Enter
key.Figure 3-1: FLTK Button Widgets
All of these buttons just need the corresponding <FL/Fl_xyz_Button.H>
header file. The constructor takes the bounding box of the button and optionally a label string:
Fl_Button *button = new Fl_Button(x, y, width, height, "label"); Fl_Light_Button *lbutton = new Fl_Light_Button(x, y, width, height); Fl_Round_Button *rbutton = new Fl_Round_Button(x, y, width, height, "label");
Each button has an associated type()
which allows it to behave as a push button, toggle button, or radio button:
For toggle and radio buttons, the value()
method returns the current button state (0 = off, 1 = on). The set()
and clear()
methods can be used on toggle buttons to turn a toggle button on or off, respectively. Radio buttons can be turned on with the setonly()
method; this will also turn off other radio buttons in the same group.
The value()
method is used to get or set the string that is displayed:
Fl_Input *input = new Fl_Input(x, y, width, height, "label"); input->value("Now is the time for all good men...");
The string is copied to the widget's own storage when you set the value()
of the widget.
The Fl_Text_Display and Fl_Text_Editor widgets use an associated Fl_Text_Buffer class for the value, instead of a simple string.
Figure 3-2: FLTK valuator widgets
The value()
method gets and sets the current value of the widget. The minimum()
and maximum()
methods set the range of values that are reported by the widget.
x()
, y()
, w()
, and h()
methods.
You can change the size and position by using the position()
, resize()
, and size()
methods:
If you change a widget's size or position after it is displayed you will have to call redraw()
on the widget's parent.
See the Colors section of Drawing Things in FLTK for implementation details.
There are symbols for naming some of the more common colors:
FL_BLACK
FL_RED
FL_GREEN
FL_YELLOW
FL_BLUE
FL_MAGENTA
FL_CYAN
FL_WHITE
FL_WHITE
FL_FOREGROUND_COLOR
FL_BACKGROUND_COLOR
FL_INACTIVE_COLOR
FL_SELECTION_COLOR
A color value can be created from its RGB components by using the fl_rgb_color
() function, and decomposed again with Fl::get_color()
:
Fl_Color c = fl_rgb_color(85, 170, 255); // RGB to Fl_Color Fl::get_color(c, r, g, b); // Fl_Color to RGB
The widget color is set using the color()
method:
button->color(FL_RED); // set color using named value
Similarly, the label color is set using the labelcolor()
method:
button->labelcolor(FL_WHITE);
The Fl_Color encoding maps to a 32-bit unsigned integer representing RGBI, so it is also possible to specify a color using a hex constant as a color map index:
button->color(0x000000ff); // colormap index #255 (FL_WHITE)
or specify a color using a hex constant for the RGB components:
button->color(0xff000000); // RGB: red button->color(0x00ff0000); // RGB: green button->color(0x0000ff00); // RGB: blue button->color(0xffffff00); // RGB: white
Figure 3-3 shows the standard box types included with FLTK.
Figure 3-3: FLTK box types
FL_NO_BOX
means nothing is drawn at all, so whatever is already on the screen remains. The FL_..._FRAME
types only draw their edges, leaving the interior unchanged. The blue color in Figure 3-3 is the area that is not drawn by the frame types.
Note: This interface has changed in FLTK 2.0! |
void xyz_draw(int x, int y, int w, int h, Fl_Color c) { ... }
A simple drawing function might fill a rectangle with the given color and then draw a black outline:
void xyz_draw(int x, int y, int w, int h, Fl_Color c) { fl_color(c); fl_rectf(x, y, w, h); fl_color(FL_BLACK); fl_rect(x, y, w, h); }
Fl_Boxtype fl_down(Fl_Boxtype b)
#define XYZ_BOX FL_FREE_BOXTYPE Fl::set_boxtype(XYZ_BOX, xyz_draw, 1, 1, 2, 2);
x
, y
, width
, and height
values that should be subtracted when drawing the label inside the box.
A complete box design contains four box types in this order: a filled, neutral box (UP_BOX
), a filled, depressed box (DOWN_BOX
), and the same as outlines only (UP_FRAME
and DOWN_FRAME
). The function fl_down(Fl_Boxtype) expects the neutral design on a boxtype with a numerical value evenly dividable by two. fl_frame(Fl_Boxtype) expects the UP_BOX
design at a value dividable by four.
label()
, align()
, labelfont()
, labelsize()
, labeltype()
, image()
, and deimage()
methods control the labeling of widgets.
label()
method sets the string that is displayed for the label. Symbols can be included with the label string by escaping them using the "@" symbol - "@@" displays a single at sign. Figure 3-4 shows the available symbols.
