marker-transforms

ImportanceOfBeingErnest · ImportanceOfBeingErnest · commit 92192aa3f992 · 2020-03-16T12:52:53.000+01:00
diff --git a/doc/users/next_whats_new/2020-03-16_markerstyle_normalization.rst b/doc/users/next_whats_new/2020-03-16_markerstyle_normalization.rst
@@ -0,0 +1,12 @@
+Allow for custom marker scaling
+-------------------------------
+`~.markers.MarkerStyle` gained a keyword argument *normalization*, which may be
+set to *"none"* to allow for custom paths to not be scaled.::
+
+    MarkerStyle(Path(...), normalization="none")
+
+`~.markers.MarkerStyle` also gained a `~.markers.MarkerStyle`.set_transform`
+method to set affine transformations to existing markers.::
+
+    m = MarkerStyle("d")
+    m.set_transform(m.get_transform() + Affine2D().rotate_deg(30))
diff --git a/examples/lines_bars_and_markers/scatter_piecharts.py b/examples/lines_bars_and_markers/scatter_piecharts.py
@@ -3,15 +3,19 @@
 Scatter plot with pie chart markers
 ===================================
 
-This example makes custom 'pie charts' as the markers for a scatter plot.
-
-Thanks to Manuel Metz for the example.
+This example shows two methods to make custom 'pie charts' as the markers
+for a scatter plot.
 """
 
+##########################################################################
+# Manually creating marker vertices
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+
 import numpy as np
 import matplotlib.pyplot as plt
 
-# first define the ratios
+# first define the cumulative ratios
 r1 = 0.2       # 20%
 r2 = r1 + 0.4  # 40%
 
@@ -36,10 +40,55 @@
 s3 = np.abs(xy3).max()
 
 fig, ax = plt.subplots()
-ax.scatter(range(3), range(3), marker=xy1, s=s1**2 * sizes, facecolor='blue')
-ax.scatter(range(3), range(3), marker=xy2, s=s2**2 * sizes, facecolor='green')
-ax.scatter(range(3), range(3), marker=xy3, s=s3**2 * sizes, facecolor='red')
+ax.scatter(range(3), range(3), marker=xy1, s=s1**2 * sizes, facecolor='C0')
+ax.scatter(range(3), range(3), marker=xy2, s=s2**2 * sizes, facecolor='C1')
+ax.scatter(range(3), range(3), marker=xy3, s=s3**2 * sizes, facecolor='C2')
+
+plt.show()
+
+
+##########################################################################
+# Using wedges as markers
+# ~~~~~~~~~~~~~~~~~~~~~~~
+#
+# An alternative is to create custom markers from the `~.path.Path` of a
+# `~.patches.Wedge`, which might be more versatile.
+#
+
+import numpy as np
+import matplotlib.pyplot as plt
+from matplotlib.patches import Wedge
+from matplotlib.markers import MarkerStyle
+
+# first define the ratios
+r1 = 0.2          # 20%
+r2 = r1 + 0.3     # 50%
+r3 = 1 - r1 - r2  # 30%
+
+
+def markers_from_ratios(ratios, width=1):
+    markers = []
+    angles = 360*np.concatenate(([0], np.cumsum(ratios)))
+    for i in range(len(angles)-1):
+        # create a Wedge within the unit square in between the given angles...
+        w = Wedge((0, 0), 0.5, angles[i], angles[i+1], width=width/2)
+        # ... and create a custom Marker from its path.
+        markers.append(MarkerStyle(w.get_path(), normalization="none"))
+    return markers
+
+# define some sizes of the scatter marker
+sizes = np.array([100, 200, 400, 800])
+# collect the markers and some colors
+markers = markers_from_ratios([r1, r2, r3], width=0.6)
+colors = plt.cm.tab10.colors[:len(markers)]
+
+fig, ax = plt.subplots()
+
+for marker, color in zip(markers, colors):
+    ax.scatter(range(len(sizes)), range(len(sizes)), marker=marker, s=sizes,
+               edgecolor="none", facecolor=color)
 
+ax.margins(0.1)
 plt.show()
 
 #############################################################################
@@ -55,3 +104,5 @@
 import matplotlib
 matplotlib.axes.Axes.scatter
 matplotlib.pyplot.scatter
+matplotlib.patches.Wedge
+matplotlib.markers.MarkerStyle
diff --git a/lib/matplotlib/markers.py b/lib/matplotlib/markers.py
@@ -201,7 +201,8 @@ class MarkerStyle:
     # TODO: Is this ever used as a non-constant?
     _point_size_reduction = 0.5
 
