// lib/post/webgl/sobel.ts
// Sobel edge detection — outlines via the Sobel gradient operator. Wraps three's
// official SobelOperatorShader in a ShaderPass. Mirrors the WebGPU
// `lib/post/webgpu/sobel.ts` effect. The shader reads `tDiffuse` and needs the
// `resolution` uniform set to the render size (update on resize).

import * as THREE from 'three'
import { ShaderPass } from 'three/addons/postprocessing/ShaderPass.js'
import { SobelOperatorShader } from 'three/addons/shaders/SobelOperatorShader.js'
import type { Pass } from 'three/addons/postprocessing/Pass.js'


export interface SobelOptions {
  width?:  number
  height?: number
}

export function createSobel (options: SobelOptions = {}): Pass {
  const { width = 1, height = 1 } = options
  const pass                      = new ShaderPass(SobelOperatorShader)
  pass.uniforms.resolution.value  = new THREE.Vector2(width, height)
  return pass
}

// perf: low. Single fullscreen pass, 3x3 luma gradient kernel per fragment.