--set flag when a drawable is built using fallback material

--this could indicate that the source asset lacks a material, or else that no materials were loaded by design (i.e. for depth sensor).

src/esp/gfx/Drawable.h

@@ -157,6 +157,13 @@ class Drawable : public Magnum::SceneGraph::Drawable3D {
     setMaterialValuesInternal(material, true);
   }
 
+  /**
+   * @brief Whether this drawable has a specified material or was assigned the
+   * default fallback material, meaning the material for the object was either
+   * not loaded or is otherwise missing.
+   */
+  bool getUsesFallbackMaterial() const { return usingFallbackMaterial_; }
+
  private:
   /**
    * Set or change this drawable's @ref Magnum::Trade::MaterialData values from passed material.
@@ -171,6 +178,15 @@ class Drawable : public Magnum::SceneGraph::Drawable3D {
       CORRADE_UNUSED bool reset) {}
 
  protected:
+  /**
+   * @brief Whether this drawable has a specified material or was assigned the
+   * default fallback material, meaning the material for the object was either
+   * not loaded or is otherwise missing.
+   */
+  void setUsesFallbackMaterial(bool _usingFallbackMaterial) {
+    usingFallbackMaterial_ = _usingFallbackMaterial;
+  }
+
   /**
    * @brief resize the jointTransformArray_
    */
@@ -253,6 +269,13 @@ class Drawable : public Magnum::SceneGraph::Drawable3D {
 
   Corrade::Containers::Array<Magnum::Matrix4> jointTransformations_;
 
+  /**
+   * @brief Whether or not this drawable is being rendered using the default
+   * fallback material, which implies either that materials were not loaded, or
+   * else no material existed for the source asset to load.
+   */
+  bool usingFallbackMaterial_ = false;
+
   bool glMeshExists() const { return mesh_ != nullptr; }
 
  private:

src/esp/gfx/GenericDrawable.cpp

@@ -120,6 +120,12 @@ void GenericDrawable::setMaterialValuesInternal(
   if (meshAttributeFlags_ & Drawable::Flag::HasVertexColor) {
     flags_ |= Mn::Shaders::PhongGL::Flag::VertexColor;
   }
+
+  // Set whether this drawable is being rendered using a fallback material; This
+  // would infer that either materials were not loaded or no materials were
+  // found for the source asset
+  setUsesFallbackMaterial(materialData->attribute<bool>("isFallbackMaterial"));
+
   // If not reset then make sure the same shader is used
   if (!reset) {
     flags_ = oldFlags;

src/esp/gfx/PbrDrawable.cpp

@@ -332,6 +332,10 @@ void PbrDrawable::setMaterialValuesInternal(
   if (meshAttributeFlags_ & Drawable::Flag::HasVertexColor) {
     flags_ |= PbrShader::Flag::VertexColor;
   }
+  // Set whether this drawable is being rendered using a fallback material; This
+  // would infer that either materials were not loaded or no materials were
+  // found for the source asset
+  setUsesFallbackMaterial(materialData->attribute<bool>("isFallbackMaterial"));
 
   // Skin support
   (skinData_ != nullptr) ? flags_ |= PbrShader::Flag::SkinnedMesh