-    def __init__(self, marker=None, fillstyle=None):
+    def __init__(self, marker=None, fillstyle=None, *,
+                 normalization="classic"):
         """
         Attributes
         ----------
@@ -213,18 +214,31 @@ def __init__(self, marker=None, fillstyle=None):
 
         Parameters
         ----------
-        marker : str or array-like, optional, default: None
+        marker : str, array-like, `~.path.Path`, or `~.markers.MarkerStyle`, \
+        default: None
             See the descriptions of possible markers in the module docstring.
 
         fillstyle : str, optional, default: 'full'
             'full', 'left", 'right', 'bottom', 'top', 'none'
+
+        normalization : str, {'classic', 'none'}, optional, default: "classic"
+            The normalization of the marker size. Only applies to custom paths
+            that are provided as array of vertices or `~.path.Path`.
+            Can take two values:
+            *'classic'*, being the default, makes sure the marker path is
+            normalized to fit within a unit-square by affine scaling.
+            *'none'*, in which case no scaling is performed on the marker path.
         """
+        if normalization not in ["classic", "none"]:
+            raise ValueError("normalization={!r} is not valid; it must be "
+                             "'classic' or 'none'".format(normalization))
+        self._normalize = normalization
         self._marker_function = None
         self.set_fillstyle(fillstyle)
         self.set_marker(marker)
 
     def _recache(self):
-        if self._marker_function is None:
+        if self._marker_function is None or self._normalize == "none":
             return
         self._path = _empty_path
         self._transform = IdentityTransform()
@@ -303,6 +317,13 @@ def get_path(self):
     def get_transform(self):
         return self._transform.frozen()
 
+    def set_transform(self, transform):
+        """
+        Sets the transform of the marker. This is the transform by which the
+        marker path is transformed.
+        """
+        self._transform = transform
+
     def get_alt_path(self):
         return self._alt_path
 
@@ -316,8 +337,9 @@ def _set_nothing(self):
         self._filled = False
 
     def _set_custom_marker(self, path):
-        rescale = np.max(np.abs(path.vertices))  # max of x's and y's.
-        self._transform = Affine2D().scale(0.5 / rescale)
+        if self._normalize == "classic":
+            rescale = np.max(np.abs(path.vertices))  # max of x's and y's.
+            self._transform = Affine2D().scale(0.5 / rescale)
         self._path = path
 
     def _set_path_marker(self):
@@ -349,8 +371,6 @@ def _set_tuple_marker(self):
     def _set_mathtext_path(self):
         """
         Draws mathtext markers '$...$' using TextPath object.
-
-        Submitted by tcb
         """
         from matplotlib.text import TextPath
 
diff --git a/lib/matplotlib/tests/test_marker.py b/lib/matplotlib/tests/test_marker.py
@@ -1,7 +1,10 @@
 import numpy as np
 from matplotlib import markers
 from matplotlib.path import Path
+from matplotlib.transforms import Affine2D
+import matplotlib.pyplot as plt
 
+from matplotlib.testing.decorators import check_figures_equal
 import pytest
 
 
@@ -26,3 +29,24 @@ def test_marker_path():
     path = Path([[0, 0], [1, 0]], [Path.MOVETO, Path.LINETO])
     # Checking this doesn't fail.
     marker_style.set_marker(path)
+
+
+@check_figures_equal(extensions=["png"])
+def test_marker_normalization(fig_test, fig_ref):
+    plt.style.use("mpl20")
+
+    ax = fig_ref.subplots()
+    ax.margins(0.3)
+    ax.scatter([0, 1], [0, 0], s=400, marker="s", c="C2")
+
+    ax = fig_test.subplots()
+    ax.margins(0.3)
+    # test normalize
+    p = Path([[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]], closed=True)
+    p1 = p.transformed(Affine2D().translate(-.5, -.5).scale(20))
+    m1 = markers.MarkerStyle(p1, normalization="none")
+    ax.scatter([0], [0], s=1, marker=m1, c="C2")
+    # test transform
+    m2 = markers.MarkerStyle("s")
+    m2.set_transform(m2.get_transform() + Affine2D().scale(20))
+    ax.scatter([1], [0], s=1, marker=m2, c="C2")
