TinySDF

TinySDF is a tiny and fast JavaScript library for generating SDF (signed distance field) from system fonts on the browser using Canvas 2D and Felzenszwalb/Huttenlocher distance transform. This is very useful for rendering text with WebGL.

This implementation is based directly on the algorithm published in the Felzenszwalb/Huttenlocher paper, and is not a port of the existing C++ implementation provided by the paper's authors.

Demo: http://mapbox.github.io/tiny-sdf/

Usage

Create a TinySDF for drawing SDFs based on font parameters:

var fontsize = 24; // Font size in pixels
var buffer = 3;    // Whitespace buffer around a glyph in pixels
var radius = 8;    // How many pixels around the glyph shape to use for encoding distance
var cutoff = 0.25  // How much of the radius (relative) is used for the inside part the glyph

var fontFamily = 'sans-serif'; // css font-family
var fontWeight = 'normal';     // css font-weight
var tinySDFGenerator = new TinySDF(fontsize, buffer, radius, cutoff, fontFamily, fontWeight);

var oneSDF = tinySDFGenerator.draw('泽');
// returns a Uint8ClampedArray array of alpha values (0–255) for a size x size square grid

// To generate glyphs with variable advances (e.g. non-ideographic glyphs),
// use `drawWithMetrics`
var sdfWithMetrics = tinySDFGenerator.drawWithMetrics('A');
// sdfWithMetrics.data is the same as in `draw`, except the size may be clipped to fit the glyph
// sdfWithMetrics.metrics contains:
//  top:        Maximum ascent of glyph from alphabetic baseline
//  left:       Currently hardwired to 0 (actual glyph differences are encoded in the rasterization)
//  width:      Width of rasterized portion of glyph
//  height
//  advance:    Layout advance
//  sdfWidth:   Width of the returned bitmap, usually but not always width + 2 * buffer
//  sdfHeight