Merge pull request #560 from kinnala/add-svg-mesh2d

Add support for visualizing 2D meshes as svg

skfem/mesh/mesh2d/mesh2d.py

@@ -1,8 +1,8 @@
 import warnings
+from typing import Optional
 
 import numpy as np
 from numpy import ndarray
-
 from skfem.mesh import Mesh
 
 
@@ -55,6 +55,12 @@ def param(self) -> float:
         return np.max(np.linalg.norm(np.diff(self.p[:, self.facets], axis=1),
                                      axis=0))
 
+    def _repr_svg_(self) -> Optional[str]:
+        from skfem.visuals.svg import draw
+        if self.t.shape[1] > 5000:
+            return None
+        return draw(self)
+
     @staticmethod
     def strip_extra_coordinates(p: ndarray) -> ndarray:
         return p[:, :2]

skfem/visuals/matplotlib.py

@@ -2,15 +2,15 @@
 
 from functools import singledispatch
 
-import matplotlib.pyplot as plt
 import numpy as np
-from matplotlib.axes import Axes
 from mpl_toolkits.mplot3d import Axes3D
 from numpy import ndarray
 
+import matplotlib.pyplot as plt
+from matplotlib.axes import Axes
+
 from ..assembly import InteriorBasis
-from ..mesh import Mesh2D, MeshLine, MeshTri,\
-    MeshTet, MeshQuad
+from ..mesh import Mesh2D, MeshLine, MeshQuad, MeshTet, MeshTri
 
 
 @singledispatch
@@ -50,14 +50,16 @@ def draw_mesh2d(m: Mesh2D, **kwargs) -> Axes:
     ax (optional)
         A preinitialised Matplotlib axes for plotting.
     node_numbering (optional)
-        If true, draw node numbering.
+        If ``True``, draw node numbering.
     facet_numbering (optional)
-        If true, draw facet numbering.
+        If ``True``, draw facet numbering.
     element_numbering (optional)
-        If true, draw element numbering.
+        If ``True``, draw element numbering.
     aspect (optional)
-        Ratio of vertical to horizontal length-scales; ignored if ax
+        Ratio of vertical to horizontal length-scales; ignored if ``ax`` is
         specified
+    boundaries_only (optional)
+        If ``True``, draw only boundary edges.
 
     Returns
     -------

skfem/visuals/svg.py

@@ -0,0 +1,67 @@
+"""Drawing meshes using svg."""
+
+from functools import singledispatch
+
+import numpy as np
+
+from ..mesh import Mesh2D
+from ..assembly import InteriorBasis
+
+
+@singledispatch
+def draw(m, **kwargs) -> str:
+    """Visualise meshes by drawing the edges.
+
+    Parameters
+    ----------
+    m
+        A mesh object.
+
+    Returns
+    -------
+    string
+        The svg xml source as a string.
+
+    """
+    raise NotImplementedError("Type {} not supported.".format(type(m)))
+
+
+@draw.register(Mesh2D)
+def draw_mesh2d(m: Mesh2D, **kwargs) -> str:
+    """Support for two-dimensional meshes."""
+    if "boundaries_only" in kwargs:
+        facets = m.facets[:, m.boundary_facets()]
+    else:
+        facets = m.facets
+    p = m.p
+    maxx = np.max(p[0])
+    minx = np.min(p[0])
+    maxy = np.max(p[1])
+    miny = np.min(p[1])
+    width = kwargs["width"] if "width" in kwargs else 300
+    if "height" in kwargs:
+        height = kwargs["height"]
+    else:
+        height = width * (maxy - miny) / (maxx - miny)
+    stroke = kwargs["stroke"] if "stroke" in kwargs else 1
+    sx = (width - 2 * stroke) / (maxx - minx)
+    sy = (height - 2 * stroke) / (maxy - miny)
+    p[0] = sx * (p[0] - miny) + stroke
+    p[1] = sy * (maxy - p[1]) + stroke
+    template = ("""<line x1="{}" y1="{}" x2="{}" y2="{}" """
+                """style="stroke:black;stroke-width:{}"/>""")
+    lines = ""
+    for s, t, u, v in zip(p[0, facets[0]],
+                          p[1, facets[0]],
+                          p[0, facets[1]],
+                          p[1, facets[1]]):
+        lines += template.format(s, t, u, v, stroke)
+    return ("""<svg xmlns="http://www.w3.org/2000/svg" version="1.1" """
+            """width="{}" height="{}">{}</svg>""").format(width, height, lines)
+
+
+@draw.register(InteriorBasis)
+def draw_basis(ib: InteriorBasis, **kwargs) -> str:
+    Nrefs = kwargs["Nrefs"] if "Nrefs" in kwargs else 2
+    m, _ = ib.refinterp(ib.mesh.p[0], Nrefs=Nrefs)
+    return draw(m, boundaries_only=True, **kwargs)