Canvas pixel operations on a point icon.
Example using an icon to symbolize a point. Click on the icon to select it, and it will be rendered using its negative image.
import Feature from 'ol/Feature.js';
import Map from 'ol/Map.js';
import Point from 'ol/geom/Point.js';
import Select from 'ol/interaction/Select.js';
import StadiaMaps from 'ol/source/StadiaMaps.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {Icon, Style} from 'ol/style.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';
function createStyle(src, img) {
return new Style({
image: new Icon({
anchor: [0.5, 0.96],
crossOrigin: 'anonymous',
src: src,
img: img,
imgSize: img ? [img.width, img.height] : undefined,
}),
});
}
const iconFeature = new Feature(new Point([0, 0]));
iconFeature.set('style', createStyle('data/icon.png', undefined));
const map = new Map({
layers: [
new TileLayer({
source: new StadiaMaps({layer: 'stamen_watercolor'}),
}),
new VectorLayer({
style: function (feature) {
return feature.get('style');
},
source: new VectorSource({features: [iconFeature]}),
}),
],
target: document.getElementById('map'),
view: new View({
center: [0, 0],
zoom: 3,
}),
});
const selectStyle = {};
const select = new Select({
style: function (feature) {
const image = feature.get('style').getImage().getImage();
if (!selectStyle[image.src]) {
const canvas = document.createElement('canvas');
const context = canvas.getContext('2d');
canvas.width = image.width;
canvas.height = image.height;
context.drawImage(image, 0, 0, image.width, image.height);
const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
const data = imageData.data;
for (let i = 0, ii = data.length; i < ii; i = i + (i % 4 == 2 ? 2 : 1)) {
data[i] = 255 - data[i];
}
context.putImageData(imageData, 0, 0);
selectStyle[image.src] = createStyle(undefined, canvas);
}
return selectStyle[image.src];
},
});
map.addInteraction(select);
map.on('pointermove', function (evt) {
map.getTargetElement().style.cursor = map.hasFeatureAtPixel(evt.pixel)
? 'pointer'
: '';
});
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Icon Pixel Operations</title>
<link rel="stylesheet" href="node_modules/ol/ol.css">
<style>
.map {
width: 100%;
height: 400px;
}
</style>
</head>
<body>
<div id="map" class="map"></div>
<script type="module" src="main.js"></script>
</body>
</html>
{
"name": "icon-negative",
"dependencies": {
"ol": "10.3.1"
},
"devDependencies": {
"vite": "^3.2.3"
},
"scripts": {
"start": "vite",
"build": "vite build"
}
}