Index: binaries/data/mods/mod/gui/common/functions_msgbox.js
===================================================================
--- binaries/data/mods/mod/gui/common/functions_msgbox.js
+++ binaries/data/mods/mod/gui/common/functions_msgbox.js
@@ -15,6 +15,24 @@
 		});
 }
 
+function timedConfirmation(mbWidth, mbHeight, mbMessage, mbTimeout, mbTitle, mbButtonCaptions, mbBtnCode, mbCallbackArgs)
+{
+	Engine.PushGuiPage(
+		"page_timedconfirmation.xml",
+		{
+			"width": mbWidth,
+			"height": mbHeight,
+			"message": mbMessage,
+			"timeout": mbTimeout,
+			"title": mbTitle,
+			"buttonCaptions": mbButtonCaptions
+		},
+		btnCode => {
+			if (mbBtnCode !== undefined && mbBtnCode[btnCode])
+				mbBtnCode[btnCode](mbCallbackArgs ? mbCallbackArgs[btnCode] : undefined);
+		});
+}
+
 function openURL(url)
 {
 	Engine.OpenURL(url);
Index: binaries/data/mods/mod/gui/msgbox/msgbox.js
===================================================================
--- binaries/data/mods/mod/gui/msgbox/msgbox.js
+++ binaries/data/mods/mod/gui/msgbox/msgbox.js
@@ -24,37 +24,7 @@
 
 	let captions = data.buttonCaptions || [translate("OK")];
 
