//以下代码复制自Cesium源码的SkyBox，然后做了一点点修改。
//SkyBoxOnGround.js

// const Cesium = window.Cesium;
const BoxGeometry = Cesium.BoxGeometry;
const Cartesian3 = Cesium.Cartesian3;
const defaultValue = Cesium.defaultValue;
const defined = Cesium.defined;
const destroyObject = Cesium.destroyObject;
const DeveloperError = Cesium.DeveloperError;
const GeometryPipeline = Cesium.GeometryPipeline;
const Matrix3 = Cesium.Matrix3;
const Matrix4 = Cesium.Matrix4;
const Transforms = Cesium.Transforms;
const VertexFormat = Cesium.VertexFormat;
const BufferUsage = Cesium.BufferUsage;
const CubeMap = Cesium.CubeMap;
const DrawCommand = Cesium.DrawCommand;
const loadCubeMap = Cesium.loadCubeMap;
const RenderState = Cesium.RenderState;
const VertexArray = Cesium.VertexArray;
const BlendingState = Cesium.BlendingState;
const SceneMode = Cesium.SceneMode;
const ShaderProgram = Cesium.ShaderProgram;
const ShaderSource = Cesium.ShaderSource;
const skyboxMatrix3 = new Matrix3();

/**
 * @class DEUGlobe.Scene.SkyBoxOnGround
 * @category  场景
 * @classdesc 近景天空盒
 * @param {Object} options - 参数。
 * @param {Object} options.sources  - 近地天空盒来源。
 */

class SkyBoxOnGround {
  constructor(options) {
    /**
     * 为了兼容高版本的Cesium，因为新版cesium中getRotation被移除
     */
    if (!Cesium.defined(Cesium.Matrix4.getRotation)) {
      Cesium.Matrix4.getRotation = Cesium.Matrix4.getMatrix3;
    }
    this.sources = options.sources;
    this._sources = undefined;
    this.show = defaultValue(options.show, true);

    this._command = new DrawCommand({
      modelMatrix: Matrix4.clone(Matrix4.IDENTITY),
      owner: this,
    });
    this._cubeMap = undefined;

    this._attributeLocations = undefined;
    this._useHdr = undefined;
  }

  update(frameState, useHdr) {
    const that = this;

    //片元着色器，直接从源码复制
    // -------------- requestWebgl1: true,--------------
    //  const SkyBoxFS =
    //  "uniform samplerCube u_cubeMap;\n\
    // varying vec3 v_texCoord;\n\
    // void main()\n\
    // {\n\
    // vec4 color = textureCube(u_cubeMap, normalize(v_texCoord));\n\
    // gl_FragColor = vec4(czm_gammaCorrect(color).rgb, czm_morphTime);\n\
    // }\n\
    // ";

    const SkyBoxFS = `precision highp float;

uniform samplerCube u_cubeMap;
in vec3 v_texCoord;
out vec4 fragColor;

void main() {
    vec4 color = texture(u_cubeMap, normalize(v_texCoord));
    fragColor = vec4(czm_gammaCorrect(color).rgb, czm_morphTime);
}`;

    //顶点着色器有修改，主要是乘了一个旋转矩阵
    // -------------- requestWebgl1: true,--------------
    // const SkyBoxVS =
    //     "attribute vec3 position;\n\
    // varying vec3 v_texCoord;\n\
    // uniform mat3 u_rotateMatrix;\n\
    // void main()\n\
    // {\n\
    // vec3 p = czm_viewRotation * u_rotateMatrix * (czm_temeToPseudoFixed * (czm_entireFrustum.y * position));\n\
    // gl_Position = czm_projection * vec4(p, 1.0);\n\
    // v_texCoord = position.xyz;\n\
    // }\n\
    // ";

    const SkyBoxVS = `#version 300 es

precision highp float;

in vec3 position;
out vec3 v_texCoord;

uniform mat3 u_rotateMatrix;

