Topic 03-declarative-layout.md - awesome API documentation

# The AwesomeWM widget system

This document explains how to define, place and manage widgets.

## The default widgets

### Widgets

Awesome provides 2 collections of widgets:

- wibox.widget: Generic widgets, containers and layouts
- `awful.widget`: The Awesome specific widgets

Name | Example
--- | ---
wibox.widget.calendar |
wibox.widget.checkbox |
wibox.widget.graph |
wibox.widget.imagebox |
wibox.widget.piechart |
wibox.widget.progressbar |
wibox.widget.separator |
wibox.widget.slider |
wibox.widget.textbox |

### Containers

A container is a widget that wraps another widget. It can be used to add decorations or to modify the content of the child widget.

Name | Example
--- | ---
wibox.container.arcchart |
wibox.container.background |
wibox.container.constraint |
wibox.container.margin |
wibox.container.mirror |
wibox.container.only_on_screen |
wibox.container.place |
wibox.container.radialprogressbar |
wibox.container.rotate |
wibox.container.scroll |

### Layouts

Layouts are collections of children widgets. They are placed according to configurable rules.

Name | Example
--- | ---
wibox.layout.align |
wibox.layout.fixed |
wibox.layout.flex |
wibox.layout.grid |
wibox.layout.manual |
wibox.layout.ratio |
wibox.layout.stack |

### The different type of widget boxes (Wibox)

The Awesome API uses the word "wibox" (widget box) to describe an area of the screen filled with widgets. There are many subvariants of wiboxes with specialized roles such as widget bars or tooltips. All variants mostly share the same characteristics, but add some extra features to make those specialized widget boxes easier to work with.

-- -- --

The normal wibox is the base class for each of these types. It is extremely flexible and allows to place just about anything on the screen. However it requires a lot of repetitive boilerplate code to use directly. For example, the user needs to compute the optimal size by hand or use awful.placement.

The awful.wibar specialization allows to attach a wibox to a screen edge and prevents clients from using this area when tiled.

The awful.popup allows to easily place widgets on the screen. It automatically resizes itself to fit the optimal widget size. It also has helper properties and methods to make it easy to place it on the screen. It supports absolute positioning, relative positioning, and manual positioning.

The awful.tooltip is a very simple wibox that allows to display text next to an object such as the mouse.

Finally, the awful.titlebar, while not technically a real wibox, acts exactly the same way and allows to attach widgets on each side of clients.

## The different syntaxes to initiate widgets

Awesome provides 2 totally different API access styles to manage widgets. Both suit different use cases. Under the hood, both produce the exact same code. Consider the declarative API to be compiled into the imperative syntax when loaded. Also note that in contrast to technologies such as QML, it is interpreted only once and isn't automatically updated when values change.

The imperative widget initialization is similar to QtWidgets, GTK and Win32. You create the object, then set the property and add the widget as a child to another already declared widget. It is quite simple to use but very verbose and full of boilerplate code. The imperative API also offers properties both with accessors or directly. It is useful when creating highly dynamic layouts where widgets are added and removed over the course of their lifecycle.

The declarative syntax resembles HTML style code written in JSON or YAML. The widget instances are created automatically and the hierarchy is related to the table nesting (indentation). It is preferred when creating static layouts that won't change over the course of their lifecycle.

Here is the same code written in both the imperative and declarative style

Imperative with accessors

Code:

    local bg = wibox.container.background()
    bg:set_bg("#ff0000")

    local tb1 = wibox.widget.textbox()
    local tb2 = wibox.widget.textbox("bar")

    tb1:set_text("foo")
    tb2:set_text("bar")

    local l = wibox.layout.fixed.vertical()
    l:add(tb1)
    l:add(tb2)

    bg:set_widget(l)

Imperative with properties

Code:

    local bg = wibox.container.background()
    bg.bg = "#ff0000"

    local tb1 = wibox.widget.textbox("foo")
    local tb2 = wibox.widget.textbox("bar")

    tb1.text = "foo"
    tb2.text = "bar"

    local l = wibox.layout.fixed.vertical()
    l:add(tb1)
    l:add(tb2)

    bg.widget = l

Declarative

Code:

    local bg = wibox.widget {
        {
            {
                text = "foo",
                widget = wibox.widget.textbox
            },
            {
                text = "bar",
                widget = wibox.widget.textbox
            },
            layout = wibox.layout.fixed.vertical
        },
        bg = "#ff0000",
        widget = wibox.container.background
    }

The Awesome documentation mostly uses the declarative style for consistency, but both are always available. Note that each style can be mixed with other styles, but this creates very confusing code and should be avoided.

