ImplicitCAD: Math Inspired CAD

Introduction

ImplicitCAD is a programmatic CAD program, implemented in haskell. Unlike traditional CAD programs, programmatic CAD programs use text descriptions of objects, as in programming. Concepts like variables, control structures and abstraction are used, just as in programming. This provides a number of advantages:

• Objects can abstracted and reused
• Repetitive tasks can be automated
• Objects can be designed parametrically
• The usual tools for software development (like version control) can be used

The traditional example of programmatic CAD is OpenSCAD.

Generally, objects in programmatic CAD are built with Constructive Solid Geometry or CSG. Unions, intersections and differences of simpler shapes slowly build the object. ImplicitCAD supports all this and much more! For example, it provides rounded unions so that one can have smooth interfaces between objects.

It also directly provides GCode generation, and has a parser for OpenSCAD to make it easier for people to transition.

ImplicitCAD is very much a work in progress. The author considers it ready for beta testers and greatly appreciates bug reports.

ExtOpenSCAD Examples

Let's being with OpenSCAD examples, since they're likely a more comfortable format that Haskell for most readers :)

ImplicitCAD supports an extended version of OpenSCAD, the popular programmatic CAD tool. This is very new functionality, so expect bugs!

Generally, normal openscad code should work. For example, save the following as file.scad.

union() {
	square([80,80]);
	translate ([80,80]) circle(30);
}

Running extopenscad file.scad will produce file.svg, which will look like:

You can read more about standard openscad functionality in OpenSCAD User Manual.

However, there are additional ImplicitCAD specific features. For example a rounded union:

union(r=14) {
	square([80,80]);
	translate ([80,80]) circle(30);
}

(For code like this that is not backwards compatible with OpenSCAD, it is recommended that you save it as a .escad file -- Extended OpenSCAD.)

Like openscad, ImplicitCAD supports extruding objects.

linear_extrude (height = 40, center=true){  
        union ( r = 8) {
                circle (10);
                translate ([22,0]) circle (10);
                translate ([0,22]) circle (10);
                translate ([-22,0]) circle (10);
                translate ([0,-22]) circle (10);
        }
}

And we allow you to twist them as you extrude.

linear_extrude (height = 40, center=true, twist=90){
        union ( r = 8) {
                circle (10);
                translate ([22,0]) circle (10);
                translate ([0,22]) circle (10);
                translate ([-22,0]) circle (10);
                translate ([0,-22]) circle (10);
        }
}

In fact, we've extended this to allow you to twist at non-constant rates and even reverse directions. You just make twist a function! (We're following the openscad convention of using degrees...)

linear_extrude (height = 40, center=true, twist(h) = 35*cos(h*2*pi/60)) {
        union ( r = 8) {
                circle (10);
                translate ([22,0]) circle (10);
                translate ([0,22]) circle (10);
                translate ([-22,0]) circle (10);
                translate ([0,-22]) circle (10);
        }
}

We also allow you to do rounded extrusions. See, we heard you like rounding, so we set this up so you can rounded extrude your rounded union...

linear_extrude (height = 40, center=true, r=5){
        union ( r = 8) {
                circle (10);
                translate ([22,0]) circle (10);
                translate ([0,22]) circle (10);
                translate ([-22,0]) circle (10);
                translate ([0,-22]) circle (10);
        }
}

This is fully compatible with twisting, of course!

linear_extrude (height = 40, center=true, twist=90, r=5){
        union ( r = 8) {
                circle (10);
                translate ([22,0]) circle (10);
                translate ([0,22]) circle (10);
                translate ([-22,0]) circle (10);
                translate ([0,-22]) circle (10);
        }
}

ImplicitCAD also provides full programmatic functionality, like variable assignment in loops, which are sadly absent in OpenSCAD. For example, the trivial program:

a = 5;
for (c = [1, 2, 3]) {
	echo(c);
	a = a*c;
	echo(a);
}

Has the output:

1.0
5.0
2.0
10.0
3.0
30.0
Nothing to render

As a functional programmer, I couldn't resist adding some other niceties to the language. For example, function currying:

f = max(4);
echo(f(5));
echo(max(4,5));

