Module Bogue.Widget

module Widget: sig .. end

Creating widgets and giving life to them

Widgets are simple graphic elements that can react to user interaction. They are the inhabitants of your GUI house. When a widget is woken up by some event, it can talk to another widget by means of a connection.

Dependency graph

type t 

The type Widget.t is a union of all kinds of widgets: Box, Button, Check box, Image, Label, Slider, Text display, and Text input, plus the Empty widget.

For instance, in the following code:

let w = label "Hello" in
let l = get_label w in

w has the generic Widget.t type, while l has the specialized Label.t type.


A connection has a source widget and a target widget. When the source widget receives a specified event, the connection is activated, executing a specified function, which is called Widget.action.

An action is always executed in a new Thread (and hence will not block the GUI), unless the priority Main is specified.

If a widget possess several connections which react to the same event, the order of execution of these connections is the same as the order they were registered.

type connection 
type action = t -> t -> Tsdl.Sdl.event -> unit 

An action is a function with three parameters w1 w2 ev, where w1 is the source widget, w2 the target widget, and ev the event (Trigger.t) that triggered the action.

The action should regularly verify Trigger.should_exit ev and quickly exit when that function returns true.

What happens when an event triggers an action while the same action (= same connection id) is already running? Several behaviours are possible, depending on the following Widget.action_priority type.

type action_priority = 
| Forget (*

discard the new action

| Join (*

execute the new after the first one has completed

| Replace (*

kill the first action (if possible) and execute the second one

| Main (*

run in the main program. So this is blocking for all subsequent actions

val connect : t ->
t ->
action ->
?priority:action_priority ->
?update_target:bool ->
?join:connection ->
Trigger.t list -> connection

connect source target action triggers creates a connection from the source widget to the target widget, but does not register it (this may change in the future...). Once it is registered (either by Main.create or Widget.add_connection), and assuming that the layout containing the source widget has focus, then when an event ev matches one of the triggers list, the action is executed with arguments source target ev.

priority : indicates the desired priority policy. Default is Forget.
val connect_main : t ->
t ->
action ->
?update_target:bool ->
?join:connection ->
Trigger.t list -> connection

Alias for connect ~priority:Main. Should be used for very fast actions that can be run in the main thread.

val add_connection : t -> connection -> unit

Registers the connection with the widget. This should systematically be done after each connection creation, when the connection is created after Main.create.

Connections that are created before Main.create should rather be passed as argument to Main.create, and not via add_connection. Although this is not strictly necessary, this indicates that these connections are more 'pure' or at least more static, in the sense that they will not be modified by Bogue. These are usually much easier to debug.

add_connection is separated from Widget.connect because it is not pure: it mutates the widget. This might change in future versions.

val update : t -> unit

update w asks the widget w to refresh at next frame. The most probable use of update is within the code of an Widget.action. It can happen that the action modifies the visual state of a widget that is neither the source or the target, and then one needs to explicitly tell this widget to re-draw itself.

Predefined connections

val on_release : release:(t -> unit) -> t -> unit

on_release ~release:f w registers on the widget w the action f, which will be executed when the mouse button is released on this widget. Uses priority=Main

val on_button_release : release:(t -> unit) -> t -> unit

Similar to Widget.on_release but specialised to button widgets. It also checks the key used to activate buttons (currently, the Return key).

val on_click : click:(t -> unit) -> t -> unit

Uses priority=Main

val mouse_over : ?enter:(t -> unit) ->
?leave:(t -> unit) -> t -> unit

Creation of Widgets

As a general rule, widgets should be created using the functions below, which belong to the Widget module and create an element of type Widget.t. However, for some specialized usage, additional features may be available from the widget underlying module (eg. Label, Box, etc.). See the conversion functions below.

Simple boxes (rectangles)

val box : ?w:int -> ?h:int -> ?style:Style.t -> unit -> t

Create a Box widget, which simply displays a rectangle, optionally with rounded corners and drop shadow. It is often used for the background of a group of widgets (i.e. a Layout.t).