void main() {
    vec3 p = czm_viewRotation * u_rotateMatrix * (czm_temeToPseudoFixed * (czm_entireFrustum.y * position));
    gl_Position = czm_projection * vec4(p, 1.0);
    v_texCoord = position;
}
`;

    if (!this.show) {
      return undefined;
    }

    if (
      frameState.mode !== SceneMode.SCENE3D &&
      frameState.mode !== SceneMode.MORPHING
    ) {
      return undefined;
    }

    if (!frameState.passes.render) {
      return undefined;
    }

    const context = frameState.context;

    if (this._sources !== this.sources) {
      this._sources = this.sources;
      const sources = this.sources;

      if (
        !defined(sources.positiveX) ||
        !defined(sources.negativeX) ||
        !defined(sources.positiveY) ||
        !defined(sources.negativeY) ||
        !defined(sources.positiveZ) ||
        !defined(sources.negativeZ)
      ) {
        throw new DeveloperError(
          "this.sources is required and must have positiveX, negativeX, positiveY, negativeY, positiveZ, and negativeZ properties."
        );
      }

      if (
        typeof sources.positiveX !== typeof sources.negativeX ||
        typeof sources.positiveX !== typeof sources.positiveY ||
        typeof sources.positiveX !== typeof sources.negativeY ||
        typeof sources.positiveX !== typeof sources.positiveZ ||
        typeof sources.positiveX !== typeof sources.negativeZ
      ) {
        throw new DeveloperError(
          "this.sources properties must all be the same type."
        );
      }

      if (typeof sources.positiveX === "string") {
        // Given urls for cube-map images.  Load them.
        loadCubeMap(context, this._sources).then(function (cubeMap) {
          that._cubeMap = that._cubeMap && that._cubeMap.destroy();
          that._cubeMap = cubeMap;
        });
      } else {
        this._cubeMap = this._cubeMap && this._cubeMap.destroy();
        this._cubeMap = new CubeMap({
          context: context,
          source: sources,
        });
      }
    }

    const command = this._command;

    command.modelMatrix = Transforms.eastNorthUpToFixedFrame(
      frameState.camera._positionWC
    );
    if (!defined(command.vertexArray)) {
      command.uniformMap = {
        u_cubeMap: function () {
          return that._cubeMap;
        },
        u_rotateMatrix: function () {
          return Matrix4.getRotation(command.modelMatrix, skyboxMatrix3);
        },
      };

      const geometry = BoxGeometry.createGeometry(
        BoxGeometry.fromDimensions({
          dimensions: new Cartesian3(2.0, 2.0, 2.0),
          vertexFormat: VertexFormat.POSITION_ONLY,
        })
      );
      const attributeLocations = (this._attributeLocations =
        GeometryPipeline.createAttributeLocations(geometry));

      command.vertexArray = VertexArray.fromGeometry({
        context: context,
        geometry: geometry,
        attributeLocations: attributeLocations,
        bufferUsage: BufferUsage._DRAW,
      });

      command.renderState = RenderState.fromCache({
        blending: BlendingState.ALPHA_BLEND,
      });
    }

    if (!defined(command.shaderProgram) || this._useHdr !== useHdr) {
      const fs = new ShaderSource({
        defines: [useHdr ? "HDR" : ""],
        sources: [SkyBoxFS],
      });
      command.shaderProgram = ShaderProgram.fromCache({
        context: context,
        vertexShaderSource: SkyBoxVS,
        fragmentShaderSource: fs,
        attributeLocations: this._attributeLocations,
      });
      this._useHdr = useHdr;
    }

    if (!defined(this._cubeMap)) {
      return undefined;
    }

    return command;
  }

  isDestroyed() {
    return false;
  }

  destroy() {
    const command = this._command;
    command.vertexArray = command.vertexArray && command.vertexArray.destroy();
    command.shaderProgram =
      command.shaderProgram && command.shaderProgram.destroy();
    this._cubeMap = this._cubeMap && this._cubeMap.destroy();
    return destroyObject(this);
  }
}