Add PBR Neutral tone mapping (#23761)

# Objective

Add a tonemapping option for for e-commerce, architecture and CAD
applications.

## Solution

Implemented [PBR
Neutral](https://github.com/KhronosGroup/ToneMapping/tree/main/PBR_Neutral)
tone mapping

- Added to 2d and 3d materials, deferred and forward rendering
- Added to bloom_2d example
- Added to tonemapping example

## Testing

Run bloom_2d and tonemapping examples

---------

Co-authored-by: Brian Chirls <brian.chirls@ambr.net>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>

crates/bevy_core_pipeline/src/tonemapping/mod.rs

@@ -160,6 +160,9 @@ pub enum Tonemapping {
     /// Somewhat neutral. Suffers from hue shifting. Brights desaturate across the spectrum.
     /// NOTE: Requires the `tonemapping_luts` cargo feature.
     BlenderFilmic,
+    /// Designed to faithfully reproduce base color under neutral lighting. Suitable for e-commerce, architecture and CAD applications.
+    /// See [the KhronosGroup spec](https://github.com/KhronosGroup/ToneMapping/tree/main/PBR_Neutral) for more information.
+    PbrNeutral,
 }
 
 impl Tonemapping {
@@ -265,6 +268,7 @@ impl SpecializedRenderPipeline for TonemappingPipeline {
                 );
                 shader_defs.push("TONEMAP_METHOD_BLENDER_FILMIC".into());
             }
+            Tonemapping::PbrNeutral => shader_defs.push("TONEMAP_METHOD_PBR_NEUTRAL".into()),
         }
         RenderPipelineDescriptor {
             label: Some("tonemapping pipeline".into()),
@@ -392,6 +396,7 @@ pub fn get_lut_bindings<'a>(
         | Tonemapping::ReinhardLuminance
         | Tonemapping::AcesFitted
         | Tonemapping::AgX
+        | Tonemapping::PbrNeutral
         | Tonemapping::SomewhatBoringDisplayTransform => &tonemapping_luts.agx,
         Tonemapping::TonyMcMapface => &tonemapping_luts.tony_mc_mapface,
         Tonemapping::BlenderFilmic => &tonemapping_luts.blender_filmic,

crates/bevy_core_pipeline/src/tonemapping/tonemapping_shared.wgsl

@@ -255,6 +255,54 @@ fn rgb_to_srgb_simple(color: vec3<f32>) -> vec3<f32> {
     return pow(color, vec3<f32>(1.0 / 2.2));
 }
 
+// PBR Neutral tone mapping
+// https://github.com/KhronosGroup/ToneMapping/blob/main/PBR_Neutral/pbrNeutral.glsl
+// Adapted under Apache 2.0, per https://github.com/KhronosGroup/ToneMapping/tree/main/LICENSES
+fn tonemapping_pbr_neutral(color_in: vec3<f32>) -> vec3<f32> {
+    // Parameter controlling when highlight compression starts
+    // (`K_s` in specification)
+    const start_compression: f32 = 0.8 - 0.04;
+
+    // Parameter controlling the speed of desaturation
+    // (`K-d` in specification)
+    const desaturation: f32 = 0.15;
+
+    // `x` in the specification equation
+    let min_channel = min(color_in.r, min(color_in.g, color_in.b));
+
+    // The amount that the "toe" adjustment reduces the color
+    // `f` in the specification equation
+    let offset = select(0.04, min_channel - 6.25 * min_channel * min_channel, min_channel < 0.08);
+
+    // The original color, minus the "toe" reduction
+    // `c_in - f` in the specification equation
+    let offset_color = color_in - offset;
+
+    // Maximum of all offset color channels
+    // `p` in the specification equation
+    let max_channel = max(offset_color.r, max(offset_color.g, offset_color.b));
+    if max_channel < start_compression {
+        // "toe" at the low-end; or uncompressed, offset color for most of the range
+        return offset_color;
+    }
+
+    // This doesn't exist in the specification equation. It is part of optimizing
+    // the math for computation.
+    let d = 1.0 - start_compression;
+
+    // Maximum color channel, scaled to asymptotically approach 1.0
+    let new_max_channel = 1.0 - d * d / (max_channel + d - start_compression);
+
+    // Full color, from offset color, with the same scale applied as `new_max_channel`
+    // `p_n` in the specification equation
+    let color = offset_color * (new_max_channel / max_channel);
+
+    // Amount to desaturate, used as the blend factor when mixing between
+    // full color and desaturated.
+    let g = 1.0 - 1.0 / (desaturation * (max_channel - new_max_channel) + 1.0);
+    return mix(color, vec3(new_max_channel), g);
+}
+
 // Source: Advanced VR Rendering, GDC 2015, Alex Vlachos, Valve, Slide 49
 // https://media.steampowered.com/apps/valve/2015/Alex_Vlachos_Advanced_VR_Rendering_GDC2015.pdf
 fn screen_space_dither(frag_coord: vec2<f32>) -> vec3<f32> {
@@ -372,6 +420,8 @@ fn tone_mapping(in: vec4<f32>, in_color_grading: ColorGrading) -> vec4<f32> {
     color = sample_tony_mc_mapface_lut(color);
 #else ifdef TONEMAP_METHOD_BLENDER_FILMIC
     color = sample_blender_filmic_lut(color.rgb);
+#else ifdef TONEMAP_METHOD_PBR_NEUTRAL
+    color = tonemapping_pbr_neutral(color.rgb);
 #endif
 
