threeJs 样例，webgl2_volume_perlin的修改
官方例子 webgl2_volume_perlin.html, 把perlin噪音绘制出来了，可以直观感受 perlin噪音的图像 形状。原例子支持立方体，我把立方体改为了球形。
<!DOCTYPE html>
<html lang="en">
<head>
<title>three.js webgl2 - volume</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
<link type="text/css" rel="stylesheet" href="main.css">
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<body>
<div id="info">
<a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> webgl2 - volume
</div>
<!-- Import maps polyfill -->
<!-- Remove this when import maps will be widely supported -->
<script async src="https://unpkg.com/[email protected]/dist/es-module-shims.js"></script>
<script type="importmap">
{
"imports": {
"three": "../build/three.module.js",
"three/addons/": "./jsm/"
}
}
</script>
<script type="module">
import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
import { ImprovedNoise } from 'three/addons/math/ImprovedNoise.js';
import { GUI } from 'three/addons/libs/lil-gui.module.min.js';
import WebGL from 'three/addons/capabilities/WebGL.js';
if ( WebGL.isWebGL2Available() === false ) {
document.body.appendChild( WebGL.getWebGL2ErrorMessage() );
}
let renderer, scene, camera;
let mesh;
init();
animate();
function init() {
renderer = new THREE.WebGLRenderer();
renderer.setPixelRatio( window.devicePixelRatio );
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );
scene = new THREE.Scene();
scene.add(new THREE.AxesHelper(2000))
camera = new THREE.PerspectiveCamera( 60, window.innerWidth / window.innerHeight, 0.1, 100 );
camera.position.set( 0, 0, 2 );
new OrbitControls( camera, renderer.domElement );
// Texture
const size = 128;
const data = new Uint8Array( size * size * size );
let i = 0;
const perlin = new ImprovedNoise();
const vector = new THREE.Vector3();
for ( let z = 0; z < size; z ++ ) {
for ( let y = 0; y < size; y ++ ) {
for ( let x = 0; x < size; x ++ ) {
vector.set( x, y, z ).divideScalar( size );
const d = perlin.noise( vector.x * 6.5, vector.y * 6.5, vector.z * 6.5 );
data[ i ++ ] = d * 128 + 128;
}
}
}
const texture = new THREE.Data3DTexture( data, size, size, size );
texture.format = THREE.RedFormat;
texture.minFilter = THREE.LinearFilter;
texture.magFilter = THREE.LinearFilter;
texture.unpackAlignment = 1;
texture.needsUpdate = true;
// Material
const vertexShader = /* glsl */`
in vec3 position;
uniform mat4 modelMatrix;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
uniform vec3 cameraPos;
out vec3 vOrigin;
out vec3 vDirection;
void main() {
vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
vOrigin = vec3( inverse( modelMatrix ) * vec4( cameraPos, 1.0 ) ).xyz;
vDirection = position - cameraPos;
gl_Position = projectionMatrix * mvPosition;
}
`;
const fragmentShader = /* glsl */`
precision highp float;
precision highp sampler3D;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
uniform vec3 cameraPos;
in vec3 vOrigin;
in vec3 vDirection;
out vec4 color;
uniform sampler3D map;
uniform float threshold;
uniform float steps;
vec2 hitSphere(vec3 orig, vec3 dir) {
const vec3 sphereCenter = vec3(0.0);
const float sphereRadius = 0.5;
vec3 toSphere = sphereCenter - orig;
float tca = dot(toSphere, dir);
float d2 = dot(toSphere, toSphere) - tca * tca;
float radius2 = sphereRadius * sphereRadius;
if (d2 > radius2) {
return vec2(1.0e6, 1.0e6);
}
float thc = sqrt(radius2 - d2);
// t0 = first intersect point - entrance on front of sphere
float t0 = tca - thc;
// t1 = second intersect point - exit point on back of sphere.
