Triple Arena Rendering

A crate enabling trait-based visualization of graphs in triple_arena::Arena<P, T>s.

There is still work to do with better compactness of large graphs, but the SVG rendering is mostly complete.

In the future, we could have more rendering styles and backends.

use triple_arena::{ptr_struct, Arena, Ptr};
use triple_arena_render::{render_to_svg_file, DebugNode, DebugNodeTrait};

// Suppose we are storing an equation evaluation tree in an arena
// with this type of node
enum MyNode<P: Ptr> {
    /// A literal value in the equation
    Literal(i64),
    /// Negation of the node this `Ptr` is pointing to
    Negation(P),
    /// Summation of all the nodes pointed to
    Summation(Vec<P>),
}

use MyNode::*;

impl<P: Ptr> DebugNodeTrait<P> for MyNode<P> {
    fn debug_node(_p_this: P, this: &Self) -> DebugNode<P> {
        // Here we manually write out the fields of the `DebugNode`,
        // but you can also use its `Default` implementation or
        // new` constructor
        match this {
            Literal(x) => DebugNode {
                sources: vec![],
                // We choose in this example to display the
                // literal value by itself
                center: vec![format!("{}", x)],
                // We choose source-to-sink convention for our
                // tree, so `sink` will always be empty
                sinks: vec![],
            },
            Negation(p) => DebugNode {
                // Have a debug edge corresponding to the real
                // edge, but leave the source description empty
                sources: vec![(*p, String::new())],
                // Display a negative sign
                center: vec!["-".to_owned()],
                sinks: vec![],
            },
            Summation(v) => DebugNode {
                // List all the inputs and number them
                sources: v
                    .iter()
                    .enumerate()
                    .map(|(i, p)| (*p, format!("in{}", i)))
                    .collect(),
                center: vec!["+".to_owned()],
                sinks: vec![],
            },
        }
    }
}

ptr_struct!(P0);

fn main() {
    let mut a: Arena<P0, MyNode<P0>> = Arena::new();

    // construct a graph representing `((-(42)) + (256 + 7) + (...))`

    let lit42 = a.insert(Literal(42));
    let neg_lit42 = a.insert(Negation(lit42));

    let lit256 = a.insert(Literal(256));
    let lit7 = a.insert(Literal(7));
    let inner_sum = a.insert(Summation(vec![lit256, lit7]));

    let will_be_removed = a.insert(Literal(10));

    let _sum = a.insert(
        Summation(vec![neg_lit42, inner_sum, will_be_removed])
    );

    // example of an invalid `Ptr` in a graph
    a.remove(will_be_removed).unwrap();

    render_to_svg_file(
        &a,
        false,
        std::path::PathBuf::from("./example.svg".to_owned()),
    )
    .unwrap();
}