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pgplotwidget.setcallback - Function

	Package	display
	Module	plotter
	Tool	pgplotwidget

set a function to be called for mouse or keyboard events

Synopsis
setcallback(name, callback)

Description
This function allows a function of yours to be called whenever a certain event happens. It is a simplification of the event-binding described in the Glish/PGPLOT chapter of the Glish manual.

The function returns an index which you can use to deactivate the callback.

At present, the events for which you may set a callback are:

motion

Called whnenver the mouse moves in the plot area.

button

Called whenever any button goes down.

button1

Called whenever button 1 goes down.

button2

Called whenever button 2 goes down.

button3

Called whenever button 3 goes down.

buttonup

Called whenever a button goes up.

key

Called whenever a key is pressed on the keyboard.

The callback functions take a single argument, which will be a record of the type described in the manual. Or of course you could just pass in the callback function:

   callback := function(rec) {print rec;}

to discover the record structure. Note that to follow a drag you merely follow the motion after a button down and before a button up.

Example
For example, here is how you could implement a little ``scribble'' application.

include 'pgplotwidget.g'
f := frame();
pg := pgplotwidget(f);
pos := [dragging=F];

# Drag starts
downcallback := function(rec) {
    global pos;
    pos := [dragging=T, xlast=rec.world[1], ylast=rec.world[2]];
}

# Draw the new line segment if we are dragging
motioncallback := function(rec) {
    global pos;
    if (pos.dragging) {
        x := rec.world[1]; y := rec.world[2];
        pg.line([pos.xlast, x], [pos.ylast, y]);
        pos.xlast := x; pos.ylast := y;
    }
}

# Drag ends
upcallback := function(rec) {
    global pos;
    pos.dragging := F;
}

pg.env(0, 1, 0, 1, 0, -1);
pg.setcallback('button', downcallback);
pg.setcallback('motion', motioncallback);
pg.setcallback('buttonup', upcallback);
pg.message('Start scribbling! Drag the mouse with a button');

The amount of code could have been reduced somewhat by having only one callback for both button and buttonup, and using the ``ButtonPress'' field of the record to distinguish up from down events.

Arguments

name		events for which to call supply callback
		Allowed:	motion,key,button,button[1-3],buttonup
callback		function to call on event
		Allowed:	single argument function

Returns
integer index (for deactivatecallback)