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16. Button-like Objects

A very important set of object classes are those for buttons. Buttons are placed on the form such that the user can push them with the mouse. The different button classes mostly are distinguished by the way they are displayed. Differences in behaviour can be achieved by using different types for a button: there exist button types that make them return to their normal state when the user releases the mouse, types for buttons that stay pushed until the user pushes them again, a radio button type for buttons that are grouped with other radio buttons and of which only one can be in the on state at a time and a touch button type for buttons that "fire" repeatedly while being pressed.


Also different shapes of buttons exist. Normal buttons are rectangles that come out of the background. When the user pushes them they go into the background (and possibly change color). Lightbuttons have a small light inside them. Pushing these buttons switches the light on. Round buttons are simple circles and, when pushed, a colored circle appears inside of them. Bitmap and pixmap buttons are buttons with an image in addition to a text label.

16.1 Adding Button Objects

Adding an object To add buttons use one of the following routines:

FL_OBJECT *fl_add_button(int type, FL_Coord x, FL_Coord y,
                         FL_Coord w, FL_Coord h,
                         const char *label);
FL_OBJECT *fl_add_lightbutton(int type, FL_Coord x, FL_Coord y,
                              FL_Coord w, FL_Coord h,
                              const char *label);
FL_OBJECT *fl_add_roundbutton(int type, FL_Coord x, FL_Coord y,
                              FL_Coord w, FL_Coord h,
                              const char *label);
FL_OBJECT *fl_add_round3dbutton(int type, FL_Coord x, FL_Coord y,
                                FL_Coord w, FL_Coord h,
                                const char *label);
FL_OBJECT *fl_add_checkbutton(int type, FL_Coord x, FL_Coord y,
                              FL_Coord w, FL_Coord h,
                              const char *label);
FL_OBJECT *fl_add_bitmapbutton(int type, FL_Coord x, FL_Coord y,
                               FL_Coord w, FL_Coord h,
                               const char *label);
FL_OBJECT *fl_add_pixmapbutton(int type, FL_Coord x, FL_Coord y,
                               FL_Coord w, FL_Coord h,
                               const char *label);
FL_OBJECT *fl_add_labelbutton(int type, FL_Coord x, FL_Coord y,
                              FL_Coord w, FL_Coord h,
                              const char *label);
FL_OBJECT *fl_add_scrollbutton(int type, FL_Coord x, FL_Coord y,
                               FL_Coord w, FL_Coord h,
                               const char *label);

These finctions create buttons of the following classes:


A standard normal button.


A button with a small embedded, colored area that changes color when the button is in the on state.


A circular button (with a label beside). The inner area of the circle changes color when the button is on. Often used for radio buttons.


Just like the FL_ROUNDBUTTON but the circle is dran in a 3D-fashion.


Button shaped in the form of a rhombus slightly raised above the forms plane when off and slightly embossed (ypically with a different color) when on.


Button decorated with a bitmap (often read in from an X bitmap file with extension xbm) in additional to a label.


Button decorated with a pixmap (often read in from an X pixmap file with extension xpm) in additional to a label. An additonal pixmap can be set for the case that the mouse hoovers over the button.


A button that does not appear to be a button, only its label is shown, can be used e.g., for hyperlinks.


A button mostly used at the ends of scrollbars - instead of a label it can only contain a triangle pointing up, down, left or right.

The meaning of the parameters is as usual. The label is by default placed inside the button for button and lightbutton. For roundbutton, round3dbutton, bitmapbutton and pixmapbutton, it is placed to the right of the circle and to the bottom of the bitmap/pixmap respectively. For scrollbutton, the label must be of some pre-determined string that indicates the direction of the scroll arrow.

16.2 Button Types

The following types of buttons are available:


Returned to fl_do_forms() (or having its callback funtion invoked) when released.


Stays pushed until user pushes it again.


Returned when pushed, useful e.g., for opening a popup when pushed.


Returned at regulat intervals as long as the user pushes it.


Push button that switches off other radio buttons.


Invisible normal button.


Returned both when pushed and when released.


Like a normal button but also reacts to the <Return> key.


Invisible return button.

Except for the FL_HIDDEN_BUTTON and FL_HIDDEN_RET_BUTTON, which are invisible, there's not much visible indication of the button type but the function is quite different. For each of the types the button gets pushed down when the user presses the mouse on top of it. What actually happens when the user does so then depends on the type of the button. An FL_NORMAL_BUTTON, FL_TOUCH_BUTTON and FL_INOUT_BUTTON gets released when the user releases the mouse button. Their difference lies in the moment at which the interaction routines return them (see below). A FL_PUSH_BUTTON remains pushed and is only released when the user pushes it again. A FL_RADIO_BUTTON is a push button with the following extra property: whenever the user pushes a radio button, all other pushed radio buttons in the same form (or in the same group) are released. In this way the user can make its choice among several possibilities. A FL_RETURN_BUTTON behaves like a normal button, but it also reacts when the <Return> key on the keyboard is pressed. When a form contains such a button (of course there can only be one) the <Return> key can no longer be used to move between input fields. For this the <Tab> key must be used.

