unified the generation of a grid of movement positions for DropCutter/PushCutter

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@759 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/Gui/Project.py

@@ -36,6 +36,7 @@ from pycam.Gui.OpenGLTools import ModelViewWindowGL
 from pycam.Toolpath import Bounds
 from pycam import VERSION
 import pycam.Physics.ode_physics
+import pycam.Toolpath.MotionGrid
 # this requires ODE - we import it later, if necessary
 #import pycam.Simulation.ODEBlocks
 import gtk
@@ -547,8 +548,9 @@ class ProjectGui:
         # connect the "consistency check" and the update-handler with all toolpath settings
         for objname in ("PushRemoveStrategy", "ContourPolygonStrategy",
                 "ContourFollowStrategy", "SurfaceStrategy",
-                "EngraveStrategy", "GridDirectionX",
-                "GridDirectionY", "GridDirectionXY"):
+                "EngraveStrategy", "GridDirectionX", "GridDirectionY",
+                "GridDirectionXY", "MillingStyleConventional",
+                "MillingStyleClimb", "MillingStyleIgnore"):
             self.gui.get_object(objname).connect("toggled",
                     self.update_process_controls)
             self.gui.get_object(objname).connect("toggled",
@@ -1318,8 +1320,10 @@ class ProjectGui:
                 "EngraveOffsetControl")
         active_controls = {
             "PushRemoveStrategy": ("GridDirectionX", "GridDirectionY",
-                    "GridDirectionXY", "MaxStepDownControl",
-                    "MaterialAllowanceControl", "OverlapPercentControl"),
+                    "GridDirectionXY", "MillingStyleConventional",
+                    "MillingStyleClimb", "MillingStyleIgnore",
+                    "MaxStepDownControl", "MaterialAllowanceControl",
+                    "OverlapPercentControl"),
             "ContourPolygonStrategy": ("GridDirectionX", "GridDirectionY",
                     "GridDirectionXY", "MillingStyleConventional",
                     "MillingStyleClimb", "MillingStyleIgnore",
@@ -2303,44 +2307,6 @@ class ProjectGui:
         elif action == "delete":
             self.append_to_queue(self.switch_bounds_table_selection)
 
-    def _get_process_details(self, strategy, direction, milling_style):
-        STRATEGY_GENERATORS = {
-                "PushRemoveStrategy": "PushCutter",
-                "ContourPolygonStrategy": "PushCutter",
-                "ContourFollowStrategy": "ContourFollow",
-                "SurfaceStrategy": "DropCutter",
-                "EngraveStrategy": "EngraveCutter"}
-        generator = STRATEGY_GENERATORS[strategy]
-        if strategy in ("PushRemoveStrategy", "SurfaceStrategy"):
-            if strategy == "PushRemoveStrategy":
-                # TODO: implement "conventional/climb" for PolygonCutter
-                processor = "PolygonCutter"
-            elif milling_style in ("conventional", "climb"):
-                processor = "PathAccumulator"
-            else:
-                processor = "ZigZagCutter"
-            if milling_style == "conventional":
-                reverse = False
-            else:
-                reverse_counter = 0
-                if direction == "y":
-                    reverse_counter += 1
-                if milling_style == "conventional":
-                    reverse_counter += 1
-                reverse = (reverse_counter % 1) == 1
-        elif strategy in ("ContourPolygonStrategy", "ContourFollowStrategy"):
-            if strategy == "ContourPolygonStrategy":
-                processor = "ContourCutter"
-            else:
-                processor = "SimpleCutter"
-            reverse = milling_style in ("climb", "ignore")
-        elif strategy == "EngraveStrategy":
-            processor = "SimpleCutter"
-            reverse = False
-        else:
-            pass
-        return generator, processor, reverse
-
     def _load_process_settings_from_gui(self, settings=None):
         if settings is None:
             settings = {}
@@ -2860,18 +2826,23 @@ class ProjectGui:
         # unit size
         toolpath_settings.set_unit_size(self.settings.get("unit"))
 
