Simplify axisartist line clipping.

anntzer · anntzer · commit ec937bef8e55 · 2021-01-30T17:00:52.000+01:00
axisartist.clip_path is currently used to clip the paths for curvilinear
grid lines and compute the angles at which the ticks are drawn.

We don't actually need to clip the lines (because we can just set a
clipbox on the gridline instead); actually we just need to find the
crossings positions and angles, which is much simpler, and now
encapsulated in the `_find_line_box_crossings` function.  Therefore,
deprecate the whole clip_path module.

The baseline images change slightly, mostly because we don't clip the
path ourselves anymore, but let the renderer do that; also because
floating point slop changes for ticks exactly at the edges.
diff --git a/doc/api/next_api_changes/deprecations/19401-AL.rst b/doc/api/next_api_changes/deprecations/19401-AL.rst
@@ -0,0 +1,3 @@
+``mpl_toolkits.axisartist.clip_path`` is deprecated
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... with no replacement.
diff --git a/lib/mpl_toolkits/axisartist/clip_path.py b/lib/mpl_toolkits/axisartist/clip_path.py
@@ -4,6 +4,9 @@
 import math
 
 
+_api.warn_deprecated("3.5", name=__name__, obj_type="module")
+
+
 def atan2(dy, dx):
     if dx == 0 and dy == 0:
         _api.warn_external("dx and dy are 0")
diff --git a/lib/mpl_toolkits/axisartist/grid_finder.py b/lib/mpl_toolkits/axisartist/grid_finder.py
@@ -2,7 +2,49 @@
 
 from matplotlib import _api, ticker as mticker
 from matplotlib.transforms import Bbox, Transform
-from .clip_path import clip_line_to_rect
+
+
+def _find_line_box_crossings(xys, bbox):
+    """
+    Find the points where a polyline crosses a bbox, and the crossing angles.
+
+    Parameters
+    ----------
+    xys : (N, 2) array
+        The polyline coordinates.
+    bbox : `.Bbox`
+        The bounding box.
+
+    Returns
+    -------
+    list of ((float, float), float)
+        Four separate lists of crossings, for the left, right, bottom, and top
+        sides of the bbox, respectively.  For each list, the entries are the
+        ``((x, y), ccw_angle_in_degrees)`` of the crossing, where an angle of 0
+        means that the polyline is moving to the right at the crossing point.
+
+        The entries are computed by linearly interpolating at each crossing
+        between the nearest points on either side of the bbox edges.
+    """
+    crossings = []
+    dxys = xys[1:] - xys[:-1]
+    for sl in [slice(None), slice(None, None, -1)]:
+        us, vs = xys.T[sl]  # "this" coord, "other" coord
+        dus, dvs = dxys.T[sl]
+        umin, vmin = bbox.min[sl]
+        umax, vmax = bbox.max[sl]
+        for u0, du0s in [(umin, us - umin), (umax, umax - us)]:
+            crossings.append([])
+            # du0 > 0 <=> polyline is on the "in" side of the edge.
+            idxs, = ((du0s[:-1] > 0) ^ (du0s[1:] > 0)).nonzero()
+            for idx in idxs:
+                v = vs[idx] + (u0 - us[idx]) * dvs[idx] / dus[idx]
+                if not vmin <= v <= vmax:
+                    continue
+                crossing = (u0, v)[sl]
+                theta = np.degrees(np.arctan2(*dxys[idx][::-1]))
+                crossings[-1].append((crossing, theta))
+    return crossings
 
 
 class ExtremeFinderSimple:
@@ -161,14 +203,12 @@ def _clip_grid_lines_and_find_ticks(self, lines, values, levs, bb):
         tck_levels = gi["tick_levels"]
         tck_locs = gi["tick_locs"]
         for (lx, ly), v, lev in zip(lines, values, levs):
-            xy, tcks = clip_line_to_rect(lx, ly, bb)
-            if not xy:
-                continue
+            tcks = _find_line_box_crossings(np.column_stack([lx, ly]), bb)
             gi["levels"].append(v)
-            gi["lines"].append(xy)
+            gi["lines"].append([(lx, ly)])
 
             for tck, direction in zip(tcks,
-                                      ["left", "bottom", "right", "top"]):
+                                      ["left", "right", "bottom", "top"]):
                 for t in tck:
                     tck_levels[direction].append(lev)
                     tck_locs[direction].append(t)
diff --git a/lib/mpl_toolkits/tests/test_axisartist_clip_path.py b/lib/mpl_toolkits/tests/test_axisartist_clip_path.py
@@ -1,9 +1,11 @@
 import numpy as np
+from matplotlib import _api
 import matplotlib.pyplot as plt
 from matplotlib.testing.decorators import image_comparison
 from matplotlib.transforms import Bbox
 
