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Each object has a number of attributes. Some of them are used by the main routine, some have a fixed meaning and should never be altered by the class routines and some are free for the class routines to use. Please always use accessor methods when available instead of using or changing the object's properties directly. Below we consider some of them that are likely to be used in new classes.
This indicates the class of the object (e.g.,
FL_NEW etc.) The user can query the class of
an object using the function
This indicates the type of the object within the class. Types are
integer constants that should be defined in a header file named after
the object class, e.g., `NEW.h'. Their use is completely free.
For example, in the slider class the type is used to distinguish
between horizontal and vertical sliders. At least one type should
exist and the user should always provide it (just for consistency).
They should be numbered from 0 upwards. The user can query the type
of an object using the function
This is the type of the bounding box for the object. The handling
routine for the object, e.g.,
handle_NEW(), has to take care
that this is actually drawn. Note that there is a routine for drawing
boxes, see below. The user can change or query the boxtype of an
object with the functions
FL_Coord x, y, w, h
These are the coordinates and sizes that indicate the bounding box of
the object. They always have to be provided when adding an object. The
system uses them e.g., to determine if the object is below the mouse.
The class routines should use them to draw the object in the correct
size, etc. Note that these values will change when the user resizes
the form window. So never assume anything about their values but
always recheck them when drawing the object. The routines
fl_get_object_size() should be used to determine position
and/or size. To change the position and/or size of an object never
change the elements of the structures directly (except in a function
fl_add_NEW()) but always use
Also note that the
y-member is always relative to the top of
the form the object belongs to, even if the user had called
fl_flip_yorigin() - this only results in
passed by and returned to the user when using functions like
fl_get_object_position() getting "flipped", internally
always the normal coordinate system is used.
unsigned int resize
Controls if the object should be resized if the form it is on is
resized. The options are
FL_RESIZE_ALL. The default is
FL_RESIZE_ALL which is the bitwise OR of
FL_RESIZE_Y. Instead of accessing this element directly better
use the functions
unsigned int nwgravity, segravity
These two variables control how the object is placed relative to its
position prior to resizing. Instead of accessing these elements
FL_COLOR col1, col2
These are two color indices in the internal color lookup table. The
class routines are free to use them or not. The user can change them
using the routine
fl_set_object_color() or inspect the
fl_get_object_color(). The routine
fl_add_NEW() should fill in defaults.
This is a pointer to an allocated text string. This can be used by
class routines to provide a label for the object. The class routines
may not forget to allocate storage for it when it sets the pointer
itself, i.e., doesn't use
fl_set_object_label() - an
empty label should be the empty string and not just a
pointer. The user can change it using the routines
fl_set_object_label_f() or ask for it using
fl_get_object_label(). The label must be drawn by the
routine handling the object when it receives a
event (or it could be part of the code for
FL_DRAW event). For
non-offsetted labels, i.e., the alignment is relative to the entire
bounding box, simply calling
should be enough.
The color of the label. The class routines can freely use this. The
user can set it with
fl_set_object_lcolor() and test it
The size of the font used to draw the label. The class routines can
freely use this. The user can set it with
and test it with
The style of the font the label os drawn in, i.e., the number of the
font in which it should be drawn. The class routines can freely use
this. The user can set it with
and test it with
The alignment of the label with respect to the object. Again it is up
to the class routines to do something useful with this. The possible
FL_ALIGN_RIGHT_BOTTOM. The value should be bitwise ORed
FL_ALIGN_INSIDE if the label will be within the
bounding box of the object. The user can set this using the routine
fl_set_object_lalign() and test it with
An integer indicating the border width of the object. Negative values
indicate the up box should look "softer" (in which case no black line
of 1 pixel width is drawn around the objects box). The user can set a
different border width using
A pointer to long containing all shortcuts (as keysyms) defined for the object (also see the previous chapter). You should never need them because they are fully handled by the main routines.
This is a pointer that points to any class specific information. For
example, for sliders it stores the minimum, maximum and current value
of the slider. Most classes (except the most simple ones like boxes
and texts) will need this. The function for adding a new object
fl_add_NEW()) has to allocate storage for it. Whenever the
object receives the event
FL_FREEMEM it should free this
Indicates whether the object is visible. The class routines don't have
to do anything with this variable. When the object is not visible the
main routine will never try to draw it or send events to it. By
default objects are visible. The visisbility of an object can be
tested using the
fl_object_is_visible() function. Note
that a this doesn't guarantee that the object is visible on the
screen, for this also the form the object belongs to needs to be
visible, in which case
fl_form_is_visible() returns true.
Indicates whether the object is active, i.e., wants to receive events
Static objects, such as text and boxes are inactive. This property
should be set in the
fl_add_NEW() routine if required. By
default objects are active. This attribute can be changed by using the
fl_activate_object() and the current state can be
determined by calling
Indicates whether this object can receive keyboard input. If not,
events related to keyboard input are not sent to the object. The
default value of
input is false. It should be set by
fl_add_NEW() if required. Note that not all keys are sent (see
An input object normally does not receive
<Return> keystrokes or any other keys except those that have
values between 0-255, the
<Right> arrow keys
are normally used to switch between input objects). By setting this
FL_KEY_TAB enforces that the object receives also
these two keys as well as the
<Down> arrow keys
<PgDn> when it has the focus. To receive
other special keys (e.g., function keys)
be set in
wantkey. By setting
FL_KEY_ALL all keys are sent to the object.
unsigned int click_timeout
If non-zero this indicates the the maximum elapsed time (in msec)
between two mouse clicks to be considered a double click. A zero value
disables double/triple click detection. The user can set or query this
value using the functions
An object is automatic if it automatically (without user actions) has
to change its contents. Automatic objects get a
about every 50 msec. For example the object class
automatic by default is false. To set this
fl_set_object_automatic() (don't set the
object member directly except from within a function like
fl_add_NEW(), in other contexts some extra work is required)
and to test the object for it use
This indicates whether the mouse is on this object. It is set and reset by the main routine. The class routines should never change it but can use it to draw or handle the object differently.
