cesium地形压平代码

cesium地形压平代码可以通过以下代码实现：

// 设置地形压平的uniforms
var uniforms = {
  u_firstPWC: { type: Cesium.UniformType.VEC3, value: Cesium.Cartesian3.fromDegrees(113.84576776093665, 34.70286868401709, 25) },
  u_first2PWC: { type: Cesium.UniformType.VEC3, value: Cesium.Cartesian3.fromDegrees(113.84676776093665, 34.70286868401709, 25) },
  u_first3PWC: { type: Cesium.UniformType.VEC3, value: Cesium.Cartesian3.fromDegrees(113.84676776093665, 34.70186868401709, 25) },
  u_first4PWC: { type: Cesium.UniformType.VEC3, value: Cesium.Cartesian3.fromDegrees(113.84576776093665, 34.70186868401709, 25) }
};

// 在vertex shader中实现压平操作
var vertexShaderText = `
void vertexMain(VertexInput vsInput, inout czm_modelVertexOutput vsOutput) {
  vec4 firstpMC = czm_inverseModel * vec4(u_firstPWC, 1);
  vec4 firstp3MC = czm_inverseModel * vec4(u_first3PWC, 1);
  
  if (vsOutput.positionMC.x > firstpMC.x && vsOutput.positionMC.x < firstp3MC.x &&
      vsOutput.positionMC.z > firstp3MC.z && vsOutput.positionMC.z < firstpMC.z) {
    vsOutput.positionMC.y = firstpMC.y;
  }
}
`;

// 将uniforms和vertex shader应用于地形
terrain.material.uniforms = uniforms;
terrain.material.vertexShaderText = vertexShaderText;
terrain.material.update();