-        generator, postprocessor, reverse = self._get_process_details(
-                process_settings["path_strategy"],
-                process_settings["path_direction"],
-                process_settings["milling_style"])
+        STRATEGY_GENERATORS = {
+                "PushRemoveStrategy": ("PushCutter", "SimpleCutter"),
+                "ContourPolygonStrategy": ("PushCutter", "ContourPolygonStrategy"),
+                "ContourFollowStrategy": ("ContourFollow", "SimpleCutter"),
+                "SurfaceStrategy": ("DropCutter", "PathAccumulator"),
+                "EngraveStrategy": ("EngraveCutter", "SimpleCutter")}
+        generator, postprocessor = STRATEGY_GENERATORS[
+                process_settings["path_strategy"]]
 
         # process settings
         toolpath_settings.set_process_settings(
                 generator, postprocessor, process_settings["path_direction"],
-                reverse, process_settings["material_allowance"],
+                process_settings["material_allowance"],
                 process_settings["overlap_percent"] / 100.0,
                 process_settings["step_down"],
-                process_settings["engrave_offset"])
+                process_settings["engrave_offset"],
+                process_settings["milling_style"])
 
         return toolpath_settings
 

src/pycam/Gui/Settings.py

@@ -586,11 +586,11 @@ class ToolpathSettings:
             "generator": str,
             "postprocessor": str,
             "path_direction": str,
-            "reverse": bool,
             "material_allowance": float,
             "overlap": float,
             "step_down": float,
             "engrave_offset": float,
+            "milling_style": str,
         },
     }
 
@@ -698,20 +698,21 @@ class ToolpathSettings:
             return "mm"
 
     def set_process_settings(self, generator, postprocessor, path_direction,
-            reverse=False, material_allowance=0.0, overlap=0.0,
-            step_down=1.0, engrave_offset=0.0):
+            material_allowance=0.0, overlap=0.0, step_down=1.0,
+            engrave_offset=0.0, milling_style="ignore"):
         # TODO: this hack should be somewhere else, I guess
         if generator in ("ContourFollow", "EngraveCutter"):
             material_allowance = 0.0
+            milling_style = "ignore"
         self.process_settings = {
                 "generator": generator,
                 "postprocessor": postprocessor,
                 "path_direction": path_direction,
-                "reverse": reverse,
                 "material_allowance": material_allowance,
                 "overlap": overlap,
                 "step_down": step_down,
                 "engrave_offset": engrave_offset,
+                "milling_style": milling_style,
         }
 
     def get_process_settings(self):

src/pycam/PathGenerators/DropCutter.py

@@ -33,7 +33,7 @@ log = pycam.Utils.log.get_logger()
 
 # We need to use a global function here - otherwise it does not work with
 # the multiprocessing Pool.
-def _process_one_grid_line((positions, minz, maxz, dim_attrs, model, cutter,
+def _process_one_grid_line((positions, minz, maxz, model, cutter,
         physics, safety_height)):
     # for now only used for triangular collision detection
     last_position = None
@@ -41,11 +41,10 @@ def _process_one_grid_line((positions, minz, maxz, dim_attrs, model, cutter,
     height_exceeded = False
     for x, y in positions:
         if physics:
-            result = get_max_height_ode(physics, x, y, minz, maxz,
-                    order=dim_attrs[:])
+            result = get_max_height_ode(physics, x, y, minz, maxz)
         else:
             result = get_max_height_triangles(model, cutter, x, y, minz, maxz,
-                    order=dim_attrs[:], last_pos=last_position)
+                    last_pos=last_position)
         if result:
             points.extend(result)
         else:
@@ -95,43 +94,35 @@ class DropCutter:
         # remember if we already reported an invalid boundary
         self._boundary_warning_already_shown = False
 
-    def GenerateToolPath(self, minx, maxx, miny, maxy, minz, maxz, d0, d1,
-            direction, draw_callback=None):
+    def GenerateToolPath(self, motion_grid, minz, maxz, draw_callback=None):
         quit_requested = False
-        # determine step size
-        num_of_x_lines = 1 + ceil(abs(maxx - minx) / d0)
-        num_of_y_lines = 1 + ceil(abs(maxy - miny) / d1)
-        x_step = abs(maxx - minx) / max(1, (num_of_x_lines - 1))
-        y_step = abs(maxy - miny) / max(1, (num_of_y_lines - 1))
-        x_steps = [(minx + i * x_step) for i in range(num_of_x_lines)]
-        y_steps = [(miny + i * y_step) for i in range(num_of_y_lines)]
-
-        # map the scales according to the order of direction
-        grid = []
-        if direction == 0:
-            # first x, then y
-            for x in x_steps:
-                grid.append(zip([x] * (len(y_steps) + 1), y_steps))
-            dim_attrs = ["x", "y"]
-        else:
-            # first y, then x
-            for y in y_steps:
-                grid.append(zip(x_steps, [y] * (len(x_steps) + 1)))
-            dim_attrs = ["y", "x"]
 
