Added Expand Modes

Added set_expand function with options of "none" "outside" or "inside" modes.
The "inside" mode is the default and will result in the original behavior. The
main benefit is being able to actually center a widget in the available space
with options of how to draw the outside widgets (expand to take the space,
or not.) Further functionality can be had by ommiting one of the outside
widgets. Set default layout mode in the constructor.

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/wibox/layout/align.lua.in

@@ -8,6 +8,7 @@ local setmetatable = setmetatable
 local table = table
 local pairs = pairs
 local type = type
+local floor = math.floor
 local base = require("wibox.layout.base")
 local widget_base = require("wibox.widget.base")
 
@@ -19,49 +20,90 @@ local align = {}
 -- @param cr The cairo context to use.
 -- @param width The available width.
 -- @param height The available height.
--- @return The total space needed by the layout.
 function align:draw(wibox, cr, width, height)
     local size_first = 0
-    local size_third = 0
+    local size_remains = self.dir == "y" and height or width
-    local size_limit = self.dir == "y" and height or width
 
+    if self._expand ~= "inside" and self.second then
+        local w, h = base.fit_widget(self.second, width, height)
+        local size_second = self.dir == "y" and h or w
+        if size_second >= size_remains then
+            base.draw_widget(wibox, cr, self.second, 0, 0, width, height)
+            return
+        else
+            size_remains = floor((size_remains - size_second) / 2)
+        end
+    end
     if self.first then
         local w, h, _ = width, height, nil
+        if self._expand ~= "outside" or not self.second then
             if self.dir == "y" then
-            _, h = base.fit_widget(self.first, w, h)
+                _, h = base.fit_widget(self.first, width, size_remains)
                 size_first = h
+                if self._expand == "inside" or not self.second then
+                    size_remains = size_remains - h
+                end
             else
-            w, _ = base.fit_widget(self.first, w, h)
+                w, _ = base.fit_widget(self.first, size_remains, height)
                 size_first = w
+                if self._expand == "inside" or not self.second then
+                    size_remains = size_remains - w
+                end
+            end
+        else
+            if self.dir == "y" then
+                h = size_remains
+            else
+                w = size_remains
+            end
         end
         base.draw_widget(wibox, cr, self.first, 0, 0, w, h)
     end
 
-    if self.third and size_first < size_limit then
+    if self.third and size_remains > 0 then
-        local w, h, x, y, _
+        local w, h, _ = width, height, nil
+        if self._expand ~= "outside" then
             if self.dir == "y" then
-            w, h = width, height - size_first
+                _, h = base.fit_widget(self.third, width, size_remains)
-            _, h = base.fit_widget(self.third, w, h)
+                if self._expand == "inside" then
-            x, y = 0, height - h
+                    size_remains = size_remains - h
-            size_third = h
-        else
-            w, h = width - size_first, height
-            w, _ = base.fit_widget(self.third, w, h)
-            x, y = width - w, 0
-            size_third = w
                 end
+            else
+                w, _ = base.fit_widget(self.third, size_remains, height)
+                if self._expand == "inside" then
+                    size_remains = size_remains - w
+                end
+            end
+        else
+            if self.dir == "y" then
+                h = size_remains
+            else
+                w = size_remains
+            end
+        end
+        local x, y = width - w, height - h
         base.draw_widget(wibox, cr, self.third, x, y, w, h)
     end
 
-    if self.second and size_first + size_third < size_limit then
+    if self.second and size_remains > 0 then
-        local x, y, w, h
+        local x, y, w, h = 0, 0, width, height
+        if self._expand == "inside" then
             if self.dir == "y" then
-            w, h = width, size_limit - size_first - size_third
+                h = size_remains
                 x, y = 0, size_first
             else
-            w, h = size_limit - size_first - size_third, height
+                w = size_remains
                 x, y = size_first, 0
             end
+        else
+            if self.dir == "y" then
+                _, h = base.fit_widget(self.second, width, size_remains)
+                y = floor( (height - h)/2 )
+            else
+                w, _ = base.fit_widget(self.second, width, size_remains)
+                x = floor( (width -w)/2 )
+            end
+        end
         base.draw_widget(wibox, cr, self.second, x, y, w, h)
     end
 end
@@ -120,6 +162,26 @@ function align:fit(orig_width, orig_height)
     end
     return used_in_dir, used_in_other
 end
+--- Set the expand mode which determines how sub widgets expand to take up
+-- unused space. Options are:
+--  "inside" - Default option. Size of outside widgets is determined using their
+--              fit function. Second, middle, or center widget expands to fill
+--              remaining space.
+-- "outside" - Center widget is sized using its fit function and placed in the
+--              center of the allowed space. Outside widgets expand (or contract)
+--              to fill remaining space on their side.
+--    "none" - All widgets are sized using their fit function, drawn to only the
+--              returned space, or remaining space, whichever is smaller. Center
+--              widget gets priority.
+-- @param mode How to use unused space. "inside" (default) "outside" or "none"
+function align:set_expand(mode)
+    if mode == "none" or mode == "outside" then
+        self._expand = mode
+    else
+        self._expand = "inside"
+    end
+    self:emit_signal("widget::updated")
+end
 
 function align:reset()
     for k, v in pairs({ "first", "second", "third" }) do
@@ -141,6 +203,8 @@ local function get_layout(dir)
         end
     end
 
+    ret:set_expand("inside")
+
     return ret
 end