如何使用着色器在 Three.js 中进行平滑过渡？

Question

我有一个基本的 Three.js 应用程序，它只向平面添加了两个纹理。我将它们作为制服传递给我的着色器，当我的鼠标进入平面时，我将它们转换为另一个。

我的问题是，有没有一种方法可以在将一个纹理更改为另一个纹理的过程中添加过渡？所以他们的变化比现在更顺利：

我的片段着色器：

uniform vec2 u_resolution;
uniform float u_time;
uniform vec2 u_mouse;
uniform float u_progress;

uniform sampler2D image;
uniform sampler2D displacementTexture;

uniform int mouseIntersects;

varying vec2 vUv;

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    vec4 mainTexture = texture2D(image, vUv);
    vec4 displacementTexture = texture2D(displacementTexture, vUv.yx);
    vec2 disaplacedUv = vec2(
        vUv.x, 
        vUv.y
    );

    if (mouseIntersects == 1) {
        disaplacedUv.y = mix(vUv.y, displacementTexture.r + 0.2, 0.2);

        gl_FragColor = texture2D(image, disaplacedUv);
    } else {

        gl_FragColor = mainTexture;
    }
}

Three.js 设置

const setup = () => {
  ...scene, camera etc

  uniforms = {
    image: { type: 't', value: new THREE.TextureLoader().load(whale) },
    displacementTexture: { type: 't', value: new THREE.TextureLoader().load(texture) },
    mouseIntersects: { type: 'f', value: 0 },
  };

  material = new THREE.ShaderMaterial({
    side: THREE.DoubleSide,
    uniforms: uniforms,
    vertexShader: vertex,
    fragmentShader: fragment,
  });

  const geometry = new THREE.PlaneGeometry(1, 1, 32, 32);

  mesh = new THREE.Mesh(geometry, material);

  scene.add(mesh);

  raycaster = new THREE.Raycaster();

  document.addEventListener('mousemove', (event) => updateMousePositions(event), false);
};

const updateMousePositions = (event) => {
  event.preventDefault();
  uniforms.u_mouse.value.x = (event.clientX / window.innerWidth) * 2 - 1;
  uniforms.u_mouse.value.y = -(event.clientY / window.innerHeight) * 2 + 1;
};

const animate = () => {
  requestAnimationFrame(animate);
  render();
};

const render = () => {
  uniforms.u_time.value += 0.05;
  camera.lookAt(scene.position);

  camera.updateMatrixWorld();
  raycaster.setFromCamera(uniforms.u_mouse.value, camera);
  const intersects = raycaster.intersectObject(mesh);
  
  if (intersects.length === 1) {
    uniforms.mouseIntersects.value = 1;
  } else {
    uniforms.mouseIntersects.value = 0;
  }

  renderer.render(scene, camera);
};

setup();
animate();

Answer 1

而不是使用 uniform int mouseIntersects; 将其设为 float，这样您就可以从 0.0 到 1.0 以平滑的渐变而不是艰难的离散步骤过渡。然后您可以在着色器中使用 mix() GLSL 命令从一个纹理平滑过渡到另一个纹理：

uniform sampler2D image;
uniform sampler2D displacementTexture;
uniform int mouseIntersects;
varying vec2 vUv;

void main() {
    vec4 mainTexture = texture2D(image, vUv);
    vec4 altTexture = texture2D(displacementTexture, vUv);

    // 0.0 outputs mainTexture, 1.0 outputs altTexture
    gl_FragColor = mix(mainTexture, altTexture, mouseIntersects);
}

最后，在 JavaScript 中，您可以在发生鼠标悬停时用 MathUtils.lerp() 插入此值：

var targetValue = 0;

const render = () => {

  // ...

  if (intersects.length === 1) {
    targetValue = 1;
  } else {
    targetValue = 0;
  }

  // This will smoothly transition from its current value to the targetValue on each frame:
  uniforms.mouseIntersects.value = THREE.MathUtils.lerp(uniforms.mouseIntersects.value, targetValue, 0.1);

  renderer.render(scene, camera);
};

...或者您可以使用 animation library like GSAP，这可能会给您更多控制权

如何使用着色器在 Three.js 中进行平滑过渡？

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