wibox: Add an input_passthrough property.

Allows, for example, to have semi translucent wibars on top of
the fullscreens clients without having issues with inputs.

docs/common/wibox.ldoc

@@ -180,6 +180,22 @@
 -- @property shape
 -- @tparam gears.shape shape
 
+--- Forward the inputs to the client below the wibox.
+--
+-- This replace the `shape_input` mask with an empty area. All mouse and
+-- keyboard events are sent to the object (such as a client) positioned below
+-- this wibox. When used alongside compositing, it allows, for example, to have
+-- a subtle transparent wibox on top a fullscreen client to display important
+-- data such as a low battery warning.
+--
+-- **Signal:**
+--
+--  * *property::input_passthrough*
+--
+-- @property input_passthrough
+-- @param[opt=false] boolean
+-- @see shape_input
+
 --- Get or set mouse buttons bindings to a wibox.
 --
 -- @param buttons_table A table of buttons objects, or nothing.

lib/wibox/init.lua

@@ -137,11 +137,6 @@ function wibox:_apply_shape()
     img:finish()
 end
 
---- Set the wibox shape.
--- @property shape
--- @tparam gears.shape A gears.shape compatible function.
--- @see gears.shape
-
 function wibox:set_shape(shape)
     self._shape = shape
     self:_apply_shape()
@@ -151,6 +146,24 @@ function wibox:get_shape()
     return self._shape
 end
 
+function wibox:set_input_passthrough(value)
+    rawset(self, "_input_passthrough", value)
+
+    if not value then
+        self.shape_input = nil
+    else
+        local img = cairo.ImageSurface(cairo.Format.A1, 0, 0)
+        self.shape_input = img._native
+        img:finish()
+    end
+
+    self:emit_signal("property::input_passthrough", value)
+end
+
+function wibox:get_input_passthrough()
+    return self._input_passthrough
+end
+
 function wibox:get_screen()
     if self.screen_assigned and self.screen_assigned.valid then
         return self.screen_assigned
@@ -324,7 +337,13 @@ local function new(args)
         ret:set_screen ( args.screen  )
     end
 
-    ret.shape = args.shape
+    if args.shape then
+        ret.shape = args.shape
+    end
+
+    if args.screen then
+        ret.input_passthrough = args.input_passthrough
+    end
 
     return ret
 end