Merge pull request #17163 from QuLogic/pdf-marker-clip

QuLogic · web-flow · commit 21c3acbc2128 · 2020-06-10T16:38:56.000-04:00
Fix clipping of markers in PDF backend.
diff --git a/lib/matplotlib/backends/backend_pdf.py b/lib/matplotlib/backends/backend_pdf.py
@@ -1618,7 +1618,14 @@ def markerObject(self, path, trans, fill, stroke, lw, joinstyle,
     def writeMarkers(self):
         for ((pathops, fill, stroke, joinstyle, capstyle),
              (name, ob, bbox, lw)) in self.markers.items():
-            bbox = bbox.padded(lw * 0.5)
+            # bbox wraps the exact limits of the control points, so half a line
+            # will appear outside it. If the join style is miter and the line
+            # is not parallel to the edge, then the line will extend even
+            # further. From the PDF specification, Section 8.4.3.5, the miter
+            # limit is miterLength / lineWidth and from Table 52, the default
+            # is 10. With half the miter length outside, that works out to the
+            # following padding:
+            bbox = bbox.padded(lw * 5)
             self.beginStream(
                 ob.id, None,
                 {'Type': Name('XObject'), 'Subtype': Name('Form'),
diff --git a/lib/matplotlib/tests/test_marker.py b/lib/matplotlib/tests/test_marker.py
@@ -139,3 +139,44 @@ def draw_ref_marker(y, style, size):
 
     ax_test.set(xlim=(-0.5, 1.5), ylim=(-0.5, 1.5))
     ax_ref.set(xlim=(-0.5, 1.5), ylim=(-0.5, 1.5))
+
+
+@check_figures_equal()
+def test_marker_clipping(fig_ref, fig_test):
+    # Plotting multiple markers can trigger different optimized paths in
+    # backends, so compare single markers vs multiple to ensure they are
+    # clipped correctly.
+    marker_count = len(markers.MarkerStyle.markers)
+    marker_size = 50
+    ncol = 7
+    nrow = marker_count // ncol + 1
+
+    width = 2 * marker_size * ncol
+    height = 2 * marker_size * nrow * 2
+    fig_ref.set_size_inches((width / fig_ref.dpi, height / fig_ref.dpi))
+    ax_ref = fig_ref.add_axes([0, 0, 1, 1])
+    fig_test.set_size_inches((width / fig_test.dpi, height / fig_ref.dpi))
+    ax_test = fig_test.add_axes([0, 0, 1, 1])
+
+    for i, marker in enumerate(markers.MarkerStyle.markers):
+        x = i % ncol
+        y = i // ncol * 2
+
+        # Singular markers per call.
+        ax_ref.plot([x, x], [y, y + 1], c='k', linestyle='-', lw=3)
+        ax_ref.plot(x, y, c='k',
+                    marker=marker, markersize=marker_size, markeredgewidth=10,
+                    fillstyle='full', markerfacecolor='white')
+        ax_ref.plot(x, y + 1, c='k',
+                    marker=marker, markersize=marker_size, markeredgewidth=10,
+                    fillstyle='full', markerfacecolor='white')
+
+        # Multiple markers in a single call.
+        ax_test.plot([x, x], [y, y + 1], c='k', linestyle='-', lw=3,
+                     marker=marker, markersize=marker_size, markeredgewidth=10,
+                     fillstyle='full', markerfacecolor='white')
+
+    ax_ref.set(xlim=(-0.5, ncol), ylim=(-0.5, 2 * nrow))
+    ax_test.set(xlim=(-0.5, ncol), ylim=(-0.5, 2 * nrow))
+    ax_ref.axis('off')
+    ax_test.axis('off')
