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.

```rust use triplearena::{ptrstruct, Arena, Ptr}; use triplearenarender::{rendertosvg_file, DebugNode, DebugNodeTrait};

// Suppose we are storing an equation evaluation tree in an arena // with this type of node enum MyNode { /// 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

), }

use MyNode::*;

impl DebugNodeTrait

for MyNode

{ fn debugnode(pthis: P, this: &Self) -> DebugNode

{ // Here we manually write out the fields of the DebugNode, // but you can also use its Default implementation or // newconstructor 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, sosink` 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!["-".toowned()], 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> = 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();

} ```