Feature: Automatic UI and font zoom levels when supported by the OS.

8 files changed, 72 insertions, 16 deletions

diff --git a/src/gfx.cpp b/src/gfx.cpp
index 54851d375..786bbb25b 100644
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -59,6 +59,10 @@ static ReusableBuffer<uint8> _cursor_backup;
 ZoomLevel _gui_zoom; ///< GUI Zoom level
 ZoomLevel _font_zoom; ///< Font Zoom level
 
+int8 _gui_zoom_cfg;  ///< GUI zoom level in config.
+int8 _font_zoom_cfg; ///< Font zoom level in config.
+
+
 /**
  * The rect for repaint.
  *
@@ -1876,3 +1880,23 @@ void SortResolutions()
 {
 	std::sort(_resolutions.begin(), _resolutions.end());
 }
+
+/**
+ * Resolve GUI zoom level, if auto-suggestion is requested.
+ */
+void UpdateGUIZoom()
+{
+	/* Determine real GUI zoom to use. */
+	if (_gui_zoom_cfg == ZOOM_LVL_CFG_AUTO) {
+		_gui_zoom = static_cast<ZoomLevel>(Clamp(VideoDriver::GetInstance()->GetSuggestedUIZoom(), _settings_client.gui.zoom_min, _settings_client.gui.zoom_max));
+	} else {
+		_gui_zoom = static_cast<ZoomLevel>(_gui_zoom_cfg);
+	}
+
+	/* Determine real font zoom to use. */
+	if (_font_zoom_cfg == ZOOM_LVL_CFG_AUTO) {
+		_font_zoom = static_cast<ZoomLevel>(VideoDriver::GetInstance()->GetSuggestedUIZoom());
+	} else {
+		_font_zoom = static_cast<ZoomLevel>(_font_zoom_cfg);
+	}
+}
diff --git a/src/gfx_func.h b/src/gfx_func.h
index 7ac26f29b..8695fa0e2 100644
--- a/src/gfx_func.h
+++ b/src/gfx_func.h
@@ -77,6 +77,7 @@ void UpdateWindows();
 void DrawMouseCursor();
 void ScreenSizeChanged();
 void GameSizeChanged();
+void UpdateGUIZoom();
 void UndrawMouseCursor();
 
 /** Size of the buffer used for drawing strings. */
diff --git a/src/lang/english.txt b/src/lang/english.txt
index 567d23820..88ef18702 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -1004,6 +1004,7 @@ STR_GAME_OPTIONS_RESOLUTION_OTHER                               :other
 STR_GAME_OPTIONS_GUI_ZOOM_FRAME                                 :{BLACK}Interface size
 STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_TOOLTIP                      :{BLACK}Select the interface element size to use
 
+STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_AUTO                         :(auto-detect)
 STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_NORMAL                       :Normal
 STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_2X_ZOOM                      :Double size
 STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_4X_ZOOM                      :Quad size
@@ -1011,6 +1012,7 @@ STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_4X_ZOOM                      :Quad size
 STR_GAME_OPTIONS_FONT_ZOOM                                      :{BLACK}Font size
 STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_TOOLTIP                     :{BLACK}Select the interface font size to use
 
+STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_AUTO                        :(auto-detect)
 STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_NORMAL                      :Normal
 STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_2X_ZOOM                     :Double size
 STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_4X_ZOOM                     :Quad size
diff --git a/src/openttd.cpp b/src/openttd.cpp
index a631bd852..b68f378cf 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -771,6 +771,7 @@ int openttd_main(int argc, char *argv[])
 
 	/* Initialize the zoom level of the screen to normal */
 	_screen.zoom = ZOOM_LVL_NORMAL;
+	UpdateGUIZoom();
 
