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Callable PBR functions (bevyengine#4939)
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# Objective

- Builds on top of bevyengine#4938 
- Make clustered-forward PBR lighting/shadows functionality callable
- See bevyengine#3969 for details

## Solution

- Add `PbrInput` struct type containing a `StandardMaterial`, occlusion, world_position, world_normal, and frag_coord
- Split functionality to calculate the unit view vector, and normal-mapped normal into `bevy_pbr::pbr_functions`
- Split high-level shading flow into `pbr(in: PbrInput, N: vec3<f32>, V: vec3<f32>, is_orthographic: bool)` function in `bevy_pbr::pbr_functions`
- Rework `pbr.wgsl` fragment stage entry point to make use of the new functions
- This has been benchmarked on an M1 Max using `many_cubes -- sphere`. `main` had a median frame time of 15.88ms, this PR 15.99ms, which is a 0.69% frame time increase, which is within noise in my opinion.

---

## Changelog

- Added: PBR shading code is now callable. Import `bevy_pbr::pbr_functions` and its dependencies, create a `PbrInput`, calculate the unit view and normal-mapped normal vectors and whether the projection is orthographic, and call `pbr()`!
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@superdump @james7132
superdump authored and james7132 committed Jun 22, 2022
1 parent 69d8da7 commit f7a189b
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Showing 3 changed files with 232 additions and 142 deletions.
8 changes: 8 additions & 0 deletions crates/bevy_pbr/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,8 @@ pub const SHADOWS_HANDLE: HandleUntyped =
HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 11350275143789590502);
pub const PBR_SHADER_HANDLE: HandleUntyped =
HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 4805239651767701046);
pub const PBR_FUNCTIONS_HANDLE: HandleUntyped =
HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 16550102964439850292);
pub const SHADOW_SHADER_HANDLE: HandleUntyped =
HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 1836745567947005696);

Expand Down Expand Up @@ -104,6 +106,12 @@ impl Plugin for PbrPlugin {
"render/shadows.wgsl",
Shader::from_wgsl
);
load_internal_asset!(
app,
PBR_FUNCTIONS_HANDLE,
"render/pbr_functions.wgsl",
Shader::from_wgsl
);
load_internal_asset!(app, PBR_SHADER_HANDLE, "render/pbr.wgsl", Shader::from_wgsl);
load_internal_asset!(
app,
Expand Down
170 changes: 28 additions & 142 deletions crates/bevy_pbr/src/render/pbr.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
#import bevy_pbr::clustered_forward
#import bevy_pbr::lighting
#import bevy_pbr::shadows
#import bevy_pbr::pbr_functions

struct FragmentInput {
[[builtin(front_facing)]] is_front: bool;
Expand All @@ -24,22 +25,31 @@ struct FragmentInput {
[[stage(fragment)]]
fn fragment(in: FragmentInput) -> [[location(0)]] vec4<f32> {
var output_color: vec4<f32> = material.base_color;
#ifdef VERTEX_COLORS
#ifdef VERTEX_COLORS
output_color = output_color * in.color;
#endif
#endif
if ((material.flags & STANDARD_MATERIAL_FLAGS_BASE_COLOR_TEXTURE_BIT) != 0u) {
output_color = output_color * textureSample(base_color_texture, base_color_sampler, in.uv);
}

// // NOTE: Unlit bit not set means == 0 is true, so the true case is if lit
// NOTE: Unlit bit not set means == 0 is true, so the true case is if lit
if ((material.flags & STANDARD_MATERIAL_FLAGS_UNLIT_BIT) == 0u) {
// Prepare a 'processed' StandardMaterial by sampling all textures to resolve
// the material members
var pbr_input: PbrInput;

pbr_input.material.base_color = output_color;
pbr_input.material.reflectance = material.reflectance;
pbr_input.material.flags = material.flags;
pbr_input.material.alpha_cutoff = material.alpha_cutoff;

// TODO use .a for exposure compensation in HDR
var emissive: vec4<f32> = material.emissive;
if ((material.flags & STANDARD_MATERIAL_FLAGS_EMISSIVE_TEXTURE_BIT) != 0u) {
emissive = vec4<f32>(emissive.rgb * textureSample(emissive_texture, emissive_sampler, in.uv).rgb, 1.0);
}
pbr_input.material.emissive = emissive;

