diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -167,7 +167,7 @@ struct AIListWindow : public Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) {
 			ResizeButtons(this, AIL_WIDGET_ACCEPT, AIL_WIDGET_CANCEL);
@@ -365,7 +365,7 @@ struct AISettingsWindow : public Window 
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) {
 			ResizeButtons(this, AIS_WIDGET_ACCEPT, AIS_WIDGET_RESET);
@@ -588,7 +588,7 @@ struct AIConfigWindow : public Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 14;
 		this->widget[AIC_WIDGET_LIST].data = (this->vscroll.cap << 8) + 1;
@@ -777,7 +777,7 @@ struct AIDebugWindow : public Window {
 		if (data == -1 || ai_debug_company == data) this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 	}
diff --git a/src/autoreplace_gui.cpp b/src/autoreplace_gui.cpp
--- a/src/autoreplace_gui.cpp
+++ b/src/autoreplace_gui.cpp
@@ -402,7 +402,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta) {
+	virtual void OnResize(Point delta) {
 		this->vscroll.cap  += delta.y / (int)this->resize.step_height;
 		this->vscroll2.cap += delta.y / (int)this->resize.step_height;
 
diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -223,7 +223,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 		this->widget[BBSW_BRIDGE_LIST].data = (this->vscroll.cap << 8) + 1;
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -1099,7 +1099,7 @@ struct BuildVehicleWindow : Window {
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0 && !this->listview_mode) {
 			ResizeButtons(this, BUILD_VEHICLE_WIDGET_BUILD, BUILD_VEHICLE_WIDGET_RENAME);
diff --git a/src/depot_gui.cpp b/src/depot_gui.cpp
--- a/src/depot_gui.cpp
+++ b/src/depot_gui.cpp
@@ -1003,7 +1003,7 @@ struct DepotWindow : Window {
 		_cursor.vehchain = false;
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 		this->hscroll.cap += delta.x / (int)this->resize.step_width;
diff --git a/src/group_gui.cpp b/src/group_gui.cpp
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -670,7 +670,7 @@ public:
 		DoCommandP(0, this->group_sel, 0, CMD_RENAME_GROUP | CMD_MSG(STR_GROUP_CAN_T_RENAME), NULL, str);
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll2.cap += delta.y / PLY_WND_PRC__SIZE_OF_ROW_TINY;
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
diff --git a/src/industry_gui.cpp b/src/industry_gui.cpp
--- a/src/industry_gui.cpp
+++ b/src/industry_gui.cpp
@@ -352,7 +352,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		/* Adjust the number of items in the matrix depending of the rezise */
 		this->vscroll.cap  += delta.y / (int)this->resize.step_height;
@@ -643,7 +643,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->viewport->width            += delta.x;
 		this->viewport->height           += delta.y;
@@ -1008,7 +1008,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 10;
 	}
diff --git a/src/misc_gui.cpp b/src/misc_gui.cpp
--- a/src/misc_gui.cpp
+++ b/src/misc_gui.cpp
@@ -1727,7 +1727,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		/* Widget 2 and 3 have to go with halve speed, make it so obiwan */
 		uint diff = delta.x / 2;
diff --git a/src/network/network_content_gui.cpp b/src/network/network_content_gui.cpp
--- a/src/network/network_content_gui.cpp
+++ b/src/network/network_content_gui.cpp
@@ -674,7 +674,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -722,7 +722,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -684,7 +684,7 @@ struct NewGRFWindow : public Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) {
 			ResizeButtons(this, SNGRFS_ADD, SNGRFS_MOVE_DOWN);
diff --git a/src/news_gui.cpp b/src/news_gui.cpp
--- a/src/news_gui.cpp
+++ b/src/news_gui.cpp
@@ -767,7 +767,7 @@ struct MessageHistoryWindow : Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 12;
 	}
diff --git a/src/order_gui.cpp b/src/order_gui.cpp
--- a/src/order_gui.cpp
+++ b/src/order_gui.cpp
@@ -1125,7 +1125,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		/* Update the scroll + matrix */
 		this->vscroll.cap = (this->widget[ORDER_WIDGET_ORDER_LIST].bottom - this->widget[ORDER_WIDGET_ORDER_LIST].top) / 10;
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -1501,7 +1501,7 @@ struct GameSettingsWindow : Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / SETTING_HEIGHT;
 		SetVScrollCount(this, _settings_main_page.Length());
diff --git a/src/signs_gui.cpp b/src/signs_gui.cpp
--- a/src/signs_gui.cpp
+++ b/src/signs_gui.cpp
@@ -136,7 +136,7 @@ struct SignListWindow : Window, SignList
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 10;
 	}
diff --git a/src/smallmap_gui.cpp b/src/smallmap_gui.cpp
--- a/src/smallmap_gui.cpp
+++ b/src/smallmap_gui.cpp
@@ -1046,7 +1046,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0 && this->map_type == SMT_INDUSTRY) this->ResizeLegend();
 	}
@@ -1166,7 +1166,7 @@ public:
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->viewport->width          += delta.x;
 		this->viewport->height         += delta.y;
diff --git a/src/station_gui.cpp b/src/station_gui.cpp
--- a/src/station_gui.cpp
+++ b/src/station_gui.cpp
@@ -546,7 +546,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 10;
 	}
@@ -975,7 +975,7 @@ struct StationViewWindow : public Window
 		DoCommandP(0, this->window_number, 0, CMD_RENAME_STATION | CMD_MSG(STR_3031_CAN_T_RENAME_STATION), NULL, str);
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) ResizeButtons(this, SVW_LOCATION, SVW_RENAME);
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
@@ -1187,7 +1187,7 @@ struct SelectStationWindow : Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap = (this->widget[JSW_PANEL].bottom - this->widget[JSW_PANEL].top) / 10;
 	}
diff --git a/src/timetable_gui.cpp b/src/timetable_gui.cpp
--- a/src/timetable_gui.cpp
+++ b/src/timetable_gui.cpp
@@ -325,7 +325,7 @@ struct TimetableWindow : Window {
 		DoCommandP(0, p1, p2, CMD_CHANGE_TIMETABLE | CMD_MSG(STR_CAN_T_TIMETABLE_VEHICLE));
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		/* Update the scroll + matrix */
 		this->vscroll.cap = (this->widget[TTV_TIMETABLE_PANEL].bottom - this->widget[TTV_TIMETABLE_PANEL].top) / 10;
diff --git a/src/toolbar_gui.cpp b/src/toolbar_gui.cpp
--- a/src/toolbar_gui.cpp
+++ b/src/toolbar_gui.cpp
@@ -1117,7 +1117,7 @@ struct MainToolbarWindow : Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (this->width <= TBP_NORMAL_MAXBUTTON * TBP_BUTTONWIDTH) {
 			SplitToolbar(this);
@@ -1311,7 +1311,7 @@ public:
 		_place_proc(tile);
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		/* There are 16 buttons plus some spacings if the space allows it.
 		 * Furthermore there are two panels of which one is non - essential
diff --git a/src/town_gui.cpp b/src/town_gui.cpp
--- a/src/town_gui.cpp
+++ b/src/town_gui.cpp
@@ -625,7 +625,7 @@ public:
 		this->SetDirty();
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / 10;
 	}
diff --git a/src/vehicle_gui.cpp b/src/vehicle_gui.cpp
--- a/src/vehicle_gui.cpp
+++ b/src/vehicle_gui.cpp
@@ -392,7 +392,7 @@ struct RefitWindow : public Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 		this->widget[3].data = (this->vscroll.cap << 8) + 1;
@@ -1152,7 +1152,7 @@ struct VehicleListWindow : public BaseVe
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->vscroll.cap += delta.y / (int)this->resize.step_height;
 		this->widget[VLW_WIDGET_LIST].data = (this->vscroll.cap << 8) + 1;
@@ -1575,7 +1575,7 @@ struct VehicleDetailsWindow : Window {
 		DoCommandP(0, this->window_number, 0, CMD_RENAME_VEHICLE | CMD_MSG(_name_vehicle_error[GetVehicle(this->window_number)->type]), NULL, str);
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		if (delta.x != 0) ResizeButtons(this, VLD_WIDGET_DETAILS_CARGO_CARRIED, VLD_WIDGET_DETAILS_TOTAL_CARGO);
 		if (delta.y == 0) return;
@@ -2037,7 +2037,7 @@ struct VehicleViewWindow : Window {
 		}
 	}
 
