Create initial tests which render two different files that should produce the same geometry but have different order of operation to prevent output from caching. Uses unmodified output, --enable sort-stl and a python script that sorts the file.

README.md

@@ -0,0 +1,11 @@
+# OpenSCAD Examples
+
+Examples and exercises for comparing features and techniques in using OpenSCAD.
+
+## Tests
+
+### Deterministically-ordered STL Output
+
+```bash
+bash deterministic_tests.sh
+```

deterministic_tests.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+
+##############
+#  BASELINE
+##############
+
+echo "Baseline..."
+openscad --version
+
+BASELINE=$(mktemp -d)
+FIRST="${BASELINE}/first.stl"
+SECOND="${BASELINE}/second.stl"
+
+openscad -q -o "${FIRST}" scad/deterministic.scad
+openscad -q -o "${SECOND}" scad/deterministic2.scad
+
+DIFF_VAL=$(diff "${FIRST}" "${SECOND}")
+
+if [[ "${DIFF_VAL}" == "" ]]; then
+	echo "Files are the same"
+else
+	#echo "${DIFF_VAL}"
+	echo "Files are different"
+fi
+
+rm -rf "${BASELINE}"
+
+##############
+#  SORT-STL
+##############
+
+echo "sort-stl..."
+
+SORTSTL=$(mktemp -d)
+FIRST="${SORTSTL}/first.stl"
+SECOND="${SORTSTL}/second.stl"
+
+openscad -q -o "${FIRST}" --enable sort-stl scad/deterministic.scad
+openscad -q -o "${SECOND}" --enable sort-stl scad/deterministic2.scad
+
+DIFF_VAL=$(diff "${FIRST}" "${SECOND}")
+
+if [[ "${DIFF_VAL}" == "" ]]; then
+	echo "Files are the same"
+else
+	#echo "${DIFF_VAL}"
+	echo "Files are different"
+fi
+
+rm -rf "${SORTSTL}"
+
+##############
+#  C14N
+##############
+
+echo "C14N..."
+
+C14N=$(mktemp -d)
+FIRST="${C14N}/first.stl"
+SECOND="${C14N}/second.stl"
+
+openscad -q -o "${FIRST}" scad/deterministic.scad
+python3 python/c14n_stl.py "${FIRST}"
+openscad -q -o "${SECOND}" scad/deterministic2.scad
+python3 python/c14n_stl.py "${SECOND}"
+
+DIFF_VAL=$(diff "${FIRST}" "${SECOND}")
+
+if [[ "${DIFF_VAL}" == "" ]]; then
+	echo "Files are the same"
+else
+	#echo "${DIFF_VAL}"
+	echo "Files are different"
+fi
+
+rm -rf "${C14N}"
+
+#--export-format asciistl
+#--export-format binstl

