Openlayers学习笔记

# 七.案例 7

# 1.在屏幕外画布中渲染的矢量瓦片

查看代码详情 
<template>
  <div ref="map" class="map">
    <pre id="info" class="info" />
  </div>
</template>

<script>
export default {
  mounted() {
    let {
      Map,
      View,
      layer: { Layer },
      source: { Source },
      control: { FullScreen },
      tilegrid: { createXYZ },
    } = ol;
    const worker = new Worker("./worker.js", { type: "module" });

    let container,
      transformContainer,
      canvas,
      rendering,
      workerFrameState,
      mainThreadFrameState;
    function updateContainerTransform() {
      if (workerFrameState) {
        const viewState = mainThreadFrameState.viewState;
        const renderedViewState = workerFrameState.viewState;
        const center = viewState.center;
        const resolution = viewState.resolution;
        const rotation = viewState.rotation;
        const renderedCenter = renderedViewState.center;
        const renderedResolution = renderedViewState.resolution;
        const renderedRotation = renderedViewState.rotation;
        const transform = create();
        if (!rotation) {
          compose(
            transform,
            (renderedCenter[0] - center[0]) / resolution,
            (center[1] - renderedCenter[1]) / resolution,
            renderedResolution / resolution,
            renderedResolution / resolution,
            rotation - renderedRotation,
            0,
            0
          );
        }
        transformContainer.style.transform = toTransformString(transform);
      }
    }
    const map = new Map({
      layers: [
        new Layer({
          render: function (frameState) {
            if (!container) {
              container = document.createElement("div");
              container.style.position = "absolute";
              container.style.width = "100%";
              container.style.height = "100%";
              transformContainer = document.createElement("div");
              transformContainer.style.position = "absolute";
              transformContainer.style.width = "100%";
              transformContainer.style.height = "100%";
              container.appendChild(transformContainer);
              canvas = document.createElement("canvas");
              canvas.style.position = "absolute";
              canvas.style.left = "0";
              canvas.style.transformOrigin = "top left";
              transformContainer.appendChild(canvas);
            }
            mainThreadFrameState = frameState;
            updateContainerTransform();
            if (!rendering) {
              rendering = true;
              worker.postMessage({
                action: "render",
                frameState: JSON.parse(stringify(frameState)),
              });
            } else {
              frameState.animate = true;
            }
            return container;
          },
          source: new Source({
            attributions: [
              '<a href="https://www.maptiler.com/copyright/" target="_blank">© MapTiler</a>',
              '<a href="https://www.openstreetmap.org/copyright" target="_blank">© OpenStreetMap contributors</a>',
            ],
          }),
        }),
      ],
      target: this.$refs.map,
      view: new View({
        resolutions: createXYZ({ tileSize: 512 }).getResolutions(),
        center: [12579156, 3274244],
        zoom: 2,
      }),
    });
    map.addControl(new FullScreen());

    map.on("pointermove", function (evt) {
      if (evt.dragging) {
        return;
      }
      const pixel = map.getEventPixel(evt.originalEvent);
      worker.postMessage({
        action: "requestFeatures",
        pixel: pixel,
      });
    });
    worker.addEventListener("message", (message) => {
      if (message.data.action === "loadImage") {
        const image = new Image();
        image.crossOrigin = "anonymous";
        image.addEventListener("load", function () {
          createImageBitmap(image, 0, 0, image.width, image.height).then(
            (imageBitmap) => {
              worker.postMessage(
                {
                  action: "imageLoaded",
                  image: imageBitmap,
                  src: message.data.src,
                },
                [imageBitmap]
              );
            }
          );
        });
        image.src = message.data.src;
      } else if (message.data.action === "getFeatures") {
        showInfo(message.data.features);
      } else if (message.data.action === "requestRender") {
        map.render();
      } else if (canvas && message.data.action === "rendered") {
        requestAnimationFrame(function () {
          const imageData = message.data.imageData;
          canvas.width = imageData.width;
          canvas.height = imageData.height;
          canvas.getContext("2d").drawImage(imageData, 0, 0);
          canvas.style.transform = message.data.transform;
          workerFrameState = message.data.frameState;
          updateContainerTransform();
        });
        rendering = false;
      }
    });
    const info = document.getElementById("info");
    function showInfo(propertiesFromFeatures) {
      if (propertiesFromFeatures.length == 0) {
        info.innerText = "";
        info.style.opacity = 0;
        return;
      }
      const properties = propertiesFromFeatures.map((e) =>
        Object.keys(e)
          .filter((key) => !key.includes(":"))
          .reduce(
            (newObj, currKey) => ((newObj[currKey] = e[currKey]), newObj),
            {}
          )
      );
      info.innerText = JSON.stringify(properties, null, 2);
      info.style.opacity = 1;
    }
  },
};
</script>
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# 2.查看 Min-Zoom

