Ilya Zverev just posted a cool use of canvas options in Leaflet. Tileset too distracting but it's already rendered and cached? Just make it grayscale . . .
Last active
August 18, 2016 20:53
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Grayscale on Watercolor
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| <html> | |
| <head> | |
| <title>B&W TileLayer Test</title> | |
| <link rel="stylesheet" href="https://npmcdn.com/leaflet@0.7.7/dist/leaflet.css" /> | |
| <script src="https://npmcdn.com/leaflet@0.7.7/dist/leaflet.js"></script> | |
| <style> | |
| body { margin: 0; } | |
| #map { height: 100%; } | |
| </style> | |
| <script> | |
| /* | |
| * L.TileLayer.Grayscale is a regular tilelayer with grayscale makeover. | |
| */ | |
| L.TileLayer.Grayscale = L.TileLayer.extend({ | |
| options: { | |
| enableCanvas: true | |
| }, | |
| initialize: function(url, options) { | |
| var canvasEl = document.createElement('canvas'); | |
| if (!(canvasEl.getContext && canvasEl.getContext('2d'))) { | |
| options.enableCanvas = false; | |
| } | |
| L.TileLayer.prototype.initialize.call(this, url, options); | |
| }, | |
| _loadTile: function(tile, tilePoint) { | |
| tile.setAttribute('crossorigin', 'anonymous'); | |
| L.TileLayer.prototype._loadTile.call(this, tile, tilePoint); | |
| }, | |
| _tileOnLoad: function() { | |
| if (this._layer.options.enableCanvas && !this.canvasContext) { | |
| var canvas = document.createElement("canvas"); | |
| canvas.width = canvas.height = this._layer.options.tileSize; | |
| this.canvasContext = canvas.getContext("2d"); | |
| } | |
| var ctx = this.canvasContext; | |
| if (ctx) { | |
| this.onload = null; // to prevent an infinite loop | |
| ctx.drawImage(this, 0, 0); | |
| var imgd = ctx.getImageData(0, 0, this._layer.options.tileSize, this._layer.options.tileSize); | |
| var pix = imgd.data; | |
| for (var i = 0, n = pix.length; i < n; i += 4) { | |
| pix[i] = pix[i + 1] = pix[i + 2] = (3 * pix[i] + 4 * pix[i + 1] + pix[i + 2]) / 8; | |
| } | |
| ctx.putImageData(imgd, 0, 0); | |
| this.removeAttribute("crossorigin"); | |
| this.src = ctx.canvas.toDataURL(); | |
| } | |
| L.TileLayer.prototype._tileOnLoad.call(this); | |
| } | |
| }); | |
| L.tileLayer.grayscale = function(url, options) { | |
| return new L.TileLayer.Grayscale(url, options); | |
| }; | |
| function init() { | |
| var map = L.map('map').setView([55.67610, 12.56834], 16); | |
| L.tileLayer.grayscale('http://tile.stamen.com/watercolor/{z}/{x}/{y}.png', { | |
| attribution: 'Map data © Stamen design & <a href="http://openstreetmap.org/">OpenStreetMap</a> contributors', | |
| maxZoom: 18, | |
| minZoom: 2 | |
| }).addTo(map); | |
| } | |
| </script> | |
| </head> | |
| <body onload="javascript:init();"> | |
| <div id="map"></div> | |
| </body> |
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Be aware: this techniqe requires some cross origin settings for map tiles which is not supported in all browsers. There may be no tiles at all i.e. in Safari prior v6.