awesome/docs/03-declarative-layout.md

The declarative layout system

This system provide an alternative to the system used in Awesome 3.5 and is inspired by the one once used by Awesome 3.2-3.4 and Qt QML system.

A simple layout

• Display my_first_widget only on screen one
• Add a background color to my_third_widget
• Dispose in a wibox.layout.fixed.horizontal layout

Code:

mywibox[s] : setup {
    s == 1 and my_first_widget, -- Only display on screen 1
    my_second_widget,
    { -- Add a background color/pattern for my_third_widget
          my_third_widget,
          bg     = beautiful.bg_focus,
          widget = wibox.widget.background,
    },
    layout = wibox.layout.fixed.horizontal,
}

In this example s == 1 is an inline expression. In the default rc.lua, there is an s variable represent to define the current screen. Any lua logic expression can be used as long as it return a valid widget, or a declarative layout, or nil.

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.widget.background (for visualization)

Code:

mywibox[s] : 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.widget.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.widget.background
        },
        left   = 10,
        right  = 10,
        top    = 1,
        bottom = 2,
        layout = wibox.layout.margin
    },
    layout = wibox.layout.fixed.horizontal,
}

Result:

Use an wibox.layout.align layout

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

Code:

mywibox[s] : 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:

mywibox[s] : 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
mywibox[s] : 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 the widget can be accessed later.

Widgets defined using setup can be access by 3 means:

• Avoid the issue by using externally created widgets
• Use my_wibox.my_first_widget.my_second_widget style access
• Use JavaScript like my_wibox:get_children_by_id("my_second_widget")[1]

The first method mixes the imperative and declarative syntax, but makes the code less readable. The second is a little verbose and only works if every node in the chain have 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 reseved name. This include all method names, existing widget attributes, layout and widget. Names should also respect the lua variable name policies (case sensitive, alphanumeric and underscore characters and non-numeric first character)

Code:

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

mywibox[s].first.second:set_markup("changed!")
mywibox[s]: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 exist. 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 catched by a lua metatable (operator overload).

Code:

-- "Monkeypatch" a new function to wibox.widget.textbox to add vicious
-- extension support
function wibox.widget.textbox:vicious(args)
    local f = unpack or table.unpack -- Lua 5.1 compat
    vicious.register(w, f(args))
end

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

In this example, the system is extended to 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
mywibox[s] : 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

mywibox[s] : setup (three_circle)