CAD and Haptics

Computer Aided Design systems.


My first real commercial job was at a startup called SensAble Technologies where I worked on FreeForm for around four years. FreeForm was a software and hardware system that simulated “virtual clay”. FreeForm is still available today, but it’s now sold by 3D Systems.

A very detailed model carved with FreeForm.

FreeForm was a complex application written entirely in C++ with close to a million lines when I left. I worked on many aspects of FreeFrom from the UI to graphics to haptics and I was a member of the four-person architecture board. We learned many lessons about design, architecture, code quality, performance and testing, plus user interfaces and the user experience.

FreeForm was often used to make toys built out of parts.


When you buy FreeForm you are also buying a haptic device called The Phantom which looks like a pen or stylus on a robotic arm. The device contains senors and motors that simulate real physical interaction. When when you push on the virtual model it feels real. When you “carve” you can feel the material being removed out from under you. It’s quite a striking effect, people tended to be amazed when they first tried it.

FreeForm plus the Phantom cost around $10,000 at the time.

With computer graphics the goal is usually to refresh the screen at least 60 times a second, which means you have 16.7 milliseconds to generate the next frame. The Phantom however had to be updated at 1000Hz to generate realistic forces, so you only had 1 millisecond to do the computation! We used a large number of performance tricks and optimizations to run that fast including the little-known Fiber API in Windows. Fibers are basically primitive co-routines, a language feature that’s hot today in Go and Python for example.