refactor Windows classes to separate EGL/WGL/Backing Window

windows/egl_context.h

@@ -0,0 +1,28 @@
+#ifndef _EGL_CONTEXT_H
+#define _EGL_CONTEXT_H
+
+#include "flutter_angle_texture.h"
+#include "backend/platforms/PlatformEGL.h"
+
+namespace polyvox_filament {
+
+class EGLContext : public FlutterRenderingContext {
+public:
+  EGLContext(flutter::PluginRegistrarWindows* pluginRegistrar, flutter::TextureRegistrar* textureRegistrar);
+  void CreateTexture(
+      uint32_t width, uint32_t height,
+      std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>> result);
+private:
+  EGLContext _context = NULL;
+  EGLConfig _eglConfig = NULL;
+  EGLDisplay _eglDisplay = NULL;
+  std::unique_ptr<FlutterAngleTexture> _active = nullptr;
+  std::unique_ptr<FlutterAngleTexture> _inactive = nullptr;
+  ID3D11Device* _D3D11Device = nullptr;
+  ID3D11DeviceContext* _D3D11DeviceContext = nullptr;
+  filament::backend::Platform* _platform = nullptr;
+}
+
+}
+
+#endif