threejs-impl-shadows

Enable shadows with three opt-in steps: set renderer.shadowMap.enabled to true, set light.castShadow to true, and set castShadow or receiveShadow on each mesh. Missing any one step produces no shadows with no error message.

Shadows fail silently when the renderer, light, or mesh flags are missing, or when the shadow camera frustum does not cover the scene. Use a CameraHelper on light.shadow.camera to visualize the frustum and verify far plane distance.

Fix shadow acne by setting shadow.bias to a small negative value like -0.0001 and shadow.normalBias around 0.02 for curved surfaces. Increasing shadow.mapSize also improves depth precision and reduces striping artifacts.

PCFSoftShadowMap uses a variable kernel for soft penumbra and ignores shadow.radius, while VSMShadowMap supports radius and blurSamples for Gaussian blur. VSM can cause light bleeding through thin geometry, so PCFSoft is the safer general choice.

Use at most one shadow-casting PointLight because each renders six cubemap faces per frame. Prefer SpotLight shadows, which cost one render pass each, and keep shadow map sizes at 512 or 1024 for PointLights.

Assign a customDepthMaterial to the mesh with a MeshDepthMaterial that matches the visible material's alphaMap and alphaTest values. Fully transparent objects without alphaTest cannot cast correct real-time shadows and need baked or contact shadows.