[render] get windowPtr from WindowManagers

vclib/render/include/vclib/glfw/window_manager.h

@@ -226,6 +226,8 @@ class WindowManager
     }
 
 protected:
+    void* windowPtr() { return reinterpret_cast<void*>(mWindow); }
+
     // callbacks
     virtual void glfwFramebufferSizeCallback(
         GLFWwindow*,

vclib/render/include/vclib/qt/widget_manager.h

@@ -137,6 +137,12 @@ class WidgetManager :
     }
 
 protected:
+    void* windowPtr()
+    {
+        // TODO: probably ImGui Drawer needs something else here - QWidget*?
+        return reinterpret_cast<void*>(winId());
+    }
+
 #if defined(VCLIB_RENDER_BACKEND_BGFX)
     void resizeEvent(QResizeEvent* event) override
     {

vclib/render/include/vclib/render/drawers/plain_drawer.h

@@ -30,6 +30,9 @@ namespace vcl {
 template<typename DerivedRenderer>
 class PlainDrawer
 {
+protected:
+    using DRT = DerivedRenderer;
+
 public:
     PlainDrawer() = default;
     PlainDrawer(uint, uint) {}
@@ -43,8 +46,6 @@ class PlainDrawer
     virtual void onDrawContent(uint viewId) {}
 
 protected:
-    using DRT = DerivedRenderer;
-
     auto* derived() { return static_cast<DRT*>(this); }
 
     const auto* derived() const { return static_cast<const DRT*>(this); }

vclib/render/include/vclib/render/renderer.h

@@ -288,6 +288,8 @@ class Renderer :
     /***** Member functions called by Drawer objects *****/
     // Documentation is in the Renderer::DRW inner class
 
+    void* dWindowPtr() { return WindowManagerType::windowPtr(); }
+
     vcl::Point2<uint> dCanvasSize() const { return CanvasType::size(); }
 
     auto dCanvasFrameBuffer() const { return CanvasType::frameBuffer(); }
@@ -555,6 +557,22 @@ class Renderer<WindowManagerT, CanvasT, Drawers...>::DRW
     //friend Drawers<Renderer<WindowManagerT, CanvasT, Drawers...>>...;
 public: // TODO - remove this when C++26 is supported
 
+    /**
+     * @brief A Drawer object can request the window pointer of the window
+     * manager (the exact meaning of the window pointer depends on the window
+     * manager implementation).
+     *
+     * To get the window pointer, the Drawer object can call the `windowPtr()`
+     * function. To know the exact meaning of the window pointer, the Drawer
+     * object should refer to the documentation of the specific window manager
+     * implementation, and check the WINDOW_MANAGER_ID of the window manager,
+     * that is a static constant of the WindowManager class.
+     *
+     * @param r
+     * @return
+     */
+    static void* windowPtr(Renderer* r) { return r->dWindowPtr(); }
+
     /**
      * @brief A Drawer object can request the size of the canvas. This function
      * is called by the Drawer object to request the size of the canvas.