Hollow out an object with a configurable offset. This is useful in
3D printing workflows, for instance, to save material and/or reduce
printing time. The operator is added to the 3d Print Tools addon, in
the transform section.

@@ -821,0 +852,4 @@
+    def execute(self, context):
+        import numpy as np
+        import pyopenvdb as vdb
+

@@ -821,0 +855,4 @@
+
+        offset = self.offset
+        resolution = self.resolution
+        join = self.join

@@ -821,0 +861,4 @@
+
+        # Target object
+        obj = context.active_object
+        m = obj.data # mesh

@@ -821,0 +867,4 @@
+        nverts = len(m.vertices)
+        ntris = len(m.loop_triangles)
+        verts = np.zeros(3*nverts, dtype=np.float32)
+        tris = np.zeros(3*ntris, dtype=np.int32)

@@ -821,0 +877,4 @@
+        half_width = max(3.0, math.ceil(abs(offset)/resolution) + 2.0) # half_width has to envelop offset
+        trans = vdb.Transform()
+        trans.scale(resolution)
+        levelset = vdb.FloatGrid.createLevelSetFromPolygons(verts, triangles=tris, 

@@ -821,0 +882,4 @@
+
+        # Generate offset surface
+        newverts, newquads = levelset.convertToQuads(offset)
+        polys = [x for x in newquads]

@@ -821,0 +885,4 @@
+        polys = [x for x in newquads]
+
+        # Instantiate new object in Blender
+        mesh = bpy.data.meshes.new(m.name + ' offset')

@@ -821,0 +888,4 @@
+        mesh = bpy.data.meshes.new(m.name + ' offset')
+        mesh.from_pydata(newverts, [], polys)
+        newobj = bpy.data.objects.new(obj.name + ' offset', mesh)
+        newobj.matrix_world = obj.matrix_world.copy()

@@ -821,0 +891,4 @@
+        newobj.matrix_world = obj.matrix_world.copy()
+        bpy.context.collection.objects.link(newobj)
+
+        if not join:

@@ -821,0 +911,4 @@
+            context.view_layer.objects.active = obj
+            bpy.ops.object.join()
+
+            if mode_orig == 'EDIT_MESH':

@@ -124,0 +138,4 @@
+        name = "Create Hollow Copy",
+        description = "Create a hollow copy of the target object, with applied modifiers and scale",
+        default = False
+        )

@@ -821,0 +828,4 @@
+    bl_idname = "mesh.print3d_hollow"
+    bl_label = "Create offset surface"
+    bl_description = "Create offset surface for hollowing objects"
+    bl_options = {'REGISTER', 'UNDO'}

@@ -821,0 +847,4 @@
+        name = "Create Hollow Copy",
+        description = "Create a hollow copy of the target object, with applied modifiers and scale",
+        default = False
+        )

@@ -821,0 +892,4 @@
+        obj_offset = bpy.data.objects.new(obj.name + ' offset', mesh_offset)
+        bpy.context.collection.objects.link(obj_offset)
+
+        if not self.create_hollow:

@@ -821,0 +898,4 @@
+            # Translate surface object to target object's position
+            obj_offset.matrix_world.translation = obj.matrix_world.translation
+            # This mesh will not be used anymore
+            bpy.data.meshes.remove(mesh_target)

@@ -821,0 +903,4 @@
+            # Create a copy of the target object with applied modifiers and scale
+            obj_hollow = bpy.data.objects.new(obj.name + " hollow", mesh_target)
+            bpy.context.collection.objects.link(obj_hollow)
+            if self.offset < 0.0:

@@ -821,0 +910,4 @@
+                # Offset surface is outside, correct normals, see above
+                mesh_offset.flip_normals()
+                # Original surface is inside, flip its normals
+                mesh_target.flip_normals()

@@ -821,0 +917,4 @@
+            obj_offset.select_set(True)
+            obj_hollow.select_set(True)
+            context.view_layer.objects.active = obj_hollow
+            bpy.ops.object.join()

@@ -821,0 +920,4 @@
+            bpy.ops.object.join()
+
+            # Translate hollow object to target object's position
+            obj_hollow.matrix_world.translation = obj.matrix_world.translation

@@ -821,0 +922,4 @@
+            # Translate hollow object to target object's position
+            obj_hollow.matrix_world.translation = obj.matrix_world.translation
+
+

@@ -121,0 +123,4 @@
+        col.prop(print_3d, "hollow_create")
+        col.prop(print_3d, "hollow_offset")
+        col.prop(print_3d, "hollow_resolution")
+        col.operator("mesh.print3d_hollow", text="Create Offset Surface")

@@ -821,0 +841,4 @@
+    voxel_size: FloatProperty(
+        name="Voxel size",
+        description="Size of the voxel used for volume evaluation. Lower values preserve finer details",
+        default=5.0,

@@ -821,0 +854,4 @@
+        name="Inside",
+        description="Offset surface inside of the object",
+        default=True,
+        )

@@ -821,0 +929,4 @@
+        print_3d.hollow_offset = self.offset
+        print_3d.hollow_voxel_size = self.voxel_size
+        print_3d.make_hollow_duplicate = self.make_hollow_duplicate
+        print_3d.make_hollow_inside = self.make_hollow_inside

@@ -821,0 +839,4 @@
+        name="Offset Direction",
+        description="Where the offset surface is created relative to the object",
+        default='inside',
+        )