-	// Set button captions and visibility
 	let mbButton = [];
-	captions.forEach((caption, i) => {
-		mbButton[i] = Engine.GetGUIObjectByName("mbButton" + (i + 1));
-		mbButton[i].caption = caption;
-		mbButton[i].hidden = false;
-		mbButton[i].onPress = () => {
-			Engine.PopGuiPage(i);
-		};
-
-		// Convention: Cancel is the first button
-		if (i == 0)
-			mbCancelHotkey.onPress = mbButton[i].onPress;
-	});
-
-	// Distribute buttons horizontally
-	let y1 = "100%-46";
-	let y2 = "100%-18";
-	switch (captions.length)
-	{
-	case 1:
-		mbButton[0].size = "18 " + y1 + " 100%-18 " + y2;
-		break;
-	case 2:
-		mbButton[0].size = "18 " + y1 + " 50%-5 " + y2;
-		mbButton[1].size = "50%+5 " + y1 + " 100%-18 " + y2;
-		break;
-	case 3:
-		mbButton[0].size = "18 " + y1 + " 33%-5 " + y2;
-		mbButton[1].size = "33%+5 " + y1 + " 66%-5 " + y2;
-		mbButton[2].size = "66%+5 " + y1 + " 100%-18 " + y2;
-		break;
-	}
+	setButtonCaptionsAndVisibitily(mbButton, captions, mbCancelHotkey, "mbButton");
+	distributeButtonsHorizontally(mbButton, captions);
 }
Index: binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.js
===================================================================
--- /dev/null
+++ binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.js
@@ -0,0 +1,46 @@
+/**
+ * Currently limited to at most 3 buttons per message box.
+ * The convention is to have "cancel" appear first.
+ */
+function init(data)
+{
+	Engine.GetGUIObjectByName("tmcTitleBar").caption = data.title;
+
+	const textObj = Engine.GetGUIObjectByName("tmcText");
+	textObj.caption = data.message;
+
+	updateDisplayedTimer(data.timeout);
+
+	Engine.GetGUIObjectByName("tmcTimer").caption = data.timeout;
+	if (data.font)
+		textObj.font = data.font;
+
+	const cancelHotkey = Engine.GetGUIObjectByName("tmcCancelHotkey");
+	cancelHotkey.onPress = Engine.PopGuiPage;
+
+	const lRDiff = data.width / 2;
+	const uDDiff = data.height / 2;
+	Engine.GetGUIObjectByName("tmcMain").size = "50%-" + lRDiff + " 50%-" + uDDiff + " 50%+" + lRDiff + " 50%+" + uDDiff;
+
+	const captions = data.buttonCaptions || [translate("OK")];
+
+	// Set button captions and visibility
+	let button = [];
+	setButtonCaptionsAndVisibitily(button, captions, cancelHotkey, "tmcButton");
+	distributeButtonsHorizontally(button, captions);
+}
+
+function onTick() {
+	const timerObj = Engine.GetGUIObjectByName("tmcTimer");
+	let time = +timerObj.caption;
+	--time;
+	if (time < 1)
+		Engine.GetGUIObjectByName("tmcButton1").onPress();
+
+	timerObj.caption = time;
+	updateDisplayedTimer(time);
+}
+
+function updateDisplayedTimer(time) {
+	Engine.GetGUIObjectByName("tmcTimerDisplay").caption = Math.ceil(time / 100);
+}
Index: binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.xml
===================================================================
--- /dev/null
+++ binaries/data/mods/mod/gui/timedconfirmation/timedconfirmation.xml
@@ -0,0 +1,56 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<objects>
+
+	<script directory="gui/common/"/>
+	<script directory="gui/timedconfirmation/"/>
+
+	<!-- Fade out the background because it's non-interactable -->
+	<object sprite="ModernFade" type="image"/>
+	<object name="tmcCancelHotkey" hotkey="cancel" />
+	<object name="tmcMain"
+			style="ModernDialog"
+			type="image"
+	>
+		<action on="Tick">
+			onTick();
+		</action>
+	<object name="tmcTitleBar"
+			style="ModernLabelText"
+			type="text"
+			size="50%-128 -18 50%+128 14"
+	/>
+	<object name="tmcTimerDisplay"
+			type="text"
+			style="ModernLabelText"
+			size="18 28 100%-18 38"
+	/>
+	<object name="tmcText"
+			type="text"
+			style="ModernLabelText"
+			size="18 40 100%-18 100%-64"
+	/>
+	<object name="tmcTimer"
+			type="text"
+			style="ModernLabelText"
+			size="18 18 100%-18 100%-64"
+			hidden="true"
+	/>
+	<!-- The size of the following buttons is set dynamically in timedconfirmation.js -->
+	<object name="tmcButton1"
+			style="ModernButtonRed"
+			type="button"
+			hidden="true"
+	/>
+	<object name="tmcButton2"
+			style="ModernButtonRed"
+			type="button"
+			hidden="true"
+	/>
+	<object name="tmcButton3"
+			style="ModernButtonRed"
+			type="button"
+			hidden="true"
+	/>
+	</object>
+</objects>
Index: binaries/data/mods/public/gui/options/options.js
===================================================================
--- binaries/data/mods/public/gui/options/options.js
+++ binaries/data/mods/public/gui/options/options.js
@@ -146,6 +146,35 @@
 			};
 		}
 	},
+	"dropdownNumber":
+	{
+		"configToValue": value => +value,
+		"valueToGui": (value, control) => {
+			control.selected = control.list_data.indexOf(""+value);
+		},
+		"guiToValue": control => +control.list_data[control.selected],
+		"guiSetter": "onSelectionChange",
+		"initGUI": (option, control) => {
+			control.list = option.list.map(e => e.label);
+			control.list_data = option.list.map(e => e.value);
+			control.onHoverChange = () => {
+				let item = option.list[control.hovered];
+				control.tooltip = item && item.tooltip || option.tooltip;
+			};
+		},
+		"timeout": (option, oldValue, hasChanges, newValue) => {
+			if (!option.timeout)
+				return;
+			timedConfirmation(
+				500, 200,
+				translate("Do you want to keep changes?"),
+				500,
+				translate("Warning"),
+				[translate("No"), translate("Yes")],
+				[() => {this.revertChange(option, +oldValue, hasChanges);}, null]
+			);
+		}
+	},
 	"slider":
 	{
 		"configToValue": value => +value,
@@ -242,14 +271,20 @@
 			if (optionType.sanitizeValue)
 				optionType.sanitizeValue(value, control, option);
 
