02Credits Blog

Day53 - Pando in the Browser

Port Pando to the browser and make a new plan


Project Page


Recently I came across a quote from an author named John Gall. He has been attributed with coming up with "Gall's Law" which when summarized, states: "No complex system was ever built from scratch. Instead all systems are built simply and modified until they are complex." With this principle in mind I have decided against rewriting much of Pando.

I have decided to abandon my plan I described here to write my own graph renderer and manipulation UI. I've decided that GraphViz produces better graphs than I can reasonably expect to draw with any algorithm I can come up with in a short period of time. So instead of rebuilding everything from scratch I will use GraphViz and instrument the produced svg with event handlers to enable a simple modification UI.

The "New" Plan

The new plan is to use the emscripten compiled version of GraphViz found here to run GraphViz in the browser, compile the Pando code to web assembly using stdweb, and add event handlers for mouse functions to the svg elements produced from GraphViz to figure out what connections to add and remove from the nodes.

The user interaction will support five operations: Add a node with a given title, remove a node, change a node status, link a node to another node, and unlink two nodes.

Overall much of the work is already finished however there are two new tasks with this plan. First, I will need to add support in the current rust code for turning a parsed pando file back into text after being modified. This will allow me to store in a clean readable fashion the modified graph. Secondly and as a result of the first, I will need to build some way to abbreviate node names. Neither of these tasks is overly hard, but will likely get a daily post about each individually.

Why tho?

I have realized that some change is needed for the way that Pando is interacted with. For the most part Pando is easy to read and understand, but modifying a Pando graph is very cumbersome as the graph gets larger. I found myself not wanting to modify my todo tree in response to new ideas which is VERY bad. So for the next couple of days I will do some work to fix things up and make the tool more easy to use.

Rusty WASM

The first step for this plan is to port Pando to Web Assembly so that it can be imported and used from javascript. There are a couple of tools for this, you can produce wasm from Cargo directly by targeting wasm-unknown-unknown, you can use cargo-web, or as I did, you can use stdweb and a plugin in Parcel. For new and exploratory projects I like to use Parcel, and at the moment the best way I have found to use it when strings are involved is to use stdweb. Stdweb adds a ton of support in Rust for running javascript code, interacting with the browser, and other related tasks, but in my case the main thing it provides is simple type translation for strings across the native/javascript barrier.

Porting Pando was pretty easy. First I added stdweb to the toml file, and changed the crate type to cdylib which will allow the wasm bindgen tool used by the parcel plugin to produce the correct wrappers.

nom = "4.2.0"
stdweb = "*"
crate-type = ["cdylib"]

Then I moved main.rs to lib.rs, deleted the now unused main function and panic handler, and added an js_export attribute to the compile function.

pub fn compile(pando_code: &str) -> String {

Finally I created a super simple html file with a link to an index.js file:

    <script src="./index.js"></script>

and created a javascript file which imports Viz.js, the compiled Pando binary, and renders a test svg to the screen:

  import {compile} from "./PandoRust/Cargo.toml";
import Viz from "viz.js";
import { Module, render } from 'viz.js/full.render.js';
import "babel-polyfill";
const viz = new Viz({ Module, render });
async function renderGraph() {
  let element = await viz.renderSVGElement(compile("x foo\n> bar [ F ]\n- baz [ B ]"));

After running the produced graph is identical to what I would have gotten from the command line version but in the browser.


And thats it for today. Tomorrow I will look into modifying the Pando rust code to allow serializing modified todo trees back into the Pando file format.

Till tomorrow,