fixed engraving of a single plane with minz==maxz

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@965 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/PathGenerators/EngraveCutter.py

@@ -78,8 +78,19 @@ class EngraveCutter:
 
         line_groups = self.contour_model.get_polygons()
         # push slices for all layers above ground
+        if maxz == minz:
+            # only one layer - use PushCutter instead of DropCutter
+            # put "last_z" clearly above the model plane
+            last_z = maxz + 1
+            push_steps = z_steps
+            drop_steps = []
+        else:
+            # multiple layers
             last_z = maxz
-        for z in z_steps[:-1]:
+            push_steps = z_steps[:-1]
+            drop_steps = [z_steps[-1]]
+
+        for z in push_steps:
             # update the progress bar and check, if we should cancel the process
             if draw_callback and draw_callback(text="Engrave: processing" \
                         + " layer %d/%d" % (current_layer, num_of_layers)):
@@ -135,12 +146,13 @@ class EngraveCutter:
                     return 0
         line_groups.sort(cmp=polygon_priority)
 
+        for z in drop_steps:
             # process the final layer with a drop cutter
             for line_group in self.contour_model.get_polygons():
                 self.pa_drop.new_direction(0)
                 self.pa_drop.new_scanline()
                 for line in line_group.get_lines():
-                self.GenerateToolPathLineDrop(self.pa_drop, line, minz, maxz,
+                    self.GenerateToolPathLineDrop(self.pa_drop, line, z, maxz,
                             horiz_step, last_z, draw_callback=draw_callback)
                     if progress_counter.increment():
                         # quit requested
@@ -151,6 +163,7 @@ class EngraveCutter:
                 # break the outer loop if requested
                 if quit_requested:
                     break
+            last_z = z
         self.pa_drop.finish()
         
         return self.pa_push.paths + self.pa_drop.paths