+			let oldValue = optionType.configToValue(Engine.ConfigDB_GetValue("user", option.config));
+
 			control.tooltip = option.tooltip + (optionType.tooltip ? "\n" + optionType.tooltip(value, option) : "");
 
+			let hasChanges = Engine.ConfigDB_HasChanges("user");
 			Engine.ConfigDB_CreateValue("user", option.config, String(value));
 			Engine.ConfigDB_SetChanges("user", true);
 
 			g_ChangedKeys.add(option.config);
 			fireConfigChangeHandlers(new Set([option.config]));
 
+			if (option.timeout)
+				optionType.timeout(option, oldValue, hasChanges, value);
+
 			if (option.function)
 				Engine[option.function](value);
 
@@ -315,6 +350,18 @@
 	revertChanges();
 }
 
+function revertChange(option, oldValue, hadChanges)
+{
+	if (!hadChanges)
+		Engine.ConfigDB_SetChanges("user", false);
+
+	Engine.ConfigDB_CreateValue("user", option.config, String(oldValue));
+	if (option.function)
+		Engine[option.function](oldValue);
+
+	displayOptions();
+}
+
 function revertChanges()
 {
 	Engine.ConfigDB_Reload("user");
Index: binaries/data/mods/public/gui/options/options.json
===================================================================
--- binaries/data/mods/public/gui/options/options.json
+++ binaries/data/mods/public/gui/options/options.json
@@ -149,6 +149,24 @@
 				"config": "adaptivefps.session",
 				"min": 20,
 				"max": 100
+			},
+			{
+				"type": "dropdownNumber",
+				"label": "GUI scale",
+				"timeout": 500,
+				"tooltip": "GUI scale",
+				"config": "gui.scale",
+				"function": "SetGUIScale",
+				"list": [
+					{ "value": 0.75, "label": "75%" },
+					{ "value": 1.00, "label": "100%" },
+					{ "value": 1.25, "label": "125%" },
+					{ "value": 1.50, "label": "150%" },
+					{ "value": 1.75, "label": "175%" },
+					{ "value": 2.00, "label": "200%" },
+					{ "value": 2.25, "label": "225%" },
+					{ "value": 2.50, "label": "250%" }
+				]
 			}
 		]
 	},
Index: binaries/data/mods/public/gui/options/options.xml
===================================================================
--- binaries/data/mods/public/gui/options/options.xml
+++ binaries/data/mods/public/gui/options/options.xml
@@ -33,6 +33,7 @@
 					</object>
 					<object name="option_control_number[n]" size="65% 0 100%-8 100%" type="input" style="ModernInput"/>
 					<object name="option_control_dropdown[n]" size="65% 0 100%-8 100%" type="dropdown" style="ModernDropDown" tooltip_style="tooltipInstant"/>
+					<object name="option_control_dropdownNumber[n]" size="65% 0 100%-8 100%" type="dropdown" style="ModernDropDown" tooltip_style="tooltipInstant"/>
 					<object name="option_control_slider[n]" size="65% 0 100%-8 100%" type="slider" style="ModernSlider"/>
 				</object>
 			</repeat>
Index: source/gui/CGUI.cpp
===================================================================
--- source/gui/CGUI.cpp
+++ source/gui/CGUI.cpp
@@ -42,6 +42,7 @@
 #include "ps/Hotkey.h"
 #include "ps/Profile.h"
 #include "ps/Pyrogenesis.h"
+#include "ps/VideoMode.h"
 #include "ps/XML/Xeromyces.h"
 #include "scriptinterface/ScriptContext.h"
 #include "scriptinterface/ScriptInterface.h"
@@ -154,7 +155,7 @@
 		// Yes the mouse position is stored as float to avoid
 		//  constant conversions when operating in a
 		//  float-based environment.
-		m_MousePos = CVector2D((float)ev->ev.motion.x / g_GuiScale, (float)ev->ev.motion.y / g_GuiScale);
+		m_MousePos = CVector2D((float)ev->ev.motion.x / g_VideoMode.GetScale(), (float)ev->ev.motion.y / g_VideoMode.GetScale());
 