Figure 3-4: FLTK label symbols
The @ sign may also be followed by the following optional "formatting" characters, in this order:
align()
method positions the label. The following constants are defined and may be OR'd together as needed:
FL_ALIGN_CENTER
- center the label in the widget. FL_ALIGN_TOP
- align the label at the top of the widget. FL_ALIGN_BOTTOM
- align the label at the bottom of the widget. FL_ALIGN_LEFT
- align the label to the left of the widget. FL_ALIGN_RIGHT
- align the label to the right of the widget. FL_ALIGN_INSIDE
- align the label inside the widget. FL_ALIGN_CLIP
- clip the label to the widget's bounding box. FL_ALIGN_WRAP
- wrap the label text as needed. FL_TEXT_OVER_IMAGE
- show the label text over the image. FL_IMAGE_OVER_TEXT
- show the label image over the text (default).labeltype()
method sets the type of the label. The following standard label types are included:
FL_NORMAL_LABEL
- draws the text. FL_NO_LABEL
- does nothing. FL_SHADOW_LABEL
- draws a drop shadow under the text. FL_ENGRAVED_LABEL
- draws edges as though the text is engraved. FL_EMBOSSED_LABEL
- draws edges as thought the text is raised. FL_ICON_LABEL
- draws the icon associated with the text.image()
and deimage()
methods set an image that will be displayed with the widget. The deimage()
method sets the image that is shown when the widget is inactive, while the image()
method sets the image that is shown when the widget is active.To make an image you use a subclass of Fl_Image.
FL_ENGRAVED_LABEL
) or with program-generated letters or symbology.
Note: This interface has changed in FLTK 2.0! |
The label should be drawn inside this bounding box, even if FL_ALIGN_INSIDE
is not enabled. The function is not called if the label value is NULL
.
The measure function is called with a pointer to a Fl_Label structure and references to the width and height:
void xyz_measure(const Fl_Label *label, int &w, int &h) { ... }
The function should measure the size of the label and set w
and h
to the size it will occupy.
#define XYZ_LABEL FL_FREE_LABELTYPE Fl::set_labeltype(XYZ_LABEL, xyz_draw, xyz_measure);
The label type number n
can be any integer value starting at the constant FL_FREE_LABELTYPE
. Once you have added the label type you can use the labeltype()
method to select your label type.
The Fl::set_labeltype() method can also be used to overload an existing label type such as FL_NORMAL_LABEL
.
To create a new symbol, you implement a drawing function void drawit(Fl_Color c)
which typically uses the functions described in Drawing Complex Shapes to generate a vector shape inside a two-by-two units sized box around the origin. This function is then linked into the symbols table using fl_add_symbol():
int fl_add_symbol(const char *name, void (*drawit)(Fl_Color), int scalable)
name
is the name of the symbol without the "@"; scalable
must be set to 1 if the symbol is generated using scalable vector drawing functions.
int fl_draw_symbol(const char *name,int x,int y,int w,int h,Fl_Color col)
This function draws a named symbol fitting the given rectangle.
void xyz_callback(Fl_Widget *w, void *data) { ... }
The callback()
method sets the callback function for a widget. You can optionally pass a pointer to some data needed for the callback:
int xyz_data; button->callback(xyz_callback, &xyz_data);
Normally callbacks are performed only when the value of the widget changes. You can change this using the Fl_Widget::when() method:
button->when(FL_WHEN_NEVER); button->when(FL_WHEN_CHANGED); button->when(FL_WHEN_RELEASE); button->when(FL_WHEN_RELEASE_ALWAYS); button->when(FL_WHEN_ENTER_KEY); button->when(FL_WHEN_ENTER_KEY_ALWAYS); button->when(FL_WHEN_CHANGED | FL_WHEN_NOT_CHANGED);
Note: You cannot delete a widget inside a callback, as the widget may still be accessed by FLTK after your callback is completed. Instead, use the Fl::delete_widget() method to mark your widget for deletion when it is safe to do so. Hint:
Many programmers new to FLTK or C++ try to use a non-static class method instead of a static class method or function for their callback. Since callbacks are done outside a C++ class, the
To work around this problem, define a static method in your class that accepts a pointer to the class, and then have the static method call the class method(s) as needed. The data pointer you provide to the
|
shortcut()
method sets the shortcut for a widget:
button->shortcut(FL_Enter); button->shortcut(FL_SHIFT + 'b'); button->shortcut(FL_CTRL + 'b'); button->shortcut(FL_ALT + 'b'); button->shortcut(FL_CTRL + FL_ALT + 'b'); button->shortcut(0); // no shortcut
The shortcut value is the key event value - the ASCII value or one of the special keys described in Fl::event_key() Values combined with any modifiers like Shift
, Alt
, and Control
.
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