add a material parameter to control shadow far attenuation

FIXES=[436680157]

NEW_RELEASE_NOTES.md

@@ -9,3 +9,4 @@ appropriate header in [RELEASE_NOTES.md](./RELEASE_NOTES.md).
 ## Release notes for next branch cut
 
 - Update CMake minimum version to 3.22.1
+- material: Add a material parameter to control shadow far attenuation (b/436680157)

docs_src/src_markdeep/Materials.md.html

@@ -1217,6 +1217,23 @@ material {
 }
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+### General: shadowFarAttenuation
+
+Type
+:    `boolean`
+
+Value
+:     `true` or `false`. Defaults to `true`.
+
+Description
+:    When set to `false`, the directional light shadow is no longer attenuated at near the far plane.
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ JSON
+material {
+    shadowFarAttenuation : true
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 ### General: quality
 
 Type

libs/filamat/include/filamat/MaterialBuilder.h

@@ -535,6 +535,9 @@ public:
     //! Enable / disable the cheapest linear fog, disabled by default.
     MaterialBuilder& linearFog(bool enabled) noexcept;
 
+    //! Enable / disable shadow far attenuation, enabled by default.
+    MaterialBuilder& shadowFarAttenuation(bool enabled) noexcept;
+
     //! Enable / disable multi-bounce ambient occlusion, disabled by default on mobile.
     MaterialBuilder& multiBounceAmbientOcclusion(bool multiBounceAO) noexcept;
 
@@ -958,6 +961,7 @@ private:
 
     bool mFlipUV = true;
     bool mLinearFog = false;
+    bool mShadowFarAttenuation = true;
 
     bool mMultiBounceAO = false;
     bool mMultiBounceAOSet = false;

libs/filamat/src/MaterialBuilder.cpp

@@ -549,6 +549,11 @@ MaterialBuilder& MaterialBuilder::linearFog(bool const enabled) noexcept {
     return *this;
 }
 
+MaterialBuilder& MaterialBuilder::shadowFarAttenuation(bool const enabled) noexcept {
+    mShadowFarAttenuation = enabled;
+    return *this;
+}
+
 MaterialBuilder& MaterialBuilder::customSurfaceShading(bool const customSurfaceShading) noexcept {
     mCustomSurfaceShading = customSurfaceShading;
     return *this;
@@ -719,6 +724,7 @@ void MaterialBuilder::prepareToBuild(MaterialInfo& info) noexcept {
     info.clearCoatIorChange = mClearCoatIorChange;
     info.flipUV = mFlipUV;
     info.linearFog = mLinearFog;
+    info.shadowFarAttenuation = mShadowFarAttenuation;
     info.requiredAttributes = mRequiredAttributes;
     info.blendingMode = mBlendingMode;
     info.postLightingBlendingMode = mPostLightingBlendingMode;

libs/filamat/src/shaders/CodeGenerator.cpp

@@ -252,6 +252,8 @@ utils::io::sstream& CodeGenerator::generateCommonProlog(utils::io::sstream& out,
     if (stage == ShaderStage::FRAGMENT) {
         CodeGenerator::generateDefine(out, "FILAMENT_LINEAR_FOG",
                 material.linearFog);
+        CodeGenerator:generateDefine(out, "FILAMENT_SHADOW_FAR_ATTENUATION",
+                material.shadowFarAttenuation);
         CodeGenerator::generateDefine(out, "MATERIAL_HAS_CUSTOM_DEPTH",
                 material.userMaterialHasCustomDepth);
     }

libs/filamat/src/shaders/MaterialInfo.h

@@ -45,6 +45,7 @@ struct UTILS_PUBLIC MaterialInfo {
     bool clearCoatIorChange;
     bool flipUV;
     bool linearFog;
+    bool shadowFarAttenuation;
     bool multiBounceAO;
     bool multiBounceAOSet;
     bool specularAOSet;

libs/filament-matp/src/ParametersProcessor.cpp

@@ -1190,6 +1190,11 @@ static bool processLinearFog(MaterialBuilder& builder, const JsonishValue& value
     return true;
 }
 
+static bool processShadowFarAttenuation(MaterialBuilder& builder, const JsonishValue& value) {
+    builder.shadowFarAttenuation(value.toJsonBool()->getBool());
+    return true;
+}
+
 static bool processMultiBounceAO(MaterialBuilder& builder, const JsonishValue& value) {
     builder.multiBounceAmbientOcclusion(value.toJsonBool()->getBool());
     return true;
@@ -1411,6 +1416,7 @@ ParametersProcessor::ParametersProcessor() {
     mParameters["stereoscopicType"]              = { &processStereoscopicType, Type::STRING };
     mParameters["useDefaultDepthVariant"]        = { &processUseDefaultDepthVariant, Type::BOOL };
     mParameters["linearFog"]                     = { &processLinearFog, Type::BOOL };
+    mParameters["shadowFarAttenuation"]          = { &processShadowFarAttenuation, Type::BOOL };
 }
 
 bool ParametersProcessor::process(MaterialBuilder& builder, const JsonishObject& jsonObject) {

shaders/src/surface_light_directional.fs

@@ -61,12 +61,14 @@ void evaluateDirectionalLight(const MaterialInputs material,
 #if defined(MATERIAL_HAS_SHADOW_STRENGTH)
             applyShadowStrength(visibility, material.shadowStrength);
 #endif
+#if defined (FILAMENT_SHADOW_FAR_ATTENUATION)
             // shadow far attenuation
             highp vec3 v = getWorldPosition() - getWorldCameraPosition();
             // (viewFromWorld * v).z == dot(transpose(viewFromWorld), v)
             highp float z = dot(transpose(getViewFromWorldMatrix())[2].xyz, v);
             highp vec2 p = frameUniforms.shadowFarAttenuationParams;
             visibility = 1.0 - ((1.0 - visibility) * saturate(p.x - z * z * p.y));
+#endif
         }
         if ((frameUniforms.directionalShadows & 0x2) != 0 && visibility > 0.0) {
             if ((object_uniforms_flagsChannels & FILAMENT_OBJECT_CONTACT_SHADOWS_BIT) != 0) {

shaders/src/surface_shading_unlit.fs

@@ -50,12 +50,14 @@ vec4 evaluateMaterial(const MaterialInputs material) {
 #if defined(MATERIAL_HAS_SHADOW_STRENGTH)
         applyShadowStrength(visibility, material.shadowStrength);
 #endif
+#if defined (FILAMENT_SHADOW_FAR_ATTENUATION)
         // shadow far attenuation
         highp vec3 v = getWorldPosition() - getWorldCameraPosition();
         // (viewFromWorld * v).z == dot(transpose(viewFromWorld), v)
         highp float z = dot(transpose(getViewFromWorldMatrix())[2].xyz, v);
         highp vec2 p = frameUniforms.shadowFarAttenuationParams;
         visibility = 1.0 - ((1.0 - visibility) * saturate(p.x - z * z * p.y));
+#endif
     }
     if ((frameUniforms.directionalShadows & 0x2) != 0 && visibility > 0.0) {
         if ((object_uniforms_flagsChannels & FILAMENT_OBJECT_CONTACT_SHADOWS_BIT) != 0) {