Add: [Win32] Automatic zoom level suggestion for Win32 video driver.

The zoom level suggestion is based on the DPI scaling set in Windows.
We use 150% scaling as the threshold for 2X zoom and 300% scaling
as the threshold for 4X zoom.

src/video/win32_v.cpp

@@ -1316,3 +1316,43 @@ Dimension VideoDriver_Win32::GetScreenSize() const
 {
 	return { static_cast<uint>(GetSystemMetrics(SM_CXSCREEN)), static_cast<uint>(GetSystemMetrics(SM_CYSCREEN)) };
 }
+
+float VideoDriver_Win32::GetDPIScale()
+{
+	typedef UINT (WINAPI *PFNGETDPIFORWINDOW)(HWND hwnd);
+	typedef UINT (WINAPI *PFNGETDPIFORSYSTEM)(VOID);
+	typedef HRESULT (WINAPI *PFNGETDPIFORMONITOR)(HMONITOR hMonitor, int dpiType, UINT *dpiX, UINT *dpiY);
+
+	static PFNGETDPIFORWINDOW _GetDpiForWindow = nullptr;
+	static PFNGETDPIFORSYSTEM _GetDpiForSystem = nullptr;
+	static PFNGETDPIFORMONITOR _GetDpiForMonitor = nullptr;
+
+	static bool init_done = false;
+	if (!init_done) {
+		init_done = true;
+
+		_GetDpiForWindow = (PFNGETDPIFORWINDOW)GetProcAddress(GetModuleHandle(_T("User32")), "GetDpiForWindow");
+		_GetDpiForSystem = (PFNGETDPIFORSYSTEM)GetProcAddress(GetModuleHandle(_T("User32")), "GetDpiForSystem");
+		_GetDpiForMonitor = (PFNGETDPIFORMONITOR)GetProcAddress(LoadLibrary(_T("Shcore.dll")), "GetDpiForMonitor");
+	}
+
+	UINT cur_dpi = 0;
+
+	if (cur_dpi == 0 && _GetDpiForWindow != nullptr && _wnd.main_wnd != nullptr) {
+		/* Per window DPI is supported since Windows 10 Ver 1607. */
+		cur_dpi = _GetDpiForWindow(_wnd.main_wnd);
+	}
+	if (cur_dpi == 0 && _GetDpiForMonitor != nullptr && _wnd.main_wnd != nullptr) {
+		/* Per monitor is supported since Windows 8.1. */
+		UINT dpiX, dpiY;
+		if (SUCCEEDED(_GetDpiForMonitor(MonitorFromWindow(_wnd.main_wnd, MONITOR_DEFAULTTOPRIMARY), 0 /* MDT_EFFECTIVE_DPI */, &dpiX, &dpiY))) {
+			cur_dpi = dpiX; // X and Y are always identical.
+		}
+	}
+	if (cur_dpi == 0 && _GetDpiForSystem != nullptr) {
+		/* Fall back to system DPI. */
+		cur_dpi = _GetDpiForSystem();
+	}
+
+	return cur_dpi > 0 ? cur_dpi / 96.0f : 1.0f; // Default Windows DPI value is 96.
+}

src/video/win32_v.h

@@ -43,6 +43,8 @@ public:
 
 protected:
 	Dimension GetScreenSize() const override;
+
+	float GetDPIScale() override;
 };
 
 /** The factory for Windows' video driver. */