Add svgutil.svgMerge() allwing to add generated box into anoterh svg

Implemetation has still many short comings. E.g. assumes units and layout of
document passed in. Also assumes to be merged document to be generated by
boxes.py.

boxes/svgutil.py

@@ -15,6 +15,7 @@
 #   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import xml.parsers.expat
+from lxml import etree as et
 import re
 
 
@@ -100,6 +101,31 @@ class SVGFile(object):
             raise ValueError("Could not understand SVG file")
 
 
+def svgMerge(box, inkscape, output):
+    parser = et.XMLParser(remove_blank_text=True)
+
+    src_tree = et.parse(box, parser)
+    dest_tree = et.parse(inkscape, parser)
+    dest_root = dest_tree.getroot()
+
+    m = re.match(r"(\d+\.?\d*)(\D+)", dest_root.get("height"))
+    height, units = m.groups()
+
+    scale = {"mm" : 1.0,
+             "pt" : 7.2, # XXX
+    }.get(units, 1.0)
+
+
+    for el in src_tree.getroot():
+        import sys
+        dest_root.append(el)
+        if el.tag.endswith("g"):
+            el.set("transform", "matrix(%f,0,0,%f, 0, %i)" % (
+                scale, scale, -10000+float(height)*scale))
+
+    # write the xml file
+    et.ElementTree(dest_root).write(output, pretty_print=True, encoding='utf-8', xml_declaration=True)
+
 if __name__ == "__main__":
     svg = SVGFile("examples/box.svg")
     svg.getEnvelope()