Fix clipping of markers in PDF backend.

QuLogic · QuLogic · commit e87606d28384 · 2020-04-16T22:01:32.000-04:00
The bbox only contains the points of the marker, but the line will extend outside by half the line width. This was handled before, except when the line is at an angle to the edge, as then the line outside is wider than half a line width. The maximum is at 45°, or √2. This fixes corners on 'v', '^', '<', '>', 'p', 'h', 'H', 'D', 'd', 'X'. Fixes #9829.
diff --git a/lib/matplotlib/backends/backend_pdf.py b/lib/matplotlib/backends/backend_pdf.py
@@ -1546,7 +1546,11 @@ 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 line is not parallel to the edge,
+            # then the line will extend even further to make a corner. The
+            # maximum is at 45°, or √2/2, ≈ 0.7071...
+            bbox = bbox.padded(lw * 0.71)
             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
@@ -133,3 +133,44 @@ 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')
diff --git a/lib/mpl_toolkits/tests/baseline_images/test_axes_grid1/divider_append_axes.pdf b/lib/mpl_toolkits/tests/baseline_images/test_axes_grid1/divider_append_axes.pdf
