dashing line collections (hlines, vlines, ...)

line-style was previously ignored for line collections, this fixes it.
Note that I did not add support for offset in line-style, which has not
existed in the first place, and I have no need for it.

There's a corresponding commit/PR in mpld3 coming.

This was done together with gpt-5.1-codex (but I reviewed and edited
a lot), here is what it has to say:

Handle collection dasharrays in exporter

- derive dash arrays from collection linestyles/dashes
- carry dasharrays through export and render_path_collection so hlines/vlines/grid keep their patterns

Author: lucasb-eyer

mplexporter/exporter.py

@@ -259,6 +259,7 @@ def draw_collection(self, ax, collection,
         styles = {'linewidth': collection.get_linewidths(),
                   'facecolor': collection.get_facecolors(),
                   'edgecolor': collection.get_edgecolors(),
+                  'dasharray': utils.get_dasharray_list(collection),
                   'alpha': collection._alpha,
                   'zorder': collection.get_zorder()}
 

mplexporter/renderers/base.py

@@ -204,8 +204,12 @@ def _iter_path_collection(paths, path_transforms, offsets, styles):
         if np.size(facecolor) == 0:
             facecolor = ['none']
 
+        dasharray = styles.get('dasharray', None)
+        if dasharray is None or np.size(dasharray) == 0:
+            dasharray = ['none']
+
         elements = [paths, path_transforms, offsets,
-                    edgecolor, styles['linewidth'], facecolor]
+                    edgecolor, styles['linewidth'], facecolor, dasharray]
 
         it = itertools
         return it.islice(py3k.zip(*py3k.map(it.cycle, elements)), N)
@@ -258,7 +262,7 @@ def draw_path_collection(self, paths, path_coordinates, path_transforms,
 
         for tup in self._iter_path_collection(paths, path_transforms,
                                               offsets, styles):
-            (path, path_transform, offset, ec, lw, fc) = tup
+            (path, path_transform, offset, ec, lw, fc, da) = tup
             vertices, pathcodes = path
             path_transform = transforms.Affine2D(path_transform)
             vertices = path_transform.transform(vertices)
@@ -268,7 +272,7 @@ def draw_path_collection(self, paths, path_coordinates, path_transforms,
             style = {"edgecolor": utils.export_color(ec),
                      "facecolor": utils.export_color(fc),
                      "edgewidth": lw,
-                     "dasharray": "10,0",
+                     "dasharray": da,
                      "alpha": styles['alpha'],
                      "zorder": styles['zorder']}
             self.draw_path(data=vertices, coordinates=path_coordinates,

mplexporter/utils.py

@@ -45,6 +45,18 @@ def _many_to_one(input_dict):
                            ('', ' ', 'None', 'none'): None})
 
 
+def _dasharray_from_linestyle(ls):
+    if ls is None:
+        return LINESTYLES['solid']
+    if isinstance(ls, tuple) and len(ls) == 2:  # NOTE: No support for offset yet.
+        return ','.join(str(val) for val in ls)
+    dasharray = LINESTYLES.get(ls, 'not found')
+    if dasharray == 'not found':
+        warnings.warn(f"line style '{ls}' not understood: defaulting to solid")
+        dasharray = LINESTYLES['solid']
+    return dasharray
+
+
 def get_dasharray(obj):
     """Get an SVG dash array for the given matplotlib linestyle
 
@@ -59,16 +71,27 @@ def get_dasharray(obj):
     dasharray : string
         The HTML/SVG dasharray code associated with the object.
     """
-    if obj.__dict__.get('_dashSeq', None) is not None:
-        return ','.join(map(str, obj._dashSeq))
+    if dashseq := getattr(obj, '_dashSeq', None):
+        return _dasharray_from_linestyle(dashseq)
+
+    ls = obj.get_linestyle()
+    if isinstance(ls, (list, tuple)) and not isinstance(ls, str):
+        ls = ls[0] if len(ls) else None
+    return _dasharray_from_linestyle(ls)
+
+
+def get_dasharray_list(collection):
+    """Return a list of SVG dash arrays for a matplotlib Collection"""
+    linestyles = None
+    if hasattr(collection, "get_dashes"):
+        linestyles = collection.get_dashes()
+    elif hasattr(collection, "get_linestyle"):
+        linestyles = collection.get_linestyle()
     else:
-        ls = obj.get_linestyle()
-        dasharray = LINESTYLES.get(ls, 'not found')
-        if dasharray == 'not found':
-            warnings.warn("line style '{0}' not understood: "
-                          "defaulting to solid line.".format(ls))
-            dasharray = LINESTYLES['solid']
-        return dasharray
+        return None
+    if not isinstance(linestyles, (list, tuple)):
+        linestyles = [linestyles]
+    return [_dasharray_from_linestyle(ls) for ls in linestyles]
 
 
 PATH_DICT = {Path.LINETO: 'L',