     // Perceptual post tonemapping grading

crates/bevy_pbr/src/deferred/mod.rs

@@ -260,6 +260,8 @@ impl SpecializedRenderPipeline for DeferredLightingLayout {
                 shader_defs.push("TONEMAP_METHOD_BLENDER_FILMIC".into());
             } else if method == MeshPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE {
                 shader_defs.push("TONEMAP_METHOD_TONY_MC_MAPFACE".into());
+            } else if method == MeshPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL {
+                shader_defs.push("TONEMAP_METHOD_PBR_NEUTRAL".into());
             }
 
             // Debanding is tied to tonemapping in the shader, cannot run without it.
@@ -502,6 +504,7 @@ pub fn prepare_deferred_lighting_pipelines(
                     }
                     Tonemapping::TonyMcMapface => MeshPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE,
                     Tonemapping::BlenderFilmic => MeshPipelineKey::TONEMAP_METHOD_BLENDER_FILMIC,
+                    Tonemapping::PbrNeutral => MeshPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL,
                 };
             }
             if let Some(DebandDither::Enabled) = dither {

crates/bevy_pbr/src/material.rs

@@ -630,6 +630,7 @@ pub const fn tonemapping_pipeline_key(tonemapping: Tonemapping) -> MeshPipelineK
         }
         Tonemapping::TonyMcMapface => MeshPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE,
         Tonemapping::BlenderFilmic => MeshPipelineKey::TONEMAP_METHOD_BLENDER_FILMIC,
+        Tonemapping::PbrNeutral => MeshPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL,
     }
 }
 

crates/bevy_pbr/src/render/mesh.rs

@@ -3093,6 +3093,7 @@ bitflags::bitflags! {
         const TONEMAP_METHOD_SOMEWHAT_BORING_DISPLAY_TRANSFORM = 5 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_TONY_MC_MAPFACE    = 6 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_BLENDER_FILMIC     = 7 << Self::TONEMAP_METHOD_SHIFT_BITS;
+        const TONEMAP_METHOD_PBR_NEUTRAL        = 8 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const SHADOW_FILTER_METHOD_RESERVED_BITS = Self::SHADOW_FILTER_METHOD_MASK_BITS << Self::SHADOW_FILTER_METHOD_SHIFT_BITS;
         const SHADOW_FILTER_METHOD_HARDWARE_2X2  = 0 << Self::SHADOW_FILTER_METHOD_SHIFT_BITS;
         const SHADOW_FILTER_METHOD_GAUSSIAN      = 1 << Self::SHADOW_FILTER_METHOD_SHIFT_BITS;
@@ -3127,7 +3128,7 @@ impl MeshPipelineKey {
     const BLEND_MASK_BITS: u64 = 0b111;
     const BLEND_SHIFT_BITS: u64 = Self::MSAA_MASK_BITS.count_ones() as u64 + Self::MSAA_SHIFT_BITS;
 