-        num_of_lines = len(grid)
-        num_of_grid_positions = num_of_x_lines * num_of_y_lines
+        # Transfer the grid (a generator) into a list of lists and count the
+        # items.
+        num_of_grid_positions = 0
+        lines = []
+        # there should be only one layer for DropCutter
+        for layer in motion_grid:
+            for line in layer:
+                lines.append(list(line))
+                num_of_grid_positions += len(lines[-1])
+            # ignore any other layers
+            break
+
+        num_of_lines = len(lines)
         progress_counter = ProgressCounter(num_of_grid_positions, draw_callback)
         current_line = 0
 
-        self.pa.new_direction(direction)
+        self.pa.new_direction(0)
 
         self._boundary_warning_already_shown = False
 
         args = []
-        for one_grid_line in grid:
-            args.append((one_grid_line, minz, maxz, dim_attrs, self.model,
-                    self.cutter, self.physics, self.model.maxz))
+        for one_grid_line in lines:
+            # simplify the data (useful for remote processing)
+            xy_coords = [(pos.x, pos.y) for pos in one_grid_line]
+            args.append((xy_coords, minz, maxz, self.model, self.cutter,
+                    self.physics, self.model.maxz))
         # ODE does not work with multi-threading
         disable_multiprocessing = not self.physics is None
         for points, height_exceeded in run_in_parallel(_process_one_grid_line,

src/pycam/PathGenerators/PushCutter.py

@@ -47,59 +47,43 @@ class PushCutter:
         self.pa = path_processor
         self.physics = physics
 
-    def GenerateToolPath(self, minx, maxx, miny, maxy, minz, maxz, dx, dy, dz,
-            draw_callback=None):
+    def GenerateToolPath(self, motion_grid, draw_callback=None):
         # calculate the number of steps
-        # Sometimes there is a floating point accuracy issue: make sure
-        # that only one layer is drawn, if maxz and minz are almost the same.
-        if abs(maxz - minz) < epsilon:
-            diff_z = 0
-        else:
-            diff_z = abs(maxz - minz)
-        num_of_layers = 1 + ceil(diff_z / dz)
-        z_step = diff_z / max(1, (num_of_layers - 1))
-
-        lines_per_layer = 0
-        if dx != 0:
-            x_lines_per_layer = 1 + ceil(abs(maxx - minx) / dx)
-            x_step = abs(maxx - minx) / max(1, (x_lines_per_layer - 1))
-            lines_per_layer += x_lines_per_layer
-        if dy != 0:
-            y_lines_per_layer = 1 + ceil(abs(maxy - miny) / dy)
-            y_step = abs(maxy - miny) / max(1, (y_lines_per_layer - 1))
-            lines_per_layer += y_lines_per_layer
-
-        progress_counter = ProgressCounter(num_of_layers * lines_per_layer,
-                draw_callback)
 
-        current_layer = 0
+        # Transfer the grid (a generator) into a list of lists and count the
+        # items.
+        grid = []
+        num_of_grid_positions = 0
+        for layer in motion_grid:
+            lines = []
+            for line in layer:
+                lines.append(list(line))
+                num_of_grid_positions += len(lines[-1])
+            grid.append(lines)
+
+        num_of_layers = len(grid)
 
-        z_steps = [(maxz - i * z_step) for i in range(num_of_layers)]
-        for z in z_steps:
+        progress_counter = ProgressCounter(num_of_grid_positions, draw_callback)
+
+        current_layer = 0
+        for layer_grid in grid:
             # update the progress bar and check, if we should cancel the process
             if draw_callback and draw_callback(text="PushCutter: processing" \
                         + " layer %d/%d" % (current_layer + 1, num_of_layers)):
                 # cancel immediately
                 break
 
