refactor Windows classes to separate EGL/WGL/Backing Window

windows/flutter_render_context.h

@@ -0,0 +1,51 @@
+#ifndef _FLUTTER_RENDER_CONTEXT_H
+#define _FLUTTER_RENDER_CONTEXT_H
+
+#include <flutter/method_channel.h>
+#include <flutter/plugin_registrar_windows.h>
+#include <flutter/standard_method_codec.h>
+#include <flutter/texture_registrar.h>
+
+#include "flutter_texture_buffer.h"
+
+namespace polyvox_filament {
+
+    class FlutterRenderContext {
+    public:
+        void DestroyTexture(std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>> result) {
+            if (!_active) {
+                result->Success("Texture has already been detroyed, ignoring");
+                return;
+            }
+
+            // if (_active->flutterTextureId != *flutterTextureId) {
+            //     result->Error("TEXTURE_MISMATCH", "Specified texture ID is not active");
+            //     return;
+            // }
+
+            auto sh = std::make_shared<
+                std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>>>(
+                    std::move(result));
+
+            _textureRegistrar->UnregisterTexture(
+                _active->flutterTextureId, [=, sharedResult = std::move(sh)]() {
+                    this->_inactive = std::move(this->_active);
+                    auto unique = std::move(*(sharedResult.get()));
+                    unique->Success(flutter::EncodableValue(true));
+                    std::cout << "Unregistered/destroyed texture." << std::endl;
+                });
+        }
+        int64_t GetFlutterTextureId() {
+            return _active->flutterTextureId;
+        }
+        void* sharedContext = nullptr;
+        
+    protected:
+        flutter::PluginRegistrarWindows* _pluginRegistrar;
+        flutter::TextureRegistrar* _textureRegistrar;
+        std::unique_ptr<FlutterTextureBuffer> _active = nullptr;
+        std::unique_ptr<FlutterTextureBuffer> _inactive = nullptr;
+    };
+}
+
+#endif