去除由 GLSL 着色器产生的波纹图案

Question

我已经设置了这个最小的测试用例，您可以很容易地看到通过使用自定义片段着色器 (jsfiddle) 对振荡红色进行欠采样而产生的波纹图案。

使用 GLSL 删除此类模式的一般技术是什么？我假设它涉及衍生品扩展，但我一直不太明白如何实现它。我想我基本上必须做抗锯齿，我想？

var canvas = document.getElementById('canvas');
var scene = new THREE.Scene();
var renderer = new THREE.WebGLRenderer({canvas: canvas, antialias: true});
var camera = new THREE.PerspectiveCamera(75, canvas.clientWidth / canvas.clientWidth, 1, 1000);

var geometry = new THREE.SphereGeometry(50, 50, 50);
var material = new THREE.ShaderMaterial({
  vertexShader: document.getElementById('vertex-shader').textContent,
  fragmentShader: document.getElementById('fragment-shader').textContent
});
var sphere = new THREE.Mesh(geometry, material);

scene.add(sphere);

camera.position.z = 100;

var period = 30;
var clock = new THREE.Clock();
render();

function render() {
  requestAnimationFrame(render);
  
  if (canvas.width !== canvas.clientWidth || canvas.height !== canvas.clientHeight) {
    renderer.setSize(canvas.clientWidth, canvas.clientHeight, false);
    camera.aspect = canvas.clientWidth /  canvas.clientHeight;
    camera.updateProjectionMatrix();
  }
  
  sphere.rotation.y -= clock.getDelta() * 2 * Math.PI / period;
  renderer.render(scene, camera);
}

html, body, #canvas {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r73/three.min.js"></script>
<canvas id="canvas"></canvas>
<script id="vertex-shader" type="x-shader/x-vertex">
  varying vec2 vUv;

  void main() {
    vUv = uv;
    gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
  }
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
  #define M_TAU 6.2831853071795864769252867665590

  varying vec2 vUv;

  void main() {
    float w = sin(500.0 * M_TAU * vUv.x) / 2.0 + 0.5;
    vec3 color = vec3(w, 0.0, 0.0);
    gl_FragColor = vec4(color, 1.0);
  }
</script>

更新：我已经尝试实施 super-sampling，不确定我是否实施正确，但似乎帮助不大。

Answer 1

不幸的是，这里的云纹图案是 high-contrast 线接近 Nyquist Frequency 的结果。换句话说，没有什么好的方法可以让 1- 或 2-pixel-wide high-contrast 线平滑地移动到下一个像素，既不会引入此类伪像，也不会模糊线以致无法区分。

您提到了导数扩展，实际上该扩展可用于确定您的 UV 在屏幕中的变化速度 space，从而计算出需要多少模糊才能对它进行排序地毯下的问题。在下面您自己的示例的修改版本中，我尝试使用 fwidth 将噪声变差的球体变成红色。尝试使用此处定义为常量的一些浮点数，看看您能找到什么。

var canvas = document.getElementById('canvas');
var scene = new THREE.Scene();
var renderer = new THREE.WebGLRenderer({canvas: canvas, antialias: true});
var camera = new THREE.PerspectiveCamera(75, canvas.clientWidth / canvas.clientWidth, 1, 1000);

var geometry = new THREE.SphereGeometry(50, 50, 50);
var material = new THREE.ShaderMaterial({
  vertexShader: document.getElementById('vertex-shader').textContent,
  fragmentShader: document.getElementById('fragment-shader').textContent
});
var sphere = new THREE.Mesh(geometry, material);

scene.add(sphere);

camera.position.z = 100;

var period = 30;
var clock = new THREE.Clock();
render();

function render() {
  requestAnimationFrame(render);
  
  if (canvas.width !== canvas.clientWidth || canvas.height !== canvas.clientHeight) {
    renderer.setSize(canvas.clientWidth, canvas.clientHeight, false);
    camera.aspect = canvas.clientWidth /  canvas.clientHeight;
    camera.updateProjectionMatrix();
  }
  
  sphere.rotation.y -= clock.getDelta() * 2 * Math.PI / period;
  renderer.render(scene, camera);
}

html, body, #canvas {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r73/three.min.js"></script>
<canvas id="canvas"></canvas>
<script id="vertex-shader" type="x-shader/x-vertex">
  varying vec2 vUv;

  void main() {
    vUv = uv;
    gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
  }
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
  #extension GL_OES_standard_derivatives : enable

  #define M_TAU 6.2831853071795864769252867665590

  varying vec2 vUv;

  void main() {
    float linecount = 200.0;
    float thickness = 0.0;
    float blendregion = 2.8;
    
    // Loosely based on https://github.com/AnalyticalGraphicsInc/cesium/blob/1.16/Source/Shaders/Materials/GridMaterial.glsl#L17-L34
    float scaledWidth = fract(linecount * vUv.s);
    scaledWidth = abs(scaledWidth - floor(scaledWidth + 0.5));
    vec2 dF = fwidth(vUv) * linecount;
    float value = 1.0 - smoothstep(dF.s * thickness, dF.s * (thickness + blendregion), scaledWidth);
    gl_FragColor = vec4(value, 0.0, 0.0, 1.0);
  }
</script>

去除由 GLSL 着色器产生的波纹图案

Removing moire patterns produced by GLSL shaders

glsl

webgl

three.js