Add ability to blend any number of transforms

lib/matplotlib/tests/test_transforms.py

@@ -850,7 +850,7 @@ def test_str_transform():
     CompositeGenericTransform(
         CompositeGenericTransform(
             TransformWrapper(
-                BlendedAffine2D(
+                BlendedAffine(
                     IdentityTransform(),
                     IdentityTransform())),
             CompositeAffine2D(
@@ -864,7 +864,7 @@ def test_str_transform():
         CompositeGenericTransform(
             PolarAffine(
                 TransformWrapper(
-                    BlendedAffine2D(
+                    BlendedAffine(
                         IdentityTransform(),
                         IdentityTransform())),
                 LockableBbox(

lib/matplotlib/transforms.py

@@ -2203,182 +2203,208 @@ def inverted(self):
 
 
 class _BlendedMixin:
-    """Common methods for `BlendedGenericTransform` and `BlendedAffine2D`."""
+    """Common methods for `BlendedGenericTransform` and `BlendedAffine`."""
 
     def __eq__(self, other):
-        if isinstance(other, (BlendedAffine2D, BlendedGenericTransform)):
-            return (self._x == other._x) and (self._y == other._y)
-        elif self._x == self._y:
-            return self._x == other
+        num_transforms = len(self._transforms)
+
+        if (isinstance(other, (BlendedGenericTransform, BlendedAffine))
+                and num_transforms == len(other._transforms)):
+            return all(self._transforms[i] == other._transforms[i]
+                       for i in range(num_transforms))
         else:
             return NotImplemented
 
     def contains_branch_seperately(self, transform):
-        return (self._x.contains_branch(transform),
-                self._y.contains_branch(transform))
+        return tuple(branch.contains_branch(transform) for branch in self._transforms)
 
-    __str__ = _make_str_method("_x", "_y")
+    def __str__(self):
+        indent = functools.partial(textwrap.indent, prefix=" " * 4)
+        return (
+            type(self).__name__ + "("
+            + ",".join([*(indent("\n" + transform.__str__())
+                          for transform in self._transforms)])
+            + ")")
 
 
 class BlendedGenericTransform(_BlendedMixin, Transform):
     """
-    A "blended" transform uses one transform for the *x*-direction, and
-    another transform for the *y*-direction.
+    A "blended" transform uses one transform for each direction
 
-    This "generic" version can handle any given child transform in the
-    *x*- and *y*-directions.
+    This "generic" version can handle any number of given child transforms, each
+    handling a different axis.
     """
-    input_dims = 2
-    output_dims = 2
     is_separable = True
     pass_through = True
 
-    def __init__(self, x_transform, y_transform, **kwargs):
+    def __init__(self, *args, **kwargs):
         """
-        Create a new "blended" transform using *x_transform* to transform the
-        *x*-axis and *y_transform* to transform the *y*-axis.
+        Create a new "blended" transform, with the first argument providing
+        a transform for the *x*-axis, the second argument providing a transform
+        for the *y*-axis, etc.
 
         You will generally not call this constructor directly but use the
         `blended_transform_factory` function instead, which can determine
         automatically which kind of blended transform to create.
         """
+        self.input_dims = self.output_dims = len(args)
+
+        for i in range(self.input_dims):
+            transform = args[i]
+            if transform.input_dims > 1 and transform.input_dims <= i:
+                raise TypeError("Invalid transform provided to"
+                                "`BlendedGenericTransform`")
+
         Transform.__init__(self, **kwargs)
-        self._x = x_transform
-        self._y = y_transform
-        self.set_children(x_transform, y_transform)
+        self.set_children(*args)
+        self._transforms = args
         self._affine = None
 
     @property
     def depth(self):
-        return max(self._x.depth, self._y.depth)
+        return max(transform.depth for transform in self._transforms)
 
     def contains_branch(self, other):
         # A blended transform cannot possibly contain a branch from two
         # different transforms.
         return False
 
-    is_affine = property(lambda self: self._x.is_affine and self._y.is_affine)
-    has_inverse = property(
-        lambda self: self._x.has_inverse and self._y.has_inverse)
+    is_affine = property(lambda self: all(transform.is_affine
+                                          for transform in self._transforms))
+    has_inverse = property(lambda self: all(transform.has_inverse
+                                            for transform in self._transforms))
 
     def frozen(self):
         # docstring inherited
-        return blended_transform_factory(self._x.frozen(), self._y.frozen())
+        return blended_transform_factory(*(transform.frozen()
+                                           for transform in self._transforms))
 