// calculate non-linear roughness from linear perceptualRoughness
var metallic: f32 = material.metallic;
var perceptual_roughness: f32 = material.perceptual_roughness;
if ((material.flags & STANDARD_MATERIAL_FLAGS_METALLIC_ROUGHNESS_TEXTURE_BIT) != 0u) {
Expand All @@ -48,158 +58,34 @@ fn fragment(in: FragmentInput) -> [[location(0)]] vec4<f32> {
metallic = metallic * metallic_roughness.b;
perceptual_roughness = perceptual_roughness * metallic_roughness.g;
}
let roughness = perceptualRoughnessToRoughness(perceptual_roughness);
pbr_input.material.metallic = metallic;
pbr_input.material.perceptual_roughness = perceptual_roughness;

var occlusion: f32 = 1.0;
if ((material.flags & STANDARD_MATERIAL_FLAGS_OCCLUSION_TEXTURE_BIT) != 0u) {
occlusion = textureSample(occlusion_texture, occlusion_sampler, in.uv).r;
}
pbr_input.occlusion = occlusion;

var N: vec3<f32> = normalize(in.world_normal);

#ifdef VERTEX_TANGENTS
#ifdef STANDARDMATERIAL_NORMAL_MAP
// NOTE: The mikktspace method of normal mapping explicitly requires that these NOT be
// normalized nor any Gram-Schmidt applied to ensure the vertex normal is orthogonal to the
// vertex tangent! Do not change this code unless you really know what you are doing.
// http://www.mikktspace.com/
var T: vec3<f32> = in.world_tangent.xyz;
var B: vec3<f32> = in.world_tangent.w * cross(N, T);
#endif
#endif
pbr_input.frag_coord = in.frag_coord;
pbr_input.world_position = in.world_position;
pbr_input.world_normal = in.world_normal;

if ((material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u) {
if (!in.is_front) {
N = -N;
#ifdef VERTEX_TANGENTS
#ifdef STANDARDMATERIAL_NORMAL_MAP
T = -T;
B = -B;
#endif
#endif
}
}
pbr_input.is_orthographic = view.projection[3].w == 1.0;

pbr_input.N = prepare_normal(
in.world_normal,
#ifdef VERTEX_TANGENTS
#ifdef STANDARDMATERIAL_NORMAL_MAP
let TBN = mat3x3<f32>(T, B, N);
// Nt is the tangent-space normal.
var Nt: vec3<f32>;
if ((material.flags & STANDARD_MATERIAL_FLAGS_TWO_COMPONENT_NORMAL_MAP) != 0u) {
// Only use the xy components and derive z for 2-component normal maps.
Nt = vec3<f32>(textureSample(normal_map_texture, normal_map_sampler, in.uv).rg * 2.0 - 1.0, 0.0);
Nt.z = sqrt(1.0 - Nt.x * Nt.x - Nt.y * Nt.y);
} else {
Nt = textureSample(normal_map_texture, normal_map_sampler, in.uv).rgb * 2.0 - 1.0;
}
// Normal maps authored for DirectX require flipping the y component
if ((material.flags & STANDARD_MATERIAL_FLAGS_FLIP_NORMAL_MAP_Y) != 0u) {
Nt.y = -Nt.y;
}
// NOTE: The mikktspace method of normal mapping applies maps the tangent-space normal from
// the normal map texture in this way to be an EXACT inverse of how the normal map baker
// calculates the normal maps so there is no error introduced. Do not change this code
// unless you really know what you are doing.
// http://www.mikktspace.com/
N = normalize(Nt.x * T + Nt.y * B + Nt.z * N);
in.world_tangent,
#endif
#endif

