7.4. Update Functions - reset_value, write_data

These functions help connect a scale or spin button to a point in the Cascade DataHub. The first function (reset_value) adjusts the value of a widget to reflect a change in the datahub, while the second function (write_data) updates the datahub point from a change entered in the widget. In this manner, a two-way connection is maintained.

   /*--------------------------------------------------------------------
    * Function:    reset_value
    * Returns:     t or nil
    * Description: Resets the value of a widget's adjustment.
    *------------------------------------------------------------------*/
   function reset_value(widget, newval, adj_id)
   {
     local newadj;
     newadj = widget.get_adjustment();
     if (adj_id)
       {
         gtk_signal_handler_block (newadj, adj_id);
         newadj.set_value(100 - newval);
         gtk_signal_handler_unblock (newadj, adj_id);
       }
     else
       newadj.set_value(newval);
   }
   

Whenever the widget's adjustment gets reset, it sends a "changed_value" signal. This has to be blocked when the adjustment is due to a change in the Cascade DataHub, otherwise the widget will send an echo back to the datahub. The echo isn't visible in this application, but it would show up in a text log. For this reason, we use the Gamma/GTK functions gtk_signal_handler_block and gtk_signal_handler_unblock (documented in the Gamma/GTK List of Functions (Non Widget Specific) appendix) to block all signals from the adjustment while we reset the value.

   /*--------------------------------------------------------------------
    * Function:    write_data
    * Returns:     t or nil
    * Description: Reads a widget that contains an adjustment value,
    *              and writes its value to the datahub.
    *------------------------------------------------------------------*/
   function write_data(widget, !ptname)
   {
     local ptval;
     ptval = widget.get_adjustment();
     write_point(string(ptname), ptval.value);
   }
   

The Gamma function write_point is used to write the values to the datahub.