WebGPURenderer: ProjectorLight unintentionally emits light from its back side

[ycw]

Description

Projectorlight is unintentionally illuminating areas behind it, see screenshots

Reproduction steps

1. Add a ProjectorLight (angle<90deg)
2. Set it facing towards -x;
3. You should see the ProjectorLight is illuminating areas behind it (+x)

Code

import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';

const renderer = new THREE.WebGPURenderer()
const scene = new THREE.Scene()
const camera = new THREE.PerspectiveCamera(75, 2, 0.1, 100)
const controls = new OrbitControls(camera, renderer.domElement)

scene.background = new THREE.Color('skyblue')
camera.position.set(0, 2, 2)
scene.add(new THREE.AxesHelper())

{ // ground
    const geom = new THREE.PlaneGeometry(10, 10).rotateX(Math.PI / -2)
    const mat = new THREE.MeshStandardMaterial()
    const mesh = new THREE.Mesh(geom, mat)
    mesh.position.y = -0.1
    scene.add(mesh)
}

{ // light
    const light = new THREE.ProjectorLight('white', 10, 2, Math.PI / 10, 0, 2)

    light.target = new THREE.Object3D()
    light.add(light.target)
    light.target.position.set(-1, 0, 0)
    light.position.set(0, 0, 0)

    scene.add(light)
    scene.add(new THREE.SpotLightHelper(light))
}

renderer.setAnimationLoop(() => {
  renderer.render(scene, camera)
  controls.update()
});

function resize(w, h, dpr = devicePixelRatio) {
  renderer.setPixelRatio(dpr)
  renderer.setSize(w, h, false)
  camera.aspect = w / h
  camera.updateProjectionMatrix()
}
addEventListener('resize', () => resize(innerWidth, innerHeight))
dispatchEvent(new Event('resize'))
document.body.prepend(renderer.domElement)

Live example

n/a

Screenshots

Version

dev

Device

No response

Browser

No response

OS

No response

[Mugen87]

I can't reproduce the issue with this fiddle: https://jsfiddle.net/wgfc0t5m/1/

Maybe some bit is missing to reproduce the issue in the live example?

[ycw]

My fault, it's ProjectorLight, not SpotLight 😑

[Mugen87]

FYI: It seems this particular bug exists right from the beginning: #24589 (comment)