python/c14n_stl.py

@@ -0,0 +1,117 @@
+#!/usr/bin/env python
+
+#
+# NopSCADlib Copyright Chris Palmer 2018
+# nop.head@gmail.com
+# hydraraptor.blogspot.com
+#
+# This file is part of NopSCADlib.
+#
+# NopSCADlib 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.
+#
+# NopSCADlib 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 NopSCADlib.
+# If not, see <https://www.gnu.org/licenses/>.
+#
+
+#
+#! OpenSCAD produces randomly ordered STL files. This script re-orders them consistently so that GIT can tell if they have changed or not.
+#
+# OpenSCAD produces randomly ordered STL files so source control like GIT can't tell if they have changed or not.
+# This scrip orders each triangle to start with the lowest vertex first (comparing x, then y, then z)
+# It then sorts the triangles to start with the one with the lowest vertices first (comparing first vertex, second, then third)
+# This has no effect on the model but makes the STL consistent. I.e. it makes a canonical form.
+#
+
+from __future__ import print_function
+
+import sys
+
+def cmz(x):
+    ''' Convert "-0" to "0". '''
+    return '0' if x == '-0' else x
+
+class Vertex:
+    def __init__(self, x, y, z):
+        self.x, self.y, self.z = x, y, z
+        self.key = (float(x), float(y), float(z))
+
+class Normal:
+    def __init__(self, dx, dy, dz):
+        self.dx, self.dy, self.dz = dx, dy, dz
+
+class Facet:
+    def __init__(self, normal, v1, v2, v3):
+        self.normal = normal
+        if v1.key < v2.key:
+            if v1.key < v3.key:
+                self.vertices = (v1, v2, v3)    #v1 is the smallest
+            else:
+                self.vertices = (v3, v1, v2)    #v3 is the smallest
+        else:
+            if v2.key < v3.key:
+                self.vertices = (v2, v3, v1)    #v2 is the smallest
+            else:
+                self.vertices = (v3, v1, v2)    #v3 is the smallest
+
+    def key(self):
+        return (self.vertices[0].x, self.vertices[0].y, self.vertices[0].z,
+                self.vertices[1].x, self.vertices[1].y, self.vertices[1].z,
+                self.vertices[2].x, self.vertices[2].y, self.vertices[2].z)
+
+class STL:
+    def __init__(self, fname):
+        self.facets = []
+
+        with open(fname) as f:
+            words = [cmz(s.strip()) for s in f.read().split()]
+
+        if words[0] == 'solid' and words[1] == 'OpenSCAD_Model':
+            i = 2
+            while words[i] == 'facet':
+                norm = Normal(words[i + 2],  words[i + 3],  words[i + 4])
+                v1   = Vertex(words[i + 8],  words[i + 9],  words[i + 10])
+                v2   = Vertex(words[i + 12], words[i + 13], words[i + 14])
+                v3   = Vertex(words[i + 16], words[i + 17], words[i + 18])
+                i += 21
+                self.facets.append(Facet(norm, v1, v2, v3))
+
+            self.facets.sort(key = Facet.key)
+        else:
+            print("Not an OpenSCAD ascii STL file")
+            sys.exit(1)
+
+    def write(self, fname):
+        mins = [float('inf'), float('inf'), float('inf')]
+        maxs = [float('-inf'), float('-inf'), float('-inf')]
+        with open(fname,"wt") as f:
+            print('solid OpenSCAD_Model', file=f)
+            for facet in self.facets:
+                print('  facet normal %s %s %s' % (facet.normal.dx, facet.normal.dy, facet.normal.dz), file=f)
+                print('    outer loop', file=f)
+                for vertex in facet.vertices:
+                    print('      vertex %s %s %s' % (vertex.x, vertex.y, vertex.z), file=f)
+                    for i in range(3):
+                        ordinate = vertex.key[i]
+                        if ordinate > maxs[i]:  maxs[i] = ordinate
+                        if ordinate < mins[i]:  mins[i] = ordinate
+                print('    endloop', file=f)
+                print('  endfacet', file=f)
+            print('endsolid OpenSCAD_Model', file=f)
+        return mins, maxs
+
+def canonicalise(fname):
+    stl = STL(fname)
+    return stl.write(fname)
+
+if __name__ == '__main__':
+    if len(sys.argv) == 2:
+        canonicalise(sys.argv[1])
+    else:
+        print("\nusage:\n\t c14n_stl file - Canonicalise an STL file created by OpenSCAD.")
+        sys.exit(1)

scad/deterministic.scad

@@ -0,0 +1,8 @@
+$fn = 100;
+
+difference () {
+	cube([40, 40, 40], center = true);
+	cylinder(r = 20/2, h = 40 + 1, center = true);
+	rotate([90, 0, 0]) cylinder(r = 20/2, h = 40 + 1, center = true);
+	rotate([0, 90, 0]) cylinder(r = 20/2, h = 40 + 1, center = true);
+}

scad/deterministic2.scad

@@ -0,0 +1,8 @@
+$fn = 100;
+
+difference () {
+	cube([40, 40, 40], center = true);
+	rotate([0, 90, 0]) cylinder(r = 20/2, h = 40 + 1, center = true);
+	rotate([90, 0, 0]) cylinder(r = 20/2, h = 40 + 1, center = true);
+	cylinder(r = 20/2, h = 40 + 1, center = true);
+}