     @_api.rename_parameter("3.8", "points", "values")
     def transform_non_affine(self, values):
         # docstring inherited
-        if self._x.is_affine and self._y.is_affine:
+        if self.is_affine:
             return values
-        x = self._x
-        y = self._y
 
-        if x == y and x.input_dims == 2:
-            return x.transform_non_affine(values)
+        if all(transform == self._transforms[0]
+               for transform in self._transforms) and self.input_dims >= 2:
+            return self._transforms[0].transform_non_affine(values)
 
-        if x.input_dims == 2:
-            x_points = x.transform_non_affine(values)[:, 0:1]
-        else:
-            x_points = x.transform_non_affine(values[:, 0])
-            x_points = x_points.reshape((len(x_points), 1))
+        all_points = []
+        masked = False
 
-        if y.input_dims == 2:
-            y_points = y.transform_non_affine(values)[:, 1:]
-        else:
-            y_points = y.transform_non_affine(values[:, 1])
-            y_points = y_points.reshape((len(y_points), 1))
+        for dim in range(self.input_dims):
+            transform = self._transforms[dim]
+            if transform.input_dims == 1:
+                points = transform.transform_non_affine(values[:, dim])
+                points = points.reshape((len(points), 1))
+            else:
+                points = transform.transform_non_affine(values)[:, dim:dim+1]
 
-        if (isinstance(x_points, np.ma.MaskedArray) or
-                isinstance(y_points, np.ma.MaskedArray)):
-            return np.ma.concatenate((x_points, y_points), 1)
+            masked = masked or isinstance(points, np.ma.MaskedArray)
+            all_points.append(points)
+
+        if masked:
+            return np.ma.concatenate(tuple(all_points), 1)
         else:
-            return np.concatenate((x_points, y_points), 1)
+            return np.concatenate(tuple(all_points), 1)
 
     def inverted(self):
         # docstring inherited
-        return BlendedGenericTransform(self._x.inverted(), self._y.inverted())
+        return BlendedGenericTransform(*(transform.inverted()
+                                         for transform in self._transforms))
 
     def get_affine(self):
         # docstring inherited
         if self._invalid or self._affine is None:
-            if self._x == self._y:
-                self._affine = self._x.get_affine()
+            if all(transform == self._transforms[0] for transform in self._transforms):
+                self._affine = self._transforms[0].get_affine()
             else:
-                x_mtx = self._x.get_affine().get_matrix()
-                y_mtx = self._y.get_affine().get_matrix()
-                # We already know the transforms are separable, so we can skip
-                # setting b and c to zero.
-                mtx = np.array([x_mtx[0], y_mtx[1], [0.0, 0.0, 1.0]])
-                self._affine = Affine2D(mtx)
+                mtx = np.identity(self.input_dims + 1)
+                for i in range(self.input_dims):
+                    transform = self._transforms[i]
+                    if transform.output_dims > 1:
+                        mtx[i] = transform.get_affine().get_matrix()[i]
+
+                self._affine = _affine_factory(mtx, dims=self.input_dims)
             self._invalid = 0
         return self._affine
 
 
-class BlendedAffine2D(_BlendedMixin, Affine2DBase):
+class BlendedAffine(_BlendedMixin, AffineImmutable):
     """
     A "blended" transform uses one transform for the *x*-direction, and
     another transform for the *y*-direction.
 
     This version is an optimization for the case where both child
-    transforms are of type `Affine2DBase`.
+    transforms are of type `AffineImmutable`.
     """
 
     is_separable = True
 
-    def __init__(self, x_transform, y_transform, **kwargs):
+    def __init__(self, *args, **kwargs):
         """
-        Create a new "blended" transform using *x_transform* to transform the
-        *x*-axis and *y_transform* to transform the *y*-axis.
+        Create a new "blended" transform, with the first argument providing
+        a transform for the *x*-axis, the second argument providing a transform
+        for the *y*-axis, etc.
 
-        Both *x_transform* and *y_transform* must be 2D affine transforms.
+        All provided transforms must be affine transforms.
 
