如何处理 WebGL GLSL 着色器中的大数字？

Question

如何在 GLSL 中处理大数字，例如下面的数字？

我正在提供一个着色器 Date.now() 作为统一，描述为：

The Date.now() method returns the number of milliseconds elapsed since January 1, 1970 00:00:00 UTC. — MDN

例如，1514678400000 是一年的最后一天。

将此值传递给我的 ShaderMaterial 不会有太多结果，除非我将值缩小很多。

具体来说，这是行为似乎与我的预期不同的部分，它将最后 2500 毫秒映射到 0–1 范围内的值：

JavaScript: ( Date.now() % 2500 ) / 2500

GLSL: mod( time, 2500.0 ) / 2500.0

我更愿意在 GPU 上进行这些计算，但不确定我应该如何处理？

下面是一个说明问题的小场景：

const scene = new THREE.Scene()
const camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 )
const renderer = new THREE.WebGLRenderer()

renderer.setSize( window.innerWidth, window.innerHeight )
camera.position.z = 0.5

document.body.appendChild( renderer.domElement )

const checkbox = document.getElementById( "toggle" )

const geo = new THREE.PlaneGeometry( 1, 1 )
const mat = new THREE.ShaderMaterial({
  vertexShader: `
    void main() {
      gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
    }
  `,
  fragmentShader: `
    uniform bool check;
    uniform float time;
    
    const float TAU = 6.2831;
    
    void main() {
      float fColor;
      
      check 
        ? fColor = ( sin( ( time * TAU ) ) + 1.0 ) / 2.0
        : fColor = ( sin( ( ( mod( time, 2500.0 ) / 2500.0 ) * TAU ) ) + 1.0 ) / 2.0;
        
      gl_FragColor = vec4( 1.0, fColor, 1.0, 1.0 );
    }
  `,
  uniforms: {
    "check": { value: false },
    "time": { value: 1.0 },
  },
})

const plane = new THREE.Mesh( geo, mat )
scene.add( plane )

const animate = function() {
  requestAnimationFrame( animate )

  if ( checkbox.checked ) {
    plane.material.uniforms.check.value = true
    plane.material.uniforms.time.value = ( Date.now() % 2500 ) / 2500
  } else {
    plane.material.uniforms.check.value = false
    plane.material.uniforms.time.value = Date.now()
  }

  renderer.render( scene, camera )
}

animate()

body {
  margin: 0;
}

canvas {
  width: 100%;
  height: 100%;
}

#config {
  position: absolute;
  color: #fff;
  cursor: pointer;
  user-select: none;
  font: bold 1em/1.5 sans-serif;
  padding: 1em;
}

#config label,
#config input {
  cursor: pointer;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/89/three.js"></script>
<div id="config">
  <input id="toggle" type="checkbox">
  <label for="toggle">Use JavaScript</label>
</div>

Answer 1

我正在为着色器提供 Date.now()

它会在着色器中产生不可预知的东西，尤其是当你使用三角函数时，比如sin()、cos()等等。原因是您将毫秒作为一个大整数传递。这就是为什么你必须将它除以 1000 才能使它们成为浮点数，即将毫秒转换为秒。

所以，划分是一种方法。另一种是使用 THREE.Clock() 及其 .getDelta() 方法。看看代码片段。

const scene = new THREE.Scene()
const camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 )
const renderer = new THREE.WebGLRenderer()

renderer.setSize( window.innerWidth, window.innerHeight )
camera.position.z = 0.5

document.body.appendChild( renderer.domElement )


const geo = new THREE.PlaneGeometry( 1, 1 )
const mat = new THREE.ShaderMaterial({
  vertexShader: `
    void main() {
      gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
    }
  `,
  fragmentShader: `
    uniform bool check;
    uniform float time;
    
    const float TAU = 6.2831;
    
    void main() {
      float fColor;
      
      fColor = ( sin( ( time * TAU ) ) + 1.0 ) / 2.0;
        
      gl_FragColor = vec4( 1.0, fColor, 1.0, 1.0 );
    }
  `,
  uniforms: {
    "check": { value: false },
    "time": { value: 1.0 },
  },
})

const plane = new THREE.Mesh( geo, mat )
scene.add( plane )

var clock = new THREE.Clock();
var time = 0;

const animate = function() {
  requestAnimationFrame( animate )
  
  time += clock.getDelta();

  plane.material.uniforms.time.value = time * 0.4; // make it 2.5 times slower

  renderer.render( scene, camera )
}

animate()

body {
  margin: 0;
}

canvas {
  width: 100%;
  height: 100%;
}

#config {
  position: absolute;
  color: #fff;
  cursor: pointer;
  user-select: none;
  font: bold 1em/1.5 sans-serif;
  padding: 1em;
}

#config label,
#config input {
  cursor: pointer;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/89/three.js"></script>

如何处理 WebGL GLSL 着色器中的大数字？

How to handle big numbers in WebGL GLSL shaders?

javascript

glsl

webgl

three.js