如何处理WebGL GLSL着色器中的大数字?

时间:2017-12-23 14:21:23

标签: javascript three.js glsl webgl

如何在GLSL中处理大数字,例如下面的数字?

我正在提供一个带有Date.now()的着色器作为制服,其描述为:

  

Date.now()方法返回自1970年1月1日00:00:00 UTC以来经过的毫秒数。 - MDN

例如,1514678400000是一年中的最后一天。

将此值传递给我的ShaderMaterial会导致不会发生太多事情,除非我将该值大幅缩减。

具体来说,这是行为似乎与我对将最后2500毫秒映射到0-1范围内的值的期望不同的部分:

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

GLSL: mod( time, 2500.0 ) / 2500.0

我宁愿在GPU上进行这些计算,但我不确定如何处理这个问题?

下面是一个小场景,说明了这个问题:

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>

1 个答案:

答案 0 :(得分:1)

我正在使用Date.now()

提供着色器

它会在着色器中生成不可预测的内容,尤其是在使用三角函数时,例如sin()cos()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以使它们成为一个浮点数,即将毫秒转换为秒。

所以,划分是一个方法。另一种方法是使用THREE.Clock()及其.getDelta()方法。看一下代码片段。

&#13;
&#13;
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()
&#13;
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;
}
&#13;
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/89/three.js"></script>
&#13;
&#13;
&#13;