Three.js / WebGL 如何镜像纹理的一侧

Question

我基本上是在尝试仅用一侧实现万花筒效果，但我正在处理很多点，所以我希望在着色器中发生这种情况。但是，如果有一个 Threejs 技巧可以镜像一半纹理或 Points 对象，那就太好了。我尝试应用转换矩阵，但无法正常工作。

我发现了一个旧的KaleidoShader，它需要使用 EffectComposer，但我想自己手动实现它（没有 EffectComposer），我正在努力这样做。我正在使用 FBO，我尝试在我的模拟和渲染着色器中添加该着色器的代码，但它根本没有任何效果。我是否必须再添加另一个 FBO 纹理，或者是否可以在现有着色器之一中进行这些计算？

供视觉参考https://ma-hub.imgix.net/wp-images/2019/01/23205110/premiere-pro-mirror-effect.jpg

我花了这么多时间没有深入了解这一点，希望有人能指出我正确的方向。

谢谢

Answer 1

我刚刚关注this article

从该仓库中粘贴代码似乎可行

body {
  margin: 0;
}
#c {
  width: 100vw;
  height: 100vh;
  display: block;
}

<canvas id="c"></canvas>
<script type="module">
import * as THREE from 'https://threejsfundamentals.org/threejs/resources/threejs/r115/build/three.module.js';
import {EffectComposer} from 'https://threejsfundamentals.org/threejs/resources/threejs/r115/examples/jsm/postprocessing/EffectComposer.js';
import {RenderPass} from 'https://threejsfundamentals.org/threejs/resources/threejs/r115/examples/jsm/postprocessing/RenderPass.js';
import {ShaderPass} from 'https://threejsfundamentals.org/threejs/resources/threejs/r115/examples/jsm/postprocessing/ShaderPass.js';
import {GUI} from 'https://threejsfundamentals.org/threejs/../3rdparty/dat.gui.module.js';

function main() {
  const canvas = document.querySelector('#c');
  const renderer = new THREE.WebGLRenderer({canvas});

  const fov = 75;
  const aspect = 2;  // the canvas default
  const near = 0.1;
  const far = 5;
  const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
  camera.position.z = 2;

  const scene = new THREE.Scene();

  {
    const color = 0xFFFFFF;
    const intensity = 2;
    const light = new THREE.DirectionalLight(color, intensity);
    light.position.set(-1, 2, 4);
    scene.add(light);
  }

  const boxWidth = 1;
  const boxHeight = 1;
  const boxDepth = 1;
  const geometry = new THREE.BoxGeometry(boxWidth, boxHeight, boxDepth);

  function makeInstance(geometry, color, x) {
    const material = new THREE.MeshPhongMaterial({color});

    const cube = new THREE.Mesh(geometry, material);
    scene.add(cube);

    cube.position.x = x;

    return cube;
  }

  const cubes = [
    makeInstance(geometry, 0x44aa88,  0),
    makeInstance(geometry, 0x8844aa, -2),
    makeInstance(geometry, 0xaa8844,  2),
  ];

  const composer = new EffectComposer(renderer);
  composer.addPass(new RenderPass(scene, camera));

  // from:
  // https://github.com/mistic100/three.js-examples/blob/master/LICENSE
  const  kaleidoscopeShader = {
    uniforms: {

      "tDiffuse": { value: null },
      "sides":    { value: 6.0 },
      "angle":    { value: 0.0 }

    },

    vertexShader: `

      varying vec2 vUv;

      void main() {

        vUv = uv;
        gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

      }

    `,

    fragmentShader: `

      uniform sampler2D tDiffuse;
      uniform float sides;
      uniform float angle;
      
      varying vec2 vUv;

      void main() {

        vec2 p = vUv - 0.5;
        float r = length(p);
        float a = atan(p.y, p.x) + angle;
        float tau = 2. * 3.1416 ;
        a = mod(a, tau/sides);
        a = abs(a - tau/sides/2.) ;
        p = r * vec2(cos(a), sin(a));
        vec4 color = texture2D(tDiffuse, p + 0.5);
        gl_FragColor = color;

      }
    `
  };


  const kaleidoscopePass = new ShaderPass(kaleidoscopeShader);
  kaleidoscopePass.renderToScreen = true;
  composer.addPass(kaleidoscopePass);

  function resizeRendererToDisplaySize(renderer) {
    const canvas = renderer.domElement;
    const width = canvas.clientWidth;
    const height = canvas.clientHeight;
    const needResize = canvas.width !== width || canvas.height !== height;
    if (needResize) {
      renderer.setSize(width, height, false);
    }
    return needResize;
  }

  const gui = new GUI();
  gui.add(kaleidoscopePass.uniforms.sides, 'value', 0, 20).name('sides');
  gui.add(kaleidoscopePass.uniforms.angle, 'value', 0, 6.28, 0.01).name('angle');
  
  let then = 0;
  function render(now) {
    now *= 0.001;  // convert to seconds
    const deltaTime = now - then;
    then = now;

    if (resizeRendererToDisplaySize(renderer)) {
      const canvas = renderer.domElement;
      camera.aspect = canvas.clientWidth / canvas.clientHeight;
      camera.updateProjectionMatrix();
      composer.setSize(canvas.width, canvas.height);
    }

    cubes.forEach((cube, ndx) => {
      const speed = 1 + ndx * .1;
      const rot = now * speed;
      cube.rotation.x = rot;
      cube.rotation.y = rot;
    });

    composer.render(deltaTime);

    requestAnimationFrame(render);
  }

  requestAnimationFrame(render);
}

main();
</script>

Answer 2

有一种纹理环绕模式可以进行镜像。

texture.wrapS = texture.wrapT = THREE.MirroredRepeatWrapping

这有帮助吗？

编辑：这是一个在两个轴上显示 mirroredrepeatwrapping 的示例：

https://glitch.com/~three-mirroredrepeatwrapping