This package is now part of the main protomaps.js repo.
Protosprites is a sprite-like system for sheets of icons. A sheet is just a single-file HTML document containing SVGs; sheets are loaded and baked into bitmaps on a canvas, where they can be sampled efficiently via Canvas 2D drawImage. This is useful for resolution-independent map symbology inside web browsers.
A protosprites sheet is a collection of SVGs organized in a specific way:
- It must be an HTML document with all SVGs as children of the
bodyelement - Each SVG element must have a width and a height in px, interpreted as CSS (not device) pixels
- Each SVG must have a unique ID attribute
Example of a valid protosprites sheet:
<html>
<body>
<svg id="foobar" width="20px" height="20px" version="1.1" xmlns="http://www.w3.org/2000/svg">
<circle cx="10" cy="10" r="8" fill="green"/>
</svg>
</body>
</html>SVGs can also be defined via inline strings, avoiding a fetch request.
const ICONS = `
<html>
<body>
<svg id="foobar" .../>
</body>
</html>
`
let sheet = new Protosprites(ICONS)a Protosprites instance asynchronously loads the sheet and renders it to an off-screen Canvas context at device-native resolution. The canvas can then be sampled by icon name via the get method:
let sheet = new Protosprites('sheet.html')
let canvas = document.getElementById("canvas")
let ctx = canvas.getContext('2d')
sheet.load().then(() => {
let s = sheet.get('foobar')
ctx.drawImage(s.canvas,s.x,s.y,s.w,s.h,0,0,s.w,s.h)
})