Image Filter

<!--
  说明：影像滤镜
  核心逻辑：Canvas filter 与像素反色生成三种图片，替换 ImageStatic 源
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>影像滤镜</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  #info{margin-left:auto}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="radio" name="f" value="none" checked> 原图</label>
  <label><input type="radio" name="f" value="gray"> 灰度</label>
  <label><input type="radio" name="f" value="invert"> 反色</label>
  <span id="info">—</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;

  function paint() {
    var canvas = document.createElement('canvas');
    canvas.width = 512;
    canvas.height = 384;
    var ctx = canvas.getContext('2d');

    var g = ctx.createLinearGradient(0, 0, 512, 384);
    g.addColorStop(0, '#1f5fd0');
    g.addColorStop(0.45, '#39a0a8');
    g.addColorStop(0.7, '#c9d34a');
    g.addColorStop(1, '#e06a3b');
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, 512, 384);

    for (var i = 0; i < 24; i++) {
      ctx.beginPath();
      ctx.arc(Math.random() * 512, Math.random() * 384, 8 + Math.random() * 30, 0, Math.PI * 2);
      ctx.fillStyle = 'rgba(255,255,255,' + (0.08 + Math.random() * 0.18) + ')';
      ctx.fill();
    }

    ctx.fillStyle = 'rgba(20,30,45,0.75)';
    ctx.font = '600 22px sans-serif';
    ctx.fillText('示例影像', 24, 44);

    return canvas;
  }

  var base = paint();

  function filtered(mode) {
    if (mode === 'none') return base.toDataURL();

    var canvas = document.createElement('canvas');
    canvas.width = base.width;
    canvas.height = base.height;
    var ctx = canvas.getContext('2d');

    if (mode === 'gray') {
      ctx.filter = 'grayscale(1) contrast(1.35)';
      ctx.drawImage(base, 0, 0);
      return canvas.toDataURL();
    }

    ctx.drawImage(base, 0, 0);
    var img = ctx.getImageData(0, 0, canvas.width, canvas.height);
    for (var i = 0; i < img.data.length; i += 4) {
      img.data[i] = 255 - img.data[i];
      img.data[i + 1] = 255 - img.data[i + 1];
      img.data[i + 2] = 255 - img.data[i + 2];
    }
    ctx.putImageData(img, 0, 0);
    return canvas.toDataURL();
  }

  var extent = ol.proj.transformExtent([106, 30, 120, 40], 'EPSG:4326', 'EPSG:3857');

  function makeSource(mode) {
    return new ol.source.ImageStatic({
      url: filtered(mode),
      imageExtent: extent,
      projection: 'EPSG:3857'
    });
  }

  var imageLayer = new ol.layer.Image({ source: makeSource('none'), opacity: 0.9 });

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }), imageLayer],
    view: new ol.View({ center: fromLonLat([113, 35]), zoom: 5, minZoom: 2, maxZoom: 19 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var info = document.getElementById('info');

  Array.prototype.forEach.call(document.querySelectorAll('input[name=f]'), function (input) {
    input.addEventListener('change', function () {
      imageLayer.setSource(makeSource(this.value));
      info.textContent = '当前滤镜：' + (this.value === 'none' ? '原图' : this.value === 'gray' ? '灰度' : '反色');
    });
  });

  info.textContent = '当前滤镜：原图';
})();
</script>
</body>
</html>