And some higher order functions, like my friend map:

echo(map(cos, [0, pi/2, pi]));

Haskell Examples

Everything you saw above can be done with the Haskell API. For example, a simple 2D example, the same as our first ExtOpenSCAD one:

import Graphics.Implicit

out = union [
	rectR 0 (-40,-40) (40,40),
	translate (40,40) (circle 30) ]

main = writeSVG 2 "test.svg" out

A rounded union:

import Graphics.Implicit

out = unionR 14 [
	rectR 0 (-40,-40) (40,40),
	translate (40,40) (circle 30) ]

main = writeSVG 2 "test.svg" out

A simple 3D example:

import Graphics.Implicit

out = union [
	rect3R 0 (0,0,0) (20,20,20),
	translate (20,20,20) (sphere 15) ]

main = writeSTL 1 "test.stl" out 

You can do a whole lot more!

Try ImplicitCAD!

1. Install GHC and cabal.
   • Debain/Ubuntu: apt-get install ghc cabal-install
   • Archlinux: pacman -S ghc cabal-install
   • Red Hat/Fedora: yum install ghc cabal-install
   • Mac OSX:
     • Homebrew: brew install ghc cabal-install
     • Fink doesn't seem to have a package for cabal Install the Haskell Platform manually as described here.
   • Windows: Follows these install instructions.
   • Other unices: If your package manager does not include ghc and cabal you should install the Haskell platform as described [here](
2. You now have two options for installation:
   • Latest release:
     • Use cabal to install ImplicitCAD: cabal update && cabal install implicit
   • Development version:
     • Install the dependencies: cabal update && cabal install hashmap parallel parsec plugins
     • Git clone this repo: git clone https://github.com/colah/ImplicitCAD.git
     • cd in: cd ImplicitCAD/
     • cabal install it: cabal configure && cabal install
3. Try it!
   • extopenscad test:
     • Make a test file: echo "circle(30);" > test.escad
     • Run extopencad: extopenscad test.escad
       • Alternatively, ~/.cabal/bin/extopenscad test.escad -- see bellow.
   • Haskell ImplicitCAD test:
     • Start ghci: ghci
     • Load ImplicitCAD: import Graphics.Implicit
     • Try it! writeSVG 1 "test.svg" (circle 30)
4. Known issues:
   • extopenscad test results in bash: extopenscad: command not found (or similar for your shell)
     • This probably means ~/.cabal/bin/ is not in your $PATH variable. Try using ~/.cabal/bin/extopenscad as your command instead.
   • Haskell test results in module is not loaded: 'Graphics.Implicit' (./Graphics/Implicit.hs)
     • This is most likely a problem with your Linux distro and cabal not playing nice. GHC is not configured to see the ImplicitCAD libraries. You can confirm this by try the test in ~/.cabal/lib/. If that works, you should be able to use ghc anywhere with the -Ldir or -llib options. Alternatively, some people have permanently fixed this by doing the cabal install as root.

Documentation

Documentation can be generated from the source code of ImplicitCAD by Haddock by running cabal haddock.

Releases of ImplicitCAD are uploaded to HackageDB which, in addition to making them avaialable through cabal install, puts the generated documentation on the Internet. So you can read the documentation for the most recent release of ImplicitCAD, 0.0.1, on HackageDB (for some reason the latest version doesn't seem to have built).

A description of the mathematical ideas underpinning ImplicitCAD are described in a blog post on colah's blog. Note that substantial changes have happened since that post. You can also look at the 0.0.1 relase notes.

Status

ImplicitCAD is very much a work in progress.

What works (Nov 2, 2011 -- regressions are possible if not probable):

• CSG, bevelled CSG, shells.
• 2D output (svg)
• 3D output (stl) -- rare bugs that can be fixed by increasing re
• gcode generation for 2D to hacklab laser cutter. Not configurable.

What still needs to be done:

• gcode generation for 3D printers, gcode generator config
• openscad parser for backwards compatibility (partially complete)

And a wishlist of things further in the future:

• More optimisation
• openGL viewer?
• openCL acceleration?