-	virtual void OnResize(Point new_size, Point delta)
+	virtual void OnResize(Point delta)
 	{
 		this->viewport->width          += delta.x;
 		this->viewport->height         += delta.y;
diff --git a/src/window.cpp b/src/window.cpp
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -920,13 +920,10 @@ void Window::FindWindowPlacementAndResiz
 
 		ResizeWindow(this, enlarge_x, enlarge_y);
 
-		Point size;
 		Point diff;
-		size.x = this->width;
-		size.y = this->height;
 		diff.x = enlarge_x;
 		diff.y = enlarge_y;
-		this->OnResize(size, diff);
+		this->OnResize(diff);
 	}
 
 	int nx = this->left;
@@ -1600,13 +1597,10 @@ static bool HandleWindowDragging()
 			/* ResizeWindow sets both pre- and after-size to dirty for redrawal */
 			ResizeWindow(w, x, y);
 
-			Point size;
 			Point diff;
-			size.x = x + w->width;
-			size.y = y + w->height;
 			diff.x = x;
 			diff.y = y;
-			w->OnResize(size, diff);
+			w->OnResize(diff);
 			return false;
 		}
 	}
@@ -2478,13 +2472,10 @@ void RelocateAllWindows(int neww, int ne
 				if (neww - w->width != 0) {
 					ResizeWindow(w, min(neww, 640) - w->width, 0);
 
-					Point size;
 					Point delta;
-					size.x = w->width;
-					size.y = w->height;
 					delta.x = neww - w->width;
 					delta.y = 0;
-					w->OnResize(size, delta);
+					w->OnResize(delta);
 				}
 
 				top = w->top;
diff --git a/src/window_gui.h b/src/window_gui.h
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -497,11 +497,10 @@ public:
 
 
 	/**
-	 * Called when the window got resized.
-	 * @param new_size the new size of the window.
-	 * @param delta    the amount of which the window size changed.
+	 * Called after the window got resized.
+	 * @param delta The amount of which the window size changed.
 	 */
-	virtual void OnResize(Point new_size, Point delta) {}
+	virtual void OnResize(Point delta) {}
 
 	/**
 	 * A dropdown option associated to this window has been selected.