEBGL2".into());

Expand Down Expand Up @@ -298,6 +301,21 @@ impl SpecializedRenderPipeline for DeferredLightingLayout {
shader_defs.push("ENVIRONMENT_MAP".into());
}

if key.contains(MeshPipelineKey::NORMAL_PREPASS) {
shader_defs.push("NORMAL_PREPASS".into());
}

if key.contains(MeshPipelineKey::DEPTH_PREPASS) {
shader_defs.push("DEPTH_PREPASS".into());
}

if key.contains(MeshPipelineKey::MOTION_VECTOR_PREPASS) {
shader_defs.push("MOTION_VECTOR_PREPASS".into());
}

// Always true, since we're in the deferred lighting pipeline
shader_defs.push("DEFERRED_PREPASS".into());

let shadow_filter_method =
key.intersection(MeshPipelineKey::SHADOW_FILTER_METHOD_RESERVED_BITS);
if shadow_filter_method == MeshPipelineKey::SHADOW_FILTER_METHOD_HARDWARE_2X2 {
Expand Down Expand Up @@ -408,14 +426,44 @@ pub fn prepare_deferred_lighting_pipelines(
Option<&EnvironmentMapLight>,
Option<&ShadowFilteringMethod>,
Option<&ScreenSpaceAmbientOcclusionSettings>,
(
Has<NormalPrepass>,
Has<DepthPrepass>,
Has<MotionVectorPrepass>,
),
),
With<DeferredPrepass>,
>,
images: Res<RenderAssets<Image>>,
) {
for (entity, view, tonemapping, dither, environment_map, shadow_filter_method, ssao) in &views {
for (
entity,
view,
tonemapping,
dither,
environment_map,
shadow_filter_method,
ssao,
(normal_prepass, depth_prepass, motion_vector_prepass),
) in &views
{
let mut view_key = MeshPipelineKey::from_hdr(view.hdr);

if normal_prepass {
view_key |= MeshPipelineKey::NORMAL_PREPASS;
}

if depth_prepass {
view_key |= MeshPipelineKey::DEPTH_PREPASS;
}

if motion_vector_prepass {
view_key |= MeshPipelineKey::MOTION_VECTOR_PREPASS;
}

// Always true, since we're in the deferred lighting pipeline
view_key |= MeshPipelineKey::DEFERRED_PREPASS;

if !view.hdr {
if let Some(tonemapping) = tonemapping {
view_key |= MeshPipelineKey::TONEMAP_IN_SHADER;
Expand Down
29 changes: 18 additions & 11 deletions crates/bevy_pbr/src/material.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use bevy_asset::{Asset, AssetApp, AssetEvent, AssetId, AssetServer, Assets, Hand
use bevy_core_pipeline::{
core_3d::{AlphaMask3d, Opaque3d, Transparent3d},
experimental::taa::TemporalAntiAliasSettings,
prepass::{DeferredPrepass, NormalPrepass},
prepass::{DeferredPrepass, DepthPrepass, MotionVectorPrepass, NormalPrepass},
tonemapping::{DebandDither, Tonemapping},
};
use bevy_derive::{Deref, DerefMut};
Expand Down Expand Up @@ -450,8 +450,12 @@ pub fn queue_material_meshes<M: Material>(
Option<&EnvironmentMapLight>,
Option<&ShadowFilteringMethod>,
Option<&ScreenSpaceAmbientOcclusionSettings>,
Option<&NormalPrepass>,
Option<&DeferredPrepass>,
(
Has<NormalPrepass>,
Has<DepthPrepass>,
Has<MotionVectorPrepass>,
Has<DeferredPrepass>,
),
Option<&TemporalAntiAliasSettings>,
&mut RenderPhase<Opaque3d>,
&mut RenderPhase<AlphaMask3d>,
Expand All @@ -468,8 +472,7 @@ pub fn queue_material_meshes<M: Material>(
environment_map,
shadow_filter_method,
ssao,
normal_prepass,
deferred_prepass,
(normal_prepass, depth_prepass, motion_vector_prepass, deferred_prepass),
taa_settings,
mut opaque_phase,
mut alpha_mask_phase,
Expand All @@ -483,11 +486,19 @@ pub fn queue_material_meshes<M: Material>(
let mut view_key = MeshPipelineKey::from_msaa_samples(msaa.samples())
| MeshPipelineKey::from_hdr(view.hdr);

if normal_prepass.is_some() {
if normal_prepass {
view_key |= MeshPipelineKey::NORMAL_PREPASS;
}

if deferred_prepass.is_some() {
if depth_prepass {
view_key |= MeshPipelineKey::DEPTH_PREPASS;
}

if motion_vector_prepass {
view_key |= MeshPipelineKey::MOTION_VECTOR_PREPASS;
}

if deferred_prepass {
view_key |= MeshPipelineKey::DEFERRED_PREPASS;
}

Expand Down Expand Up @@ -554,10 +565,6 @@ pub fn queue_material_meshes<M: Material>(
}
mesh_key |= alpha_mode_pipeline_key(material.properties.alpha_mode);

if deferred_prepass.is_some() && !forward {
mesh_key |= MeshPipelineKey::DEFERRED_PREPASS;
}

let pipeline_id = pipelines.specialize(
&pipeline_cache,
&material_pipeline,
Expand Down
5 changes: 5 additions & 0 deletions crates/bevy_pbr/src/prepass/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -378,6 +378,11 @@ where
let mut shader_defs = Vec::new();
let mut vertex_attributes = Vec::new();

// Let the shader code know that it's running in a prepass pipeline.
// (PBR code will use this to detect that it's running in deferred mode,
// since that's the only time it gets called from a prepass pipeline.)
shader_defs.push("PREPASS_PIPELINE".into());

