add macOS implementation

macos/include/material/StandardMaterialProvider.hpp

@@ -0,0 +1,53 @@
+#ifndef UNLIT_MATERIAL_PROVIDER
+#define UNLIT_MATERIAL_PROVIDER
+
+#include "material/standard.h"
+
+namespace polyvox {
+  class StandardMaterialProvider : public MaterialProvider {
+
+      const Material* _m;
+      const Material* _ms[1];
+
+      const Engine* _engine;
+
+      public:
+        StandardMaterialProvider(Engine* engine) {
+          _engine = engine;
+          _m = Material::Builder()
+            .package(	STANDARD_STANDARD_DATA, STANDARD_STANDARD_SIZE)
+            .build(*engine);
+          _ms[0] = _m;
+        }
+
+        filament::MaterialInstance* createMaterialInstance(MaterialKey* config, UvMap* uvmap,
+                const char* label = "material", const char* extras = nullptr) {
+          MaterialInstance* d = (MaterialInstance*)_m->getDefaultInstance();
+          return d;
+        }
+
+        /**
+        * Gets a weak reference to the array of cached materials.
+        */
+        const filament::Material* const* getMaterials() const noexcept {
+          return _ms;
+        }
+
+        /**
+        * Gets the number of cached materials.
+        */
+        size_t getMaterialsCount() const noexcept {
+          return (size_t)1;
+        }
+
+        void destroyMaterials() {
+          // TODO - do we need to do anything here?
+        }
+
+        bool needsDummyData(filament::VertexAttribute attrib) const noexcept {
+          return false;
+        }
+  };
+}
+
+#endif