Chapter 595: ShadowMesh

Core Idea

A Shadow Mesh that follows a shadow-casting mesh in the scene, but is confined to a single plane. This technique can be used as a very performant alternative to classic shadow mapping. However, it has serious limitations like:

• Shadows can only be casted on flat planes.
• No soft shadows support.

Key Concepts

• frustumCulled : boolean: Overwritten to disable view-frustum culling by default.
• isShadowMesh : boolean (readonly): This flag can be used for type testing.
• matrixAutoUpdate : boolean: Overwritten to disable automatic matrix update. The local matrix is computed manually in ShadowMesh#update.
• meshMatrix : Matrix4: Represent the world matrix of the reference mesh.

Code Examples

const cubeShadow = new ShadowMesh( cube );
scene.add( cubeShadow );

• What it demonstrates: Typical usage of ShadowMesh.

Reference Tables

Constructor

Signature
new ShadowMesh( mesh : Mesh )

Properties

Property	Description
.frustumCulled : boolean	Overwritten to disable view-frustum culling by default.
.isShadowMesh : boolean (readonly)	This flag can be used for type testing.
.matrixAutoUpdate : boolean	Overwritten to disable automatic matrix update. The local matrix is computed manually in ShadowMesh#update.
.meshMatrix : Matrix4	Represent the world matrix of the reference mesh.

Methods

Method	Description
.update( plane : Plane, lightPosition4D : Vector4 )	Updates the shadow mesh so it follows its shadow-casting reference mesh.

Key Takeaways

1. ShadowMesh extends: EventDispatcher → Object3D → Mesh
2. Most relevant properties: frustumCulled, isShadowMesh, matrixAutoUpdate, meshMatrix.
3. Key methods: update.

Connects To

• EventDispatcher: parent class
• Object3D: parent class
• Mesh: parent class
• Source: examples/jsm/objects/ShadowMesh.js