Merge pull request #237 from enthought/feature-slider-update

Feature slider update

enaml/qt/qt_slider.py

@@ -44,9 +44,11 @@ def create(self, tree):
 
         """
         super(QtSlider, self).create(tree)
-        self.set_value(tree['value'])
-        self.set_maximum(tree['maximum'])
+        # Initialize the value after the minimum and maximum to avoid
+        # the potential for premature internal clipping of the value.
         self.set_minimum(tree['minimum'])
+        self.set_maximum(tree['maximum'])
+        self.set_value(tree['value'])
         self.set_orientation(tree['orientation'])
         self.set_page_step(tree['page_step'])
         self.set_single_step(tree['single_step'])

enaml/stdlib/slider_transforms.py

@@ -0,0 +1,229 @@
+#------------------------------------------------------------------------------
+#  Copyright (c) 2013, Enthought, Inc.
+#  All rights reserved.
+#------------------------------------------------------------------------------
+""" Enaml Standard Library - Slider Transforms
+
+This module contains declarative classes which can be used as children
+of a `Slider` to transform the integer range of the slider into an
+alternative data space.
+
+"""
+from traits.api import Any, Bool, Float, Range, on_trait_change
+
+from enaml.core.declarative import Declarative
+
+
+class SliderTransform(Declarative):
+    """ A base class for creating declarative slider transforms.
+
+    A SliderTransform must be subclassed to be useful. The abstract api
+    defined below must be implemented by the subclass.
+
+    When using a transform with a slider, the transform takes complete
+    ownership of the slider range. That is, no effort is made to listen
+    for outside changes to the slider range, so all changes should be
+    made on the transform.
+
+    """
+    #: The data-space minimum for the transform. This may be redefined
+    #: by a subclass to enforce stronger typing.
+    minimum = Any
+
+    #: The data-space maximum for the transform. This may be redefined
+    #: by a subclass to enforce stronger typing.
+    maximum = Any
+
+    #: The data-space value for the transform. This may be redefined
+    #: by a subclass to enforce stronger typing.
+    value = Any
+
+    #: A boolean flag used to prevent loopback cycles.
+    _guard = Bool(False)
+
+    #--------------------------------------------------------------------------
+    # Private API
+    #--------------------------------------------------------------------------
+    def pre_initialize(self):
+        """ A pre-initialization handler.
+
+        The parent slider values are initialized during the transform
+        initialization pass.
+
+        """
+        self._apply_transform()
+
+    def _apply_transform(self, minimum=True, maximum=True, value=True):
+        """ Apply the current transform to the parent slider.
+
+        Parameters
+        ----------
+        minimum : bool, optional
+            Whether or not to update the slider minimum. The default
+            is False.
+
+        maximum : bool, optional
+            Whether or not to update the slider maximum. The default
+            is False.
+
+        value : bool, optional
+            Whether or not to update the slider value. The default
+            is False.
+
+        """
+        parent = self.parent
+        if parent is not None:
+            if minimum:
+                parent.minimum = self.get_minimum()
+            if maximum:
+                parent.maximum = self.get_maximum()
+            if value:
+                parent.value = self.get_value()
+
+    @on_trait_change('parent:value')
+    def _update_value(self, val):
+        """ Update the transformed value when slider changes.
+
+        """
+        if self.is_active:
+            self._guard = True
+            try:
+                self.set_value(val)
+            finally:
+                self._guard = False
+
+    def _minimum_changed(self):
+        """ Update the slider minimum on transform minimum change.
+
+        """
+        if self.is_active:
+            self._apply_transform(maximum=False, value=False)
+
+    def _maximum_changed(self):
+        """ Update the slider maximum on transform maximum change.
+
+        """
+        if self.is_active:
+            self._apply_transform(minimum=False, value=False)
+
+    def _value_changed(self):
+        """ Update the slider value on transform value change.
+
+        """
+        if self.is_active and not self._guard:
+            self._apply_transform(minimum=False, maximum=False)
+
+    #--------------------------------------------------------------------------
+    # Abstract API
+    #--------------------------------------------------------------------------
+    def get_minimum(self):
+        """ Get the minimum value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The minimum value of the transform converted to an int.
+
+        """
+        raise NotImplementedError
+
+    def get_maximum(self):
+        """ Get the maximum value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The maximum value of the transform converted to an int.
+
+        """
+        raise NotImplementedError
+
+    def get_value(self):
+        """ Get the value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The value of the transform converted to an int.
+
+        """
+        raise NotImplementedError
+
+    def set_value(self, value):
+        """ Set the value of the transform from an int.
+
+        Parameters
+        ----------
+        value : int
+            The integer value of the slider.
+
+        """
+        raise NotImplementedError
+
+
+class FloatTransform(SliderTransform):
+    """ A concreted SliderTransform for floating point values.
+
+    """
+    #: A redeclared parent class trait which enforces float values.
+    minimum = Float(0.0)
+
+    #: A redeclared parent class trait which enforces float values.
+    maximum = Float(1.0)
+
+    #: A redeclared parent class trait which enforces float values.
+    value = Float(0.0)
+
+    #: The number of stops to use between the minimum and maximum.
+    precision = Range(low=1, value=100)
+
+    #--------------------------------------------------------------------------
+    # Abstract API Implementation
+    #--------------------------------------------------------------------------
+    def get_minimum(self):
+        """ Get the minimum value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The minimum value of the transform converted to an int.
+
+        """
+        return 0
+
+    def get_maximum(self):
+        """ Get the maximum value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The maximum value of the transform converted to an int.
+
+        """
+        return self.precision
+
+    def get_value(self):
+        """ Get the value of the transform as an int.
+
+        Returns
+        -------
+        result : int
+            The value of the transform converted to an int.
+
+        """
+        offset = self.value - self.minimum
+        delta = self.maximum - self.minimum
+        return int(offset * self.precision / delta)
+
+    def set_value(self, val):
+        """ Set the value of the transform from an int.
+
+        Parameters
+        ----------
+        value : int
+            The integer value of the slider.
+
+        """
+        delta = self.maximum - self.minimum
+        self.value = (val * delta / self.precision) + self.minimum
+