A FL_HIDDEN_BUTTON behaves like a normal button but is invisible. A FL_HIDDEN_RET_BUTTON is like a hidden button but also reacts to <Return> key presses.

16.3 Button Interaction

FL_NORMAL_BUTTONs, FL_PUSH_BUTTONs, FL_RADIO_BUTTONs, FL_RETURN_BUTTONs and FL_HIDDEN_BUTTONs are returned at the moment the user releases the mouse after having pressed it on the button. A FL_MENU_BUTTON, in contrast, is returned already on a mouse press. A FL_INOUT_BUTTON is returned both when the user presses it and when the user releases it. A FL_TOUCH_BUTTON is returned all the time as long as the user keeps the mouse button pressed while the mouse is on top of it. A FL_RETURN_BUTTON and a FL_HIDDEN_RET_BUTTON are also returned when the user presses the <Return> key.

As for other "active" objects, you can control under which conditions a button object gets returned or its callback invoked by using the function

int fl_set_object_return(FL_OBJECT *obj, unsigned int when);

where reasonable values for when are


Never return object or invoke callback.


Return object or invoke callback when mouse button is released and at the same moment the state of the button changed.


Return object or invoke callback whenever the state of the button changes.


Return object or invoke callback when mouse button is released


Return object or invoke callback on all of the above condtions.

Most buttons will always return FL_RETURN_END and FL_RETURN_CHANGED at the same time. Exceptions are FL_INOUT_BUTTONs and FL_TOUCH_BUTTONs. The former returns FL_RETURN_CHANGED when pushed and both FL_RETURN_END and FL_RETURN_CHANGED together when released. FL_TOUCH_BUTTONs return when pressed, then FL_RETURN_CHANGED at regular time intervals while being pressed and finally FL_RETURN_END when released.

See demo `butttypes.c' for a feel of the different button types.

16.4 Other Button Routines

The application program can also set a button to be pushed or not itself without a user action. To this end use the routine

void fl_set_button(FL_OBJECT *obj, int pushed);

pushed indicates whether the button should be set to be pushed (1) or released (0). When setting a FL_RADIO_BUTTON to be pushed this automatically releases the currently pushed radio button in the same form (or group). Also note that this routine only simulates the visual appearance but does not affect the program flow in any way, i.e., setting a button as being pushed does not invoke its callback or results in the button becoming returned to the program. For that follow up the call of fl_set_button() with a call of fl_trigger_object() (or fl_call_object_callback()).

To figure out whether a button is pushed or not use(12)

int fl_get_button(FL_OBJECT *obj);

Sometimes you want to give the button a different meaning depending on which mouse button gets pressed on it. To find out which mouse button was used at the last push (or release) use the routine

int fl_get_button_numb(FL_OBJECT *obj);

It returns one of the constants FL_LEFT_MOUSE, FL_MIDDLE_MOUSE, FL_RIGHT_MOUSE, FL_SCROLLUP_MOUSE or FL_SCROLLDOWN_MOUSE (the latter two are from the scroll wheel of the mouse). If the last push was triggered by a shortcut (see below), the function returns the keysym (ASCII value if the key used is between 0 and 127) of the key plus FL_SHORTCUT. For example, if a button has <Ctrl>-C as its shortcut the button number returned upon activation of the shortcut will be FL_SHORTCUT + 3 (the ASCII value of <Ctrl>-C is 3).

It can also be controlled which mouse buttons a buttons reacts to (per default a button reacts to all mouse buttons, including the scroll wheel). To set which mouse buttons the button reacts to use

void fl_set_button_mouse_buttons(FL_OBJECT *obj, int mbuttons);

mbuttons is the bitwise OR of the numbers 1 for the left mouse button, 2 for the middle, 4 for the right mouse button, 8 for moving the scroll wheel up "button" and 16 for scrolling down "button". Per default a button reacts to all mouse buttons.

To determine which mouse buttons a button is reacting to use

void fl_get_button_mouse_buttons(FL_OBJECT *obj,
                                 unsigned int *mbuttons);

The value returned via mbuttons is the same value as would be used in fl_set_button_mouse_buttons().

In a number of situations it is useful to define a keyboard equivalent for a button. You might e.g., want to define that <Ctrl>Q has the same meaning as pressing the "Quit" button. This can be achieved using the following call:

void fl_set_button_shortcut(FL_OBJECT *obj, const char *str,
                            int showUL);

Note that str is a string, not a single character. This string is a list of all the characters to become keyboard shortcuts for the button. E.g., if you use string "^QQq" the button will react on the keys q, Q and <Ctrl>Q. (As you see you can use the symbol ^ to indicate the control key. Similarly you can use the symbol # to indicate the <Alt> key.) Be careful with your choices. When the form also contains input fields you probably don't want to use the normal printable characters because they can no longer be used for input in the input fields. Shortcuts are always evaluated before input fields. Other special keys, such as <F1> etc., can also be used as shortcuts. See section Shortcuts, for details. Finally, keep in mind that a button of type FL_RETURN_BUTTON is in fact nothing more than a normal button, just with the <Return> key set as the shortcut. So don't change the shortcuts for such a button.

