Next: , Up: Part I Free Objects   [Contents][Index]


5.1 Free Object

To add a free object to a form use the call

FL_OBJECT *fl_add_free(int type, FL_Coord x, FL_Coord y,
                       FL_Coord w, FL_Coord h,
                       const char *label, int (*handle)());

type indicates the type of free object, see below for a list and their meaning. x, y, w and h are the bounding box. The label is normally not drawn unless the handle routine takes care of this. handle is the routine that does the redrawing and handles the interaction with the free object. The application program must supply this routine.

This routine handle is called by the library whenever an action has to be performed. The routine should have the form:

int handle(FL_OBJECT *obj, int event, FL_Coord mx, FL_Coord my,
           int key, void *xev);

where obj is the object to which the event applies. event indicates what has to happen to the object. See below for a list of possible events. mx and my indicate the position of the mouse (only meaningful with mouse related events) relative to the form origin and key is the KeySym of the key typed in by the user (only for FL_KEYPRESS events). xev is the (cast) XEvent that causes the invocation of this handler. event and xev->type can both be used to obtain the event types. The routine should return whether the status of the object has changed, i.e., whether fl_do_forms() or fl_check_forms() should return this object.

The following types of events exist for which the routine must take action:

FL_DRAW

The object has to be redrawn. To figure out the size of the object you can use the fields obj->x, obj->y, obj->w and obj->h. Some other aspects might also influence the way the object has to be drawn. E.g., you might want to draw the object differently when the mouse is on top of it or when the mouse is pressed on it. This can be figured out as follows. The field obj->belowmouse indicates whether the object is below the mouse. The field obj->pushed indicates whether the object is currently being pushed with the mouse. Finally, obj->focus indicates whether input focus is directed towards this object. When required, the label should also be drawn. This label can be found in the field obj->label. The drawing should be done such that it works correctly in the visual/depth the current form is in. Complete information is available on the state of the current form as well as several routines that will help you to tackle the trickiest (also the most tedious) part of X programming. In particular, the return value of fl_get_vclass() can be used as an index into a table of structures, fl_state[], from which all information about current active visual can be obtained. See Drawing Objects, for details on drawing objects and the routines.

FL_DRAWLABEL

This event is not always generated. It typically follows FL_DRAW and indicates the object label needs to be (re)drawn. You can ignore this event if (a) the object handler always draws the label upon receiving FL_DRAW or (b) the object label is not drawn at all9.

FL_ENTER

This event is sent when the mouse has entered the bounding box. This might require some action. Note that also the field belowmouse in the object is being set. If entering only changes the appearance redrawing the object normally suffices. Don’t do this directly! Always redraw the object using the routine fl_redraw_object(). It will send an FL_DRAW event to the object but also does some other things (like setting window id’s, taking care of double buffering and some other bookkeeping tasks).

FL_LEAVE

The mouse has left the bounding box. Again, normally a redraw is enough (or nothing at all).

FL_MOTION

A motion event is sent between FL_ENTER and FL_LEAVE events when the mouse position changes on the object. The mouse position is given with the routine.

FL_PUSH

The user has pushed a mouse button in the object. Normally this requires some action.

FL_RELEASE

The user has released the mouse button. This event is only sent if a FL_PUSH event was sent earlier.

FL_DBLCLICK

The user has pushed a mouse button twice within a certain time limit (FL_CLICK_TIMEOUT), which by default is about 400 msec.

FL_TRPLCLICK

The user has pushed a mouse button three times within a certain time window between each push. This event is sent after a FL_DBLCLICK, FL_PUSH, FL_RELEASE sequence.

FL_UPDATE

The mouse position has changed. This event is sent to an object between an FL_PUSH and an FL_RELEASE event (actually this event is sent periodically, even if mouse has not moved). The mouse position is given as the parameter mx and my and action can be taken based on the position.

FL_FOCUS

Input got focussed to this object. This event and the next two are only sent to a free object of type FL_INPUT_FREE (see below).

FL_UNFOCUS

Input is no longer focussed on this object.

FL_KEYPRESS

A key was pressed. The KeySym is given with the routine. This event only happens between FL_FOCUS and FL_UNFOCUS events.

FL_STEP

A step event is sent all the time (at most 50 times per second but often less because of time consuming redraw operations) to a free object of type FL_CONTINUOUS_FREE such that it can update its state or appearance.

FL_SHORTCUT

Hotkeys for the object have been triggered. Typically this should result in the returning of the free object.

FL_FREEMEM

Upon receiving this event, the handler should free all object class specific memory allocated.

FL_OTHER

Some other events typically caused by window manager events or inter-client events. All information regarding the details of the events is in xev.

Many of these events might make it necessary to (partially) redraw the object. Always do this using the routine fl_redraw_object().

As indicated above not all events are sent to all free objects. It depends on their types. The following types exist (all objects are sent FL_OTHER when it occurs):

FL_NORMAL_FREE

The object will receive the events FL_DRAW, FL_ENTER, FL_LEAVE, FL_MOTION, FL_PUSH, FL_RELEASE and FL_MOUSE.

FL_INACTIVE_FREE

The object only receives FL_DRAW events. This should be used for objects without interaction (e.g., a picture).

FL_INPUT_FREE

Same as FL_NORMAL_FREE but the object also receives FL_FOCUS, FL_UNFOCUS and FL_KEYPRESS events. The obj->wantkey is by default set to FL_KEY_NORMAL, i.e., the free object will receive all normal keys (0-255) except <Tab> and <Return> key. If you’re interested in <Tab> or <Return> key, you need to change obj->wantkey to FL_KEY_TAB or FL_KEY_ALL. See Events, for details.

FL_CONTINUOUS_FREE

Same as FL_NORMAL_FREE but the object also receives FL_STEP events. This should be used for objects that change themselves continuously.

FL_ALL_FREE

The object receives all types of events.

See free1.c for a (terrible) example of the use of free objects. See also freedraw.c, which is a nicer example of the use of free objects.

Free objects provide all the generality you want from the Forms Library. Because free objects behave a lot like new object classes it is recommended that you also read part IV of this documentation before designing free objects.


Footnotes

(9)

Label for free objects can’t be drawn outside of the bounding box because of the clippings by the dispatcher.


Next: , Up: Part I Free Objects   [Contents][Index]