Add functions to import and draw paths from an SVG.

boxes/svg_import.py

@@ -0,0 +1,61 @@
+"""Allow paths to be imported from an SVG file into boxes.py.
+
+This is intended to make it easier to add custom cut-outs and engraving.
+Currently, only a single path can be imported. This is generally sufficient
+to import shapes drawn in OpenSCAD.
+"""
+
+import svg.path
+from lxml import etree
+from boxes.drawing import Context
+import numpy as np
+
+def draw_path_on_ctx(ctx: Context, path: svg.path.Path):
+    """Draw an SVG path into the current context.
+
+    This transforms the points according to the current context, but otherwise
+    should just add the commands from the path into the output.
+    """
+    for seg in path:
+        if isinstance(seg, svg.path.Move):
+            ctx.move_to(seg.end.real, seg.end.imag)
+        if isinstance(seg, svg.path.Close) or isinstance(seg, svg.path.Line):
+            ctx.line_to(seg.end.real, seg.end.imag)
+        elif isinstance(seg, svg.path.CubicBezier):
+            ctx.curve_to(
+                seg.control1.real,
+                seg.control1.imag,
+                seg.control2.real,
+                seg.control2.imag,
+                seg.end.real,
+                seg.end.imag,
+            )
+
+def path_extent(path: svg.path.Path) -> tuple[tuple[float, float], tuple[float, float]]:
+    """Determine max/min x,y positions in a path."""
+    extent_x = [np.inf, -np.inf]
+    extent_y = [np.inf, -np.inf]
+    for seg in path:
+        x, y = seg.end.real, seg.end.imag
+        for extent, point in [(extent_x, x), (extent_y, y)]:
+            extent[0] = min(extent[0], point)
+            extent[1] = max(extent[1], point)
+    return tuple(extent_x), tuple(extent_y)
+
+def path_centre(path: svg.path.Path) -> tuple[float, float]:
+    """Determine the middle point of a path."""
+    (x0, x1), (y0, y1) = path_extent(path)
+    return (x0 + x1)/2, (y0 + y1)/2
+
+def load_path_from_svg(filename: str) -> svg.path.Path:
+    """Load a path from an SVG file.
+
+    This assumes there is a single path in the file, as is true for OpenSCAD
+    exports.
+    """
+    tree = etree.parse(filename)
+    path_nodes = tree.xpath("//svg:path", namespaces={'svg': "http://www.w3.org/2000/svg"})
+    if len(path_nodes) > 1:
+        raise RuntimeError("I can only cope with one path in an SVG!")
+    data = path_nodes[0].get("d")
+    return svg.path.parse_path(data)