Change: Determine automatic interface scale by window size. (#14627)

Replace OS-dependent interface scaling with scaling dependent on the window size.

This works on all platforms and should provide a more comfortable experience for new players. Manual interface scale setting works as before.

src/gfx.cpp

@@ -1325,6 +1325,10 @@ void ScreenSizeChanged()
 
 	/* screen size changed and the old bitmap is invalid now, so we don't want to undraw it */
 	_cursor.visible = false;
+
+	if (VideoDriver::GetInstance() != nullptr) {
+		if (AdjustGUIZoom(true)) ReInitAllWindows(true);
+	}
 }
 
 void UndrawMouseCursor()
@@ -1785,7 +1789,12 @@ void UpdateGUIZoom()
 {
 	/* Determine real GUI zoom to use. */
 	if (_gui_scale_cfg == -1) {
-		_gui_scale = VideoDriver::GetInstance()->GetSuggestedUIScale();
+		/* Minimum design size of the game is 640x480. */
+		float xs = _screen.width / 640.f;
+		float ys = _screen.height / 480.f;
+		int scale = std::min(xs, ys) * 100;
+		/* Round down scaling to 25% increments and clamp to limits. */
+		_gui_scale = Clamp((scale / 25) * 25, MIN_INTERFACE_SCALE, MAX_INTERFACE_SCALE);
 	} else {
 		_gui_scale = Clamp(_gui_scale_cfg, MIN_INTERFACE_SCALE, MAX_INTERFACE_SCALE);
 	}

src/settings_gui.cpp

@@ -417,10 +417,11 @@ struct GameOptionsWindow : Window {
 
 	GameSettings *opt = nullptr;
 	bool reload = false;
+	bool gui_scale_changed = false;
 	int gui_scale = 0;
 	static inline WidgetID active_tab = WID_GO_TAB_GENERAL;
 
-	GameOptionsWindow(WindowDesc &desc) : Window(desc), filter_editbox(50), gui_scale(_gui_scale)
+	GameOptionsWindow(WindowDesc &desc) : Window(desc), filter_editbox(50)
 	{
 		this->opt = &GetGameSettings();
 
@@ -453,6 +454,7 @@ struct GameOptionsWindow : Window {
 	void OnInit() override
 	{
 		_setting_circle_size = maxdim(GetSpriteSize(SPR_CIRCLE_FOLDED), GetSpriteSize(SPR_CIRCLE_UNFOLDED));
+		this->gui_scale = _gui_scale;
 	}
 
 	void Close([[maybe_unused]] int data = 0) override
@@ -1057,7 +1059,16 @@ struct GameOptionsWindow : Window {
 #endif /* HAS_TRUETYPE_FONT */
 
 			case WID_GO_GUI_SCALE:
+				/* Any click on the slider deactivates automatic interface scaling, setting it to the current value before being adjusted. */
+				if (_gui_scale_cfg == -1) {
+					_gui_scale_cfg = this->gui_scale;
+					this->SetWidgetLoweredState(WID_GO_GUI_SCALE_AUTO, false);
+					this->SetWidgetDirty(WID_GO_GUI_SCALE_AUTO);
+					this->SetWidgetDirty(WID_GO_GUI_SCALE_AUTO_TEXT);
+				}
+
 				if (ClickSliderWidget(this->GetWidget<NWidgetBase>(widget)->GetCurrentRect(), pt, MIN_INTERFACE_SCALE, MAX_INTERFACE_SCALE, _ctrl_pressed ? 0 : SCALE_NMARKS, this->gui_scale)) {
+					this->gui_scale_changed = true;
 					this->SetWidgetDirty(widget);
 				}
 
@@ -1383,8 +1394,9 @@ struct GameOptionsWindow : Window {
 
 	void OnMouseLoop() override
 	{
-		if (_left_button_down || this->gui_scale == _gui_scale) return;
+		if (_left_button_down || !this->gui_scale_changed) return;
 
+		this->gui_scale_changed = false;
 		_gui_scale_cfg = this->gui_scale;
 
 		if (AdjustGUIZoom(false)) {

src/video/cocoa/cocoa_v.h

@@ -64,7 +64,6 @@ protected:
 	bool buffer_locked; ///< Video buffer was locked by the main thread.
 