 	NetworkStartUp(); // initialize network-core
 
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index e04c50ac3..8bf118e76 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -58,6 +58,7 @@ static const StringID _autosave_dropdown[] = {
 };
 
 static const StringID _gui_zoom_dropdown[] = {
+	STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_AUTO,
 	STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_NORMAL,
 	STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_2X_ZOOM,
 	STR_GAME_OPTIONS_GUI_ZOOM_DROPDOWN_4X_ZOOM,
@@ -65,6 +66,7 @@ static const StringID _gui_zoom_dropdown[] = {
 };
 
 static const StringID _font_zoom_dropdown[] = {
+	STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_AUTO,
 	STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_NORMAL,
 	STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_2X_ZOOM,
 	STR_GAME_OPTIONS_FONT_ZOOM_DROPDOWN_4X_ZOOM,
@@ -291,16 +293,16 @@ struct GameOptionsWindow : Window {
 				break;
 
 			case WID_GO_GUI_ZOOM_DROPDOWN: {
-				*selected_index = ZOOM_LVL_OUT_4X - _gui_zoom;
+				*selected_index = _gui_zoom_cfg != ZOOM_LVL_CFG_AUTO ? ZOOM_LVL_OUT_4X - _gui_zoom + 1 : 0;
 				const StringID *items = _gui_zoom_dropdown;
 				for (int i = 0; *items != INVALID_STRING_ID; items++, i++) {
-					list.emplace_back(new DropDownListStringItem(*items, i, _settings_client.gui.zoom_min > ZOOM_LVL_OUT_4X - i));
+					list.emplace_back(new DropDownListStringItem(*items, i, i != 0 && _settings_client.gui.zoom_min > ZOOM_LVL_OUT_4X - i + 1));
 				}
 				break;
 			}
 
 			case WID_GO_FONT_ZOOM_DROPDOWN: {
-				*selected_index = ZOOM_LVL_OUT_4X - _font_zoom;
+				*selected_index = _font_zoom_cfg != ZOOM_LVL_CFG_AUTO ? ZOOM_LVL_OUT_4X - _font_zoom + 1 : 0;
 				const StringID *items = _font_zoom_dropdown;
 				for (int i = 0; *items != INVALID_STRING_ID; items++, i++) {
 					list.emplace_back(new DropDownListStringItem(*items, i, false));
@@ -333,8 +335,8 @@ struct GameOptionsWindow : Window {
 			case WID_GO_AUTOSAVE_DROPDOWN:   SetDParam(0, _autosave_dropdown[_settings_client.gui.autosave]); break;
 			case WID_GO_LANG_DROPDOWN:       SetDParamStr(0, _current_language->own_name); break;
 			case WID_GO_RESOLUTION_DROPDOWN: SetDParam(0, GetCurRes() == _resolutions.size() ? STR_GAME_OPTIONS_RESOLUTION_OTHER : SPECSTR_RESOLUTION_START + GetCurRes()); break;
-			case WID_GO_GUI_ZOOM_DROPDOWN:   SetDParam(0, _gui_zoom_dropdown[ZOOM_LVL_OUT_4X - _gui_zoom]); break;
-			case WID_GO_FONT_ZOOM_DROPDOWN:  SetDParam(0, _font_zoom_dropdown[ZOOM_LVL_OUT_4X - _font_zoom]); break;
+			case WID_GO_GUI_ZOOM_DROPDOWN:   SetDParam(0, _gui_zoom_dropdown[_gui_zoom_cfg != ZOOM_LVL_CFG_AUTO ? ZOOM_LVL_OUT_4X - _gui_zoom_cfg + 1 : 0]); break;
+			case WID_GO_FONT_ZOOM_DROPDOWN:  SetDParam(0, _font_zoom_dropdown[_font_zoom_cfg != ZOOM_LVL_CFG_AUTO ? ZOOM_LVL_OUT_4X - _font_zoom_cfg + 1 : 0]); break;
 			case WID_GO_BASE_GRF_DROPDOWN:   SetDParamStr(0, BaseGraphics::GetUsedSet()->name.c_str()); break;
 			case WID_GO_BASE_GRF_STATUS:     SetDParam(0, BaseGraphics::GetUsedSet()->GetNumInvalid()); break;
 			case WID_GO_BASE_SFX_DROPDOWN:   SetDParamStr(0, BaseSounds::GetUsedSet()->name.c_str()); break;
@@ -538,7 +540,8 @@ struct GameOptionsWindow : Window {
 
 			case WID_GO_GUI_ZOOM_DROPDOWN:
 				GfxClearSpriteCache();
-				_gui_zoom = (ZoomLevel)(ZOOM_LVL_OUT_4X - index);
+				_gui_zoom_cfg = index > 0 ? ZOOM_LVL_OUT_4X - index + 1 : ZOOM_LVL_CFG_AUTO;
+				UpdateGUIZoom();
 				UpdateCursorSize();
 				UpdateAllVirtCoords();
 				FixTitleGameZoom();
@@ -547,7 +550,8 @@ struct GameOptionsWindow : Window {
 