 		SGUIMessage msg(GUIM_MOUSE_MOTION);
 		m_BaseObject->RecurseObject(&IGUIObject::IsHiddenOrGhost, &IGUIObject::HandleMessage, msg);
@@ -179,7 +180,7 @@
 	CVector2D oldMousePos = m_MousePos;
 	if (ev->ev.type == SDL_MOUSEBUTTONDOWN || ev->ev.type == SDL_MOUSEBUTTONUP)
 	{
-		m_MousePos = CVector2D((float)ev->ev.button.x / g_GuiScale, (float)ev->ev.button.y / g_GuiScale);
+		m_MousePos = CVector2D((float)ev->ev.button.x / g_VideoMode.GetScale(), (float)ev->ev.button.y / g_VideoMode.GetScale());
 	}
 
 	// Allow the focused object to pre-empt regular GUI events.
@@ -420,7 +421,7 @@
 
 CSize2D CGUI::GetWindowSize() const
 {
-	return CSize2D{static_cast<float>(g_xres) / g_GuiScale, static_cast<float>(g_yres) / g_GuiScale};
+	return CSize2D{static_cast<float>(g_xres) / g_VideoMode.GetScale(), static_cast<float>(g_yres) / g_VideoMode.GetScale() };
 }
 
 void CGUI::SetFocusedObject(IGUIObject* pObject)
Index: source/gui/CGUIText.cpp
===================================================================
--- source/gui/CGUIText.cpp
+++ source/gui/CGUIText.cpp
@@ -26,12 +26,12 @@
 #include "gui/ObjectBases/IGUIObject.h"
 #include "gui/SettingTypes/CGUIString.h"
 #include "ps/CStrInternStatic.h"
+#include "ps/VideoMode.h"
 #include "renderer/Renderer.h"
 
 #include <math.h>
 
 extern int g_xres, g_yres;
-extern float g_GuiScale;
 
 // TODO Gee: CRect => CPoint ?
 void SGenerateTextImage::SetupSpriteCall(
@@ -439,12 +439,13 @@
 		clipping.left = std::ceil(clipping.left);
 		clipping.right = std::floor(clipping.right);
 
+		float scale = g_VideoMode.GetScale();
 		glEnable(GL_SCISSOR_TEST);
 		glScissor(
-			std::ceil(clipping.left * g_GuiScale),
-			std::ceil(g_yres - clipping.bottom * g_GuiScale),
-			std::floor(clipping.GetWidth() * g_GuiScale),
-			std::floor(clipping.GetHeight() * g_GuiScale));
+			std::ceil(clipping.left * scale),
+			std::ceil(g_yres - clipping.bottom * scale),
+			std::floor(clipping.GetWidth() * scale),
+			std::floor(clipping.GetHeight() * scale));
 	}
 
 	CTextRenderer textRenderer;
Index: source/gui/GUIMatrix.cpp
===================================================================
--- source/gui/GUIMatrix.cpp
+++ source/gui/GUIMatrix.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2019 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -18,16 +18,15 @@
 #include "precompiled.h"
 
 #include "GUIMatrix.h"
-
+#include "ps/VideoMode.h"
 #include "maths/Matrix3D.h"
 
 extern int g_xres, g_yres;
-extern float g_GuiScale;
 
 CMatrix3D GetDefaultGuiMatrix()
 {
-	float xres = g_xres / g_GuiScale;
-	float yres = g_yres / g_GuiScale;
+	float xres = g_xres / g_VideoMode.GetScale();
+	float yres = g_yres / g_VideoMode.GetScale();
 
 	CMatrix3D m;
 	m.SetIdentity();
Index: source/gui/ObjectTypes/CInput.cpp
===================================================================
--- source/gui/ObjectTypes/CInput.cpp
+++ source/gui/ObjectTypes/CInput.cpp
@@ -31,6 +31,7 @@
 #include "ps/GameSetup/Config.h"
 #include "ps/Globals.h"
 #include "ps/Hotkey.h"
+#include "ps/VideoMode.h"
 #include "renderer/Renderer.h"
 
 #include <sstream>
@@ -1238,12 +1239,13 @@
 
 	if (cliparea != CRect())
 	{
+		float scale = g_VideoMode.GetScale();
 		glEnable(GL_SCISSOR_TEST);
 		glScissor(
-			cliparea.left * g_GuiScale,
-			g_yres - cliparea.bottom * g_GuiScale,
-			cliparea.GetWidth() * g_GuiScale,
-			cliparea.GetHeight() * g_GuiScale);
+			cliparea.left * scale,
+			g_yres - cliparea.bottom * scale,
+			cliparea.GetWidth() * scale,
+			cliparea.GetHeight() * scale);
 	}
 
 	// These are useful later.
Index: source/ps/CConsole.cpp
===================================================================
--- source/ps/CConsole.cpp
+++ source/ps/CConsole.cpp
@@ -45,6 +45,7 @@
 #include "ps/Hotkey.h"
 #include "ps/Profile.h"
 #include "ps/Pyrogenesis.h"
+#include "ps/VideoMode.h"
 #include "scriptinterface/ScriptInterface.h"
 #include "scriptinterface/JSON.h"
 
@@ -116,8 +117,8 @@
 	m_fX = 0;
 	m_fY = 0;
 	float height = h * 0.6f;
-	m_fWidth = w / g_GuiScale;
-	m_fHeight = height / g_GuiScale;
+	m_fWidth = w / g_VideoMode.GetScale();
+	m_fHeight = height / g_VideoMode.GetScale();
 }
 
 void CConsole::ToggleVisible()
Index: source/ps/GameSetup/Config.h
===================================================================
--- source/ps/GameSetup/Config.h
+++ source/ps/GameSetup/Config.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2020 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -24,7 +24,6 @@
 extern bool g_PauseOnFocusLoss;
 
 extern int g_xres, g_yres;
-extern float g_GuiScale;
 
 extern bool g_Quickstart;
 extern bool g_DisableAudio;
Index: source/ps/GameSetup/Config.cpp
===================================================================
--- source/ps/GameSetup/Config.cpp
+++ source/ps/GameSetup/Config.cpp
@@ -34,7 +34,6 @@
 bool g_PauseOnFocusLoss = false;
 
 int g_xres, g_yres;
-float g_GuiScale = 1.0f;
 
 bool g_Quickstart = false;
 bool g_DisableAudio = false;
@@ -47,11 +46,8 @@
 static void LoadGlobals()
 {
 	CFG_GET_VAL("pauseonfocusloss", g_PauseOnFocusLoss);
-
-	CFG_GET_VAL("gui.scale", g_GuiScale);
 }
 
-
 static void ProcessCommandLineArgs(const CmdLineArgs& args)
 {
 	// TODO: all these options (and the ones processed elsewhere) should
Index: source/ps/GameSetup/GameSetup.cpp
===================================================================
--- source/ps/GameSetup/GameSetup.cpp
+++ source/ps/GameSetup/GameSetup.cpp
@@ -291,7 +291,7 @@
 		CStrW cursorName = g_CursorName;
 		if (cursorName.empty())
 		{
-			cursor_draw(g_VFS, NULL, g_mouse_x, g_yres-g_mouse_y, g_GuiScale, false);
+			cursor_draw(g_VFS, NULL, g_mouse_x, g_yres-g_mouse_y, g_VideoMode.GetScale(), false);
 		}
 		else
 		{
@@ -316,7 +316,7 @@
 #if OS_ANDROID
 #warning TODO: cursors for Android
 #else
-			if (cursor_draw(g_VFS, cursorName.c_str(), g_mouse_x, g_yres-g_mouse_y, g_GuiScale, forceGL) < 0)
+			if (cursor_draw(g_VFS, cursorName.c_str(), g_mouse_x, g_yres-g_mouse_y, g_VideoMode.GetScale(), forceGL) < 0)
 				LOGWARNING("Failed to draw cursor '%s'", utf8_from_wstring(cursorName));
 #endif
 