-            if dy > 0:
-                self.pa.new_direction(0)
-                self.GenerateToolPathSlice(minx, maxx, miny, maxy, z, 0, y_step,
-                        draw_callback, progress_counter)
-                self.pa.end_direction()
-            if dx > 0:
-                self.pa.new_direction(1)
-                self.GenerateToolPathSlice(minx, maxx, miny, maxy, z, x_step, 0,
-                        draw_callback, progress_counter)
-                self.pa.end_direction()
+            self.pa.new_direction(0)
+            self.GenerateToolPathSlice(layer_grid, draw_callback, progress_counter)
+            self.pa.end_direction()
             self.pa.finish()
 
             current_layer += 1
 
         return self.pa.paths
 
-    def GenerateToolPathSlice(self, minx, maxx, miny, maxy, z, dx, dy,
-            draw_callback=None, progress_counter=None):
+    def GenerateToolPathSlice(self, layer_grid, draw_callback=None,
+            progress_counter=None):
         """ only dx or (exclusive!) dy may be bigger than zero
         """
         # max_deviation_x = dx/accuracy
@@ -107,34 +91,15 @@ class PushCutter:
         max_depth = 20
 
         # calculate the required number of steps in each direction
-        if dx > 0:
-            depth = math.log(accuracy * abs(maxx - minx) / dx) / math.log(2)
-            depth = max(ceil(depth), 4)
-            depth = min(depth, max_depth)
-            num_of_x_lines = 1 + ceil(abs(maxx - minx) / dx)
-            x_step = abs(maxx - minx) / max(1, (num_of_x_lines - 1))
-            x_steps = [minx + i * x_step for i in range(num_of_x_lines)]
-            y_steps = [None] * num_of_x_lines
-        elif dy != 0:
-            depth = math.log(accuracy * abs(maxy - miny) / dy) / math.log(2)
-            depth = max(ceil(depth), 4)
-            depth = min(depth, max_depth)
-            num_of_y_lines = 1 + ceil(abs(maxy - miny) / dy)
-            y_step = abs(maxy - miny) / max(1, (num_of_y_lines - 1))
-            y_steps = [miny + i * y_step for i in range(num_of_y_lines)]
-            x_steps = [None] * num_of_y_lines
-        else:
-            # nothing to be done
-            return
+        distance = layer_grid[0][-1].sub(layer_grid[0][0]).norm
+        step_width = distance / len(layer_grid[0])
+        depth = math.log(accuracy * distance / step_width) / math.log(2)
+        depth = max(ceil(depth), 4)
+        depth = min(depth, max_depth)
 
         args = []
-        if dx > 0:
-            depth = depth_
-        for x, y in zip(x_steps, y_steps):
-            if dx > 0:
-                p1, p2 = Point(x, miny, z), Point(x, maxy, z)
-            else:
-                p1, p2 = Point(minx, y, z), Point(maxx, y, z)
+        for line in layer_grid:
+            p1, p2 = line
             args.append((p1, p2, depth, self.model, self.cutter, self.physics))
 
         # ODE does not work with multi-threading

src/pycam/PathGenerators/__init__.py

@@ -159,7 +159,7 @@ def get_free_paths_ode(physics, p1, p2, depth=8):
     physics.reset_drill()
     return points
 
-def get_max_height_ode(physics, x, y, minz, maxz, order=None):
+def get_max_height_ode(physics, x, y, minz, maxz):
     low, high = minz, maxz
     trip_start = 20
     safe_z = None
@@ -196,17 +196,13 @@ def get_max_height_ode(physics, x, y, minz, maxz, order=None):
     else:
         return [Point(x, y, safe_z)]
 
-def get_max_height_triangles(model, cutter, x, y, minz, maxz, order=None,
-        last_pos=None):
-    # TODO: "order" should be replaced with a direction vector
+def get_max_height_triangles(model, cutter, x, y, minz, maxz, last_pos=None):
     result = []
     if last_pos is None:
         last_pos = {}
     for key in ("triangle", "cut"):
         if not key in last_pos:
             last_pos[key] = None
-    if order is None:
-        order = ["x", "y"]
     p = Point(x, y, maxz)
     height_max = None
     cut_max = None