// NOTE: Eventually, it would be nice to only add this when the shaders are overloaded by the Material.
// The main limitation right now is that bind group order is hardcoded in shaders.
bind_group_layouts.insert(1, self.material_layout.clone());
Expand Down
6 changes: 3 additions & 3 deletions crates/bevy_pbr/src/prepass/prepass_utils.wgsl
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

#import bevy_pbr::mesh_view_bindings as view_bindings

#ifndef DEPTH_PREPASS
#ifdef DEPTH_PREPASS
fn prepass_depth(frag_coord: vec4<f32>, sample_index: u32) -> f32 {
#ifdef MULTISAMPLED
let depth_sample = textureLoad(view_bindings::depth_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
Expand All @@ -13,7 +13,7 @@ fn prepass_depth(frag_coord: vec4<f32>, sample_index: u32) -> f32 {
}
#endif // DEPTH_PREPASS

#ifndef NORMAL_PREPASS
#ifdef NORMAL_PREPASS
fn prepass_normal(frag_coord: vec4<f32>, sample_index: u32) -> vec3<f32> {
#ifdef MULTISAMPLED
let normal_sample = textureLoad(view_bindings::normal_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
Expand All @@ -24,7 +24,7 @@ fn prepass_normal(frag_coord: vec4<f32>, sample_index: u32) -> vec3<f32> {
}
#endif // NORMAL_PREPASS

#ifndef MOTION_VECTOR_PREPASS
#ifdef MOTION_VECTOR_PREPASS
fn prepass_motion_vector(frag_coord: vec4<f32>, sample_index: u32) -> vec2<f32> {
#ifdef MULTISAMPLED
let motion_vector_sample = textureLoad(view_bindings::motion_vector_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
Expand Down
19 changes: 19 additions & 0 deletions crates/bevy_pbr/src/render/mesh.rs
Original file line number Diff line number Diff line change
Expand Up @@ -772,6 +772,9 @@ impl SpecializedMeshPipeline for MeshPipeline {
let mut shader_defs = Vec::new();
let mut vertex_attributes = Vec::new();

// Let the shader code know that it's running in a mesh pipeline.
shader_defs.push("MESH_PIPELINE".into());

shader_defs.push("VERTEX_OUTPUT_INSTANCE_INDEX".into());

if layout.contains(Mesh::ATTRIBUTE_POSITION) {
Expand Down Expand Up @@ -870,6 +873,22 @@ impl SpecializedMeshPipeline for MeshPipeline {
is_opaque = true;
}

if key.contains(MeshPipelineKey::NORMAL_PREPASS) {
shader_defs.push("NORMAL_PREPASS".into());
}

if key.contains(MeshPipelineKey::DEPTH_PREPASS) {
shader_defs.push("DEPTH_PREPASS".into());
}

if key.contains(MeshPipelineKey::MOTION_VECTOR_PREPASS) {
shader_defs.push("MOTION_VECTOR_PREPASS".into());
}

if key.contains(MeshPipelineKey::DEFERRED_PREPASS) {
shader_defs.push("DEFERRED_PREPASS".into());
}

if key.contains(MeshPipelineKey::NORMAL_PREPASS) && key.msaa_samples() == 1 && is_opaque {
shader_defs.push("LOAD_PREPASS_NORMALS".into());
}
Expand Down
14 changes: 7 additions & 7 deletions crates/bevy_pbr/src/render/pbr.wgsl
Original file line number Diff line number Diff line change
Expand Up @@ -16,13 +16,13 @@
#import bevy_pbr::gtao_utils gtao_multibounce
#endif

#ifdef DEFERRED_PREPASS
#ifdef PREPASS_PIPELINE
#import bevy_pbr::pbr_deferred_functions deferred_gbuffer_from_pbr_input
#import bevy_pbr::pbr_prepass_functions calculate_motion_vector
#import bevy_pbr::prepass_io VertexOutput, FragmentOutput
#else // DEFERRED_PREPASS
#else // PREPASS_PIPELINE
#import bevy_pbr::forward_io VertexOutput, FragmentOutput
#endif // DEFERRED_PREPASS
#endif // PREPASS_PIPELINE

#ifdef MOTION_VECTOR_PREPASS
@group(0) @binding(2)
Expand Down Expand Up @@ -159,7 +159,7 @@ fn fragment(
pbr_input.V = V;

} else { // if UNLIT_BIT != 0
#ifdef DEFERRED_PREPASS
#ifdef PREPASS_PIPELINE
// in deferred mode, we need to fill some of the pbr input data even for unlit materials
// to pass through the gbuffer to the deferred lighting shader
pbr_input = pbr_types::pbr_input_new();
Expand All @@ -179,7 +179,7 @@ fn fragment(

// generate output
// ---------------
#ifdef DEFERRED_PREPASS
#ifdef PREPASS_PIPELINE
// write the gbuffer
out.deferred = deferred_gbuffer_from_pbr_input(pbr_input);
out.deferred_lighting_pass_id = pbr_bindings::material.deferred_lighting_pass_id;
Expand All @@ -190,7 +190,7 @@ fn fragment(
out.motion_vector = calculate_motion_vector(in.world_position, in.previous_world_position);
#endif // MOTION_VECTOR_PREPASS

#else // DEFERRED_PREPASS
#else // PREPASS_PIPELINE

// in forward mode, we calculate the lit color immediately, and then apply some post-lighting effects here.
// in deferred mode the lit color and these effects will be calculated in the deferred lighting shader
Expand Down Expand Up @@ -222,7 +222,7 @@ fn fragment(
// write the final pixel color
out.color = output_color;

#endif //DEFERRED_PREPASS
#endif // PREPASS_PIPELINE

return out;
}

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