         You will generally not call this constructor directly but use the
         `blended_transform_factory` function instead, which can determine
         automatically which kind of blended transform to create.
         """
-        is_affine = x_transform.is_affine and y_transform.is_affine
-        is_separable = x_transform.is_separable and y_transform.is_separable
-        is_correct = is_affine and is_separable
-        if not is_correct:
-            raise ValueError("Both *x_transform* and *y_transform* must be 2D "
-                             "affine transforms")
-
+        dims = len(args)
         Transform.__init__(self, **kwargs)
-        self._x = x_transform
-        self._y = y_transform
-        self.set_children(x_transform, y_transform)
+        AffineImmutable.__init__(self, dims=dims, **kwargs)
+
+        if not all(transform.is_affine and transform.is_separable
+                   for transform in args):
+            raise ValueError("Given transforms must be affine")
+
+        for i in range(self.input_dims):
+            transform = args[i]
+            if transform.input_dims > 1 and transform.input_dims <= i:
+                raise TypeError("Invalid transform provided to"
+                                "`BlendedGenericTransform`")
+
+        self._transforms = args
+        self.set_children(*args)
 
-        Affine2DBase.__init__(self)
         self._mtx = None
 
     def get_matrix(self):
         # docstring inherited
         if self._invalid:
-            if self._x == self._y:
-                self._mtx = self._x.get_matrix()
+            if all(transform == self._transforms[0] for transform in self._transforms):
+                self._mtx = self._transforms[0].get_matrix()
             else:
-                x_mtx = self._x.get_matrix()
-                y_mtx = self._y.get_matrix()
                 # We already know the transforms are separable, so we can skip
-                # setting b and c to zero.
-                self._mtx = np.array([x_mtx[0], y_mtx[1], [0.0, 0.0, 1.0]])
+                # setting non-diagonal values to zero.
+                self._mtx = np.array(
+                    [self._transforms[i].get_affine().get_matrix()[i]
+                     for i in range(self.input_dims)] +
+                    [[0.0] * self.input_dims + [1.0]])
             self._inverted = None
             self._invalid = 0
         return self._mtx
 
 
-def blended_transform_factory(x_transform, y_transform):
+@_api.deprecated("3.9", alternative="BlendedAffine")
+class BlendedAffine2D(BlendedAffine):
+    pass
+
+
+def blended_transform_factory(*args):
     """
     Create a new "blended" transform using *x_transform* to transform
     the *x*-axis and *y_transform* to transform the *y*-axis.
 
     A faster version of the blended transform is returned for the case
     where both child transforms are affine.
     """
-    if (isinstance(x_transform, Affine2DBase) and
-            isinstance(y_transform, Affine2DBase)):
-        return BlendedAffine2D(x_transform, y_transform)
-    return BlendedGenericTransform(x_transform, y_transform)
+    if all(isinstance(transform, AffineImmutable) for transform in args):
+        return BlendedAffine(*args)
+    return BlendedGenericTransform(*args)
 
 
 class CompositeGenericTransform(Transform):
@@ -2479,8 +2505,9 @@ def get_affine(self):
         if not self._b.is_affine:
             return self._b.get_affine()
         else:
-            return Affine2D(np.dot(self._b.get_affine().get_matrix(),
-                                   self._a.get_affine().get_matrix()))
+            return _affine_factory(np.dot(self._b.get_affine().get_matrix(),
+                                   self._a.get_affine().get_matrix()),
+                                   dims=self.input_dims)
 
     def inverted(self):
         # docstring inherited

lib/matplotlib/transforms.pyi

@@ -258,26 +258,25 @@ class _BlendedMixin:
     def contains_branch_seperately(self, transform: Transform) -> Sequence[bool]: ...
 
 class BlendedGenericTransform(_BlendedMixin, Transform):
-    input_dims: Literal[2]
-    output_dims: Literal[2]
     pass_through: bool
     def __init__(
-        self, x_transform: Transform, y_transform: Transform, **kwargs
+        self, *args: Transform, **kwargs
     ) -> None: ...
     @property
     def depth(self) -> int: ...
     def contains_branch(self, other: Transform) -> Literal[False]: ...
     @property
     def is_affine(self) -> bool: ...
 
-class BlendedAffine2D(_BlendedMixin, Affine2DBase):
-    def __init__(
-        self, x_transform: Transform, y_transform: Transform, **kwargs
-    ) -> None: ...
+class BlendedAffine(_BlendedMixin, AffineImmutable):
+    def __init__(self, *args: Transform, **kwargs) -> None: ...
+
+class BlendedAffine2D(BlendedAffine):
+    pass
 
 def blended_transform_factory(
-    x_transform: Transform, y_transform: Transform
-) -> BlendedGenericTransform | BlendedAffine2D: ...
+    *args: Transform
+) -> BlendedGenericTransform | BlendedAffine: ...
 
 class CompositeGenericTransform(Transform):
     pass_through: bool