Make the piechart deterministic (#1258)

Previously, the API to set the data that should be displayed was
:set_data(t) where t is a table. This table has the labels to use as its
keys and the numbers as its values. With this API, it was not possible
to influence the order in which the "pie pieces" were drawn.

This commit adds and uses a new API called :set_data_list(t). Here, t is
a table with integer keys and tables as values, thus one can iterate
over this with ipairs() and the order is well-defined. The tables used
as values contain the label as their first entry and the number as their
second entry.

Fixes: https://github.com/awesomeWM/awesome/issues/1249
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/wibox/widget/piechart.lua

@@ -51,18 +51,18 @@ end
 
 local function compute_sum(data)
     local ret = 0
-    for _,v in pairs(data) do
+    for _, entry in ipairs(data) do
-        ret = ret + v
+        ret = ret + entry[2]
     end
 
     return ret
 end
 
 local function draw(self, _, cr, width, height)
-    if not self._private.data then return end
+    if not self._private.data_list then return end
 
     local radius = (height > width and width or height) / 4
-    local sum, start, count = compute_sum(self._private.data),0,0
+    local sum, start, count = compute_sum(self._private.data_list),0,0
     local has_label = self._private.display_labels ~= false
 
     -- Labels need to be drawn later so the original source is kept
@@ -81,7 +81,8 @@ local function draw(self, _, cr, width, height)
     local colors = self:get_colors()
     local col_count = colors and #colors or 0
 
-    for k,v in pairs(self._private.data) do
+    for _, entry in ipairs(self._private.data_list) do
+        local k, v = entry[1], entry[2]
         local end_angle = start + 2*math.pi*(v/sum)
 
         local col = colors and color(colors[math.fmod(count,col_count)+1]) or nil
@@ -135,6 +136,11 @@ local function fit(_, _, width, height)
     return width, height
 end
 
+--- The pie chart data list.
+-- @property data_list
+-- @tparam table data_list Sorted table where each entry has a label as its
+-- first value and a number as its second value.
+
 --- The pie chart data.
 -- @property data
 -- @tparam table data Labels as keys and number as value.
@@ -180,12 +186,15 @@ end
 -- @tparam table colors A table of colors, one for each elements
 -- @see gears.color
 
-for _, prop in ipairs {"data", "border_color", "border_width", "colors",
+for _, prop in ipairs {"data_list", "border_color", "border_width", "colors",
     "display_labels"
   } do
     piechart["set_"..prop] = function(self, value)
         self._private[prop] = value
         self:emit_signal("property::"..prop)
+        if prop == "data_list" then
+            self:emit_signal("property::data")
+        end
         self:emit_signal("widget::redraw_needed")
     end
     piechart["get_"..prop] = function(self)
@@ -193,7 +202,23 @@ for _, prop in ipairs {"data", "border_color", "border_width", "colors",
     end
 end
 
-local function new(data)
+function piechart:set_data(value)
+    local list = {}
+    for k, v in pairs(value) do
+        table.insert(list, { k, v })
+    end
+    self:set_data_list(list)
+end
+
+function piechart:get_data()
+    local list = {}
+    for _, entry in ipairs(self:get_data_list()) do
+        list[entry[1]] = entry[2]
+    end
+    return list
+end
+
+local function new(data_list)
 
     local ret = base.make_widget(nil, nil, {
         enable_properties = true,
@@ -204,7 +229,7 @@ local function new(data)
     rawset(ret, "fit" , fit )
     rawset(ret, "draw", draw)
 
-    ret:set_data(data)
+    ret:set_data_list(data_list)
 
     return ret
 end

tests/examples/wibox/widget/defaults/piechart.lua

@@ -5,10 +5,10 @@ local beautiful = require( "beautiful" ) --DOC_HIDE
 parent:add( --DOC_HIDE
 
 wibox.widget {
-    data = {
+    data_list = {
-        ['L1'] = 100,
+        { 'L1', 100 },
-        ['L2'] = 200,
+        { 'L2', 200 },
-        ['L3'] = 300,
+        { 'L3', 300 },
     },
     border_width = 1,
     forced_height = 50, --DOC_HIDE

tests/examples/wibox/widget/piechart/border_color.lua

@@ -8,10 +8,10 @@ parent:add(l)
 
 for _, v in ipairs {"#ff0000", "#00ff00", "#0000ff"} do
     l:add(wibox.widget {
-        data = {
+        data_list = {
-            ['L1'] = 100,
+            { 'L1', 100 },
-            ['L2'] = 200,
+            { 'L2', 200 },
-            ['L3'] = 300,
+            { 'L3', 300 },
         },
         border_width = 1,
         border_color = v,

tests/examples/wibox/widget/piechart/border_width.lua

@@ -8,10 +8,10 @@ parent:add(l)
 
 for _, v in ipairs {0,1,3,5} do
     l:add(wibox.widget {
-        data = {
+        data_list = {
-            ['L1'] = 100,
+            { 'L1', 100 },
-            ['L2'] = 200,
+            { 'L2', 200 },
-            ['L3'] = 300,
+            { 'L3', 300 },
         },
         border_width = v,
         forced_height = 50,

tests/examples/wibox/widget/piechart/label.lua

@@ -11,10 +11,10 @@ parent:add(wibox.widget {
         },
         {
             {
-                data = {
+                data_list = {
-                    ['L1'] = 100,
+                    { 'L1', 100 },
-                    ['L2'] = 200,
+                    { 'L2', 200 },
-                    ['L3'] = 300,
+                    { 'L3', 300 },
                 },
                 border_width = 1,
                 forced_height = 50,
@@ -40,10 +40,10 @@ parent:add(wibox.widget {
         },
         {
             {
-                data = {
+                data_list = {
-                    ['L1'] = 100,
+                    { 'L1', 100 },
-                    ['L2'] = 200,
+                    { 'L2', 200 },
-                    ['L3'] = 300,
+                    { 'L3', 300 },
                 },
                 border_width = 1,
                 forced_height = 50,