## Creating and placing widgets using the declarative style

The examples below explain in detail how to use the declarative layout system. The imperative system is quite self explanatory and the respective widget API documentation should be enough for most.

### A simple layout

- Display `my_first_widget` only on primary screen
- Display `my_second_widget` only on screen two
- Add a background color to `my_fourth_widget`
- Dispose in a wibox.layout.fixed.horizontal layout

Code:

    s.mywibox : setup {
        {
            layout = awful.widget.only_on_screen,
            screen = "primary", -- Only display on primary screen
            my_first_widget,
        },
        {
            layout = awful.widget.only_on_screen,
            screen = 2, -- Only display on screen 2
            my_second_widget,
        },
        my_third_widget, -- Displayed on all screens
        { -- Add a background color/pattern for my_fourth_widget
              my_fourth_widget,
              bg     = beautiful.bg_focus,
              widget = wibox.container.background,
        },
        layout = wibox.layout.fixed.horizontal,
    }

This examples uses the awful.widget.only_on_screen container to display widgets only on some screens.

### Composite widgets

    -- The progressbars will be on top of each other
     local mycpubar1 = wibox.widget {
        { value  = 0.2, color = grad1,
            widget = wibox.widget.progressbar },
        { value  = 0.4, color = grad2,
            widget = wibox.widget.progressbar },
        { value  = 0.6, color = grad3,
            widget = wibox.widget.progressbar },
        layout = wibox.layout.flex.vertical,
     }
    -- Now, add a rotate container, the height will become the width.
    -- It act as if the wibox.layout.flex.vertical was
    -- wibox.layout.flex.horizontal
     local mycpubar2 = wibox.widget {
        {
            { value  = 0.2, color = grad1,
                widget = wibox.widget.progressbar },
            { value  = 0.4, color = grad2,
                widget = wibox.widget.progressbar },
            { value  = 0.6, color = grad3,
                widget = wibox.widget.progressbar },
            layout = wibox.layout.flex.vertical,
        },
        direction = 'east',
        widget    = wibox.container.rotate
     }

### Define widgets inline and place them

- Create a wibox.widget.textbox with various properties
- Force the textbox size using `wibox.layout.constraint`
- Add a margin around another textbox
- Add a wibox.container.background (for visualization)

Code:

    s.mywibox : setup {
        {
            -- Force the textbox to always be 300 pixel long
            {
                {
                    markup = "<b>Hello World!</b>",
                    align  = "center",
                    widget = wibox.widget.textbox
                },
                bg     = "#ff0000",
                widget = wibox.container.background,
            },
            width    = 300,
            strategy = "min",
            layout   = wibox.layout.constraint
        },
        {
            -- Add a border around the background
            {
                {
                    markup = "Foobar",
                    widget = wibox.widget.textbox
                },
                bg     = "#0000ff",
                widget = wibox.container.background
            },
            left   = 10,
            right  = 10,
            top    = 1,
            bottom = 2,
            layout = wibox.container.margin
        },
        layout = wibox.layout.fixed.horizontal,
    }

Result:

### Use a wibox.layout.align layout

The wibox.layout.align is a little different. While most layouts will ignore any `nil` lines, the `align` layout relies on them so `left`, `middle` and `right` can be defined.

