audio: Create a custom ScalePlus widget

For giving GtkScales increment() and decrement() functionality that
triggers the "change-value" signal

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

audio/scale.py

@@ -0,0 +1,34 @@
+# Copyright 2021 (c) Anna Schumaker.
+from gi.repository import Gtk
+
+class ScalePlus(Gtk.Scale):
+    def __init__(self, min, max, step, page):
+        Gtk.Scale.__init__(self)
+        self.set_range(min, max)
+        self.set_increments(step, page)
+        self.set_value(min)
+        self.set_draw_value(True)
+        self.set_hexpand(True)
+        self.set_format_value_func(self.format_value)
+
+    def __change_value__(self, n, scroll):
+        value = self.get_value()
+        self.set_value(value + n)
+        new = self.get_value()
+        if value == new:
+            return None
+        self.emit("change-value", scroll, new)
+        return new
+
+    def decrement(self):
+        adjustment = self.get_adjustment()
+        return self.__change_value__(-adjustment.get_step_increment(),
+                                      Gtk.ScrollType.STEP_BACKWARD)
+
+    def increment(self):
+        adjustment = self.get_adjustment()
+        return self.__change_value__(adjustment.get_step_increment(),
+                                     Gtk.ScrollType.STEP_FORWARD)
+
+    def format_value(self, scale, value):
+        return str(value)

audio/test_scale.py

@@ -0,0 +1,52 @@
+# Copyright 2021 (c) Anna Schumaker.
+import unittest
+from gi.repository import Gtk
+from . import scale
+
+class TestScalePlus(unittest.TestCase):
+    def on_change_value(self, scale, scroll, value):
+        self.change_value = (scroll, value)
+
+    def test_scale_plus_init(self):
+        splus = scale.ScalePlus(1, 10, 2, 5)
+        adj = splus.get_adjustment()
+
+        self.assertIsInstance(splus, Gtk.Scale)
+        self.assertTrue(splus.get_draw_value())
+        self.assertTrue(splus.get_hexpand())
+        self.assertEqual(splus.get_value_pos(), Gtk.PositionType.TOP)
+
+        self.assertEqual(adj.get_value(), 1)
+        self.assertEqual(adj.get_lower(), 1)
+        self.assertEqual(adj.get_upper(), 10)
+        self.assertEqual(adj.get_step_increment(), 2)
+        self.assertEqual(adj.get_page_increment(), 5)
+
+    def test_scale_plus_decrement(self):
+        splus = scale.ScalePlus(1, 10, 2, 5)
+        splus.set_value(10)
+        splus.connect("change-value", self.on_change_value)
+
+        for i in [ 8, 6, 4, 2, 1 ]:
+            self.assertEqual(splus.decrement(), i)
+            self.assertEqual(splus.format_value(splus, i), str(i))
+            self.assertEqual(self.change_value,
+                            (Gtk.ScrollType.STEP_BACKWARD, i))
+
+        self.change_value = None
+        self.assertIsNone(splus.decrement())
+        self.assertIsNone(self.change_value)
+
+    def test_scale_plus_increment(self):
+        splus = scale.ScalePlus(1, 10, 2, 5)
+        splus.connect("change-value", self.on_change_value)
+
+        for i in [ 3, 5, 7, 9, 10 ]:
+            self.assertEqual(splus.increment(), i)
+            self.assertEqual(splus.format_value(splus, i), str(i))
+            self.assertEqual(self.change_value,
+                            (Gtk.ScrollType.STEP_FORWARD, i))
+
+        self.change_value = None
+        self.assertIsNone(splus.increment())
+        self.assertIsNone(self.change_value)