src/pycam/Toolpath/Generator.py

@@ -26,6 +26,7 @@ from pycam.Geometry.utils import number
 import pycam.PathProcessors
 import pycam.Cutters
 import pycam.Toolpath.SupportGrid
+import pycam.Toolpath.MotionGrid
 import pycam.Geometry.Model
 from pycam.Utils import ProgressCounter
 import pycam.Utils.log
@@ -45,14 +46,12 @@ def generate_toolpath_from_settings(model, tp_settings, callback=None):
     process = tp_settings.get_process_settings()
     grid = tp_settings.get_support_grid()
     backend = tp_settings.get_calculation_backend()
-    bounds_obj = tp_settings.get_bounds()
-    bounds_low, bounds_high = bounds_obj.get_absolute_limits()
     return generate_toolpath(model, tp_settings.get_tool_settings(),
-            bounds_low, bounds_high, process["path_direction"],
+            tp_settings.get_bounds(), process["path_direction"],
             process["generator"], process["postprocessor"],
-            process["reverse"],
             process["material_allowance"], process["overlap"],
             process["step_down"], process["engrave_offset"],
+            process["milling_style"],
             grid["type"], grid["distance_x"], grid["distance_y"],
             grid["thickness"], grid["height"], grid["offset_x"],
             grid["offset_y"], grid["adjustments_x"], grid["adjustments_y"],
@@ -60,10 +59,10 @@ def generate_toolpath_from_settings(model, tp_settings, callback=None):
             backend, callback)
 
 def generate_toolpath(model, tool_settings=None,
-        bounds_low=None, bounds_high=None, direction="x",
+        bounds=None, direction="x",
         path_generator="DropCutter", path_postprocessor="ZigZagCutter",
-        reverse=False,
         material_allowance=0, overlap=0, step_down=0, engrave_offset=0,
+        milling_style="ignore",
         support_grid_type=None, support_grid_distance_x=None,
         support_grid_distance_y=None, support_grid_thickness=None,
         support_grid_height=None, support_grid_offset_x=None,
@@ -127,15 +126,13 @@ def generate_toolpath(model, tool_settings=None,
     overlap = number(overlap)
     step_down = number(step_down)
     engrave_offset = number(engrave_offset)
-    if bounds_low is None:
+    if bounds is None:
         # no bounds were given - we use the boundaries of the model
         minx, miny, minz = (model.minx, model.miny, model.minz)
-    else:
-        minx, miny, minz = [number(value) for value in bounds_low]
-    if bounds_high is None:
-        # no bounds were given - we use the boundaries of the model
         maxx, maxy, maxz = (model.maxx, model.maxy, model.maxz)
     else:
+        bounds_low, bounds_high = bounds.get_absolute_limits()
+        minx, miny, minz = [number(value) for value in bounds_low]
         maxx, maxy, maxz = [number(value) for value in bounds_high]
     # trimesh model or contour model?
     if isinstance(model, pycam.Geometry.Model.Model):
@@ -259,42 +256,38 @@ def generate_toolpath(model, tool_settings=None,
     for next_model in trimesh_models[1:]:
         combined_models += next_model
     generator = _get_pathgenerator_instance(combined_models, contour_model,
-            cutter, path_generator, path_postprocessor, reverse, physics)
+            cutter, path_generator, path_postprocessor, milling_style, physics)
     if isinstance(generator, basestring):
         return generator
     if (overlap < 0) or (overlap >= 1):
         return "Invalid overlap value (%f): should be greater or equal 0 " \
                 + "and lower than 1"
     # factor "2" since we are based on radius instead of diameter
-    stepping = 2 * number(tool_settings["tool_radius"]) * (1 - overlap)
+    line_stepping = 2 * number(tool_settings["tool_radius"]) * (1 - overlap)
+    if path_generator == "PushCutter":
+        step_width = None
+    else:
+        # TODO: the step_width should be configurable
+        step_width = tool_settings["tool_radius"] / 10.0
     if path_generator == "DropCutter":
-        if direction == "x":
-            direction_param = 0
-        elif direction == "y":
-            direction_param = 1
-        else:
-            return "Invalid direction value (%s): not one of %s" \
-                    % (direction, DIRECTIONS)
-        toolpath = generator.GenerateToolPath(minx, maxx, miny, maxy, minz,
-                maxz, stepping, stepping, direction_param, callback)
+        layer_distance = None
+    else:
+        layer_distance = step_down
+    direction_dict = {"x": pycam.Toolpath.MotionGrid.GRID_DIRECTION_X,
+            "y": pycam.Toolpath.MotionGrid.GRID_DIRECTION_Y,
+            "xy": pycam.Toolpath.MotionGrid.GRID_DIRECTION_XY}
+    milling_style_grid = {
+            "ignore": pycam.Toolpath.MotionGrid.MILLING_STYLE_IGNORE,
+            "conventional": pycam.Toolpath.MotionGrid.MILLING_STYLE_CONVENTIONAL,
+            "climb": pycam.Toolpath.MotionGrid.MILLING_STYLE_CLIMB}
+    motion_grid = pycam.Toolpath.MotionGrid.get_fixed_grid(bounds,
+            layer_distance, line_stepping, step_width=step_width,
+            grid_direction=direction_dict[direction],
+            milling_style=milling_style_grid[milling_style])
+    if path_generator == "DropCutter":
+        toolpath = generator.GenerateToolPath(motion_grid, minz, maxz, callback)
     elif path_generator == "PushCutter":
-        if step_down > 0:
-            dz = step_down
-        else:
-            dz = maxz - minz
-            if dz <= 0:
-                dz = 1
-        if direction == "x":
-            dx, dy = 0, stepping
-        elif direction == "y":
-            dx, dy = stepping, 0
-        elif direction == "xy":
-            dx, dy = stepping, stepping
-        else:
-            return "Invalid direction (%s): not one of %s" \
-                    % (direction, DIRECTIONS)
-        toolpath = generator.GenerateToolPath(minx, maxx, miny, maxy, minz,
-                maxz, dx, dy, dz, callback)
+        toolpath = generator.GenerateToolPath(motion_grid, callback)
     elif path_generator == "EngraveCutter":
         if step_down > 0:
             dz = step_down

