ENH: add arbitrary-scale functionality

jklymak · jklymak · commit 4b22def379e0 · 2018-11-16T14:41:06.000-08:00
API: add ability to set formatter and locators from scale init
diff --git a/lib/matplotlib/scale.py b/lib/matplotlib/scale.py
@@ -82,6 +82,94 @@ def get_transform(self):
         return IdentityTransform()
 
 
+class ArbitraryTransform(Transform):
+     """
+     A simple transform that takes and arbitrary function for the
+     forward and inverse transform.
+     """
+
+     input_dims = 1
+     output_dims = 1
+     is_separable = True
+     has_inverse = True
+
+     def __init__(self, forward, inverse):
+         """
+         Parameters
+         ----------
+
+         forward: The forward function for the transform
+
+         inverse: The inverse of the forward function.
+         """
+         super().__init__()
+         if callable(forward) and callable(inverse):
+             self._forward = forward
+             self._inverse = inverse
+         else:
+             raise ValueError('arguments to ArbitraryTransform must '
+                              'be functions')
+
+     def transform_non_affine(self, values):
+         return self._forward(values)
+
+     def inverted(self):
+         return ArbitraryTransform(self._inverse, self._forward)
+
+
+class ArbitraryScale(ScaleBase):
+     """
+     Provide an arbitrary scale for the axis.
+     """
+
+     name = 'arbitrary'
+
+     def __init__(self, axis, functions, *,
+                  major_locator_class=AutoLocator,
+                  minor_locator_class=NullLocator,
+                  major_formatter_class=ScalarFormatter,
+                  minor_formatter_class=NullFormatter):
+         """
+         Parameters
+         ----------
+
+         axis: the axis for the scale
+
+         functions: (forward, inverse)
+            two-tuple of the forward and inverse functions for the scale.
+
+        Examples
+        --------
+
+            TODO
+         """
+
+         forward, inverse = functions
+         transform = ArbitraryTransform(forward, inverse)
+         self._transform = transform
+         self._major_locator_class = major_locator_class
+         self._minor_locator_class = minor_locator_class
+         self._major_formatter_class = major_formatter_class
+         self._minor_formatter_class = minor_formatter_class
+
+     def get_transform(self):
+         """
+         The transform for linear scaling is just the
+         :class:`~matplotlib.transforms.IdentityTransform`.
+         """
+         return self._transform
+
+     def set_default_locators_and_formatters(self, axis):
+         """
+         Set the locators and formatters to reasonable defaults for
+         linear scaling.
+         """
+         axis.set_major_locator(self._major_locator_class())
+         axis.set_major_formatter(self._major_formatter_class())
+         axis.set_minor_locator(self._minor_locator_class())
+         axis.set_minor_formatter(self._minor_formatter_class())
+
+
 class LogTransformBase(Transform):
     input_dims = 1
     output_dims = 1
@@ -545,6 +633,7 @@ def limit_range_for_scale(self, vmin, vmax, minpos):
     'log':    LogScale,
     'symlog': SymmetricalLogScale,
     'logit':  LogitScale,
+    'arbitrary': ArbitraryScale,
     }
 
 