查看代码详情 
<template>
  <div ref="map" class="map"></div>
</template>

<script>
export default {
  mounted() {
    let {
      Map,
      View,
      layer: { Tile: TileLayer },
      source: { OSM },
    } = ol
    const viewport = this.$refs.map
    function getMinZoom() {
      const width = viewport.clientWidth
      return Math.ceil(Math.LOG2E * Math.log(width / 256))
    }
    const initialZoom = getMinZoom()
    const view = new View({
      center: [12579156, 3274244],
      minZoom: initialZoom,
      zoom: initialZoom,
    })
    const map = new Map({
      layers: [
        new TileLayer({
          source: new OSM(),
        }),
      ],
      target: this.$refs.map,
      view: view,
    })
    window.addEventListener("resize", function () {
      const minZoom = getMinZoom()
      if (minZoom !== view.getMinZoom()) {
        view.setMinZoom(minZoom)
      }
    })
  },
}
</script>
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# 3.查看填充物

查看代码详情 
<template>
  <div>
    <div class="mapcontainer">
      <div ref="map" class="map"></div>
      <div class="padding-top"></div>
      <div class="padding-left"></div>
      <div class="padding-right"></div>
      <div class="padding-bottom"></div>
    </div>
    <button ref="zoomtoswitzerland">移动到瑞士</button>
    <button ref="centerlausanne">瑞士洛桑中心</button>
  </div>
</template>

<script>
export default {
  mounted() {
    let {
      format: { GeoJSON },
      Map,
      View,
      layer: { Tile: TileLayer, Vector: VectorLayer },
      source: { OSM, Vector: VectorSource },
      style: { Circle: CircleStyle, Fill, Stroke, Style },
      proj: { fromLonLat },
    } = ol;
    const source = new VectorSource({
      url: this.$withBase("/data/geojson/switzerland.geojson"),
      format: new GeoJSON(),
    });
    const style = new Style({
      fill: new Fill({
        color: "rgba(255, 255, 255, 0.6)",
      }),
      stroke: new Stroke({
        color: "#319FD3",
        width: 1,
      }),
      image: new CircleStyle({
        radius: 5,
        fill: new Fill({
          color: "rgba(255, 255, 255, 0.6)",
        }),
        stroke: new Stroke({
          color: "#319FD3",
          width: 1,
        }),
      }),
    });
    const vectorLayer = new VectorLayer({
      source: source,
      style: style,
    });
    const view = new View({
      center: fromLonLat([6.6339863, 46.5193823]),
      padding: [170, 50, 30, 150],
      zoom: 6,
    });
    const map = new Map({
      layers: [
        new TileLayer({
          source: new OSM(),
        }),
        vectorLayer,
      ],
      target: this.$refs.map,
      view: view,
    });
    vectorLayer.getSource().on(
      "featuresloadend",
      function () {
        this.$refs.zoomtoswitzerland.addEventListener(
          "click",
          function () {
            const feature = source.getFeatures()[0];
            const polygon = feature.getGeometry();
            view.fit(polygon);
          },
          false
        );
        this.$refs.centerlausanne.addEventListener(
          "click",
          function () {
            const feature = source.getFeatures()[1];
            const point = feature.getGeometry();
            view.setCenter(point.getCoordinates());
          },
          false
        );
      }.bind(this)
    );
  },
};
</script>
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← 八.案例 8 →