-from mpl_toolkits.axisartist.clip_path import clip_line_to_rect
+with _api.suppress_matplotlib_deprecation_warning():
+    from mpl_toolkits.axisartist.clip_path import clip_line_to_rect
 
 
 @image_comparison(['clip_path.png'], style='default')
diff --git a/lib/mpl_toolkits/tests/test_axisartist_grid_finder.py b/lib/mpl_toolkits/tests/test_axisartist_grid_finder.py
@@ -1,6 +1,27 @@
+from matplotlib.transforms import Bbox
 from mpl_toolkits.axisartist.grid_finder import (
-    FormatterPrettyPrint,
-    MaxNLocator)
+    _find_line_box_crossings, FormatterPrettyPrint, MaxNLocator)
+
+import numpy as np
+import pytest
+
+
+def test_find_line_box_crossings():
+    x = np.array([-3, -2, -1, 0., 1, 2, 3, 2, 1, 0, -1, -2, -3, 5])
+    y = np.arange(len(x))
+    bbox = Bbox.from_extents(-2, 3, 2, 12.5)
+    left, right, bottom, top = _find_line_box_crossings(
+        np.column_stack([x, y]), bbox)
+    ((lx0, ly0), la0), ((lx1, ly1), la1), = left
+    ((rx0, ry0), ra0), ((rx1, ry1), ra1), = right
+    ((bx0, by0), ba0), = bottom
+    ((tx0, ty0), ta0), = top
+    assert (lx0, ly0, la0) == (-2, 11, 135)
+    assert (lx1, ly1, la1) == pytest.approx((-2., 12.125, 7.125016))
+    assert (rx0, ry0, ra0) == (2, 5, 45)
+    assert (rx1, ry1, ra1) == (2, 7, 135)
+    assert (bx0, by0, ba0) == (0, 3, 45)
+    assert (tx0, ty0, ta0) == pytest.approx((1., 12.5, 7.125016))
 
 
 def test_pretty_print_format():
diff --git a/lib/mpl_toolkits/tests/test_axisartist_grid_helper_curvelinear.py b/lib/mpl_toolkits/tests/test_axisartist_grid_helper_curvelinear.py
@@ -1,5 +1,4 @@
 import numpy as np
-import platform
 
 import matplotlib.pyplot as plt
 from matplotlib.path import Path
@@ -16,8 +15,7 @@
     GridHelperCurveLinear
 
 
-@image_comparison(['custom_transform.png'], style='default',
-                  tol=0.03 if platform.machine() == 'x86_64' else 0.034)
+@image_comparison(['custom_transform.png'], style='default', tol=0.2)
 def test_custom_transform():
     class MyTransform(Transform):
         input_dims = output_dims = 2
@@ -79,8 +77,7 @@ def inverted(self):
     ax1.grid(True)
 
 
-@image_comparison(['polar_box.png'], style='default',
-                  tol={'aarch64': 0.04}.get(platform.machine(), 0.03))
+@image_comparison(['polar_box.png'], style='default', tol=0.04)
 def test_polar_box():
     # Remove this line when this test image is regenerated.
     plt.rcParams['text.kerning_factor'] = 6
@@ -143,7 +140,7 @@ def test_polar_box():
     ax1.grid(True)
 
 
-@image_comparison(['axis_direction.png'], style='default', tol=0.03)
+@image_comparison(['axis_direction.png'], style='default', tol=0.07)
 def test_axis_direction():
     # Remove this line when this test image is regenerated.
     plt.rcParams['text.kerning_factor'] = 6

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+``mpl_toolkits.axisartist.clip_path`` is deprecated
	`2`	`+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
	`3`	`+... with no replacement.`