Question

我已经设置了这个最小的测试用例，您可以使用自定义片段着色器（jsfiddle）轻松查看通过对示波器红色进行欠采样而产生的莫尔图案。

使用GLSL删除此类模式的一般技术是什么？我认为它涉及衍生物扩展，但我从未完全理解如何实现它。我想基本上我必须做抗锯齿吗？

"~all"

"~all".

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);
}

更新：我已尝试实施super-sampling，不确定我是否已正确实施，但似乎没有太多帮助。

Answer 1

不幸的是，这里的莫尔条纹是高对比度线接近Nyquist Frequency的结果。换句话说，没有好的办法让1或2像素宽的高对比度线平滑地移动到下一个像素，而不会引入这样的伪像，或模糊线条难以区分。

你提到了衍生物扩展，实际上这个扩展可以用来计算你的紫外线在屏幕空间中的变化速度，从而弄清楚需要多少模糊来解决这个问题。在下面您自己的示例的修改版本中，我尝试使用fwidth将球体变为红色，噪音变坏。尝试使用一些定义为常量的浮点数，看看你能找到什么。

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GLSL着色器产生的波纹图案

1 个答案: