Fix #9993: Handle DPI changes on macOS and Windows

os/windows/openttd.manifest

@@ -10,6 +10,7 @@
   <application xmlns="urn:schemas-microsoft-com:asm.v3">
     <windowsSettings>
       <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">True/PM</dpiAware>
+      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2,PerMonitor</dpiAwareness>
     </windowsSettings>
   </application>
   <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">

src/gfx.cpp

@@ -17,10 +17,12 @@
 #include "settings_type.h"
 #include "network/network.h"
 #include "network/network_func.h"
+#include "window_gui.h"
 #include "window_func.h"
 #include "newgrf_debug.h"
 #include "thread.h"
 #include "core/backup_type.hpp"
+#include "viewport_func.h"
 
 #include "table/palettes.h"
 #include "table/string_colours.h"
@@ -2042,6 +2044,38 @@ void UpdateGUIZoom()
 	}
 }
 
+/**
+ * Resolve GUI zoom level and adjust GUI to new zoom, if auto-suggestion is requested.
+ * @returns true when the zoom level has changed, caller must call ReInitAllWindows(true)
+ * after resizing the application's window/buffer.
+ */
+bool AdjustGUIZoom()
+{
+	auto old_zoom = _gui_zoom;
+	UpdateGUIZoom();
+	if (old_zoom == _gui_zoom) return false;
+	GfxClearSpriteCache();
+	VideoDriver::GetInstance()->ClearSystemSprites();
+	ClearFontCache();
+	GfxClearSpriteCache();
+	UpdateAllVirtCoords();
+
+	/* Adjust all window sizes to match the new zoom level, so that they don't appear
+	   to move around when the application is moved to a screen with different DPI. */
+	auto zoom_shift = old_zoom - _gui_zoom;
+	for (Window *w : Window::Iterate()) {
+		w->left = AdjustByZoom(w->left, zoom_shift);
+		w->top = AdjustByZoom(w->top, zoom_shift);
+		w->width = AdjustByZoom(w->width, zoom_shift);
+		w->height = AdjustByZoom(w->height, zoom_shift);
+		if (w->viewport != nullptr) {
+			w->viewport->zoom = Clamp(ZoomLevel(w->viewport->zoom - zoom_shift), _settings_client.gui.zoom_min, _settings_client.gui.zoom_max);
+		}
+	}
+
+	return true;
+}
+
 void ChangeGameSpeed(bool enable_fast_forward)
 {
 	if (enable_fast_forward) {

src/gfx_func.h

@@ -80,6 +80,7 @@ void DrawMouseCursor();
 void ScreenSizeChanged();
 void GameSizeChanged();
 void UpdateGUIZoom();
+bool AdjustGUIZoom();
 void UndrawMouseCursor();
 
 /** Size of the buffer used for drawing strings. */

src/video/cocoa/cocoa_wnd.mm

@@ -1269,8 +1269,12 @@ void CocoaDialog(const char *title, const char *message, const char *buttonLabel
 /** Screen the window is on changed. */
 - (void)windowDidChangeBackingProperties:(NSNotification *)notification
 {
+	bool did_adjust = AdjustGUIZoom();
+
 	/* Reallocate screen buffer if necessary. */
 	driver->AllocateBackingStore();
+
+	if (did_adjust) ReInitAllWindows(true);
 }
 
 /** Presentation options to use for full screen mode. */

src/video/win32_v.cpp

@@ -38,6 +38,10 @@
 #define PM_QS_INPUT 0x20000
 #endif
 
+#ifndef WM_DPICHANGED
+#define WM_DPICHANGED 0x02E0
+#endif
+
 bool _window_maximize;
 static Dimension _bck_resolution;
 DWORD _imm_props;
@@ -670,6 +674,24 @@ LRESULT CALLBACK WndProcGdi(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 			return TRUE;
 		}
 
+		case WM_DPICHANGED: {
+			auto did_adjust = AdjustGUIZoom();
+
+			/* Resize the window to match the new DPI setting. */
+			RECT *prcNewWindow = (RECT *)lParam;
+			SetWindowPos(hwnd,
+				NULL,
+				prcNewWindow->left,
+				prcNewWindow->top,
+				prcNewWindow->right - prcNewWindow->left,
+				prcNewWindow->bottom - prcNewWindow->top,
+				SWP_NOZORDER | SWP_NOACTIVATE);
+
+			if (did_adjust) ReInitAllWindows(true);
+
+			return 0;
+		}
+
 /* needed for wheel */
 #if !defined(WM_MOUSEWHEEL)
 # define WM_MOUSEWHEEL 0x020A

src/window.cpp

@@ -3343,6 +3343,13 @@ void HideVitalWindows()
 	CloseWindowById(WC_STATUS_BAR, 0);
 }
 
+void ReInitWindow(Window *w, bool zoom_changed)
+{
+	if (w == nullptr) return;
+	if (zoom_changed) w->nested_root->AdjustPaddingForZoom();
+	w->ReInit();
+}
+
 /** Re-initialize all windows. */
 void ReInitAllWindows(bool zoom_changed)
 {
@@ -3352,9 +3359,13 @@ void ReInitAllWindows(bool zoom_changed)
 	extern void InitDepotWindowBlockSizes();
 	InitDepotWindowBlockSizes();
 
+	/* When _gui_zoom has changed, we need to resize toolbar and statusbar first,
+	 * so EnsureVisibleCaption uses the updated size information. */
+	ReInitWindow(FindWindowById(WC_MAIN_TOOLBAR, 0), zoom_changed);
+	ReInitWindow(FindWindowById(WC_STATUS_BAR, 0), zoom_changed);
 	for (Window *w : Window::Iterate()) {
-		if (zoom_changed) w->nested_root->AdjustPaddingForZoom();
-		w->ReInit();
+		if (w->window_class == WC_MAIN_TOOLBAR || w->window_class == WC_STATUS_BAR) continue;
+		ReInitWindow(w, zoom_changed);
 	}
 
 	void NetworkReInitChatBoxSize();

src/zoom_func.h

@@ -36,6 +36,17 @@ static inline int UnScaleByZoom(int value, ZoomLevel zoom)
 	return (value + (1 << zoom) - 1) >> zoom;
 }
 
+/**
+ * Adjust by zoom level; zoom < 0 shifts right, zoom >= 0 shifts left
+ * @param value value to shift
+ * @param zoom zoom level to shift to
+ * @return shifted value
+ */
+static inline int AdjustByZoom(int value, int zoom)
+{
+	return zoom < 0 ? UnScaleByZoom(value, ZoomLevel(-zoom)) : ScaleByZoom(value, ZoomLevel(zoom));
+}
+
 /**
  * Scale by zoom level, usually shift left (when zoom > ZOOM_LVL_NORMAL)
  * @param value value to shift