--initial commit; Make fallback material noticeable

--make material color magenta
--add flag that this material is a fallback for an object lacking any other materials
--remove default phong material function; specifying phong shader to use should be sufficient for depth sensor.

src/esp/assets/ResourceManager.cpp

@@ -2138,7 +2138,8 @@ Mn::Trade::MaterialData ResourceManager::setMaterialDefaultUserAttributes(
     ObjectInstanceShaderType shaderTypeToUse,
     bool hasVertObjID,
     bool hasTxtrObjID,
-    int txtrIdx) const {
+    int txtrIdx,
+    bool isFallback) const {
   // New material's attributes
   Cr::Containers::Array<Mn::Trade::MaterialAttributeData> newAttributes;
   arrayAppend(newAttributes, Cr::InPlaceInit, "hasPerVertexObjectId",
@@ -2150,6 +2151,8 @@ Mn::Trade::MaterialData ResourceManager::setMaterialDefaultUserAttributes(
   arrayAppend(newAttributes, Cr::InPlaceInit, "shaderTypeToUse",
               static_cast<int>(shaderTypeToUse));
 
+  arrayAppend(newAttributes, Cr::InPlaceInit, "isFallbackMaterial", isFallback);
+
   Cr::Containers::Optional<Mn::Trade::MaterialData> finalMaterial =
       Mn::MaterialTools::merge(
           material, Mn::Trade::MaterialData{{}, std::move(newAttributes), {}});
@@ -2250,9 +2253,20 @@ void ResourceManager::initDefaultMaterials() {
 
   // Build default material for fallback material
   Mn::Trade::MaterialData fallbackMaterial = buildDefaultMaterial();
-  // Set expected user-defined attributes
+  // Make fallback magenta so visibly obvious
+  fallbackMaterial.mutableAttribute<Mn::Color4>(
+      Mn::Trade::MaterialAttribute::AmbientColor) =
+      Mn::Color4{1.0f, 0.0f, 1.0f, 1.0f};
+  fallbackMaterial.mutableAttribute<Mn::Color4>(
+      Mn::Trade::MaterialAttribute::DiffuseColor) =
+      Mn::Color4{1.0f, 0.0f, 1.0f, 1.0f};
+  fallbackMaterial.mutableAttribute<Mn::Color4>(
+      Mn::Trade::MaterialAttribute::SpecularColor) =
+      Mn::Color4{1.0f, 0.0f, 1.0f, 1.0f};
+  // Set expected user-defined attributes - specify Phong shader to use
   fallbackMaterial = setMaterialDefaultUserAttributes(
-      fallbackMaterial, ObjectInstanceShaderType::Flat);
+      fallbackMaterial, ObjectInstanceShaderType::Phong, false, false, -1,
+      true);
   // Add to shaderManager as fallback material
   shaderManager_.setFallback<Mn::Trade::MaterialData>(
       std::move(fallbackMaterial));

src/esp/assets/ResourceManager.h

@@ -751,14 +751,17 @@ class ResourceManager {
    * ids for semantics.
    * @param txtrIdx The absolute index in the @ref textures_ store for the semantic
    * annotation texture.
+   * @param isFallback This material is default fallback material for missing
+   * materials.
    * @return the updated material
    */
   Mn::Trade::MaterialData setMaterialDefaultUserAttributes(
       const Mn::Trade::MaterialData& material,
       ObjectInstanceShaderType shaderTypeToUse,
       bool hasVertObjID = false,
       bool hasTxtrObjID = false,
-      int txtrIdx = -1) const;
+      int txtrIdx = -1,
+      bool isFallback = false) const;
 
   /**
    * @brief Configure the importerManager_ GL Extensions appropriately based on