add macOS implementation

macos/include/ResourceBuffer.hpp

@@ -0,0 +1,81 @@
+#ifndef RESOURCE_BUFFER_H
+#define RESOURCE_BUFFER_H
+
+#include <stdint.h>
+#if defined(__cplusplus)
+#include "Log.hpp"
+extern "C" {
+#endif
+    // 
+    // Pairs a memory buffer with an ID that can be used to unload the backing asset if needed.
+    // Use this when you want to load an asset from a resource that requires more than just `free` on the underlying buffer.
+    // e.g. 
+    // ```
+    // uint64_t id = get_next_resource_id();
+    // AAsset *asset = AAssetManager_open(am, name, AASSET_MODE_BUFFER);
+    // off_t length = AAsset_getLength(asset);
+    // const void * buffer = AAsset_getBuffer(asset);
+    // uint8_t *buf = new uint8_t[length ];
+    // memcpy(buf,buffer,  length);
+    // ResourceBuffer rb(buf, length, id);
+    // ...
+    // ...
+    // (elsewhere)
+    // AAsset* asset = get_asset_from_id(rb.id);
+    // AAsset_close(asset);
+    // free_asset_id(rb.id);
+    //
+    struct ResourceBuffer {
+        #if defined(__cplusplus)
+        ResourceBuffer(const void* const data, const uint32_t size, const uint32_t id) : data(data), size(size), id(id) {};
+        #endif
+        const void * const data;
+        const uint32_t size;
+        const uint32_t id;
+    };
+
+    typedef struct ResourceBuffer ResourceBuffer;
+    typedef ResourceBuffer (*FlutterFilamentLoadResource)(const char* uri);
+    typedef ResourceBuffer (*LoadResourceFromOwner)(const char* const, void* const owner);
+    typedef void (*FlutterFilamentFreeResource)(ResourceBuffer);
+    typedef void (*FreeResourceFromOwner)(ResourceBuffer, void* const owner);
+    
+    // this may be compiled as either C or C++, depending on which compiler is being invoked (e.g. binding to Swift will compile as C).
+    // the former does not allow default initialization to be specified inline), so we need to explicitly set the unused members to nullptr
+    struct ResourceLoaderWrapper {
+      #if defined(__cplusplus)
+        ResourceLoaderWrapper(FlutterFilamentLoadResource loader, FlutterFilamentFreeResource freeResource) : mLoadResource(loader), mFreeResource(freeResource), mLoadResourceFromOwner(nullptr), mFreeResourceFromOwner(nullptr),
+        mOwner(nullptr) {}
+        
+        ResourceLoaderWrapper(LoadResourceFromOwner loader, FreeResourceFromOwner freeResource, void* const owner) : mLoadResource(nullptr), mFreeResource(nullptr), mLoadResourceFromOwner(loader), mFreeResourceFromOwner(freeResource), mOwner(owner) {
+            
+        };
+
+        ResourceBuffer load(const char* uri) const {
+          if(mLoadResourceFromOwner) {
+            return mLoadResourceFromOwner(uri, mOwner);
+          }
+          return mLoadResource(uri);
+        }
+
+        void free(ResourceBuffer rb) const {
+          if(mFreeResourceFromOwner) {
+            mFreeResourceFromOwner(rb, mOwner);
+          } else {
+            mFreeResource(rb);
+          }
+        }
+      #endif
+        FlutterFilamentLoadResource mLoadResource;
+        FlutterFilamentFreeResource mFreeResource;
+        LoadResourceFromOwner mLoadResourceFromOwner;
+        FreeResourceFromOwner mFreeResourceFromOwner;
+        void* mOwner;
+    };
+    typedef struct ResourceLoaderWrapper ResourceLoaderWrapper;
+    
+    
+#if defined(__cplusplus)
+}
+#endif
+#endif