What is OFFBuilder?

OFFBuilder generates OFF files for convex polytopes from their coordinates. It's meant for use with Stella and Miratope. Runs (mostly) in the browser.

OFFBuilder v.2 is a rework of the original OFFBuilder v.1. It's meant to be compatible with all platforms and to be more extensible than the original software.

How to use?

To generate an OFF file, you'll have to follow a simple step-by-step process. Steps 1–2 only need to be ran once.

1. Open OFFBuilder from its website.
2. Download Qhull, extract the ZIP file, and copy qconvex into its own separate folder. Let's call it offbuilder.
3. Write the coordinates of the polytope into the Coordinates field. You can either add a single point, or add the point along with sign changes and permutations of some of its coordinates. Alternatively, you can use the API to add coordinates programmatically: see below.
4. When you're done adding the coordinates, click on the Export button. Save the file as polytope_input.txt on the same folder you placed qconvex.
5. Run qconvex with the following parameters:

   qconvex.exe C0.00001 -o TI polytope_input.txt TO polytope_output.txt

   This will generate the polytope_output.txt file on the offbuilder folder.
6. Import polytope_output.txt into OFFBuilder. The resulting file is the OFF file corresponding to the input vertices.

OFFBuilder API

If you want to add a more complicated set of coordinates, OFFBuilder provides a Code textbox where you can run code and input coordinates manually. You can enter any JavaScript code and run it by pressing Ctrl + Enter. For instance, you can declare auxiliary variables for the coordinates by writing

this.variable_name = value;

on the code field. These can then be called simply by their variable name.

The coordinate field is encapsulated by the coordinates object. It provides two methods to append coordinates: push, which adds them directly, and add, which also applies any sign changes and permutations to them. Both methods take either points (that is, numerical arrays), or arrays of points.

// Adds the point (1, 2).
coordinates.push([1, 2]);

// Adds the points (3, 4) and (5, 6), applies permutations and sign changes.
coordinates.add([[3, 4], [5, 6]]);

There's also a few helper methods like polygon and prism to generate point sets. For their specific documentations, check the source code in the extras folder.

Extend OFFBuilder

If the existing methods aren't enough for you, you can always extend OFFBuilder's functionality. To do this, add a file with your code on the extras folder. You should write it as a module so that other parts of the code can access it if necessary, but add the functions to the global namespace so that the end user can access it too. Here's a simple example:

// extras/square.js

/**
 * Builds a square with a given side.
 *
 * @param {number} side The side length of the square.
 * @returns {Point[]} The array of the square's vertices.
 */
export const square = function(side) {
	const x = side / 2;
	return [[x, x], [x, -x], [-x, x], [-x, -x]];
}
globalThis.square = square;

To have your code actually plugged into the main application, add the corresponding import to main.js. In this example, this would be:

import "./extras/square.js";

If your extension has the potential to be useful to other users, be sure to add it to the repository.

Credits

The core application was coded by @vihdzp. As dependencies, it uses ace.js, decimal.js, and svd.js, all under the MIT license.