Begin shifting group edges, not working yet

Author: iosonofabio

iplotx/groups.py

@@ -14,13 +14,15 @@
 from .heuristics import normalise_layout, normalise_grouping
 from .styles import get_style
 from .tools.geometry import convex_hull
+from .tools.geometry import _compute_group_path_with_vertex_padding
 
 
 class GroupingArtist(PatchCollection):
     def __init__(
         self,
         grouping: GroupingType,
         layout: LayoutType,
+        vertexpadding: Union[None, int] = None,
         *args,
         **kwargs,
     ):
@@ -34,6 +36,11 @@ def __init__(
                 vertices are assumed to have IDs corresponding to integers starting from
                 zero.
         """
+        if vertexpadding is not None:
+            self._vertexpadding = vertexpadding
+        else:
+            style = get_style(".grouping")
+            self._vertexpadding = style.get("vertexpadding", 10)
         patches, grouping, layout = self._create_patches(grouping, layout, **kwargs)
         self._grouping = grouping
         self._layout = layout
@@ -45,6 +52,7 @@ def _create_patches(self, grouping, layout, **kwargs):
         layout = normalise_layout(layout)
         grouping = normalise_grouping(grouping, layout)
         style = get_style(".grouping")
+        style.pop("vertexpadding", None)
 
         style.update(kwargs)
 
@@ -57,15 +65,55 @@ def _create_patches(self, grouping, layout, **kwargs):
             idx_hull = convex_hull(coords)
             coords_hull = coords[idx_hull]
 
-            patches.append(
-                mpl.patches.Polygon(
-                    coords_hull,
-                    label=name,
-                    # NOTE: the transform is set later on
-                    **style,
-                )
+            # NOTE: the transform is set later on
+            patch = _compute_group_patch_stub(
+                coords_hull,
+                self._vertexpadding,
+                label=name,
+                **style,
             )
+
+            patches.append(patch)
         return patches, grouping, layout
 
     def _process(self):
         self.set_transform(self.axes.transData)
+        if self._vertexpadding > 0:
+            for i, path in enumerate(self._paths):
+                self._paths[i].vertices = _compute_group_path_with_vertex_padding(
+                    path.vertices,
+                    self.get_transform(),
+                    vertexpadding=self._vertexpadding,
+                )
+
+
+def _compute_group_patch_stub(
+    points,
+    vertexpadding,
+    **kwargs,
+):
+    if vertexpadding == 0:
+        return mpl.patches.Polygon(
+            points,
+            **kwargs,
+        )
+
+    vertices = []
+    codes = []
+    for point in points:
+        vertices.extend([point] * 3)
+        codes.extend(["LINETO", "CURVE3", "CURVE3"])
+    codes[0] = "MOVETO"
+    vertices.append(vertices[0])
+    codes.append("CLOSEPOLY")
+
+    codes = [getattr(mpl.path.Path, x) for x in codes]
+    patch = mpl.patches.PathPatch(
+        mpl.path.Path(
+            vertices,
+            codes=codes,
+        ),
+        **kwargs,
+    )
+
+    return patch

iplotx/styles.py

@@ -34,6 +34,7 @@
         "edgecolor": "black",
         "linewidth": 1.5,
         "alpha": 0.5,
+        "vertexpadding": 10,
     },
 }
 

iplotx/tools/geometry.py

@@ -1,3 +1,4 @@
+from math import tan, atan2
 import numpy as np
 
 
@@ -132,3 +133,48 @@ def _convex_hull_Graham_scan(points):
     stack = np.asarray(stack)
 
     return stack
+
+
+def _compute_group_path_with_vertex_padding(
+    points,
+    transform,
+    vertexpadding=10,
+):
+    """Offset path for a group based on vertex padding.
+
+    At the input, the structure is [v1, v1, v1, v2, v2, v2, ...]
+    """
+
+    # Transform into figure coordinates
+    trans = transform.transform
+    trans_inv = transform.inverted().transform
+    points = trans(points)
+
+    # Compute all shift vectors by diff, arctan2, then add 90 degrees, tan, norm
+    # This maintains chirality
+
+    # Diff
+    vpoints = points[:-1:3].copy()
+    vpoints[1:] -= vpoints[:-1]
+    vpoints[0] -= vpoints[-1]
+
+    # Argtan etc
+    angles = np.arctan2(vpoints[:, 1], vpoints[:, 0])
+    angles_orth = angles + np.pi / 2
+    m_orth = np.tan(angles_orth)
+
+    # Normalise to 1
+    vpads = (np.vstack([np.ones_like(m_orth), m_orth]) / (1 + m_orth**2) ** 0.5).T
+    vpads_rot = np.zeros_like(vpads)
+    vpads_rot[:-1] = vpads[1:]
+    vpads_rot[-1] = vpads[0]
+
+    # Shift the points
+    points[:-1:3] += vpads_rot * vertexpadding
+    points[1:-1:3] += (vpads + vpads_rot) * vertexpadding
+    points[2:-1:3] += vpads * vertexpadding
+
+    # Transform back to data coordinates
+    points = trans_inv(points)
+
+    return points