Per window DPI

Source/Engine/Platform/Windows/WindowsWindow.cpp

@@ -16,6 +16,8 @@
 // TODO: finish better borderless window on windows (fix mouse pos offset when maximized and fix white flicker on window show)
 #define WINDOWS_USE_NEW_BORDER_LESS 0
 
+#define DefaultDPI 96
+
 #if WINDOWS_USE_NEW_BORDER_LESS
 #pragma comment(lib, "Gdi32.lib")
 #endif
@@ -95,6 +97,23 @@ WindowsWindow::WindowsWindow(const CreateWindowSettings& settings)
         nullptr,
         (HINSTANCE)Platform::Instance,
         nullptr);
+    
+    _dpi = DefaultDPI;
+    // TODO: Is this the correct way of doing this?
+    const HMODULE user32Dll = LoadLibraryW(L"user32.dll");
+    if (user32Dll)
+    {
+        typedef UINT(STDAPICALLTYPE* GetDpiForWindowProc)(HWND hwnd);
+        const GetDpiForWindowProc getDpiForWindowProc = (GetDpiForWindowProc)GetProcAddress(user32Dll, "GetDpiForWindow");
+
+        if (getDpiForWindowProc)
+        {
+            _dpi = getDpiForWindowProc(_handle);
+        }
+        FreeLibrary(user32Dll);
+    }
+
+    _dpiScale = (float)_dpi / (float)DefaultDPI;
 
     // Validate result
     if (!HasHWND())
@@ -966,6 +985,28 @@ LRESULT WindowsWindow::WndProc(UINT msg, WPARAM wParam, LPARAM lParam)
         break;
     }
 
+    case WM_DPICHANGED:
+    {
+        // Maybe https://stackoverflow.com/a/45110656
+        _dpi = HIWORD(wParam);
+        _dpiScale = (float)_dpi / (float)DefaultDPI;
+
+        
+        RECT* windowRect = (RECT*)lParam;
+        SetWindowPos(_handle,
+            nullptr,
+            windowRect->left,
+            windowRect->top,
+            windowRect->right - windowRect->left,
+            windowRect->bottom - windowRect->top,
+            SWP_NOZORDER | SWP_NOACTIVATE);
+
+
+        // Todo: Recalculate fonts
+
+        return 0;
+    }
+
     case WM_ENTERSIZEMOVE:
     {
         _isResizing = true;