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The main, all-purpose graphics container.

A layout is a "box" (a rectangle) whose purpose is to place onscreen the various elements composing the GUI. It can contain a single widget, or a list of sub-layouts. In Bogue, we use the housing metaphor: a layout is a house that contains either a single resident, or several rooms. Each room can be seen as a sub-house, and can contain a resident or sub-rooms. Houses and rooms have the type t, while a resident has the type Widget.t.

Technically, the usual metaphor in computer science is a Tree. A layout is a tree, each vertex (or node) has any number of branches (or children). A leaf (terminal node: without any child) is either empty or contains a widget. However, the tree is upside-down (as often): we think of the trunk (or top-layout) to be a the top, and the leaves at the bottom.

Dependency graph
type t
exception Fatal_error of t * string
type room_content =
  1. | Rooms of t list
  2. | Resident of Widget.t
type adjust =
  1. | Fit
  2. | Width
  3. | Height
  4. | Nothing

Not implemented.


type background

Warning, the background type corresponds actually to the Style.t type, which means is includes color backgrounds, image patterns, corner and shadow styles.

val color_bg : Draw.color -> background

Construct a background from an RGBA color.

val opaque_bg : Draw.rgb -> background

Construct a background from a RGB (ie non-transparent) color.

val style_bg : Style.t -> background

Construct a background from the given Style.

val theme_bg : background

This is the background constructed from the current theme's BG_COLOR.

val set_background : t -> background option -> unit
val unload_background : t -> unit

Free the texture associated with the background (if any). This can be used to force recreating it.

Creation of layouts

Remark: all layouts have an optional name property, which is used only for debugging.

val empty : ?name:string -> ?background:background -> w:int -> h:int -> unit -> t

An empty layout can reserve some space without stealing focus.

Create layouts from widgets

val resident : ?name:string -> ?x:int -> ?y:int -> ?w:int -> ?h:int -> ?background:background -> ?draggable:bool -> ?canvas:Draw.canvas -> ?layer:Draw.layer -> ?keyboard_focus:bool -> Widget.t -> t

Create a layout (=room) from a single Widget (=resident). The content of such a layout cannot be modified.

val flat_of_w : ?name:string -> ?sep:int -> ?h:int -> ?align:Draw.align -> ?background:background -> ?widget_bg:background -> ?canvas:Draw.canvas -> ?scale_content:bool -> Widget.t list -> t

Horizontal arrangement. See flat.

val tower_of_w : ?name:string -> ?sep:int -> ?w:int -> ?align:Draw.align -> ?background:background -> ?widget_bg:background -> ?canvas:Draw.canvas -> ?scale_content:bool -> Widget.t list -> t

Vertical arrangement. See tower.

Create layouts from other layouts

val flat : ?name:string -> ?sep:int -> ?adjust:adjust -> ?hmargin:int -> ?vmargin:int -> ?margins:int -> ?align:Draw.align -> ?background:background -> ?shadow:Style.shadow -> ?canvas:Draw.canvas -> ?scale_content:bool -> t list -> t

Create a horizontal arrangement from a list of rooms.

val tower : ?name:string -> ?sep:int -> ?margins:int -> ?hmargin:int -> ?vmargin:int -> ?align:Draw.align -> ?adjust:adjust -> ?background:background -> ?shadow:Style.shadow -> ?canvas:Draw.canvas -> ?clip:bool -> ?scale_content:bool -> t list -> t

Create a vertical arrangement from a list of rooms.

val superpose : ?w:int -> ?h:int -> ?name:string -> ?background:background -> ?canvas:Draw.canvas -> ?center:bool -> ?scale_content:bool -> t list -> t

Create a new layout by superposing a list of layouts without changing their (x,y) position.

Remark: when creating a house (a layout) with flat*, tower*, or superpose, the size of the inner rooms will be automatically updated whenever the size of the house is modified. However, as soon as one manually sets the size or the position of a room inside this house with set_width, setx and alikes, then the room will stop reacting to changes of the house size.