This indicates whether the mouse is pushed within the bounding box of the object. It is set and reset by the main routine. Class routines should never change it but can use it to draw or handle objects differently.
Indicates whether keyboard input is sent to this object. It is set and reset by the main routine. Never change it but you can use its value.
This is a pointer to the interaction handling routine for the object.
fl_add_NEW() sets this by providing the correct handling
routine. Normally it is never used (except by the main routine) or
changed although there might be situations in which you want to change
the interaction handling routine for an object, due to some user
FL_OBJECT *next, *prev
These are pointers to other objects in the form and to the form itself. They are used by the main routines. The class routines should not change them.
A void pointer for the class routine. The main module does not reference or modify this field in any way. The object classes, including the built-in ones, may use this field.
A char pointer for the class routine. The main module does not reference or modify this field in any way. The object classes, including the built-in ones, may use this field.
A long variable for the class routine. The main module does not reference or modify this field in any way. The object classes, including the built-in ones, may use this field.
A void pointer for the application program. The main module does not reference or modify this field in any way and neither should the class routines.
A char pointer for the application program. The main module does not reference or modify this field in any way and neither should the class routines.
A long variable provided for the application program.
The callback routine that the application program assigned to the object and that the system invokes when the user does something with the object.
The argument to be passed to the callback routine when invoked.
Determines under what circumstances the object is returned by e.g.,
fl_do_forms() or the callback function for the object is
invoked. This can be either
Object gets never returned or its callback invoked
Return object or invoke callback when state of object changed.
Return object or invoke callback at end of interaction, normally when the mouse key is released or, in the case of input objects, the object has lost focus.
Return object or invoke callback only when interaction has ended and the state of the object has changed.
Return object or invoke callback if e.g., in a browser a line was selected.
Return object or invoke callback if e.g., in a browser a line was deselected.
Return object or invoke callback whenever interaction has ended or the state of the object has changed.
Never change this element of the structure directly but use the
fl_set_object_return() instead! Especially in
the case of objects having child objects also the corresponding
settings for child objects may need changes and which automatically
get adjusted when the above function is used.
Set to what calling the object handling function did return (and
pruned to what the object is supposed to return according to the
how_return element). Can be either
Handling function did
Handling function detected a change of the objects state.
Handling function detected end of interaction with object.
FL_RETURN_END are bits
that can be bitwise ored. If both are set this indicates that the
objects state was changed and the interaction ended.
The generic object construction routine
typedef int (*FL_HANDLEPTR)(FL_OBJECT *obj, int event, FL_Coord mx, FL_Coord my, int key, void *raw_event); FL_OBJECT *fl_make_object(int objclass, int type, FL_Coord x, FL_Coord y, FL_Coord w, FL_Coord h, const char *label, FL_HANDLEPTR handle);
allocates a chunk of memory appropriate for all object classes and initializes the newly allocated object to the following state:
obj->resize = FL_RESIZE_X | FL_RESIZE_Y; obj->nwgravity = obj->segravity = FL_NoGravity; obj->boxtype = FL_NO_BOX; obj->align = FL_ALIGN_CENTER | FL_ALIGN_INSIDE; obj->lcol = FL_BLACK; obj->lsize = FL_DEFAULT_SIZE; obj->lstyle = FL_NORMAL_STYLE; obj->col1 = FL_COL1; obj->col2 = FL_MCOL; obj->wantkey = FL_KEY_NORMAL; obj->active = 1; obj->visible = 1; obj->bw = borderWidth_resource_set ? resource_val : FL_BOUND_WIDTH; obj->u_ldata = 0; obj->u_vdata = 0; obj->spec = NULL; obj->how_return = FL_RETURN_CHANGED
In some situations it can be also useful to make an object a child
of another object. An example is the scrollbar object. It has three
child objects, a slider and two buttons, which all three are children
of the scrollbar object. To make an object
child a child
object of an object named
parent use the function
void fl_add_child(FL_OBJECT *parent, FL_OBJECT *child);
When creating a composite object you will typically add callbacks
for the child object that handle what happens on events for these
child objects (e.g., for the scrollbar the buttons have callbacks
that update the internal state for the scrollbar object and result
in the slider getting shifted). Within these callback functions
returned elements of the parent can be changed to
influence if and what gets reported to the application via
There is rarely any need for the new object class to know how the
object is added to a form and how the Forms Library manages the
geometry, e.g., does an object have its own window etc. Nonetheless
if this information is required, use
FL_ObjWin() on the
object to obtain the window resource ID of the window the object
belongs to. Beware that an object window ID may be shared with other
objects(14). Always remove an object
from the screen with
The class routine/application may reference the following members of
FL FORM structure to obtain information on the status of
the form, but should not modify them directly:
Indicates if the form is visible on the screen (mapped). Never change
it directly, use
Indicates if the form is deactivated. Never change it directly, use
FL OBJECT *focusobj
This pointer points to the object on the form that has the input focus.
FL OBJECT *first
The first object on the form. Pointer to a linked list.
The forms window.
The only exception is the canvas class where the window ID is guaranteed to be non-shared.
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