if ((material.flags & STANDARD_MATERIAL_FLAGS_ALPHA_MODE_OPAQUE) != 0u) {
// NOTE: If rendering as opaque, alpha should be ignored so set to 1.0
output_color.a = 1.0;
} else if ((material.flags & STANDARD_MATERIAL_FLAGS_ALPHA_MODE_MASK) != 0u) {
if (output_color.a >= material.alpha_cutoff) {
// NOTE: If rendering as masked alpha and >= the cutoff, render as fully opaque
output_color.a = 1.0;
} else {
// NOTE: output_color.a < material.alpha_cutoff should not is not rendered
// NOTE: This and any other discards mean that early-z testing cannot be done!
discard;
}
}

var V: vec3<f32>;
// If the projection is not orthographic
let is_orthographic = view.projection[3].w == 1.0;
if (is_orthographic) {
// Orthographic view vector
V = normalize(vec3<f32>(view.view_proj[0].z, view.view_proj[1].z, view.view_proj[2].z));
} else {
// Only valid for a perpective projection
V = normalize(view.world_position.xyz - in.world_position.xyz);
}

// Neubelt and Pettineo 2013, "Crafting a Next-gen Material Pipeline for The Order: 1886"
let NdotV = max(dot(N, V), 0.0001);

// Remapping [0,1] reflectance to F0
// See https://google.github.io/filament/Filament.html#materialsystem/parameterization/remapping
let reflectance = material.reflectance;
let F0 = 0.16 * reflectance * reflectance * (1.0 - metallic) + output_color.rgb * metallic;

// Diffuse strength inversely related to metallicity
let diffuse_color = output_color.rgb * (1.0 - metallic);

let R = reflect(-V, N);

// accumulate color
var light_accum: vec3<f32> = vec3<f32>(0.0);

let view_z = dot(vec4<f32>(
view.inverse_view[0].z,
view.inverse_view[1].z,
view.inverse_view[2].z,
view.inverse_view[3].z
), in.world_position);
let cluster_index = fragment_cluster_index(in.frag_coord.xy, view_z, is_orthographic);
let offset_and_count = unpack_offset_and_count(cluster_index);
for (var i: u32 = offset_and_count[0]; i < offset_and_count[0] + offset_and_count[1]; i = i + 1u) {
let light_id = get_light_id(i);
let light = point_lights.data[light_id];
var shadow: f32 = 1.0;
if ((mesh.flags & MESH_FLAGS_SHADOW_RECEIVER_BIT) != 0u
&& (light.flags & POINT_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
shadow = fetch_point_shadow(light_id, in.world_position, in.world_normal);
}
let light_contrib = point_light(in.world_position.xyz, light, roughness, NdotV, N, V, R, F0, diffuse_color);
light_accum = light_accum + light_contrib * shadow;
}

let n_directional_lights = lights.n_directional_lights;
for (var i: u32 = 0u; i < n_directional_lights; i = i + 1u) {
let light = lights.directional_lights[i];
var shadow: f32 = 1.0;
if ((mesh.flags & MESH_FLAGS_SHADOW_RECEIVER_BIT) != 0u
&& (light.flags & DIRECTIONAL_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
shadow = fetch_directional_shadow(i, in.world_position, in.world_normal);
}
let light_contrib = directional_light(light, roughness, NdotV, N, V, R, F0, diffuse_color);
light_accum = light_accum + light_contrib * shadow;
}

let diffuse_ambient = EnvBRDFApprox(diffuse_color, 1.0, NdotV);
let specular_ambient = EnvBRDFApprox(F0, perceptual_roughness, NdotV);

output_color = vec4<f32>(
light_accum +
(diffuse_ambient + specular_ambient) * lights.ambient_color.rgb * occlusion +
emissive.rgb * output_color.a,
output_color.a);

output_color = cluster_debug_visualization(
output_color,
view_z,
is_orthographic,
offset_and_count,
cluster_index,
in.uv,
in.is_front,
);
pbr_input.V = calculate_view(in.world_position, pbr_input.is_orthographic);

// tone_mapping
output_color = vec4<f32>(reinhard_luminance(output_color.rgb), output_color.a);
// Gamma correction.
// Not needed with sRGB buffer
// output_color.rgb = pow(output_color.rgb, vec3(1.0 / 2.2));
output_color = pbr(pbr_input);
}

return output_color;
Expand Down
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