Some useful layout combinations

val make_clip : ?w:int -> ?scrollbar:bool -> ?scrollbar_inside:bool -> ?scrollbar_width:int -> h:int -> t -> t

Clip a layout inside a smaller container and make it scrollable, and optionally add a scrollbar widget.

Get layout attributes

val xpos : t -> int

get current absolute x position of the layout (relative to the top-left corner of the window). Not necessarily up-to-date.

val ypos : t -> int

see xpos

val width : t -> int
val height : t -> int
val get_size : t -> int * int

get_size l is equivalent to (width l, height l)

val get_physical_size : t -> int * int

multiplies get_size by the Theme scaling factor. This gives in principle the correct size in physical pixels, up to an error of +/- 1pixel, due to rounding error.

val getx : t -> int

Compute the relative x position of the room with respect to its house, using animations if any. Because of this, this function should not be called by the animation itself! Use get_oldx instead.

val get_oldx : t -> int

Return the last computed value for the relative x position of the layout.

val gety : t -> int
val get_oldy : t -> int
val widget : t -> Widget.t

Return the resident widget, or

  • raises Not_found

    if the layout is not a leaf.

val top_house : t -> t

Return the top of the layout tree (the "house" that contains the given layout and that is not contained in another layout). It is the only layout that is directly attached to a "physical" (SDL) window.

val get_content : t -> room_content
val get_rooms : t -> t list
val has_resident : t -> bool

Modify existing layouts

These functions will not work if there is an animation running acting of the variable we want to set. Most of these functions will stop the automatic resizing mechanism of the room. Use auto_scale to reactivate it.

val auto_scale : t -> unit

Set the layout to automatically scale its inner rooms when the layout size is modified.

val disable_resize : t -> unit

This makes sure that nothing is executed when someone tries to resize the layout.

val on_resize : t -> (unit -> unit) -> unit

on_resize room f will execute f () upon resizing the room's house (or the room's window, in case the room is the top house, see top_house), in addition to the already registered resized functions. Warning: placing the room in another layout will likely reset the resize function (unless you set the scale_content flag to false, see eg. flat and the remark below that). Hence on_resize should be called after the room is hosted in its house.

val set_width : ?keep_resize:bool -> ?check_window:bool -> ?update_bg:bool -> t -> int -> unit
val set_height : ?keep_resize:bool -> ?check_window:bool -> ?update_bg:bool -> t -> int -> unit
val set_size : ?keep_resize:bool -> ?check_window:bool -> ?update_bg:bool -> t -> (int * int) -> unit
val setx : ?keep_resize:bool -> t -> int -> unit
val sety : ?keep_resize:bool -> t -> int -> unit
val set_show : t -> bool -> unit
val set_shadow : t -> Style.shadow option -> unit
val fix_content : t -> unit

Disable automatic resizing of the rooms inside this layout.

val fit_content : ?sep:int -> t -> unit

Adapt the size of the layout (and their houses) to the disposition of the contained rooms.

val set_rooms : t -> ?sync:bool -> t list -> unit

Modify the layout content by replacing the former content by a new list of rooms. Use sync=true (the default) as much as possible in order to avoid multi-threading problems. Then the changes will be applied by the main thread at next frame (see Sync).

val replace_room : by:t -> t -> unit

Replace "room" by "by" inside "house" in lieu and place of the intial room. No size adjustments are made. Of course this is dangerous, because it modifies both the house and "by". Beware of circular dependencies... Of course this assumes that "room" already belongs to "house".

val unload_textures : t -> unit

Use this to free the textures stored by the layout (and its children) for reducing memory. The layout can still be used without any impact, the textures will be recreated on the fly.

val lock : t -> unit
val unlock : t -> unit

Since layouts can be modified by different threads, it might be useful to lock it with a mutex. This does *not* always prevent from modifying it, but another lock statement will wait for the previous lock to be removed by unlock.


Position, size, alpha channel, and rotation of Layouts use Avar variables and hence can be easily animated. Most predefined animations have a default duration of 300ms.

