源码分析之Openlayers中SimpleGeometry类

概述

本文主要介绍 Openlayers 中的SimplyGeometry类，该类继承于Geometry类，可以参考源码分析之Openlayers中Geometry基类介绍，也是普通几何对象如点线面的基类或父类。SimplyGeometry类一般地也不会被实例化，只会被继承，因为它不会被渲染。

源码分析

`SimplyGeometry`类源码

SimplyGeometry类源码实现如下：

class SimplyGeometry extends Geometry {
  constructor() {}
  computedExtent(extent) {
    return createOrUpdateFromFlatCoordinates(
      this.flatCoordinates,
      0,
      this.flatCoordinates.length,
      this.stride,
      extent
    );
  }
  getCoordinates() {
    return abstract();
  }
  getFirstCoordinate() {
    return this.flatCoordinates.slice(0, this.stride);
  }
  getFlatCoordinates() {
    return this.flatCoordinates;
  }
  getLastCoordinate() {
    return this.flatCoordinates.slice(
      this.flatCoordinates.length - this.stride
    );
  }
  getLayout() {
    return this.layout;
  }
  getSimplifiedGeometry(squaredTolerance) {
    if (this.simplifiedGeometryRevision !== this.getRevision()) {
      this.simplifiedGeometryMaxMinSquaredTolerance = 0;
      this.simplifiedGeometryRevision = this.getRevision();
    }
    if (
      squaredTolerance < 0 ||
      (this.simplifiedGeometryMaxMinSquaredTolerance !== 0 &&
        squaredTolerance <= this.simplifiedGeometryMaxMinSquaredTolerance)
    ) {
      return this;
    }

    const simplifiedGeometry =
      this.getSimplifiedGeometryInternal(squaredTolerance);
    const simplifiedFlatCoordinates = simplifiedGeometry.getFlatCoordinates();
    if (simplifiedFlatCoordinates.length < this.flatCoordinates.length) {
      return simplifiedGeometry;
    }
    this.simplifiedGeometryMaxMinSquaredTolerance = squaredTolerance;
    return this;
  }

  getSimplifiedGeometryInternal(squaredTolerance) {
    return this;
  }

  getStride() {
    return this.stride;
  }
  setFlatCoordinates(layout, flatCoordinates) {
    this.stride = getStrideForLayout(layout);
    this.layout = layout;
    this.flatCoordinates = flatCoordinates;
  }

  setCoordinates(coordinates, layout) {
    abstract();
  }
  setLayout(layout, coordinates, nesting) {
    let stride;
    if (layout) {
      stride = getStrideForLayout(layout);
    } else {
      for (let i = 0; i < nesting; ++i) {
        if (coordinates.length === 0) {
          this.layout = "XY";
          this.stride = 2;
          return;
        }
        coordinates = /** @type {Array<unknown>} */ (coordinates[0]);
      }
      stride = coordinates.length;
      layout = getLayoutForStride(stride);
    }
    this.layout = layout;
    this.stride = stride;
  }
  applyTransform(transformFn) {
    if (this.flatCoordinates) {
      transformFn(
        this.flatCoordinates,
        this.flatCoordinates,
        this.layout.startsWith("XYZ") ? 3 : 2,
        this.stride
      );
      this.changed();
    }
  }
  rotate(angle, anchor) {
    const flatCoordinates = this.getFlatCoordinates();
    if (flatCoordinates) {
      const stride = this.getStride();
      rotate(
        flatCoordinates,
        0,
        flatCoordinates.length,
        stride,
        angle,
        anchor,
        flatCoordinates
      );
      this.changed();
    }
  }
  scale(sx, sy, anchor) {
    if (sy === undefined) {
      sy = sx;
    }
    if (!anchor) {
      anchor = getCenter(this.getExtent());
    }
    const flatCoordinates = this.getFlatCoordinates();
    if (flatCoordinates) {
      const stride = this.getStride();
      scale(
        flatCoordinates,
        0,
        flatCoordinates.length,
        stride,
        sx,
        sy,
        anchor,
        flatCoordinates
      );
      this.changed();
    }
  }

  translate(deltaX, deltaY) {
    const flatCoordinates = this.getFlatCoordinates();
    if (flatCoordinates) {
      const stride = this.getStride();
      translate(
        flatCoordinates,
        0,
        flatCoordinates.length,
        stride,
        deltaX,
        deltaY,
        flatCoordinates
      );
      this.changed();
    }
  }
}

`SimplyGeometry`类的构造函数

SimplyGeometry类的构造函数就是定义了如下变量：

this.layout：默认值为XY，表示二维坐标，可选值还有XYZ（表示三维坐标）、XYM（表示二维坐标，M为附加属性）和XYZM（表示三维坐标，M为附加属性）。
this.stride:默认值为 2，步幅，可以理解为this.layout的长度。
this.flatCoordinates:是一个一维数组，用来存储几何图形的坐标数据。

`SimplyGeometry`类主要方法

SimplyGeometry类的主要方法如下：

computeExtent方法：内部就是调用createOrUpdateFromFlatCoordinate方法去计算几何对象的包围盒extent
getCoordinates方法：未实现，实际上就是获取几何对象的坐标
getFirstCoordinate方法：获取几何对象的第一个坐标
getFlatCoordinates方法：获取几何对象的一维数组，即this.flatCoordinates
getLastCoordinate方法：获取几何对象的最后一个坐标
getLayout方法：获取变量this.layout的值
getSimplifiedGeometry方法：创建一个简化的几何对象，运用Douglas Peucker算法
getSimplifiedGeometryInternal方法：获取简化几何对象
getStride方法：获取步幅，即this.stride的值
setFlatCoordinates方法：接受两个参数layout和flatCoordinates，调用getStrideForLayout通过参数layout计算stride，赋值this.layout和this.flatCoordinates
setCoordinates方法：未实现
setLayout方法：设置this.layout和this.stride
applyTransform方法:应用转换函数，参数是一个函数；判断若this.flatCoordinates存在，则调用转换函数，最后调用this.changed方法
rotate方法:给定一个坐标，使几何对象绕着该坐标旋转一定角度；接受两个参数angle旋转角度和anchor锚点；调用this.getFlatCoordinates获取几何对象的一维坐标，若它存在，则调用this.getStride获取步幅，然后调用rotate方法进行旋转，这操作会修改flatCoordinates;最后调用this.changed方法
scale方法:接受三个参数，水平方向缩放因子sx、垂直方向缩放因子sy和锚点anchor;判断，sy不存在时，则sy=sx；判断，若锚点anchor不存在，则以几何对象的包围盒的中心点为锚点；调用this.getFlatCoordinates获取this.flatCoordinates,判断，若它存在，则调用scale方法对几何对象进行缩放，最后调用this.changed方法
translate方法:接受两个参数deltaX和deltaY,分别表示在水平方向和垂直方向的偏移量，实际上是调用translate方法对几何对象在水平垂直两个方向上进行平移变化，最后调用this.changed方法