Inline and optimize ContourLabeler.get_label_coords.

anntzer · anntzer · commit ff2fe6b5b93c · 2020-11-26T11:41:37.000+01:00
`get_label_coords` is clearly an internal helper to `locate_label`; e.g.
the `distances` parameter needs to be filled in with a very specific
array that's internally computed by `locate_label`.  Inline it, which
also makes clearer the possibility to save some further computation for
`locate_label` to return a linearized index (the part that was commented
"There must be a more efficient way..."; indeed converting the array to
a list of tuples to get back the index seems pretty inefficient).

Also better document the implementation of `get_label_coords` (I'm not
actually changing any of the code logic).
diff --git a/doc/api/next_api_changes/deprecations/19018-AL.rst b/doc/api/next_api_changes/deprecations/19018-AL.rst
@@ -0,0 +1,3 @@
+``ContourLabeler.get_label_coords`` is deprecated
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is considered an internal helper.
diff --git a/lib/matplotlib/contour.py b/lib/matplotlib/contour.py
@@ -217,6 +217,7 @@ def too_close(self, x, y, lw):
         return any((x - loc[0]) ** 2 + (y - loc[1]) ** 2 < thresh
                    for loc in self.labelXYs)
 
+    @_api.deprecated("3.4")
     def get_label_coords(self, distances, XX, YY, ysize, lw):
         """
         Return x, y, and the index of a label location.
@@ -278,21 +279,20 @@ def locate_label(self, linecontour, labelwidth):
         """
         Find good place to draw a label (relatively flat part of the contour).
         """
-
-        # Number of contour points
-        nsize = len(linecontour)
+        contour_size = len(linecontour)
         if labelwidth > 1:
-            xsize = int(np.ceil(nsize / labelwidth))
+            n_blocks = int(np.ceil(contour_size / labelwidth))
         else:
-            xsize = 1
-        if xsize == 1:
-            ysize = nsize
+            n_blocks = 1
+        if n_blocks == 1:
+            block_size = contour_size
         else:
-            ysize = int(labelwidth)
-
-        XX = np.resize(linecontour[:, 0], (xsize, ysize))
-        YY = np.resize(linecontour[:, 1], (xsize, ysize))
-        # I might have fouled up the following:
+            block_size = int(labelwidth)
+        # Split contour into blocks of length ``block_size``, filling the last
+        # block by cycling the contour start (per `np.resize` semantics).  (Due
+        # to cycling, the index returned is taken modulo contour_size.)
+        XX = np.resize(linecontour[:, 0], (n_blocks, block_size))
+        YY = np.resize(linecontour[:, 1], (n_blocks, block_size))
         yfirst = YY[:, :1]
         ylast = YY[:, -1:]
         xfirst = XX[:, :1]
@@ -301,14 +301,21 @@ def locate_label(self, linecontour, labelwidth):
         L = np.hypot(xlast - xfirst, ylast - yfirst)
         # Ignore warning that divide by zero throws, as this is a valid option
         with np.errstate(divide='ignore', invalid='ignore'):
-            dist = np.sum(np.abs(s) / L, axis=-1)
-        x, y, ind = self.get_label_coords(dist, XX, YY, ysize, labelwidth)
-
-        # There must be a more efficient way...
-        lc = [tuple(l) for l in linecontour]
-        dind = lc.index((x, y))
-
-        return x, y, dind
+            distances = np.sum(np.abs(s) / L, axis=-1)
+        # Labels are drawn in the middle of the block (``hbsize``) where the
+        # contour is the closest (per ``distances``) to a straight line, but
+        # not `too_close()` to a preexisting label.
+        hbsize = block_size // 2
+        adist = np.argsort(distances)
+        for idx in adist:
+            x, y = XX[idx, hbsize], YY[idx, hbsize]
+            if self.too_close(x, y, labelwidth):
+                continue
+            return x, y, (idx * block_size + hbsize) % contour_size
+        # If all candidates are `too_close()`, just use the straightest part.
+        idx = adist[0]
+        x, y = XX[idx, hbsize], YY[idx, hbsize]
+        return x, y, hbsize % contour_size
 
     def calc_label_rot_and_inline(self, slc, ind, lw, lc=None, spacing=5):
         """

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+``ContourLabeler.get_label_coords`` is deprecated
	`2`	`+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
	`3`	`+It is considered an internal helper.`