Dave Conway-Jones
3 years ago
parent
4fb075d28c
commit
0a04418eee
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/*
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* L.TileLayer.PixelFilter
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* https://github.com/greeninfo/L.TileLayer.PixelFilter
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* http://greeninfo-network.github.io/L.TileLayer.PixelFilter/
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*/
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L.tileLayerPixelFilter = function (url, options) {
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return new L.TileLayer.PixelFilter(url, options);
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}
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L.TileLayer.PixelFilter = L.TileLayer.extend({
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// the constructor saves settings and throws a fit if settings are bad, as typical
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// then adds the all-important 'tileload' event handler which basically "detects" an unmodified tile and performs the pxiel-swap
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initialize: function (url, options) {
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options = L.extend({}, L.TileLayer.prototype.options, {
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matchRGBA: null,
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missRGBA: null,
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pixelCodes: [],
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crossOrigin: 'Anonymous', // per issue 15, this is how you do it in Leaflet 1.x
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}, options);
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L.TileLayer.prototype.initialize.call(this, url, options);
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L.setOptions(this, options);
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// go ahead and save our settings
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this.setMatchRGBA(this.options.matchRGBA);
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this.setMissRGBA(this.options.missRGBA);
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this.setPixelCodes(this.options.pixelCodes);
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// and add our tile-load event hook which triggers us to do the pixel-swap
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this.on('tileload', function (event) {
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this.applyFiltersToTile(event.tile);
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});
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},
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// settings setters
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setMatchRGBA: function (rgba) {
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// save the setting
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if (rgba !== null && (typeof rgba !== 'object' || typeof rgba.length !== 'number' || rgba.length !== 4) ) throw "L.TileLayer.PixelSwap expected matchRGBA to be RGBA [r,g,b,a] array or else null";
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this.options.matchRGBA = rgba;
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// force a redraw, which means new tiles, which mean new tileload events; the circle of life
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this.redraw(true);
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},
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setMissRGBA: function (rgba) {
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// save the setting
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if (rgba !== null && (typeof rgba !== 'object' || typeof rgba.length !== 'number' || rgba.length !== 4) ) throw "L.TileLayer.PixelSwap expected missRGBA to be RGBA [r,g,b,a] array or else null";
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this.options.missRGBA = rgba;
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// force a redraw, which means new tiles, which mean new tileload events; the circle of life
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this.redraw(true);
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},
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setPixelCodes: function (pixelcodes) {
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// save the setting
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if (typeof pixelcodes !== 'object' || typeof pixelcodes.length !== 'number') throw "L.TileLayer.PixelSwap expected pixelCodes to be a list of triplets: [ [r,g,b], [r,g,b], ... ]";
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this.options.pixelCodes = pixelcodes;
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// force a redraw, which means new tiles, which mean new tileload events; the circle of life
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this.redraw(true);
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},
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// extend the _createTile function to add the .crossOrigin attribute, since loading tiles from a separate service is a pretty common need
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// and the Canvas is paranoid about cross-domain image data. see issue #5
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// this is really only for Leaflet 0.7; as of 1.0 L.TileLayer has a crossOrigin setting which we define as a layer option
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_createTile: function () {
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var tile = L.TileLayer.prototype._createTile.call(this);
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tile.crossOrigin = "Anonymous";
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return tile;
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},
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// the heavy lifting to do the pixel-swapping
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// called upon 'tileload' and passed the IMG element
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// tip: when the tile is saved back to the IMG element that counts as a tileload event too! thus an infinite loop, as wel as comparing the pixelCodes against already-replaced pixels!
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// so, we tag the already-swapped tiles so we know when to quit
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// if the layer is redrawn, it's a new IMG element and that means it would not yet be tagged
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applyFiltersToTile: function (imgelement) {
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// already processed, see note above
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if (imgelement.getAttribute('data-PixelFilterDone')) return;
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// copy the image data onto a canvas for manipulation
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var width = imgelement.width;
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var height = imgelement.height;
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var canvas = document.createElement("canvas");
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canvas.width = width;
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canvas.height = height;
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var context = canvas.getContext("2d");
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context.drawImage(imgelement, 0, 0);
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// create our target imagedata
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var output = context.createImageData(width, height);
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// extract out our RGBA trios into separate numbers, so we don't have to use rgba[i] a zillion times
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var matchRGBA = this.options.matchRGBA, missRGBA = this.options.missRGBA;
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if (matchRGBA !== null) {
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var match_r = matchRGBA[0], match_g = matchRGBA[1], match_b = matchRGBA[2], match_a = matchRGBA[3];
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}
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if (missRGBA !== null) {
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var miss_r = missRGBA[0], miss_g = missRGBA[1], miss_b = missRGBA[2], miss_a = missRGBA[3];
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}
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// go over our pixel-code list and generate the list of integers that we'll use for RGB matching
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// 1000000*R + 1000*G + B = 123123123 which is an integer, and finding an integer inside an array is a lot faster than finding an array inside an array
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var pixelcodes = [];
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for (var i=0, l=this.options.pixelCodes.length; i<l; i++) {
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var value = 1000000 * this.options.pixelCodes[i][0] + 1000 * this.options.pixelCodes[i][1] + this.options.pixelCodes[i][2];
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pixelcodes.push(value);
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}
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// iterate over the pixels (each one is 4 bytes, RGBA)
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// and see if they are on our list (recall the "addition" thing so we're comparing integers in an array for performance)
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// per issue #5 catch a failure here, which is likely a cross-domain problem
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try {
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var pixels = context.getImageData(0, 0, width, height).data;
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} catch(e) {
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throw "L.TileLayer.PixelFilter getImageData() failed. Likely a cross-domain issue?";
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}
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for(var i = 0, n = pixels.length; i < n; i += 4) {
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var r = pixels[i ];
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var g = pixels[i+1];
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var b = pixels[i+2];
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var a = pixels[i+3];
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// bail condition: if the alpha is 0 then it's already transparent, likely nodata, and we should skip it
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if (a == 0) {
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output.data[i ] = 255;
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output.data[i+1] = 255;
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output.data[i+2] = 255;
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output.data[i+3] = 0;
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continue;
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}
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// default to matching, so that if we are not in fact filtering by code it's an automatic hit
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// number matching trick: 1000000*R + 1000*G + 1*B = 123,123,123 a simple number that either is or isn't on the list
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var match = true;
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if (pixelcodes.length) {
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var sum = 1000000 * r + 1000 * g + b;
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if (-1 === pixelcodes.indexOf(sum)) match = false;
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}
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// did it match? either way we push a R, a G, and a B onto the image blob
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// if the target RGBA is a null, then we push exactly the same RGBA as we found in the source pixel
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output.data[i ] = match ? (matchRGBA===null ? r : match_r) : (missRGBA===null ? r : miss_r);
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output.data[i+1] = match ? (matchRGBA===null ? g : match_g) : (missRGBA===null ? g : miss_g);
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output.data[i+2] = match ? (matchRGBA===null ? b : match_b) : (missRGBA===null ? b : miss_b);
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output.data[i+3] = match ? (matchRGBA===null ? a : match_a) : (missRGBA===null ? a : miss_a);
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}
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// write the image back to the canvas, and assign its base64 back into the on-screen tile to visualize the change
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// tag the tile as having already been updated, so we don't process a 'load' event again and re-process a tile that surely won't match any target RGB codes, in an infinite loop!
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context.putImageData(output, 0, 0);
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imgelement.setAttribute('data-PixelFilterDone', true);
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imgelement.src = canvas.toDataURL();
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}
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});
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