Check boxes

The standard on/off check boxes.

val check_box : ?state:bool -> ? -> unit -> t
val set_check_state : t -> bool -> unit

Text display

Use this for multi-line text.

val text_display : ?w:int -> ?h:int -> string -> t
val rich_text : ?size:int ->
?w:int -> ?h:int -> Text_display.words list -> t
val verbatim : string -> t
val html : ?w:int -> ?h:int -> string -> t

Display basic html text by interpreting the following tags: <em>,</em>, <b>,</b>, <strong>,</strong>, <p>,</p>, <br>

Labels or icons

val label : ?size:int ->
?fg:Draw.color ->
?font:Label.font -> ?align:Draw.align -> string -> t

Create a Label widget with a one-line text.

val icon : ?size:int -> ?fg:Draw.color -> string -> t

Create a Label widget with a FontAwesome icon.

For instance icon ~size:24 "star" creates a widget that displays the "fa-star" fontawesome icon.


val empty : w:int -> h:int -> unit -> t

Create a widget that does not display anything but still gets focus and reacts to events.


val image : ?w:int ->
?h:int ->
?bg:Draw.color ->
?noscale:bool -> ?angle:float -> string -> t

Load image file.

val image_from_svg : ?w:int -> ?h:int -> ?bg:Draw.color -> string -> t

Requires rsvg.

val image_copy : ?rotate:float -> t -> t

Return a new "Image" widget linked to the same image (same underlying Image.t, hence same texture.)

Text input

val text_input : ?text:string ->
?prompt:string ->
?size:int ->
?filter:Text_input.filter -> ?max_size:int -> unit -> t

size is the font size. max_size is the maximum number of chars allowed. The prompt is used to display a message when there is no user input. It also influences the size of the widget.


val button : ?kind:Button.kind ->
?label:Label.t ->
?label_on:Label.t ->
?label_off:Label.t ->
?fg:Draw.color ->
?bg_on:Style.background ->
?bg_off:Style.background ->
?bg_over:Style.background option ->
?state:bool ->
?border_radius:int ->
?border_color:Draw.color ->
?action:(bool -> unit) -> string -> t


val slider : ?priority:action_priority ->
?step:int ->
?value:int ->
?kind:Slider.kind ->
?var:(int Avar.t, int) Tvar.t ->
?length:int ->
?thickness:int ->
?tick_size:int -> ?lock:bool -> ?w:int -> ?h:int -> int -> t
val slider_with_action : ?priority:action_priority ->
?step:int ->
?kind:Slider.kind ->
value:int ->
?length:int ->
?thickness:int ->
?tick_size:int -> action:(int -> unit) -> int -> t

Create a slider that executes an action each time the local value of the slider is modified by the user.

Sdl Area

You can use an Sdl_area widget to draw whatever you want using all the power of the SDL Renderer API.

val sdl_area : w:int -> h:int -> ?style:Style.t -> unit -> t

See Sdl_area.create regarding the size (w,h).

Creation of combined widgets

val check_box_with_label : string -> t * t

let b,l = check_box_with_label text creates a check box b, a label l, and connect them so that clicking on the text will also act on the check box.

Generic functions on widgets

These generic functions work on all types of widgets, and emit an error in the log (without raising any exception) whenever the type of the argument makes no sense for the function.

These functions are very handy, but sometimes can hide a bug. For instance if you want to use get_state t, while you know that t should always be of type Button, then it will help debugging to use instead the slightly longer form Button.state (get_button t). Indeed the latter will fail if t happens not to be a Button.

val get_state : t -> bool

Query a boolean state. Works for Button and Check.

val get_text : t -> string

Return the text of the widget. Works for Button, TextDisplay, Label, and TextInput.

val size : t -> int * int

If the widget is not rendered yet, a default size may be returned instead of the true size.

val set_state : t -> bool -> unit

Set a boolean state. Works for Button and Check.

val set_text : t -> string -> unit

Change the text of a widget. Works for Button, TextDisplay, Label, and TextInput.

val set_cursor : t -> Tsdl.Sdl.cursor option -> unit

Set the cursor that should be displayed for this widget. Note that the Sdl functions for creating cursor are only available after SDL initialization. One can use a Lazy type or Sync.push for delaying their execution.

Conversions from the generic Widget type to the specialized inner type

These functions raise Invalid_argument whenever their argument is not of the correct type.

val get_box : t -> Box.t
val get_check : t -> Check.t
val get_label : t -> Label.t
val get_button : t -> Button.t
val get_slider : t -> Slider.t
val get_text_display : t -> Text_display.t
val get_text_input : t -> Text_input.t
val get_image : t -> Image.t
val get_sdl_area : t -> Sdl_area.t

Generic actions

val map_text : (string -> string) -> action

map_text f is a Widget.action that replaces the text of the second widget by f applied to the text of the first widget.