Using MeshDistanceMaterial for Transparent Shadow Casting

To create a softer shadow for a transparent cube in Three.js, you need to use the MeshDistanceMaterial and assign it to the object's customDistanceMaterial property. This is specifically designed to customize how shadows are cast, ensuring that transparent areas don't cast full shadows.

Solution Approach

Based on your code snippet and requirements, here's how you can implement this:

JAVASCRIPTCopied
// Create your cube with transparent material
const cubeGeometry = new THREE.BoxGeometry();
const cubeMaterial = new THREE.MeshStandardMaterial({
    transparent: true,
    opacity: 0.5,
});
const cube = new THREE.Mesh(cubeGeometry, cubeMaterial);
cube.castShadow = true;
scene.add(cube);

// Create a custom distance material for shadow mapping
const customDistanceMaterial = new THREE.MeshDistanceMaterial({
    transparent: true,
    opacity: 0.5 // Match the opacity of your main material
});

// Assign it to the cube
cube.customDistanceMaterial = customDistanceMaterial;

About alphaMap

If you want to use an alphaMap instead of a uniform opacity:

1. Create a texture to use as your alphaMap
2. Apply it to both your main material and the customDistanceMaterial

JAVASCRIPTCopied
// Load a texture to use as alphaMap
const textureLoader = new THREE.TextureLoader();
const alphaTexture = textureLoader.load('path/to/alpha-texture.png');

// Apply to main material
cubeMaterial.alphaMap = alphaTexture;

// Apply to custom distance material
customDistanceMaterial.alphaMap = alphaTexture;

The key is ensuring that both materials use the same transparency settings so that the shadow accurately represents the visible parts of your object.

Important Notes

• Make sure your light has castShadow set to true
• The MeshDistanceMaterial is specifically used with PointLight shadow mapping
• For other light types, you might need to use customDepthMaterial instead
• Remember to enable shadows in your renderer: renderer.shadowMap.enabled = true

This approach should give you the softer shadows you're looking for with your transparent cube.