Add reverse_direction Gauge config parameter

docs/documentation/configuration/specific_options.rst

@@ -30,6 +30,21 @@ half_pie
   pie_chart.add('Opera', 2.3)
 
 
+
+reverse_direction
+-----------------
+
+You can reverse the direction of the gauge by setting ``reverse_direction=True``:
+
+.. pygal-code::
+
+  gauge_chart = pygal.Gauge(reverse_direction=True)
+  gauge_chart.add('Chrome', 8212)
+  gauge_chart.add('Firefox', 8099)
+  gauge_chart.add('Opera', 2933)
+  gauge_chart.add('IE', 41)
+
+
 inner_radius
 ------------
 

docs/documentation/types/gauge.rst

@@ -15,3 +15,18 @@ Gauge chart:
   gauge_chart.add('Firefox', 8099)
   gauge_chart.add('Opera', 2933)
   gauge_chart.add('IE', 41)
+
+Reverse
+~~~~~~~
+
+Gauge chart can be reversed:
+
+.. pygal-code:: 600 550
+
+  gauge_chart = pygal.Gauge(human_readable=True, reverse_direction=True)
+  gauge_chart.title = 'DeltaBlue V8 benchmark results'
+  gauge_chart.range = [0, 10000]
+  gauge_chart.add('Chrome', 8212)
+  gauge_chart.add('Firefox', 8099)
+  gauge_chart.add('Opera', 2933)
+  gauge_chart.add('IE', 41)

pygal/config.py

@@ -324,6 +324,10 @@ class Config(CommonConfig):
 
     half_pie = Key(False, bool, "Look", "Create a half-pie chart")
 
+    reverse_direction = Key(
+        False, bool, "Look", "Reverse the direction of the gauge"
+    )
+
     x_labels = Key(
         None, list, "Label", "X labels, must have same len than data.",
         "Leave it to None to disable x labels display.", str

pygal/graph/gauge.py

@@ -132,7 +132,10 @@ def _compute(self):
             self.min_ -= 1
             self.max_ += 1
 
-        self._box.set_polar_box(0, 1, self.min_, self.max_)
+        if self.reverse_direction:
+            self._box.set_polar_box(0, 1, self.max_, self.min_)
+        else:
+            self._box.set_polar_box(0, 1, self.min_, self.max_)
 
     def _compute_x_labels(self):
         pass

pygal/test/test_gauge.py

@@ -0,0 +1,35 @@
+from pygal import Gauge
+
+
+def test_gauge_reverse_direction():
+    """Test that reverse_direction config is respected"""
+    gauge = Gauge(reverse_direction=True)
+    assert gauge.config.reverse_direction is True
+
+    gauge.add('A', 10)
+    gauge.range = (0, 10)
+    gauge.setup()
+
+    # When reversed, the polar box should be (0, 1, max, min)
+    # min=0, max=10
+    # reversed: (0, 1, 10, 0)
+    assert gauge._box._tmin == 10
+    assert gauge._box._tmax == 0
+    assert gauge._box._rmin == 0
+    assert gauge._box._rmax == 1
+
+def test_gauge_normal_direction():
+    """Test that normal direction works as expected"""
+    gauge = Gauge()
+    assert gauge.config.reverse_direction is False
+
+    gauge.add('A', 10)
+    gauge.range = (0, 10)
+    gauge.setup()
+
+    # min=0, max=10
+    # normal: (0, 1, 0, 10)
+    assert gauge._box._tmin == 0
+    assert gauge._box._tmax == 10
+    assert gauge._box._rmin == 0
+    assert gauge._box._rmax == 1