Img-bfs is a JavaScript library for breadth-first traversal in image.

API

Main function

The main function of the library is

bfs(<HTMLImageElement | HTMLCanvasElement> img, <Coord | Array> startCoord, <Object> eventMap, <Array> blacklist);

It starts searching in img image from startCoord coordinate(s) and skips all pixels from the blacklist.

Events

You can subscribe to events via eventMap param. For example:

bfs(img, {x: 10, y: 10}, {
    onvisit: function(e) {
        console.log(e);
    }
});

Currently, only onvisit event is supported. This event is fired when img-bfs visits each pixel.

Event object structure:

{
    pixel: {
        coord: {x: Number, y: Number},
        color: [Number, Number, Number, Number]
    },
    stop: Function,
    skip: Function
}

Property pixel contains information about visited pixel: coordinates and color (rgba).

Function stop stops search. Useful if you found a pixel which was needed and you want to stop search.

Function skip skips neighbors. When you call this function all neighbors of the visited pixel won't be added to the processing queue. Useful if you found a boundary pixel of the shape, but you want to continue search within the shape without going beyond its boundaries.

Example

We have an image with 3 markers:

When user clicks on one of them we need to add mask on top of it:

To implement this feature we need to get all pixels of the clicked marker and draw our mask on the given positions. Let's find pixels and draw mask on the canvas overlay:

window.onload = function() {
    var img = document.getElementById('myImg'),
        canv = document.getElementById("canv"),
        ctx = canv.getContext("2d");

    ctx.fillStyle = "rgba(0, 0, 0, 0.3)";

    canv.onclick = function(e) {
        bfs(img, {x: e.offsetX, y: e.offsetY}, {
            onvisit: draw
        });
    }

    function draw(e) {
        // skip neighbors of the white pixels,
        // white pixels do not belong to the marker
        if (e.pixel.color[0] === 255 &&
            e.pixel.color[1] === 255 &&
            e.pixel.color[2] === 255) {
            e.skip();
        } else {
            ctx.beginPath();
            ctx.arc(e.pixel.coord.x, e.pixel.coord.y, 1, 0, 2 * Math.PI, true);
            ctx.fill();
            ctx.closePath();
        }
    }
}

See full code of this example here.

TODO

• Add more examples

Changelog

0.1.3 — 30.06.2018

• Updated readme and example

0.1.2 — 04.02.2015

• package.json changed

0.1.1 — 26.10.2014

• Blacklist added
• package.json added

0.1.0 — 15.08.2014

• First Img-bfs release