src/pycam/Toolpath/MotionGrid.py

+# -*- coding: utf-8 -*-
+"""
+$Id$
+
+Copyright 2010 Lars Kruse <devel@sumpfralle.de>
+
+This file is part of PyCAM.
+
+PyCAM is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+PyCAM is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with PyCAM.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+from pycam.Geometry.Point import Point
+from pycam.Geometry.utils import epsilon
+import math
+
+
+GRID_DIRECTION_X = 0
+GRID_DIRECTION_Y = 1
+GRID_DIRECTION_XY = 2
+
+MILLING_STYLE_IGNORE = 0
+MILLING_STYLE_CONVENTIONAL = 1
+MILLING_STYLE_CLIMB = 2
+
+START_X = 0x1
+START_Y = 0x2
+START_Z = 0x4
+
+def isiterable(obj):
+    try:
+        iter(obj)
+        return True
+    except TypeError:
+        return False
+
+def floatrange(start, end, inc=None, steps=None, reverse=False):
+    if reverse:
+        start, end = end, start
+        # 'inc' will be adjusted below anyway
+    if abs(start - end) < epsilon:
+        yield start
+    elif inc is None and steps is None:
+        raise ValueError("floatrange: either 'inc' or 'steps' must be provided")
+    elif (not steps is None) and (steps < 2):
+        raise ValueError("floatrange: 'steps' must be greater than 1")
+    else:
+        # the input is fine
+        # reverse increment, if it does not suit start/end
+        if steps is None:
+            if ((end - start) > 0) != (inc > 0):
+                inc = -inc
+            steps = int(math.ceil(float(end - start) / inc) + 1)
+        inc = float(end - start) / (steps - 1)
+        for index in range(steps):
+            yield start + inc * index
+
+def get_fixed_grid_line(start, end, line_pos, z, step_width=None,
+        grid_direction=GRID_DIRECTION_X):
+    if step_width is None:
+        # useful for PushCutter operations
+        steps = (start, end)
+    elif isiterable(step_width):
+        steps = step_width
+    else:
+        steps = floatrange(start, end, inc=step_width)
+    if grid_direction == GRID_DIRECTION_X:
+        get_point = lambda pos: Point(pos, line_pos, z)
+    else:
+        get_point = lambda pos: Point(line_pos, pos, z)
+    for pos in steps:
+        yield get_point(pos)
+
+def get_fixed_grid_layer(minx, maxx, miny, maxy, z, line_distance,
+        step_width=None, grid_direction=GRID_DIRECTION_X,
+        milling_style=MILLING_STYLE_IGNORE, start_position=0):
+    if grid_direction == GRID_DIRECTION_XY:
+        raise ValueError("'get_one_layer_fixed_grid' does not accept XY " \
+                + "direction")
+    # zigzag is only available if the milling 
+    zigzag = (milling_style == MILLING_STYLE_IGNORE)
+    # If we happen to start at a position that collides with the milling style,
+    # then we need to move to the closest other corner. Here we decide, which
+    # would be the best alternative.
+    def get_alternative_start_position(start):
+        if (maxx - minx) <= (maxy - miny):
+            # toggle the X position bit
+            return start ^ START_X
+        else:
+            # toggle the Y position bit
+            return start ^ START_Y
+    if grid_direction == GRID_DIRECTION_X:
+        primary_dir = START_X
+        secondary_dir = START_Y
+    else:
+        primary_dir = START_Y
+        secondary_dir = START_X
+    # Determine the starting direction (assuming we begin at the lower x/y
+    # coordinates.
+    if milling_style == MILLING_STYLE_IGNORE:
