Function HandleAutoscroll

src/window.cpp:2750–2785

* If needed and switched on, perform auto scrolling (automatically * moving window contents when mouse is near edge of the window). */

 * moving window contents when mouse is near edge of the window).
 */
static void HandleAutoscroll()
{
	if (_game_mode == GM_MENU || HasModalProgress()) return;
	if (_settings_client.gui.auto_scrolling == VA_DISABLED) return;
	if (_settings_client.gui.auto_scrolling == VA_MAIN_VIEWPORT_FULLSCREEN && !_fullscreen) return;

	int x = _cursor.pos.x;
	int y = _cursor.pos.y;
	Window *w = FindWindowFromPt(x, y);
	if (w == nullptr || w->flags.Test(WindowFlag::DisableVpScroll)) return;
	if (_settings_client.gui.auto_scrolling != VA_EVERY_VIEWPORT && w->window_class != WC_MAIN_WINDOW) return;

	Viewport *vp = IsPtInWindowViewport(w, x, y);
	if (vp == nullptr) return;

	x -= vp->left;
	y -= vp->top;

	/* here allows scrolling in both x and y axis */
	/* If we succeed at scrolling in any direction, stop following a vehicle. */
	static const int SCROLLSPEED = 3;
	if (x - 15 < 0) {
		w->viewport->CancelFollow(*w);
		w->viewport->dest_scrollpos_x += ScaleByZoom((x - 15) * SCROLLSPEED, vp->zoom);
	} else if (15 - (vp->width - x) > 0) {
		w->viewport->CancelFollow(*w);
		w->viewport->dest_scrollpos_x += ScaleByZoom((15 - (vp->width - x)) * SCROLLSPEED, vp->zoom);
	}
	if (y - 15 < 0) {
		w->viewport->CancelFollow(*w);
		w->viewport->dest_scrollpos_y += ScaleByZoom((y - 15) * SCROLLSPEED, vp->zoom);
	} else if (15 - (vp->height - y) > 0) {
		w->viewport->CancelFollow(*w);
		w->viewport->dest_scrollpos_y += ScaleByZoom((15 - (vp->height - y)) * SCROLLSPEED, vp->zoom);
	}
}

enum MouseClick : uint8_t {
	MC_NONE = 0,