support negative engraving offsets

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@554 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/Geometry/Line.py

@@ -431,8 +431,9 @@ class LineGroup(TransformableContainer):
                 # Prolong the line at the beginning and at the end - to allow
                 # overlaps. Use factor "2" to take care for star-like structure
                 # where a complete convex triangle would get cropped (two lines
-                # get lost instead of just one).
-                in_line = line.dir().mul(2 * offset)
+                # get lost instead of just one). Use the "abs" value to
+                # compensate negative offsets.
+                in_line = line.dir().mul(2 * abs(offset))
                 return Line(line.p1.add(cross_offset).sub(in_line),
                         line.p2.add(cross_offset).add(in_line))
         def do_lines_intersection(l1, l2):

src/pycam/Toolpath/Generator.py

@@ -162,7 +162,7 @@ def generate_toolpath(model, tool_settings=None,
         trimesh_model += support_grid_model
     # Adapt the contour_model to the engraving offset. This offset is
     # considered to be part of the material_allowance.
-    if (not contour_model is None) and (engrave_offset > 0):
+    if (not contour_model is None) and (engrave_offset != 0):
         if not callback is None:
             callback(text="Preparing contour model with offset ...")
             progress_callback = ProgressCounter(