-    const TONEMAP_METHOD_MASK_BITS: u64 = 0b111;
+    const TONEMAP_METHOD_MASK_BITS: u64 = 0b1111;
     const TONEMAP_METHOD_SHIFT_BITS: u64 =
         Self::BLEND_MASK_BITS.count_ones() as u64 + Self::BLEND_SHIFT_BITS;
 
@@ -3546,6 +3547,8 @@ impl SpecializedMeshPipeline for MeshPipeline {
                 shader_defs.push("TONEMAP_METHOD_BLENDER_FILMIC".into());
             } else if method == MeshPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE {
                 shader_defs.push("TONEMAP_METHOD_TONY_MC_MAPFACE".into());
+            } else if method == MeshPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL {
+                shader_defs.push("TONEMAP_METHOD_PBR_NEUTRAL".into());
             }
 
             // Debanding is tied to tonemapping in the shader, cannot run without it.

crates/bevy_sprite_render/src/mesh2d/material.rs

@@ -579,6 +579,7 @@ pub const fn tonemapping_pipeline_key(tonemapping: Tonemapping) -> Mesh2dPipelin
         }
         Tonemapping::TonyMcMapface => Mesh2dPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE,
         Tonemapping::BlenderFilmic => Mesh2dPipelineKey::TONEMAP_METHOD_BLENDER_FILMIC,
+        Tonemapping::PbrNeutral => Mesh2dPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL,
     }
 }
 

crates/bevy_sprite_render/src/mesh2d/mesh.rs

@@ -479,6 +479,7 @@ bitflags::bitflags! {
         const TONEMAP_METHOD_SOMEWHAT_BORING_DISPLAY_TRANSFORM = 5 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_TONY_MC_MAPFACE    = 6 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_BLENDER_FILMIC     = 7 << Self::TONEMAP_METHOD_SHIFT_BITS;
+        const TONEMAP_METHOD_PBR_NEUTRAL        = 8 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const STRIP_INDEX_FORMAT_RESERVED_BITS        = Self::INDEX_FORMAT_MASK_BITS << Self::INDEX_FORMAT_SHIFT_BITS;
         const STRIP_INDEX_FORMAT_NONE                 = 0 << Self::INDEX_FORMAT_SHIFT_BITS;
         const STRIP_INDEX_FORMAT_U32                  = 1 << Self::INDEX_FORMAT_SHIFT_BITS;
@@ -493,7 +494,7 @@ impl Mesh2dPipelineKey {
     const MSAA_SHIFT_BITS: u32 = 32 - Self::MSAA_MASK_BITS.count_ones();
     const PRIMITIVE_TOPOLOGY_MASK_BITS: u32 = 0b111;
     const PRIMITIVE_TOPOLOGY_SHIFT_BITS: u32 = Self::MSAA_SHIFT_BITS - 3;
-    const TONEMAP_METHOD_MASK_BITS: u32 = 0b111;
+    const TONEMAP_METHOD_MASK_BITS: u32 = 0b1111;
     const TONEMAP_METHOD_SHIFT_BITS: u32 =
         Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS - Self::TONEMAP_METHOD_MASK_BITS.count_ones();
     pub const INDEX_FORMAT_MASK_BITS: u32 = 0b11;
@@ -652,6 +653,9 @@ impl SpecializedMeshPipeline for Mesh2dPipeline {
                 Mesh2dPipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE => {
                     shader_defs.push("TONEMAP_METHOD_TONY_MC_MAPFACE".into());
                 }
+                Mesh2dPipelineKey::TONEMAP_METHOD_PBR_NEUTRAL => {
+                    shader_defs.push("TONEMAP_METHOD_PBR_NEUTRAL".into());
+                }
                 _ => {}
             }
             // Debanding is tied to tonemapping in the shader, cannot run without it.