If the third parameter showUL is true and one of the letters in the object label matches the shortcut the matching letter will be underlined. This applies to non-printable characters (such as #A) as well in the sense that if the label contains the letter a or A it will be underlined (i.e., special characters such as # and ^ are ignored when matching). A false value (0) for showUL turns off underlining without affecting the shortcut. Note that although the entire object label is searched for matching character to underline of the shortcut string itself only the first (non-special) character is considered, thus a shortcut string of "Yy" for the label "Yes" will result in the letter Y becoming underlined while for "yY" it won't.

To set the bitmap to use for a bitmap button the following functions can be used:

void fl_set_bitmapbutton_data(FL_OBJECT *obj, int w, int h,
                              unsigned char *bits);
void fl_set_bitmapbutton_file(FL_OBJECT *obj, const char *filename);

Similarly, to set the pixmap to use for a pixmap button the following routines can be used:

void fl_set_pixmapbutton_data(FL_OBJECT *obj, unsigned char **bits);
void fl_set_pixmapbutton_file(FL_OBJECT *obj, const char *file);
void fl_set_pixmapbutton_pixmap(FL_OBJECT *obj, Pixmap id,
                                 Pixmap mask);

To use the first routine, you #include the pixmap file into your source code and use the pixmap definition data (an array of char pointers) directly. For the second routine the filename file that contains the pixmap definition is used to specify the pixmap. The last routine assumes that you already have a X Pixmap resource ID for the pixmap you want to use. Note that these routines do not free a pixmap already associated with the button. To free the pixmaps use the function

void fl_free_pixmapbutton_pixmap(FL_OBJECT *obj);

This function frees the pixmap and mask together with all the colors allocated for them.

To get the pixmap and mask that is currently being displayed, use the following routine

Pixmap fl_get_pixmapbutton_pixmap(FL_OBJECT *obj,
                                  Pixmap &pixmap, Pixmap &mask);

Pixmaps are by default displayed centered inside the bounding box. However, this can be changed using the following routine

void fl_set_pixmapbutton_align(FL_OBJECT *obj, int align,
                               int xmargin, int ymargin);

where align is the same as that used for labels. See section Label Attributes and Fonts, for a list. xmargin and ymargin are extra margins to leave in addition to the object border width. Note that although you can place a pixmap outside of the bounding box, it probably is not a good idea.

When the mouse enters a pixmap button an outline of the button is shown. If required, a different pixmap (the focus pixmap) can also be shown. To set such a focus pixmap the following functions are available:

void fl_set_pixmapbutton_focus_data(FL_OBJECT *obj,
                                     unsigned char **bits);
void fl_set_pixmapbutton_focus_file(FL_OBJECT *obj,
                                    const char *file);
void fl_set_pixmapbutton_focus_pixmap(FL_OBJECT *obj, Pixmap id,
                                      Pixmap mask);

The meanings of the parameters are the same as that in the regular pixmap routines.

Finally, there's a function that can be used to enable or disable the focus outline

void fl_set_pixmapbutton_focus_outline(FL_OBJECT *obj, int yes_no);

See also Pixmap Object, for pixmap color and transparency handling.

To get rid of a focus pixmap of a pixmap button use the function

void fl_free_pixmap_focus_pixmap(FL_OBJECT *obj);

16.5 Button Attributes

For normal buttons the first color argument (col1) to fl_set_object_color() controls the normal color and the second (col2) the color the button has when pushed. For lightbuttons col1 is the color of the light when off and col2 the color when on. For round buttons, col1 is the color of the circle and col2 the color of the circle that is placed inside it when pushed. For round3dbutton, col1 is the color of the inside of the circle and col2 the color of the embedded circle. For bitmapbuttons, col1 is the normal box color (or bitmap background if boxtype is not FL_NO_BOX) and col2 is used to indicate the focus color. The foreground color of the bitmap is controlled by label color (as set via fl_set_object_lcolor(). For scrollbutton, col1 is the overall boundbox color (if boxtype is not FL_NO_BOX), col2 is the arrow color. The label of a scrollbutton must be a string with a number between 1 and 9 (except 5), indicating the arrow direction like on the numerical key pad. The label can have an optional prefix # to indicate uniform scaling. For example, the label "#9" tells that the arrow should be pointing up-right and the arrow has the identical width and height regardless the overall bounding box size.

16.6 Remarks

See all demo programs, in particular `pushbutton.c' and `buttonall.c' for the use of buttons.



fl_mouse_button() can also be used.

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