Index: source/ps/VideoMode.h
===================================================================
--- source/ps/VideoMode.h
+++ source/ps/VideoMode.h
@@ -47,6 +47,11 @@
 	bool ResizeWindow(int w, int h);
 
 	/**
+	 * Tell dependent compoenent to recompute sizes because scaling have changed.
+	 */
+	void Rescale(float scale);
+
+	/**
 	 * Switch to fullscreen or windowed mode.
 	 */
 	bool SetFullscreen(bool fullscreen);
@@ -84,6 +89,8 @@
 	int GetDesktopBPP() const;
 	int GetDesktopFreq() const;
 
+	float GetScale() const;
+
 	SDL_Window* GetWindow();
 
 	void SetWindowIcon();
@@ -109,6 +116,8 @@
 	int m_PreferredBPP = 0;
 	int m_PreferredFreq = 0;
 
+	float m_Scale = 1.0f;
+
 	// Config file settings (0 if unspecified)
 	int m_ConfigW = 0;
 	int m_ConfigH = 0;
Index: source/ps/VideoMode.cpp
===================================================================
--- source/ps/VideoMode.cpp
+++ source/ps/VideoMode.cpp
@@ -70,6 +70,8 @@
 	CFG_GET_VAL("windowed", windowed);
 	m_ConfigFullscreen = !windowed;
 
+	CFG_GET_VAL("gui.scale", m_Scale);
+
 	CFG_GET_VAL("xres", m_ConfigW);
 	CFG_GET_VAL("yres", m_ConfigH);
 	CFG_GET_VAL("bpp", m_ConfigBPP);
@@ -359,6 +361,18 @@
 	return true;
 }
 
+void CVideoMode::Rescale(float scale)
+{
+	ENSURE(m_IsInitialised);
+	m_Scale = scale;
+	UpdateRenderer(m_CurrentW, m_CurrentH);
+}
+
+float CVideoMode::GetScale() const
+{
+	return m_Scale;
+}
+
 bool CVideoMode::SetFullscreen(bool fullscreen)
 {
 	// This might get called before initialisation by psDisplayError;
Index: source/ps/scripting/JSInterface_ConfigDB.cpp
===================================================================
--- source/ps/scripting/JSInterface_ConfigDB.cpp
+++ source/ps/scripting/JSInterface_ConfigDB.cpp
@@ -21,6 +21,7 @@
 
 #include "ps/ConfigDB.h"
 #include "ps/CLogger.h"
+#include "ps/VideoMode.h"
 #include "scriptinterface/FunctionWrapper.h"
 #include "scriptinterface/ScriptRequest.h"
 
@@ -188,6 +189,11 @@
 	return true;
 }
 
+void SetGUIScale(float scale)
+{
+	g_VideoMode.Rescale(scale);
+}
+
 void RegisterScriptFunctions(const ScriptRequest& rq)
 {
 	ScriptFunction::Register<&HasChanges>(rq, "ConfigDB_HasChanges");
@@ -201,5 +207,6 @@
 	ScriptFunction::Register<&CreateAndWriteValueToFile>(rq, "ConfigDB_CreateAndWriteValueToFile");
 	ScriptFunction::Register<&SetFile>(rq, "ConfigDB_SetFile");
 	ScriptFunction::Register<&Reload>(rq, "ConfigDB_Reload");
+	ScriptFunction::Register<&SetGUIScale>(rq, "SetGUIScale");
 }
 }