使用ol-ext插件实现凸显多变形

效果如图

1、创建openlayer

var map;
var view;
var tileLayer, source, vector;

function init() {
  tileLayer = new ol.layer.Tile({
    source: new ol.source.TileArcGISRest({
      url: "http://map.geoq.cn/arcgis/rest/services/ChinaOnlineStreetPurplishBlue/MapServer"
    }) //
  });
  view = new ol.View({
    center: [113, 23],
    projection: 'EPSG:4326',
    zoom: 10
  });
  map = new ol.Map({
    layers: [tileLayer],
    target: 'map',
    view: view
  });


}

2、添加图层和多变形

function addpolygon() {
  var source = new ol.source.Vector({wrapX: false});
  var vector = new ol.layer.Vector({
    source: source,
  });
  map.addLayer(vector);

  var array = [
    [113.0, 23.0],
    [113.5, 23.0],
    [113.5, 23.5],
    [113.0, 23.0]
  ];
  var p = new ol.geom.Polygon([array]);
  var features = new ol.Feature({
    geometry: p,
    name: 'My Polygon',
    names: 'My Polygon'
  });
  source.addFeature(features);


  //ol-ext插件
  let r3D = new ol.render3D({
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({
        color: 'rgba(142,66,66,0.5)',
        width: 1
      }),
      fill: new ol.style.Fill({
        color: 'rgba(12,45,210,0.8)'
      })
    }),
    /** 初始高度 **/
    height: 0.1,
    //ghost: true,
    /** 最大可视分辨率 **/
    maxResolution: 0.1
  })
  vector.setRender3D(r3D)
  r3D.drawFeature3D_ = drawFeature3D_;//重新改写该函数

}

3、改写ol-ext的render3D中的函数

function drawFeature3D_(ctx, build) {
  var i, j, b, k
  // Construct
  var fillStyle=    ctx.fillStyle;
  for (i = 0; i < build.length; i++) {
    switch (build[i].type) {
      case "MultiPolygon": {
        for (j = 0; j < build[i].geom.length; j++) {
          b = build[i].geom[j]
// 绘制侧边渐变墙
          for (k = 0; k < b.length - 1; k++) {
            ctx.beginPath()
            ctx.moveTo(b[k].p0[0], b[k].p0[1])
            ctx.lineTo(b[k].p1[0], b[k].p1[1])
            ctx.lineTo(b[k + 1].p1[0], b[k + 1].p1[1])
            ctx.lineTo(b[k + 1].p0[0], b[k + 1].p0[1])
            ctx.lineTo(b[k].p0[0], b[k].p0[1])
            var m = [(b[k].p0[0] + b[k + 1].p0[0]) / 2, (b[k].p0[1] + b[k + 1].p0[1]) / 2]
            var h = [b[k].p0[1] - b[k + 1].p0[1], -b[k].p0[0] + b[k + 1].p0[0]]
            var c = ol.coordinate.getIntersectionPoint(
              [m, [m[0] + h[0], m[1] + h[1]]],
              [b[k].p1, b[k + 1].p1]
            )
            var gradient = ctx.createLinearGradient(
              m[0], m[1],
              c[0], c[1]
            )
            //设置渐变色带
            gradient.addColorStop(0, 'rgba(220,29,29,0.5)')
            gradient.addColorStop(0.2, 'rgba(220,29,29,0.5)')
            gradient.addColorStop(0.4, 'rgba(45,222,180,0.5)')
            gradient.addColorStop(0.6, 'rgba(219,194,36,0.5)')
            gradient.addColorStop(0.8, 'rgba(193,36,227,0.5)')
            gradient.addColorStop(1, 'rgba(20,92,238,0.5)')
            ctx.fillStyle = gradient
            ctx.fill()
          }
        }
        break
      }
      case "Point": {
        var g = build[i].geom
        ctx.beginPath()
        ctx.moveTo(g.p0[0], g.p0[1])
        ctx.lineTo(g.p1[0], g.p1[1])
        ctx.stroke()
        break
      }
      default: break
    }
  }

  // Roof
     ctx.fillStyle=fillStyle;

  for (i = 0; i < build.length; i++) {
    switch (build[i].type) {
      case "MultiPolygon": {
        ctx.beginPath()
        for (j = 0; j < build[i].geom.length; j++) {
          b = build[i].geom[j]
          if (j == 0) {
            ctx.moveTo(b[0].p1[0], b[0].p1[1])
            for (k = 1; k < b.length; k++) {
              ctx.lineTo(b[k].p1[0], b[k].p1[1])
            }
          } else {
            ctx.moveTo(b[0].p1[0], b[0].p1[1])
            for (k = b.length - 2; k >= 0; k--) {
              ctx.lineTo(b[k].p1[0], b[k].p1[1])
            }
          }
          ctx.closePath()
        }
        ctx.fill("evenodd")
        ctx.stroke()
        break
      }
      case "Point": {
        b = build[i]
        var t = b.feature.get('label')
        if (t) {
          var p = b.geom.p1
          var f = ctx.fillStyle
          ctx.fillStyle = ctx.strokeStyle
          ctx.textAlign = 'center'
          ctx.textBaseline = 'bottom'
          ctx.fillText(t, p[0], p[1])
          var m = ctx.measureText(t)
          var h = Number(ctx.font.match(/\d+(\.\d+)?/g).join([]))
          ctx.fillStyle = "rgba(255,255,255,0.5)"
          ctx.fillRect(p[0] - m.width / 2 - 5, p[1] - h - 5, m.width + 10, h + 10)
          ctx.strokeRect(p[0] - m.width / 2 - 5, p[1] - h - 5, m.width + 10, h + 10)
          ctx.fillStyle = f
          //console.log(build[i].feature.getProperties())
        }
        break
      }
      default: break
    }
  }
}