Get a widget's currently active control surface
unsigned char PtWidgetActiveSurface( PtWidget_t *widget );
This macro retrieves the provided widget's currently “active” surface. The active surface is the last surface that consumed an event of type Ph_EV_BUT_PRESS.
The ID of the currently active control surface, or 0 if there isn't one.
Control Surfaces chapter of the Photon Programmer's Guide