如何在THREE.MeshBasicMaterial中关闭网格

Question

我正在使用THREE.js绘制图像及其反射。如何关闭反射中出现的网格？它似乎只发生在我改变alpha通道时。

    imageReflection = document.createElement('canvas');
    imageReflection.width = 480;
    imageReflection.height = 204;

    imageReflectionContext = imageReflection.getContext('2d');
    imageReflectionContext.fillStyle = '#000000';
    imageReflectionContext.fillRect(0, 0, 480, 204);

    textureReflection = new THREE.Texture(imageReflection);
    var materialReflection = new THREE.MeshBasicMaterial({map:textureReflection, side:THREE.BackSide, transparent:true, overdraw:0.5});