+        # just move forward - milling style is not important
+        pass
+    elif (milling_style == MILLING_STYLE_CLIMB) == (grid_direction == GRID_DIRECTION_X):
+        if bool(start_position & START_X) == bool(start_position & START_Y):
+            # we can't start from here - choose an alternative
+            start_position = get_alternative_start_position(start_position)
+    elif (milling_style == MILLING_STYLE_CONVENTIONAL) == (grid_direction == GRID_DIRECTION_X):
+        if bool(start_position & START_X) != bool(start_position & START_Y):
+            # we can't start from here - choose an alternative
+            start_position = get_alternative_start_position(start_position)
+    else:
+        raise ValueError("Invalid milling style given: %s" % str(milling_style))
+    # sort out the coordinates (primary/secondary)
+    if grid_direction == GRID_DIRECTION_X:
+        start, end = minx, maxx
+        line_start, line_end = miny, maxy
+    else:
+        start, end = miny, maxy
+        line_start, line_end = minx, maxx
+    # switch start/end if we move from high to low
+    if start_position & primary_dir:
+        start, end = end, start
+    if start_position & secondary_dir:
+        line_start, line_end = line_end, line_start
+    # calculate the line positions
+    if isiterable(line_distance):
+        lines = line_distance
+    else:
+        lines = floatrange(line_start, line_end, inc=line_distance)
+    # at the end of the layer we will be on the other side of the 2nd direction
+    end_position = start_position ^ secondary_dir
+    # the final position will probably be on the other side (primary)
+    if not zigzag:
+        end_position ^= primary_dir
+    # calculate each line
+    def get_lines(start, end, end_position):
+        result = []
+        for line_pos in lines:
+            result.append(get_fixed_grid_line(start, end, line_pos, z,
+                    step_width=step_width, grid_direction=grid_direction))
+            if zigzag:
+                start, end = end, start
+                end_position ^= primary_dir
+        return result, end_position
+    return get_lines(start, end, end_position)
+
+def get_fixed_grid(bounds, layer_distance, line_distance, step_width=None,
+        grid_direction=GRID_DIRECTION_X, milling_style=MILLING_STYLE_IGNORE,
+        start_position=START_Z):
+    """ Calculate the grid positions for toolpath movements
+    """
+    low, high = bounds.get_absolute_limits()
+    if isiterable(layer_distance):
+        layers = layer_distance
+    elif layer_distance is None:
+        # useful for DropCutter
+        layers = [low[2]]
+    else:
+        layers = floatrange(low[2], high[2], inc=layer_distance,
+                reverse=bool(start_position & START_Z))
+    def get_layers_with_direction(layers):
+        for layer in layers:
+            if grid_direction != GRID_DIRECTION_Y:
+                yield (layer, GRID_DIRECTION_X)
+            if grid_direction != GRID_DIRECTION_X:
+                yield (layer, GRID_DIRECTION_Y)
+    for z, direction in get_layers_with_direction(layers):
+        result, start_position = get_fixed_grid_layer(low[0], high[0],
+                low[1], high[1], z, line_distance, step_width=step_width,
+                grid_direction=direction, milling_style=milling_style,
+                start_position=start_position)
+        yield result
+