gcode raymarching simulator

This is an experiment to test the viability of visualizing material removal in the context of a 2.5 cnc milling machine.

This approach could probably be used for FDM 3d printing as well, but that is not my primary focus at this time.

how does it work?

rough history

The main approach here is called "raymarching signed distance fields" and derives from a technique popularized in the 4k demo scene by Iñigo Quílez. The foundation of ray marching comes from a technique called "Sphere Marching"

nitty gritty

We're not going to get into the intimate details of raymarching here, but more into the way this experiment is tied together. If you want to learn more see the further reading section below.

To start, we have a quad that we fill the entire screen with. A vertex shader that does next to nothing is provided to send geometry to the fragment shader. The fragment shader is where all of the work is done.

There is a timer that moves a cutterPosition around the scene and a couple of ndarrays, which can be thought of as depth textures.

ndarray 1

refered to by the name tool

The first ndarray is precomputed to be the shape of the end of the cutting tool in question this is essentially a rasterization operation that only needs to be computed once as we are going to apply it to the second ndarray as the tool moves around in the scene.

ndarray 2

refered to by depthTexture

This ndarray is as big as possible (for now), and it represents the history of the tool location. This history is achieved by applying tool to the larger array every time the cutterPosition moves. If any dexel in the tool texture + the cutterPosition.y is "deeper" than what is represented in the depthTexture then the dexel is applied to the texture.

i.e. depthTexture[x][y] = max(depthTexture[x][z], tool[x][z] + cutterPosition.y)

Rendering this depthTexture is done via raymarching and thus fits fairly well into the flow. This is implemented in the solid_depthmap function in shaders/raymarch.frag.

further reading

• "Rendering worlds with 2 triangles" - http://www.iquilezles.org/www/material/nvscene2008/rwwtt.pdf
• "Sphere Marching" - http://mathinfo.univ-reims.fr/IMG/pdf/hart94sphere.pdf
• "GPU Ray Marching of Distance Fields" - http://csokavar.hu/raytrace/imm6392.pdf

how do I run this thing?

you'll need node.js and git to clone this repo

git clone https://github.com/tmpvar/gcode-raymarch-sim.git
cd gcode-raymarch-sim
npm install

Now you can run the development server

npm run dev

this should open a browser tab to http://localhost:8000, if it does not you can just navigate there. Tested in chrome