float t1 = tca + thc;
if (t1 < 0.0) {
// t1 is behind the ray
return vec2(1.0e6, 1.0e6);
}
if (t0 < 0.0) {
// t0 is behind the ray
// the ray is inside the sphere, in order to always return an intersect point that is in front of the ray
return vec2(t1, t0);
}
return vec2(t0, t1);
}
vec2 hitBox( vec3 orig, vec3 dir ) {
const vec3 box_min = vec3( - 0.5 );
const vec3 box_max = vec3( 0.5 );
vec3 inv_dir = 1.0 / dir;
vec3 tmin_tmp = ( box_min - orig ) * inv_dir;
vec3 tmax_tmp = ( box_max - orig ) * inv_dir;
vec3 tmin = min( tmin_tmp, tmax_tmp );
vec3 tmax = max( tmin_tmp, tmax_tmp );
float t0 = max( tmin.x, max( tmin.y, tmin.z ) );
float t1 = min( tmax.x, min( tmax.y, tmax.z ) );
return vec2( t0, t1 );
}
float sample1( vec3 p ) {
return texture( map, p ).r;
}
#define epsilon .0001
vec3 normal( vec3 coord ) {
if ( coord.x < epsilon ) return vec3( 1.0, 0.0, 0.0 );
if ( coord.y < epsilon ) return vec3( 0.0, 1.0, 0.0 );
if ( coord.z < epsilon ) return vec3( 0.0, 0.0, 1.0 );
if ( coord.x > 1.0 - epsilon ) return vec3( - 1.0, 0.0, 0.0 );
if ( coord.y > 1.0 - epsilon ) return vec3( 0.0, - 1.0, 0.0 );
if ( coord.z > 1.0 - epsilon ) return vec3( 0.0, 0.0, - 1.0 );
float step = 0.01;
float x = sample1( coord + vec3( - step, 0.0, 0.0 ) ) - sample1( coord + vec3( step, 0.0, 0.0 ) );
float y = sample1( coord + vec3( 0.0, - step, 0.0 ) ) - sample1( coord + vec3( 0.0, step, 0.0 ) );
float z = sample1( coord + vec3( 0.0, 0.0, - step ) ) - sample1( coord + vec3( 0.0, 0.0, step ) );
return normalize( vec3( x, y, z ) );
}
void main(){
vec3 rayDir = normalize( vDirection );
// vec2 bounds = hitBox( cameraPos, rayDir );
vec2 bounds = hitSphere( cameraPos, rayDir );
if ( bounds.x > bounds.y ) discard;
bounds.x = max( bounds.x, 0.0 );
vec3 p = cameraPos + bounds.x * rayDir;
vec3 inc = 1.0 / abs( rayDir );
float delta = min( inc.x, min( inc.y, inc.z ) );
delta /= steps;
// color.rgb = normal( p + 0.5 ) * 0.5 + ( p * 1.5 + 0.25 );
// color.rgb = p;
// color.a = 1.;
for ( float t = bounds.x; t < bounds.y; t += delta ) {
float d = sample1( p + 0.5 );
if ( d > threshold ) {
color.rgb = normal( p + 0.5 ) * 0.5 + ( p * 1.5 + 0.25 );
color.a = 1.;
break;
}
p += rayDir * delta;
}
if ( color.a == 0.0 ) discard;
}
`;
// const geometry = new THREE.BoxGeometry( 1, 1, 1 );
const geometry = new THREE.SphereGeometry(1)
const material = new THREE.RawShaderMaterial( {
glslVersion: THREE.GLSL3,
uniforms: {
map: { value: texture },
cameraPos: { value: new THREE.Vector3() },
threshold: { value: 0.6 },
steps: { value: 200 }
},
vertexShader,
fragmentShader,
side: THREE.BackSide,
} );
mesh = new THREE.Mesh( geometry, material );
scene.add( mesh );
//
const parameters = { threshold: 0.6, steps: 200 };
function update() {
material.uniforms.threshold.value = parameters.threshold;
material.uniforms.steps.value = parameters.steps;
}
const gui = new GUI();
gui.add( parameters, 'threshold', 0, 1, 0.01 ).onChange( update );
gui.add( parameters, 'steps', 0, 300, 1 ).onChange( update );
window.addEventListener( 'resize', onWindowResize );
}
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize( window.innerWidth, window.innerHeight );
}
function animate() {
requestAnimationFrame( animate );
mesh.material.uniforms.cameraPos.value.copy( camera.position );
renderer.render( scene, camera );
}
</script>
</body>
</html>
片源着色器中的 hitBox( vec3 orig, vec3 dir ) 函数和 src/math/Ray.js 中的
intersectBox( box, target ) 是一样的。为方便理解，可以代入几个特殊变量，比如 ray origin 为 （10，10， 0），ray direction为 y = x 的射线，和x轴的夹角为 45度，这条射线去撞击 中心在原点，边长为1的正方体。
需要注意的是
// color.rgb = p;
// color.a = 1.;
这两行代码取消注释，之后的代码注释掉，运行代码，可以得到一个彩色立方体，为什么在坐标 （-1，-1，-1）所在的空间象限，立方体的这个部分是黑色的呢？
应该是这行代码 vec3 p = cameraPos + bounds.x * rayDir; 得到的 p点实际上是始终位于 被撞击立方体的表面，（-1，-1，-1）附近的 p点，rgb三个分量都是负数，负数被截取为零，所以 （-1，-1，-1）空间象限的 p点 呈现为黑色
color.rgb = normal( p + 0.5 ) * 0.5 + ( p * 1.5 + 0.25 );
以上代码 为什么 有p + 0.5 ，因为p的三个分量 始终位于闭区间 [-0.5, 0.5]，加0.5后 变为[0, 1]的闭区间
for ( float t = bounds.x; t < bounds.y; t += delta ) {
float d = sample1( p + 0.5 );
if ( d > threshold ) {
color.rgb = normal( p + 0.5 ) * 0.5 + ( p * 1.5 + 0.25 );
color.a = 1.;
break;
}
p += rayDir * delta;
}
上面的代码 长得像 光线步进 ray marching 算法，但不完全是，因为每次步进的距离都是一个常数，实际是 沿光线 匀速的前进，在光线的等距间隔点上采样 三维的 perlin 噪音纹理；大于某个阈值就停止继续步进。阈值越大，得到的图形越稀疏。