 			case WID_GO_FONT_ZOOM_DROPDOWN:
 				GfxClearSpriteCache();
-				_font_zoom = (ZoomLevel)(ZOOM_LVL_OUT_4X - index);
+				_font_zoom_cfg = index > 0 ? ZOOM_LVL_OUT_4X - index + 1 : ZOOM_LVL_CFG_AUTO;
+				UpdateGUIZoom();
 				ClearFontCache();
 				LoadStringWidthTable();
 				UpdateAllVirtCoords();
diff --git a/src/table/misc_settings.ini b/src/table/misc_settings.ini
index be5088ec9..8cb6d4211 100644
--- a/src/table/misc_settings.ini
+++ b/src/table/misc_settings.ini
@@ -334,19 +334,19 @@ proc     = ZoomMinMaxChanged
 
 [SDTG_VAR]
 name     = ""gui_zoom""
-type     = SLE_UINT8
-var      = _gui_zoom
-def      = ZOOM_LVL_OUT_4X
-min      = ZOOM_LVL_MIN
+type     = SLE_INT8
+var      = _gui_zoom_cfg
+def      = ZOOM_LVL_CFG_AUTO
+min      = ZOOM_LVL_CFG_AUTO
 max      = ZOOM_LVL_OUT_4X
 cat      = SC_BASIC
 
 [SDTG_VAR]
 name     = ""font_zoom""
-type     = SLE_UINT8
-var      = _font_zoom
-def      = ZOOM_LVL_OUT_4X
-min      = ZOOM_LVL_MIN
+type     = SLE_INT8
+var      = _font_zoom_cfg
+def      = ZOOM_LVL_CFG_AUTO
+min      = ZOOM_LVL_CFG_AUTO
 max      = ZOOM_LVL_OUT_4X
 cat      = SC_BASIC
 
diff --git a/src/video/video_driver.hpp b/src/video/video_driver.hpp
index d4e750134..bc445d92d 100644
--- a/src/video/video_driver.hpp
+++ b/src/video/video_driver.hpp
@@ -13,6 +13,7 @@
 #include "../driver.h"
 #include "../core/geometry_type.hpp"
 #include "../core/math_func.hpp"
+#include "../zoom_type.h"
 #include <vector>
 
 extern std::string _ini_videodriver;
@@ -106,6 +107,18 @@ public:
 	virtual void EditBoxGainedFocus() {}
 
 	/**
+	 * Get a suggested default GUI zoom taking screen DPI into account.
+	 */
+	virtual ZoomLevel GetSuggestedUIZoom()
+	{
+		float dpi_scale = this->GetDPIScale();
+
+		if (dpi_scale >= 3.0f) return ZOOM_LVL_NORMAL;
+		if (dpi_scale >= 1.5f) return ZOOM_LVL_OUT_2X;
+		return ZOOM_LVL_OUT_4X;
+	}
+
+	/**
 	 * Get the currently active instance of the video driver.
 	 */
 	static VideoDriver *GetInstance() {
@@ -113,12 +126,18 @@ public:
 	}
 
 protected:
-	/*
+	/**
 	 * Get the resolution of the main screen.
 	 */
 	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.
 	 */
 	void UpdateAutoResolution()
diff --git a/src/zoom_type.h b/src/zoom_type.h
index 2606e0767..0945e1cc0 100644
--- a/src/zoom_type.h
+++ b/src/zoom_type.h
@@ -15,6 +15,8 @@
 static uint const ZOOM_LVL_SHIFT = 2;
 static uint const ZOOM_LVL_BASE  = 1 << ZOOM_LVL_SHIFT;
 
+static const int8 ZOOM_LVL_CFG_AUTO = -1;
+
 /** All zoom levels we know. */
 enum ZoomLevel : byte {
 	/* Our possible zoom-levels */
@@ -48,6 +50,9 @@ enum ZoomLevel : byte {
 };
 DECLARE_POSTFIX_INCREMENT(ZoomLevel)
 
+extern int8 _gui_zoom_cfg;
+extern int8 _font_zoom_cfg;
+
 extern ZoomLevel _gui_zoom;
 extern ZoomLevel _font_zoom;
 #define ZOOM_LVL_GUI (_gui_zoom)