Merge pull request #17444 from anntzer/odddash

QuLogic · web-flow · commit 16ae35780ff6 · 2020-05-19T17:38:08.000-04:00
Support odd-length dash patterns in Agg.
diff --git a/lib/matplotlib/tests/test_lines.py b/lib/matplotlib/tests/test_lines.py
@@ -217,3 +217,9 @@ def test_marker_as_markerstyle():
 
     assert_array_equal(line2.get_marker().vertices, triangle1.vertices)
     assert_array_equal(line3.get_marker().vertices, triangle1.vertices)
+
+
+@check_figures_equal()
+def test_odd_dashes(fig_test, fig_ref):
+    fig_test.add_subplot().plot([1, 2], dashes=[1, 2, 3])
+    fig_ref.add_subplot().plot([1, 2], dashes=[1, 2, 3, 1, 2, 3])
diff --git a/src/py_converters.cpp b/src/py_converters.cpp
@@ -226,7 +226,6 @@ int convert_dashes(PyObject *dashobj, void *dashesp)
     PyObject *dash_offset_obj = NULL;
     double dash_offset = 0.0;
     PyObject *dashes_seq = NULL;
-    Py_ssize_t nentries;
 
     if (!PyArg_ParseTuple(dashobj, "OO:dashes", &dash_offset_obj, &dashes_seq)) {
         return 0;
@@ -256,18 +255,17 @@ int convert_dashes(PyObject *dashobj, void *dashesp)
         return 0;
     }
 
-    nentries = PySequence_Size(dashes_seq);
-    if (nentries % 2 != 0) {
-        PyErr_Format(PyExc_ValueError, "dashes sequence must have an even number of elements");
-        return 0;
-    }
+    Py_ssize_t nentries = PySequence_Size(dashes_seq);
+    // If the dashpattern has odd length, iterate through it twice (in
+    // accordance with the pdf/ps/svg specs).
+    Py_ssize_t dash_pattern_length = (nentries % 2) ? 2 * nentries : nentries;
 
-    for (Py_ssize_t i = 0; i < nentries; ++i) {
+    for (Py_ssize_t i = 0; i < dash_pattern_length; ++i) {
         PyObject *item;
         double length;
         double skip;
 
-        item = PySequence_GetItem(dashes_seq, i);
+        item = PySequence_GetItem(dashes_seq, i % nentries);
         if (item == NULL) {
             return 0;
         }
@@ -280,7 +278,7 @@ int convert_dashes(PyObject *dashobj, void *dashesp)
 
         ++i;
 
-        item = PySequence_GetItem(dashes_seq, i);
+        item = PySequence_GetItem(dashes_seq, i % nentries);
         if (item == NULL) {
             return 0;
         }