Code:

    s.mywibox : setup {
        my_textbox1, -- Left
        nil,         -- Nothing in the middle
        my_textbox2, -- Right
        layout = wibox.layout.fixed.horizontal,
    }

### Define new widgets

New trivial widgets can be created directly in the layout declaration. Here is a simple circle widget:

Code:

    s.mywibox : setup {
        fit    = function(self, context, width, height)
            return height, height -- A square taking the full height
        end,
        draw   = function(self, context, cr, width, height)
            cr:set_source_rgb(1, 0, 0) -- Red
            cr:arc(height/2, height/2, height/2, 0, math.pi*2)
            cr:fill()
        end,
        layout = wibox.widget.base.make_widget,
    }

Result:

For more information about how to draw widgets, refer to the `Cairo` API:

- Path
- Context
- Pattern
- transformation
- Operator
- Pango text

### Externally defined widgets and layouts

This is useful when the widget is provided by an external module or when it requires complex manipulations which would make the declaration unreadable.

Code:

    local tb = wibox.widget.textbox()
    tb:set_markup("Hello world! ")

    -- Repeat "tb" 3 times
    s.mywibox : setup {
        tb,
        tb,
        tb,
        layout = wibox.layout.fixed.horizontal,
    }

### Accessing widgets

For each widget or container, it is possible to add an `identifier` attribute so that it can be accessed later.

Widgets defined using `setup` can be accessed using these methods:

- Avoiding the issue by using externally created widgets
- Using `my_wibox.my_first_widget.my_second_widget` style access
- Using JavaScript like `my_wibox:get_children_by_id("my_second_widget")[1]`

The first method mixes the imperative and declarative syntax, and makes the code less readable. The second is a little verbose and only works if every node in the chain has a valid identifier. The last one doesn't require long paths, but it is not easy to get a specific instance if multiple widgets have the same identifier.

WARNING: The widget identifier must not use a reserved name. This includes all method names, existing widget attributes, `layout` and `widget`. Names should also respect the Lua variable conventions (case-sensitive, alphanumeric, underscore characters and non-numeric first character).

Code:

    s.mywibox : setup {
        {
            id     = "second",
            widget = wibox.widget.textbox
        },
        {
            id     = "third",
            widget = wibox.widget.textbox
        },
        id     = "first",
        layout = wibox.layout.fixed.horizontal,
    }

    s.mywibox.first.second:set_markup("changed!")
    s.mywibox:get_children_by_id("third")[1]:set_markup("Also changed!")

### Extending the system

This system is very flexible. Each section attribute (the entries with string keys) is directly linked to the layout or widget API. When setting the imaginary `myproperty`, it will first check if `set_myproperty` exists. If it doesn't, it will check if there is a `myproperty` method. Finally, it will just set the `mywidget.myproperty` directly in case it is used later or caught by a Lua `metatable` (operator overload).

Code:

    -- "Monkeypatch" a new function to 3 widget classes to add vicious
    -- extension support
    for _, wdg in ipairs {
        wibox.widget.textbox , wibox.widget.progressbar, wibox.widget.graph
    } do
        function wdg:vicious(args)
            local f = unpack or table.unpack -- Lua 5.1 compat
            vicious.register(self, f(args))
        end
    end

    s.mywibox : setup {
        {
            vicious = {vicious.widgets.cpu, "CPU: $1%", 3},
            widget  = wibox.widget.textbox
        },
        layout = wibox.layout.fixed.horizontal,
    }

In this example, the system is extended so that the popular Vicious extension module can be used directly in the layout declaration. This example will update the textbox every 3 seconds to show the CPU usage.

### Handling sections

The system allows sections to be defined externally, then composed into the final layout declaration. Here is an example re-using one of the above example:

Code:

    local circle = {
        fit    = function(self, context, width, height)
            return height, height -- A square taking the full height
        end,
        draw   = function(self, context, cr, width, height)
            cr:set_source_rgb(1, 0, 0) -- Red
            cr:arc(height/2, height/2, height/2, 0, math.pi*2)
            cr:fill()
        end,
        layout = wibox.widget.base.make_widget,
    }

    -- Define a layout with the imperative syntax
    local l = wibox.widget.align()

    -- 3 circle
    s.mywibox : setup {
        circle,
        circle,
        circle,
        l,
        layout = wibox.layout.align.horizontal
    }

    -- This can be done instead
    local three_circle = {layout = wibox.layout.align.horizontal}
    for i=1, 3 do
        table.insert(three_circle, circle)
    end

    s.mywibox : setup (three_circle)

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