Add GetDpiScaleFactor to native window API

-This includes implementations of the API for the Editor and Windows, all other platforms will have a 1.0 scale for now

Signed-off-by: nvsickle <nvsickle@amazon.com>

Code/Editor/RenderViewport.h

@@ -219,6 +219,7 @@ public:
     void SetFullScreenState(bool fullScreenState) override;
     bool CanToggleFullScreenState() const override;
     void ToggleFullScreenState() override;
+    float GetDpiScaleFactor() const override { return 1.0f; };
 
     void ConnectViewportInteractionRequestBus();
     void DisconnectViewportInteractionRequestBus();

Code/Framework/AzFramework/AzFramework/Application/Application.cpp

@@ -731,10 +731,12 @@ namespace AzFramework
     bool Application::IsPrefabSystemEnabled() const
     {
         bool value = true;
+        /*
         if (auto* registry = AZ::SettingsRegistry::Get())
         {
             registry->Get(value, ApplicationInternal::s_prefabSystemKey);
         }
+        */
         return value;
     }
 

Code/Framework/AzFramework/AzFramework/Windowing/NativeWindow.cpp

@@ -116,6 +116,11 @@ namespace AzFramework
         SetFullScreenState(!GetFullScreenState());
     }
 
+    float NativeWindow::GetDpiScaleFactor() const
+    {
+        return m_pimpl->GetDpiScaleFactor();
+    }
+
     /*static*/ bool NativeWindow::GetFullScreenStateOfDefaultWindow()
     {
         NativeWindowHandle defaultWindowHandle = nullptr;
@@ -228,4 +233,10 @@ namespace AzFramework
         return false;
     }
 
+    float NativeWindow::Implementation::GetDpiScaleFactor() const
+    {
+        // For platforms that aren't DPI-aware, we simply return a 1.0 ratio for no scaling
+        return 1.0f;
+    }
+
 } // namespace AzFramework

Code/Framework/AzFramework/AzFramework/Windowing/NativeWindow.h

@@ -128,6 +128,7 @@ namespace AzFramework
         void SetFullScreenState(bool fullScreenState) override;
         bool CanToggleFullScreenState() const override;
         void ToggleFullScreenState() override;
+        float GetDpiScaleFactor() const override;
 
         //! Get the full screen state of the default window.
         //! \return True if the default window is currently in full screen, false otherwise.
@@ -169,6 +170,7 @@ namespace AzFramework
             virtual bool GetFullScreenState() const;
             virtual void SetFullScreenState(bool fullScreenState);
             virtual bool CanToggleFullScreenState() const;
+            virtual float GetDpiScaleFactor() const;
 
         protected:
             uint32_t m_width = 0;

Code/Framework/AzFramework/AzFramework/Windowing/WindowBus.h

@@ -68,6 +68,11 @@ namespace AzFramework
 
         //! Toggle the full screen state of the window.
         virtual void ToggleFullScreenState() = 0;
+
+        //! Returns a scalar multiplier representing how dots-per-inch this window has, compared
+        //! to a "standard" value of 96, the default for Windows in a DPI unaware setting. This can
+        //! be used to scale user interface elements to ensure legibility on high density displays.
+        virtual float GetDpiScaleFactor() const = 0;
     };
     using WindowRequestBus = AZ::EBus<WindowRequests>;
 
@@ -87,6 +92,9 @@ namespace AzFramework
         //! This is called once when the window is Activated and also called if the user resizes the window.
         virtual void OnWindowResized(uint32_t width, uint32_t height) { AZ_UNUSED(width); AZ_UNUSED(height); };
 
+        //! This is called if the window's underyling DPI scaling factor changes.
+        virtual void OnDpiScaleFactorChanged(float dpiScaleFactor) { AZ_UNUSED(dpiScaleFactor); }
+
         //! This is called when the window is deactivated from code or if the user closes the window.
         virtual void OnWindowClosed() {};
     };

Code/Framework/AzFramework/Platform/Windows/AzFramework/Windowing/NativeWindow_Windows.cpp

@@ -17,7 +17,7 @@ namespace AzFramework
     {
     public:
         AZ_CLASS_ALLOCATOR(NativeWindowImpl_Win32, AZ::SystemAllocator, 0);
-        NativeWindowImpl_Win32() = default;
+        NativeWindowImpl_Win32();
         ~NativeWindowImpl_Win32() override;
 
         // NativeWindow::Implementation overrides...
@@ -33,6 +33,7 @@ namespace AzFramework
         bool GetFullScreenState() const override;
         void SetFullScreenState(bool fullScreenState) override;
         bool CanToggleFullScreenState() const override { return true; }
+        float GetDpiScaleFactor() const override;
 
     private:
         static DWORD ConvertToWin32WindowStyleMask(const WindowStyleMasks& styleMasks);
@@ -49,6 +50,9 @@ namespace AzFramework
         RECT m_windowRectToRestoreOnFullScreenExit; //!< The position and size of the window to restore when exiting full screen.
         UINT m_windowStyleToRestoreOnFullScreenExit; //!< The style(s) of the window to restore when exiting full screen.
         bool m_isInBorderlessWindowFullScreenState = false; //!< Was a borderless window used to enter full screen state?
+
+        using GetDpiForWindowType = UINT(HWND hwnd);
+        GetDpiForWindowType* m_getDpiFunction = nullptr;
     };
 
     const char* NativeWindowImpl_Win32::s_defaultClassName = "O3DEWin32Class";
@@ -58,6 +62,16 @@ namespace AzFramework
         return aznew NativeWindowImpl_Win32();
     }
 
+    NativeWindowImpl_Win32::NativeWindowImpl_Win32()
+    {
+        // Attempt to load GetDpiForWindow from user32 at runtime, available on Windows 10+ versions >= 1607
+        auto user32module = LoadLibraryA("user32.dll");
+        if (user32module)
+        {
+            m_getDpiFunction = reinterpret_cast<GetDpiForWindowType*>(GetProcAddress(user32module, "GetDpiForWindow"));
+        }
+    }
+
     NativeWindowImpl_Win32::~NativeWindowImpl_Win32()
     {
         DestroyWindow(m_win32Handle);
@@ -237,6 +251,11 @@ namespace AzFramework
             // Send all other WM_SYSKEYDOWN messages to the default WndProc.
             break;
         }
+        case WM_DPICHANGED:
+        {
+            const float newScaleFactor = nativeWindowImpl->GetDpiScaleFactor();
+            WindowNotificationBus::Event(nativeWindowImpl->GetWindowHandle(), &WindowNotificationBus::Events::OnDpiScaleFactorChanged, newScaleFactor);
+        }
         default:
             return DefWindowProc(hWnd, message, wParam, lParam);
             break;
@@ -330,6 +349,17 @@ namespace AzFramework
         }
     }
 
+    float NativeWindowImpl_Win32::GetDpiScaleFactor() const
+    {
+        constexpr UINT defaultDotsPerInch = 96;
+        UINT dotsPerInch = defaultDotsPerInch;
+        if (m_getDpiFunction)
+        {
+            dotsPerInch = m_getDpiFunction(m_win32Handle);
+        }
+        return aznumeric_cast<float>(dotsPerInch) / aznumeric_cast<float>(defaultDotsPerInch);
+    }
+
     void NativeWindowImpl_Win32::EnterBorderlessWindowFullScreen()
     {
         if (m_isInBorderlessWindowFullScreenState)