Understanding DirectionalLight Shadows in Three.js

Based on your issue with unexpected shadows appearing in your GLTF model when using DirectionalLight, I can provide some insights about how shadows work in Three.js.

Common Shadow Issues with DirectionalLight

When working with DirectionalLight and shadows, several factors could cause unexpected shadow behavior:

1. Shadow Camera Configuration: DirectionalLight uses a DirectionalLightShadow which requires proper configuration of the shadow camera.

2. Shadow Map Resolution: Low resolution shadow maps can cause blurry or inaccurate shadows.

3. Shadow Bias: Incorrect bias settings can cause shadow acne or peter-panning effects.

Potential Solutions

Here's how you might address these issues:

JAVASCRIPTCopied
// Enable shadows on your renderer
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap; // or another type

// Configure your directional light
const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
directionalLight.position.set(5, 10, 7.5);
directionalLight.castShadow = true;

// Configure the shadow properties
directionalLight.shadow.mapSize.width = 1024;  // Higher resolution
directionalLight.shadow.mapSize.height = 1024; // Higher resolution
directionalLight.shadow.camera.near = 0.5;
directionalLight.shadow.camera.far = 50;

// Adjust the shadow camera frustum to fit your scene
directionalLight.shadow.camera.left = -10;
directionalLight.shadow.camera.right = 10;
directionalLight.shadow.camera.top = 10;
directionalLight.shadow.camera.bottom = -10;

// Adjust bias to prevent shadow acne
directionalLight.shadow.bias = -0.001;

// Make sure your objects can cast and receive shadows
yourModel.traverse(function(node) {
  if (node.isMesh) {
    node.castShadow = true;
    node.receiveShadow = true;
  }
});

Debugging Shadows

To debug shadow issues:

1. Visualize the shadow camera frustum:

JAVASCRIPTCopied
const helper = new THREE.CameraHelper(directionalLight.shadow.camera);
scene.add(helper);

2. Check if shadows are enabled on both the light and the renderer.

3. Ensure your model's materials are configured to receive shadows.

4. Try adjusting the shadow bias value to eliminate shadow artifacts.

If you need more specific help, consider sharing your light setup code and more details about your scene configuration.