container: Add an placement container.

It should be called "align", but the name is already taken

It doesn't use awful.placement because it would break the dependency
graph.

Some cases previously required 2 wibox.layout.align layouts,
one for each axis. This is massively overkill to simply place
a widget at the center of a larger area.

lib/wibox/container/init.lua

@@ -16,6 +16,7 @@ return setmetatable({
     background = require("wibox.container.background");
     radialprogressbar = require("wibox.container.radialprogressbar");
     arcchart = require("wibox.container.arcchart");
+    place = require("wibox.container.place");
 }, {__call = function(_, args) return base.make_widget_declarative(args) end})
 
 -- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

lib/wibox/container/place.lua

@@ -0,0 +1,203 @@
+---------------------------------------------------------------------------
+-- A container used to place smaller widgets into larger space.
+--
+--@DOC_wibox_container_defaults_place_EXAMPLE@
+-- @author Emmanuel Lepage Vallee <elv1313@gmail.com>
+-- @copyright 2016 Emmanuel Lepage Vallee
+-- @release @AWESOME_VERSION@
+-- @classmod wibox.container.place
+---------------------------------------------------------------------------
+
+local setmetatable = setmetatable
+local base = require("wibox.widget.base")
+local util = require("awful.util")
+
+local place = { mt = {} }
+
+-- Take the widget width/height and compute the position from the full
+-- width/height
+local align_fct = {
+    left   = function(_  , _   ) return 0                         end,
+    center = function(wdg, orig) return math.max(0, (orig-wdg)/2) end,
+    right  = function(wdg, orig) return math.max(0, orig-wdg    ) end,
+}
+align_fct.top, align_fct.bottom = align_fct.left, align_fct.right
+
+-- Layout this layout
+function place:layout(context, width, height)
+
+    if not self._private.widget then
+        return
+    end
+
+    local w, h = base.fit_widget(self, context, self._private.widget, width, height)
+
+    if self._private.content_fill_horizontal then
+        w = width
+    end
+
+    if self._private.content_fill_vertical then
+        h = height
+    end
+
+    local valign = self._private.valign or "center"
+    local halign = self._private.halign or "center"
+
+    local x, y = align_fct[halign](w, width), align_fct[valign](h, height)
+
+    return { base.place_widget_at(self._private.widget, x, y, w, h) }
+end
+
+-- Fit this layout into the given area
+function place:fit(context, width, height)
+    if not self._private.widget then
+        return 0, 0
+    end
+
+    local w, h = base.fit_widget(self, context, self._private.widget, width, height)
+
+    return (self._private.fill_horizontal or self._private.content_fill_horizontal)
+        and width or w,
+    (self._private.fill_vertical or self._private.content_fill_vertical)
+        and height or h
+end
+
+--- The widget to be placed.
+-- @property widget
+-- @tparam widget widget The widget
+
+function place:set_widget(widget)
+    if widget then
+        base.check_widget(widget)
+    end
+    self._private.widget = widget
+    self:emit_signal("widget::layout_changed")
+end
+
+function place:get_widget()
+    return self._private.widget
+end
+
+--- Get the number of children element
+-- @treturn table The children
+function place:get_children()
+    return {self._private.widget}
+end
+
+--- Replace the layout children
+-- This layout only accept one children, all others will be ignored
+-- @tparam table children A table composed of valid widgets
+function place:set_children(children)
+    self:set_widget(children[1])
+end
+
+--- Reset this layout. The widget will be removed and the rotation reset.
+function place:reset()
+    self:set_widget(nil)
+end
+
+--- The vertical alignment.
+--
+-- Possible values are:
+--
+-- * *top*
+-- * *center* (default)
+-- * *bottom*
+--
+-- @property valign
+-- @param[opt="center"] string
+
+--- The horizontal alignment.
+--
+-- Possible values are:
+--
+-- * *left*
+-- * *center* (default)
+-- * *right*
+--
+-- @property halign
+-- @param[opt="center"] string
+
+function place:set_valign(value)
+    if value ~= "center" and value ~= "top" and value ~= "bottom" then
+        return
+    end
+
+    self._private.valign = value
+    self:emit_signal("widget::layout_changed")
+end
+
+function place:set_halign(value)
+    if value ~= "center" and value ~= "left" and value ~= "right" then
+        return
+    end
+
+    self._private.halign = value
+    self:emit_signal("widget::layout_changed")
+end
+
+--- Fill the vertical space.
+-- @property fill_vertical
+-- @param[opt=false] boolean
+
+function place:set_fill_vertical(value)
+    self._private.fill_vertical = value
+    self:emit_signal("widget::layout_changed")
+end
+
+--- Fill the horizontal space.
+-- @property fill_horizontal
+-- @param[opt=false] boolean
+
+function place:set_fill_horizontal(value)
+    self._private.fill_horizontal = value
+    self:emit_signal("widget::layout_changed")
+end
+
+--- Stretch the contained widget so it takes all the vertical space.
+-- @property content_fill_vertical
+-- @param[opt=false] boolean
+
+function place:set_content_fill_vertical(value)
+    self._private.content_fill_vertical = value
+    self:emit_signal("widget::layout_changed")
+end
+
+--- Stretch the contained widget so it takes all the horizontal space.
+-- @property content_fill_horizontal
+-- @param[opt=false] boolean
+
+function place:set_content_fill_horizontal(value)
+    self._private.content_fill_horizontal = value
+    self:emit_signal("widget::layout_changed")
+end
+
+--- Returns a new place container.
+-- @param[opt] widget The widget to display.
+-- @tparam[opt="center"] string halign The horizontal alignment
+-- @tparam[opt="center"] string valign The vertical alignment
+-- @treturn table A new place container.
+-- @function wibox.container.place
+local function new(widget, halign, valign)
+    local ret = base.make_widget(nil, nil, {enable_properties = true})
+
+    util.table.crush(ret, place, true)
+
+    ret:set_widget(widget)
+    ret:set_halign(halign)
+    ret:set_valign(valign)
+
+    return ret
+end
+
+function place.mt:__call(_, ...)
+    return new(_, ...)
+end
+
+--@DOC_widget_COMMON@
+
+--@DOC_object_COMMON@
+
+return setmetatable(place, place.mt)
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80