Generate files suitable for use with Graphviz

The render function generates output (e.g., an output.dot file) for use with Graphviz by walking a labeled graph. (Graphviz can then automatically lay out the nodes and edges of the graph, and also optionally render the graph as an image or other output formats, such as SVG.)

Rather than impose some particular graph data structure on clients, this library exposes two traits that clients can implement on their own structs before handing them over to the rendering function.

Note: This library does not yet provide access to the full expressiveness of the DOT language. For example, there are many attributes related to providing layout hints (e.g., left-to-right versus top-down, which algorithm to use, etc). The current intention of this library is to emit a human-readable .dot file with very regular structure suitable for easy post-processing.

Examples

The first example uses a very simple graph representation: a list of pairs of ints, representing the edges (the node set is implicit). Each node label is derived directly from the int representing the node, while the edge labels are all empty strings.

This example also illustrates how to use Cow<[T]> to return an owned vector or a borrowed slice as appropriate: we construct the node vector from scratch, but borrow the edge list (rather than constructing a copy of all the edges from scratch).

The output from this example renders five nodes, with the first four forming a diamond-shaped acyclic graph and then pointing to the fifth which is cyclic.

#![feature(rustc_private)]

use std::io::Write;
use graphviz as dot;

type Nd = isize;
type Ed = (isize,isize);
struct Edges(Vec<Ed>);

pub fn render_to<W: Write>(output: &mut W) {
    let edges = Edges(vec![(0,1), (0,2), (1,3), (2,3), (3,4), (4,4)]);
    dot::render(&edges, output).unwrap()
}

impl<'a> dot::Labeller<'a> for Edges {
    type Node = Nd;
    type Edge = Ed;
    fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example1").unwrap() }

    fn node_id(&'a self, n: &Nd) -> dot::Id<'a> {
        dot::Id::new(format!("N{}", *n)).unwrap()
    }
}

impl<'a> dot::GraphWalk<'a> for Edges {
    type Node = Nd;
    type Edge = Ed;
    fn nodes(&self) -> dot::Nodes<'a,Nd> {
        // (assumes that |N| \approxeq |E|)
        let &Edges(ref v) = self;
        let mut nodes = Vec::with_capacity(v.len());
        for &(s,t) in v {
            nodes.push(s); nodes.push(t);
        }
        nodes.sort();
        nodes.dedup();
        nodes.into()
    }

    fn edges(&'a self) -> dot::Edges<'a,Ed> {
        let &Edges(ref edges) = self;
        (&edges[..]).into()
    }

    fn source(&self, e: &Ed) -> Nd { let &(s,_) = e; s }

    fn target(&self, e: &Ed) -> Nd { let &(_,t) = e; t }
}

pub fn main() {
    use std::fs::File;
    let mut f = File::create("example1.dot").unwrap();
    render_to(&mut f)
}

Output from first example (in example1.dot):

digraph example1 {
    N0[label="N0"];
    N1[label="N1"];
    N2[label="N2"];
    N3[label="N3"];
    N4[label="N4"];
    N0 -> N1[label=""];
    N0 -> N2[label=""];
    N1 -> N3[label=""];
    N2 -> N3[label=""];
    N3 -> N4[label=""];
    N4 -> N4[label=""];
}

The second example illustrates using node_label and edge_label to add labels to the nodes and edges in the rendered graph. The graph here carries both nodes (the label text to use for rendering a particular node), and edges (again a list of (source,target) indices).

This example also illustrates how to use a type (in this case the edge type) that shares substructure with the graph: the edge type here is a direct reference to the (source,target) pair stored in the graph's internal vector (rather than passing around a copy of the pair itself). Note that this implies that fn edges(&'a self) must construct a fresh Vec<&'a (usize,usize)> from the Vec<(usize,usize)> edges stored in self.

Since both the set of nodes and the set of edges are always constructed from scratch via iterators, we use the collect() method from the Iterator trait to collect the nodes and edges into freshly constructed growable Vec values (rather than using Cow as in the first example above).

The output from this example renders four nodes that make up the Hasse-diagram for the subsets of the set {x, y}. Each edge is labeled with the ⊆ character (specified using the HTML character entity &sube).