 	Dimension GetScreenSize() const override;
-	float GetDPIScale() override;
 	void InputLoop() override;
 	bool LockVideoBuffer() override;
 	void UnlockVideoBuffer() override;

src/video/cocoa/cocoa_v.mm

@@ -283,12 +283,6 @@ Dimension VideoDriver_Cocoa::GetScreenSize() const
 	return { static_cast<uint>(NSWidth(frame)), static_cast<uint>(NSHeight(frame)) };
 }
 
-/** Get DPI scale of our window. */
-float VideoDriver_Cocoa::GetDPIScale()
-{
-	return this->cocoaview != nil ? [ this->cocoaview getContentsScale ] : 1.0f;
-}
-
 /** Lock video buffer for drawing if it isn't already mapped. */
 bool VideoDriver_Cocoa::LockVideoBuffer()
 {

src/video/video_driver.hpp

@@ -166,16 +166,6 @@ public:
 		return {};
 	}
 
-	/**
-	 * Get a suggested default GUI scale taking screen DPI into account.
-	 */
-	virtual int GetSuggestedUIScale()
-	{
-		float dpi_scale = this->GetDPIScale();
-
-		return Clamp(dpi_scale * 100, MIN_INTERFACE_SCALE, MAX_INTERFACE_SCALE);
-	}
-
 	virtual std::string_view GetInfoString() const
 	{
 		return this->GetName();
@@ -233,12 +223,6 @@ protected:
 	 */
 	virtual Dimension GetScreenSize() const { return { DEFAULT_WINDOW_WIDTH, DEFAULT_WINDOW_HEIGHT }; }
 
-	/**
-	 * Get DPI scaling factor of the screen OTTD is displayed on.
-	 * @return 1.0 for default platform DPI, > 1.0 for higher DPI values, and < 1.0 for smaller DPI values.
-	 */
-	virtual float GetDPIScale() { return 1.0f; }
-
 	/**
 	 * Apply resolution auto-detection and clamp to sensible defaults.
 	 */

src/video/win32_v.cpp

@@ -1079,47 +1079,6 @@ Dimension VideoDriver_Win32Base::GetScreenSize() const
 	return { static_cast<uint>(GetSystemMetrics(SM_CXSCREEN)), static_cast<uint>(GetSystemMetrics(SM_CYSCREEN)) };
 }
 
-float VideoDriver_Win32Base::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;
-		static LibraryLoader _user32("user32.dll");
-		static LibraryLoader _shcore("shcore.dll");
-		_GetDpiForWindow = _user32.GetFunction("GetDpiForWindow");
-		_GetDpiForSystem = _user32.GetFunction("GetDpiForSystem");
-		_GetDpiForMonitor = _shcore.GetFunction("GetDpiForMonitor");
-	}
-
-	UINT cur_dpi = 0;
-
-	if (cur_dpi == 0 && _GetDpiForWindow != nullptr && this->main_wnd != nullptr) {
-		/* Per window DPI is supported since Windows 10 Ver 1607. */
-		cur_dpi = _GetDpiForWindow(this->main_wnd);
-	}
-	if (cur_dpi == 0 && _GetDpiForMonitor != nullptr && this->main_wnd != nullptr) {
-		/* Per monitor is supported since Windows 8.1. */
-		UINT dpiX, dpiY;
-		if (SUCCEEDED(_GetDpiForMonitor(MonitorFromWindow(this->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.
-}
-
 bool VideoDriver_Win32Base::LockVideoBuffer()
 {
 	if (this->buffer_locked) return false;

src/video/win32_v.h

@@ -49,7 +49,6 @@ protected:
 	bool buffer_locked;     ///< Video buffer was locked by the main thread.
 
 	Dimension GetScreenSize() const override;
-	float GetDPIScale() override;
 	void InputLoop() override;
 	bool LockVideoBuffer() override;
 	void UnlockVideoBuffer() override;