Generic animations

These functions assign an animated variable if type Avar.t to one of the properties of the layout (position, width, etc.)

val animate_x : t -> int Avar.t -> unit

Assign an Avar to the layout x position.

val animate_y : t -> int Avar.t -> unit
val stop_pos : t -> unit

Stop animations of the variables x and y.

val animate_w : t -> int Avar.t -> unit
val animate_h : t -> int Avar.t -> unit
val animate_alpha : t -> float Avar.t -> unit
val animate_angle : t -> float Avar.t -> unit

Predefined animations

val hide : ?duration:int -> ?towards:Avar.direction -> t -> unit

See show.

val show : ?duration:int -> ?from:Avar.direction -> t -> unit

Does nothing if the layout is already fully displayed. Only the Avar.Top and Avar.Bottom directions are currently implemented. For these directions, hide and show do not modify the position variables (x,y) of the layout, they use a special variable called voffset.

val fade_in : ?duration:int -> ?from_alpha:float -> ?to_alpha:float -> t -> unit

Animate the alpha channel of the layout. Can be combined with animations involving the other animated variables. Does not modify the show status of the layout. By default, from_alpha=0. (transparent) and to_alpha=1. (opaque).

val fade_out : ?duration:int -> ?from_alpha:float -> ?to_alpha:float -> ?hide:bool -> t -> unit

See fade_in. WARNING: fading out to alpha=0 results in a completely transparent layout, but the layout is still there (it's not "hidden"). Which means it can still get mouse focus. If you want to hide it, then use hide=true. By default, hide=false, from_alpha is the current alpha of the layout, and to_alpha=0.

val rotate : ?duration:int -> ?from_angle:float -> angle:float -> t -> unit

Rotate all widgets inside the layout around their respective centers. For a global rotation, use a Snapshot.

val slide_in : ?duration:int -> ?from:Avar.direction -> ?dst:t -> t -> unit
val slide_to : ?duration:int -> t -> (int * int) -> unit

slide_to room (x0,y0) will translate the room to the position (x0,y0).

val follow_mouse : ?dx:int -> ?dy:int -> ?modifierx:(int -> int) -> ?modifiery:(int -> int) -> t -> unit
val oscillate : ?duration:int -> ?frequency:float -> int -> t -> unit
val zoom : ?duration:int -> from_factor:float -> to_factor:float -> t -> unit
val reflat : ?align:Draw.align -> ?hmargin:int -> ?vmargin:int -> ?margins:int -> ?duration:int -> t -> unit

Adjust an existing layout to arrange its rooms in a "flat" fashion, as if they were created by Layout.flat. Will be animated if duration <> 0.

val retower : ?align:Draw.align -> ?hmargin:int -> ?vmargin:int -> ?margins:int -> ?duration:int -> t -> unit


An SDL window is created for each Layout in the list sent to Main.make.

val window_opt : t -> Tsdl.Sdl.window option

Return the SDL window containing the layout. It will return None if the window was not created yet, or was previously destroyed. Note that SDL windows are created by, not before.

val show_window : t -> unit

Make the window containing the layout appear onscreen, using set_show and Sdl.show_window. (If the layout was hidden at startup, Sdl.show_window is not enough to display the layout: use this function instead.)

val hide_window : t -> unit

Hide the window containing the layout.

val set_window_pos : t -> (int * int) -> unit

set_window_pos layout x y sets the position of the window containing layout to (x,y), in physical pixels. (0,0) is top-left. This should be run after Main.make.

val get_window_pos : t -> int option * int option

Return the window position within the desktop, in physical pixels.

val push_close : t -> unit

Emit the close-window event to the window containing the layout, as if the user clicked on the close button. This should close the window at the next graphics frame, or execute the function registered by Window.on_close.

val destroy_window : t -> unit

Emit the destroy_window event to ask Bogue to destroy the SDL window containing the layout.


val claim_keyboard_focus : t -> unit
val set_cursor : t option -> unit

Set the current cursor to the default value for this layout.

val containing_widget : Widget.t -> t option

Search for the room containing the widget, if any.