我使用 THREE.js r49 创建了 2 个带有定向光的立方体几何体，在它们上投射阴影，得到的结果如下图所示。
我注意到不应该出现绿色圆圈中的阴影，因为定向光在两个立方体的后面。我想这是材质的问题，我尝试过更改各种材质参数以及更改材质类型本身，但结果仍然相同。我还用 r50 和 r51 测试了相同的代码，得到了相同的结果。
谁能给我一些提示如何摆脱那个阴影。
两个立方体都是使用CubeGeometry和MeshLambertMaterial创建的，如下代码。
编码：
// ambient
var light = new THREE.AmbientLight( 0xcccccc );
scene.add( light );
// the large cube
var p_geometry = new THREE.CubeGeometry(10, 10, 10);
var p_material = new THREE.MeshLambertMaterial({ambient: 0x808080, color: 0xcccccc});
var p_mesh = new THREE.Mesh( p_geometry, p_material );
p_mesh.position.set(0, -5, 0);
p_mesh.castShadow = true;
p_mesh.receiveShadow = true;
scene.add(p_mesh);
// the small cube
var geometry = new THREE.CubeGeometry( 2, 2, 2 );
var material = new THREE.MeshLambertMaterial({ambient: 0x808080, color: Math.random() * 0xffffff});
var mesh = new THREE.Mesh( geometry, material );
mesh.position.set(0, 6, 3);
mesh.castShadow = true;
mesh.receiveShadow = true;
// add small cube as the child of large cube
p_mesh.add(mesh);
p_mesh.quaternion.setFromAxisAngle(new THREE.Vector3(0, 1, 0), 0.25 * Math.PI );
// the light source
var light = new THREE.DirectionalLight( 0xffffff );
light.castShadow = true;
light.position.set(0, 10, -8); // set it light source to top-behind the cubes
light.target = p_mesh // target the light to the large cube
light.shadowCameraNear = 5;
light.shadowCameraFar = 25;
light.shadowCameraRight = 10;
light.shadowCameraLeft = -10;
light.shadowCameraTop = 10;
light.shadowCameraBottom = -10;
light.shadowCameraVisible = true;
scene.add( light );