From lechner  Sat Nov 10 02:26:18 2001
Subject: bdeOOMenu2CanvasInterface.txt
To: 01f522
Date: Sat, 10 Nov 2001 02:26:10 -0500 (EST)

$CASE/01f522/bdeOOMenu2CanvasInterface.txt:

This note contains more info on dobuttonevent's  interface to *ops.cc files, 
using as an example the node_delete method in nodeops.cc..

Example Interface: 
buttonevent.cc/dobuttonevent  calls  nodeops.cc/node_delete::
================================================
bde/src/buttonevent.cc contains one routine:
void dobuttonevent(Widget, XtPointer, XEvent, Boolean)	
/* Description:
 *      Dobuttonevent is a callback routine called by X to handle button
 *      events.  It divides up work and calls the appropriate functions.

Practically all  class*method state name combinations are handled here.
See the various *ops.cc function calls from dobuttonevent cases. 
 */

For example, both node-delete states call the same node_delete method:
----------------
case  SDnode1:
       	case SDnode2:        // redefined by hcpatel & mmaliset
                        node_delete(event,
                                selected.getstate(),
                                &(attr.node),
                                button_op);
                        break;
-----------------

Notice that BOTH states of that machine call node_delete(...) in nodeops.cc.
(Moving node methods there began the partitioning of  bde methods into classes.)
nodeops.cc dooes the switch(state) again, but now responds only
to the SDnode1 and SDnode2 cases):   Here is the beginning of  nodeops.cc:
----------------------
//Name: nodeops.cc
//
// Description:
//
// This file contains all BDE code responsible for controlling node
// operations.  The code has been taken from the BDE 1.0 buttondown.cc,
// buttonup.cc and buttonmoved.cc files.
//
// Routines  :node_create();node_delete();node_move();position_text()
//            node_resize();node_fit_to_text();
...
================================================


Here is the entire node_delete() method, with its two state case blocks:
/************************************************************
 * Name:
 *   void node_delete(XButtonEvent*, int, node_attributes *, int)
 *  . ..
 *   A generic selction routine is used for selecting a Node which searches
 *   the whole object list till it finds a Node. This routine implements the
 *   improved state model suggested by Prof.Lechner.
 * Description:
 *   This performs the node deletion operation.  It does this based on the
 *   button event and other variables passed in to it. (Note that attribute
 *   is not actually used for the delete operation.  We don't need to know
 *   whether the node was a circle or rectangle to delete it.)
 *   All code within this function  was lifted from the button*.cc files.
 *   button_op is one of: BUTTON_UP, BUTTON_DOWN, BUTTON_MOVED
 * Uses:
 *   DCtoWC(), Ggroup class method select_HN(widget, int, int),
 *   changeCanvasCursor(), changeAttribState(), docut()
 * Side effects:
 *   NONE
 ******************************************************************
void node_delete (XButtonEvent *event,
                  int state, /* Canvas State (eventually just NodeCreate)*/
                  node_attributes *attribute, /* circle, square, etc. */
                  int button_op /* BUTTON_UP, BUTTON_DOWN, BUTTON_MOVED */
                 )
{
    float sx, sy;
    static graphobject *selected_node = NULL;
    DCtoWC(event->x, event->y, &sx, &sy);
    switch (state) {
        /*
           Note that once the canvas state has been changed to be more
           meaningful, the following state case should eventually
           be replaced by a line of the form "case NodeDelete:"
        */
       case SDnode1:
            switch (button_op) {
                    case BUTTON_DOWN_EVENT:
                        topobject->select_HN(canvas, (int)sx, (int)sy);
                        selected_node = currentselection;
                        if (currentselection != NULL) {
                          selected.changeAttribState(SDnode2);
                          changeCanvasCursor(pirate);
                         }
                         break;
                      case BUTTON_UP_EVENT:
                         break;
                      case BUTTON_MOVED_EVENT:
                         break;
                      default:
//add PostErrorMsg() to handle error message - phsia 12/8/95
                        PostErrorMsg(SDnode1);
                        break;
                        }
            break;

        case SDnode2:
            switch (button_op) {
                case BUTTON_DOWN_EVENT:
                    topobject->select_HN(canvas, (int)sx, (int)sy);
                    if(currentselection != NULL
                       && selected_node == currentselection) {
                         docut((Widget) 0,0,0);
                     selected.changeAttribState(SDnode1);
                     changeCanvasCursor(arrow);
                       } else
                         selected_node = currentselection;
                     break;
                case BUTTON_UP_EVENT:
                     break;
                case BUTTON_MOVED_EVENT:
                    break;
                default: /* illegal value for button_op variable */
//add PostErrorMsg() to handle error message - phsia 12/8/95
                    PostErrorMsg(SDnode2);
                    break;
            }
            break;

        default: /* illegal value for state variable */
          fprintf(stderr, "Out of State in function node_delete.\n");
          fprintf(stderr, "switch on state\n");
          fprintf(stderr, "Report this to Professor Lechner.\n");
          break;
    }
}
// end void node_delete()
// (other methods follow in nodeops.cc)