Added convex hull plugin

extensions/fablabchemnitz_convexhull.inx

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<inkscape-extension xmlns="http://www.inkscape.org/namespace/inkscape/extension">
+    <name>Convex Hull</name>
+    <id>fablabchemnitz.de.convexhull</id>
+    <effect needs-live-preview="false">
+		<object-type>all</object-type>
+            <effects-menu>
+                <submenu name="Convex Hull"/>
+            </effects-menu>       
+    </effect>
+    <script>
+        <command location="inx" interpreter="python">fablabchemnitz_convexhull.py</command>
+    </script>
+</inkscape-extension>

extensions/fablabchemnitz_convexhull.py

@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+
+import inkex
+import sys
+import numpy as n
+from inkex.paths import CubicSuperPath
+from inkex.transforms import Transform
+from lxml import etree
+
+link = lambda a,b: n.concatenate((a,b[1:]))
+edge = lambda a,b: n.concatenate(([a],[b]))
+
+'''
+
+Convex Hull routine by Markus Kohler, found at https://gist.github.com/kohlerm/0337f7c64df42f21f96405b3f8e895f2, which itself is an implementation of:
+https://github.com/flengyel/REST/blob/master/quickhull.py
+Compute the convex hull of a set of points in the plane
+Adapted from en.literateprograms.org/Quickhull_(Python,arrays)
+Content available under MIT/X11 License at 
+http://en.literateprograms.org/LiteratePrograms:Copyrights
+Copyright (c) 2008 the authors listed in the page history
+(see http://en.literateprograms.org/index.php?title=Quickhull_(Python,_arrays)&action=history)
+Permission is hereby granted, free of charge, to any person obtaining a copy 
+of this software and associated documentation files (the "Software"), to deal 
+in the Software without restriction, including without limitation the rights 
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
+copies of the Software, and to permit persons to whom the Software is 
+furnished to do so, subject to the following conditions:
+The above copyright notice and this permission notice shall be included in 
+all copies or substantial portions of the Software.
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 
+IN THE SOFTWARE.
+'''
+
+def qhull(sample):
+    def dome(sample,base): 
+        h, t = base
+        dists = n.dot(sample-h, n.dot(((0,-1),(1,0)),(t-h)))
+        outer = n.repeat(sample, dists>0, 0)
+
+        if len(outer):
+            pivot = sample[n.argmax(dists)]
+            return link(dome(outer, edge(h, pivot)),
+                        dome(outer, edge(pivot, t)))
+        else:
+            return base
+    if len(sample) > 2:
+    	axis = sample[:,0]
+    	base = n.take(sample, [n.argmin(axis), n.argmax(axis)], 0)
+    	return link(dome(sample, base),
+                    dome(sample, base[::-1]))
+    else:
+        return sample
+   
+class ConvexHull(inkex.Effect):
+    def __init__(self):
+        inkex.Effect.__init__(self)
+        self.paths = {}
+        self.paths_clone_transform = {}
+        
+    def joinWithNode (self, node, path, makeGroup=False, cloneTransform=None):
+        if (not path) or (len(path) == 0 ):
+            return
+        g = self.document.getroot()   
+        # Now make a <path> element which contains the twist & is a child
+        # of the new <g> element
+        style = { 'stroke': '#000000', 'fill': 'none', 'stroke-width': '1' }
+        line_attribs = { 'style':str(inkex.Style(style)), 'd': path }
+        if (cloneTransform != None ) and (cloneTransform != '' ):
+            line_attribs['transform'] = cloneTransform
+        etree.SubElement(g, inkex.addNS('path', 'svg' ), line_attribs) 
+
+    def effect(self):
+        global output_nodes, points
+        #Loop through all the selected items in Inkscape
+        for node in self.svg.selected.values():
+            #create numpy array of nodes
+            n_array = []
+                    
+            #Iterate through all the selected objects in Inkscape
+            for  node in self.svg.selected.values():
+                #Check if the node is a path ("svg:path" node in XML )
+                #id = node.id
+                if node.tag == inkex.addNS('path','svg'):
+                    # bake (or fuse) transform
+                    node.apply_transform()
+                    #turn into cubicsuperpath
+                    d = node.get('d')
+                    p = CubicSuperPath(d)
+                    for subpath in p: # there may be several paths joined together (e.g. holes)
+                        for csp in subpath: # groups of three to handle control points.
+                            # just the points no control points (handles)
+                            n_array.append(csp[1][0])
+                            n_array.append(csp[1][1])
+
+        k = n.asarray(n_array)
+        length = int(len(k)/2)
+        c = k.reshape(length,2)
+        hull_pts = qhull(c)
+        
+        pdata = ''
+        for vertex in hull_pts:
+            if pdata == '':
+                pdata = 'M%f,%f' % (vertex[0], vertex[1] )
+            else:
+                pdata += 'L %f,%f' %  (vertex[0], vertex[1] )
+        pdata += ' Z'        
+        path = 'polygon'
+        makeGroup = False
+        paths_clone_transform = None
+        self.joinWithNode(path, pdata, makeGroup, paths_clone_transform )
+    
+ConvexHull().run()