Add "opacity" property for widgets

lib/wibox/drawable.lua

@@ -59,7 +59,10 @@ local function do_redraw(self)
     self._widget_geometries = {}
     if self.widget and self.widget.visible then
         cr:set_source(self.foreground_color)
+        cr:push_group()
         self.widget:draw(self.widget_arg, cr, width, height)
+        cr:pop_group_to_source()
+        cr:paint_with_alpha(self.widget.opacity)
         self:widget_at(self.widget, 0, 0, width, height)
     end
 

lib/wibox/layout/base.lua

@@ -66,11 +66,14 @@ function base.draw_widget(wibox, cr, widget, x, y, width, height)
     cr:rectangle(0, 0, width, height)
     cr:clip()
 
+    cr:push_group()
     -- Let the widget draw itself
     local success, msg = pcall(widget.draw, widget, wibox, cr, width, height)
     if not success then
         print("Error while drawing widget: " .. msg)
     end
+    cr:pop_group_to_source()
+    cr:paint_with_alpha(widget.opacity)
 
     -- Register the widget for input handling
     wibox:widget_at(widget, base.rect_to_device_geometry(cr, 0, 0, width, height))

lib/wibox/widget/base.lua

@@ -116,6 +116,15 @@ function base.make_widget(proxy, widget_name)
         end
     end
 
+    -- Add opacity property and setter.
+    ret.opacity = 1
+    function ret:set_opacity(b)
+        if b ~= self.opacity then
+            self.opacity = b
+            self:emit_signal("widget::updated")
+        end
+    end
+
     -- Add __tostring method to metatable.
     ret.widget_name = widget_name or object.modulename(3)
     local mt = {}