#![feature(rustc_private)]

use std::io::Write;
use graphviz as dot;

type Nd = usize;
type Ed<'a> = &'a (usize, usize);
struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }

pub fn render_to<W: Write>(output: &mut W) {
    let nodes = vec!["{x,y}","{x}","{y}","{}"];
    let edges = vec![(0,1), (0,2), (1,3), (2,3)];
    let graph = Graph { nodes: nodes, edges: edges };

    dot::render(&graph, output).unwrap()
}

impl<'a> dot::Labeller<'a> for Graph {
    type Node = Nd;
    type Edge = Ed<'a>;
    fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example2").unwrap() }
    fn node_id(&'a self, n: &Nd) -> dot::Id<'a> {
        dot::Id::new(format!("N{}", n)).unwrap()
    }
    fn node_label<'b>(&'b self, n: &Nd) -> dot::LabelText<'b> {
        dot::LabelText::LabelStr(self.nodes[*n].into())
    }
    fn edge_label<'b>(&'b self, _: &Ed) -> dot::LabelText<'b> {
        dot::LabelText::LabelStr("&sube;".into())
    }
}

impl<'a> dot::GraphWalk<'a> for Graph {
    type Node = Nd;
    type Edge = Ed<'a>;
    fn nodes(&self) -> dot::Nodes<'a,Nd> { (0..self.nodes.len()).collect() }
    fn edges(&'a self) -> dot::Edges<'a,Ed<'a>> { self.edges.iter().collect() }
    fn source(&self, e: &Ed) -> Nd { let & &(s,_) = e; s }
    fn target(&self, e: &Ed) -> Nd { let & &(_,t) = e; t }
}

pub fn main() {
    use std::fs::File;
    let mut f = File::create("example2.dot").unwrap();
    render_to(&mut f)
}

The third example is similar to the second, except now each node and edge now carries a reference to the string label for each node as well as that node's index. (This is another illustration of how to share structure with the graph itself, and why one might want to do so.)

The output from this example is the same as the second example: the Hasse-diagram for the subsets of the set {x, y}.

#![feature(rustc_private)]

use std::io::Write;
use graphviz as dot;

type Nd<'a> = (usize, &'a str);
type Ed<'a> = (Nd<'a>, Nd<'a>);
struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }

pub fn render_to<W: Write>(output: &mut W) {
    let nodes = vec!["{x,y}","{x}","{y}","{}"];
    let edges = vec![(0,1), (0,2), (1,3), (2,3)];
    let graph = Graph { nodes: nodes, edges: edges };

    dot::render(&graph, output).unwrap()
}

impl<'a> dot::Labeller<'a> for Graph {
    type Node = Nd<'a>;
    type Edge = Ed<'a>;
    fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example3").unwrap() }
    fn node_id(&'a self, n: &Nd<'a>) -> dot::Id<'a> {
        dot::Id::new(format!("N{}", n.0)).unwrap()
    }
    fn node_label<'b>(&'b self, n: &Nd<'b>) -> dot::LabelText<'b> {
        let &(i, _) = n;
        dot::LabelText::LabelStr(self.nodes[i].into())
    }
    fn edge_label<'b>(&'b self, _: &Ed<'b>) -> dot::LabelText<'b> {
        dot::LabelText::LabelStr("&sube;".into())
    }
}

impl<'a> dot::GraphWalk<'a> for Graph {
    type Node = Nd<'a>;
    type Edge = Ed<'a>;
    fn nodes(&'a self) -> dot::Nodes<'a,Nd<'a>> {
        self.nodes.iter().map(|s| &s[..]).enumerate().collect()
    }
    fn edges(&'a self) -> dot::Edges<'a,Ed<'a>> {
        self.edges.iter()
            .map(|&(i,j)|((i, &self.nodes[i][..]),
                          (j, &self.nodes[j][..])))
            .collect()
    }
    fn source(&self, e: &Ed<'a>) -> Nd<'a> { let &(s,_) = e; s }
    fn target(&self, e: &Ed<'a>) -> Nd<'a> { let &(_,t) = e; t }
}

pub fn main() {
    use std::fs::File;
    let mut f = File::create("example3.dot").unwrap();
    render_to(&mut f)
}

References

• Graphviz

• DOT language