Gamma/Photon : Using Gamma™ with the Photon microGUI®, Version 3.4
	Widget Functions

`PtAttachCallback`

PtAttachCallback — associates an action with a Photon event.

Syntax

PtAttachCallback (widget, callback_number, callback_function,
eventmask?|key_cap?, key_mods?, key_flags?)

Arguments

widget: The widget to attach the callback function on.
callback_number: The callback to trigger on.
callback_function: The function to call when the event occurs.
eventmask: An optional filter, for the callback only.
callbacks: Those that match this eventmask trigger the function.
keycap: Optional keyboard capture ID.
key_mods: Optional keyboard modifiers to the keycap (e.g. SHIFT, CTRL, ALT).
key_flags: Optional key flags (e.g. key up, key down, key repeat).

Returns

t when successful.

Description

The PtAttachCallback function is one of the most useful functions to use with Photon in Gamma. This functions allows an action to be associated with a Photon event.

The callback_number is usually expressed as a constant. For example, Pt_CB_ACTIVATE, Pt_CB_RAW, Pt_CB_SELECTION. A list of the available callbacks is given with each widget definition in the widget reference.

The callback_function is protected using quote operators (#, `, and @) and is evaluated only when the callback occurs.

The eventmask is used to look for specific events. For example, the callback number Pt_CB_BUT_PRESS can be masked with the event mask constant Pt_EV_BUT_RELEASE so that the callback function is only called when the mouse button is released.

Example

This example, ex_PtAttachCallback.g, is included in the product distribution.

#!/usr/cogent/bin/phgamma

require_lisp("PhotonWidgets.lsp");
PtInit(nil);

win = new(PtWindow);
win.SetDim(200,50);

function pressed (held)
{
  if (!held)
    widget.text_string = string("Pressed: cb called ",counter++," times");
  else
    widget.text_string = string("Held: cb called ",counter++," times");
}

counter = 1;
button = new(PtButton);
button.SetPos(10, 10);
button.text_string = "------ Press Me ------";
PtAttachCallback(button,Pt_CB_ACTIVATE,#pressed(nil));
PtAttachCallback(button,Pt_CB_REPEAT,#pressed(t));

PtRealizeWidget(win);
PtMainLoop();

See the Callback Functions section of the Photon Functions chapter (Tutorial One), or the Photon: the Controller window of the Controller Functions chapter (Tutorial Two) in the Cogent Tools Demo and Tutorials book for an example of this function used in context.


PtAddResource		PtCollideWidget

PtAttachCallback