Method OnMouseWheel

src/viewport_gui.cpp:127–133

	}

	void OnMouseWheel(int wheel, WidgetID widget) override
	{
		if (widget != WID_EV_VIEWPORT) return;
		if (_settings_client.gui.scrollwheel_scrolling != SWS_OFF) {
			ZoomInOrOutToCursorWindow(wheel < 0, this);
		}
	}

	/**
	 * Some data on this window has become invalid.