crates/bevy_sprite_render/src/render/mod.rs

@@ -112,6 +112,8 @@ bitflags::bitflags! {
         const TONEMAP_METHOD_SOMEWHAT_BORING_DISPLAY_TRANSFORM = 5 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_TONY_MC_MAPFACE    = 6 << Self::TONEMAP_METHOD_SHIFT_BITS;
         const TONEMAP_METHOD_BLENDER_FILMIC     = 7 << Self::TONEMAP_METHOD_SHIFT_BITS;
+        const TONEMAP_METHOD_PBR_NEUTRAL        = 8 << Self::TONEMAP_METHOD_SHIFT_BITS;
+
     }
 }
 
@@ -120,7 +122,7 @@ impl SpritePipelineKey {
     const COLOR_TARGET_FORMAT_SHIFT_BITS: u32 = 4;
     const MSAA_MASK_BITS: u32 = 0b111;
     const MSAA_SHIFT_BITS: u32 = 32 - Self::MSAA_MASK_BITS.count_ones();
-    const TONEMAP_METHOD_MASK_BITS: u32 = 0b111;
+    const TONEMAP_METHOD_MASK_BITS: u32 = 0b1111;
     const TONEMAP_METHOD_SHIFT_BITS: u32 =
         Self::MSAA_SHIFT_BITS - Self::TONEMAP_METHOD_MASK_BITS.count_ones();
 
@@ -191,6 +193,8 @@ impl SpecializedRenderPipeline for SpritePipeline {
                 shader_defs.push("TONEMAP_METHOD_BLENDER_FILMIC".into());
             } else if method == SpritePipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE {
                 shader_defs.push("TONEMAP_METHOD_TONY_MC_MAPFACE".into());
+            } else if method == SpritePipelineKey::TONEMAP_METHOD_PBR_NEUTRAL {
+                shader_defs.push("TONEMAP_METHOD_PBR_NEUTRAL".into());
             }
 
             // Debanding is tied to tonemapping in the shader, cannot run without it.
@@ -549,6 +553,7 @@ pub fn queue_sprites(
                     }
                     Tonemapping::TonyMcMapface => SpritePipelineKey::TONEMAP_METHOD_TONY_MC_MAPFACE,
                     Tonemapping::BlenderFilmic => SpritePipelineKey::TONEMAP_METHOD_BLENDER_FILMIC,
+                    Tonemapping::PbrNeutral => SpritePipelineKey::TONEMAP_METHOD_PBR_NEUTRAL,
                 };
             }
             if let Some(DebandDither::Enabled) = dither {

examples/2d/bloom_2d.rs

@@ -209,6 +209,7 @@ fn next_tonemap(tonemapping: &Tonemapping) -> Tonemapping {
         Tonemapping::Reinhard => Tonemapping::ReinhardLuminance,
         Tonemapping::ReinhardLuminance => Tonemapping::SomewhatBoringDisplayTransform,
         Tonemapping::SomewhatBoringDisplayTransform => Tonemapping::TonyMcMapface,
-        Tonemapping::TonyMcMapface => Tonemapping::None,
+        Tonemapping::TonyMcMapface => Tonemapping::PbrNeutral,
+        Tonemapping::PbrNeutral => Tonemapping::None,
     }
 }

examples/3d/tonemapping.rs

@@ -310,6 +310,8 @@ fn toggle_tonemapping_method(
         **tonemapping = Tonemapping::TonyMcMapface;
     } else if keys.just_pressed(KeyCode::Digit8) {
         **tonemapping = Tonemapping::BlenderFilmic;
+    } else if keys.just_pressed(KeyCode::Digit9) {
+        **tonemapping = Tonemapping::PbrNeutral;
     }
 
     **color_grading = (*per_method_settings
@@ -497,6 +499,14 @@ fn update_ui(
             ""
         }
     ));
+    text.push_str(&format!(
+        "(9) {} PBR Neutral\n",
+        if tonemapping == Tonemapping::PbrNeutral {
+            ">"
+        } else {
+            ""
+        }
+    ));
 
     text.push_str("\n\nColor Grading:\n");
     text.push_str("(arrow keys)\n");
@@ -588,6 +598,7 @@ impl Default for PerMethodSettings {
             Tonemapping::SomewhatBoringDisplayTransform,
             Tonemapping::TonyMcMapface,
             Tonemapping::BlenderFilmic,
+            Tonemapping::PbrNeutral,
         ] {
             settings.insert(
                 method,