【发布时间】：2018-10-27 09:40:58
【问题描述】：
我正在尝试通过使用 WebGL 实例化的线框 (https://threejs.org/examples/?q=wire#webgl_materials_wireframe) 的 threejs 示例。
这个简单的复制代码笔 (https://codepen.io/ubermario/pen/gzByjP?editors=1000) 显示，当使用 THREE.BufferAttribute 将“中心”属性传递给顶点/片段着色器时，会呈现线框立方体。
但是，当“中心”属性通过 THREE.InstancedBufferAttribute 传递给相同的着色器时，它不会呈现为线框。
不会产生错误。想法？
<html lang="en">
<head>
<title>Adopted from three.js webgl - materials - wireframe</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
<style>
body {
margin: 0px;
background-color: #000000;
overflow: hidden;
}
</style>
</head>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r83/three.js"></script>
<script type="x-shader/x-vertex" id="vertexShader">
attribute vec3 center;
varying vec3 vCenter;
void main() {
vCenter = center;
gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
}
</script>
<script type="x-shader/x-fragment" id="fragmentShader">
varying vec3 vCenter;
float edgeFactorTri() {
vec3 d = fwidth( vCenter.xyz );
vec3 a3 = smoothstep( vec3( 0.0 ), d * 1.5, vCenter.xyz );
return min( min( a3.x, a3.y ), a3.z );
}
void main() {
gl_FragColor.rgb = mix( vec3( 1.0 ), vec3( 0.0 ), edgeFactorTri() );
gl_FragColor.a = 1.0;
}
</script>
<script>
var camera, scene, renderer;
init();
renderer.render( scene, camera );
function init() {
var bufferGeometry, material, mesh;
camera = new THREE.PerspectiveCamera( 40, window.innerWidth / window.innerHeight, 1, 2000 );
camera.position.z = 700;
scene = new THREE.Scene();
var geometry1 = new THREE.BoxBufferGeometry( 100, 100,100 );
geometry1.addAttribute( 'center', new THREE.BufferAttribute( fnGetFloat32ArrayCenters( geometry1 ), 3 ) );
var material_1 = new THREE.ShaderMaterial( {
uniforms: {},
vertexShader: document.getElementById( 'vertexShader' ).textContent,
fragmentShader: document.getElementById( 'fragmentShader' ).textContent
} );
material_1.extensions.derivatives = true;
mesh1 = new THREE.Mesh( geometry1, material_1 );
mesh1.position.x = -100;
scene.add( mesh1 );
var bufferGeometry = new THREE.BoxBufferGeometry( 100, 100,100 );
var geometry2 = new THREE.InstancedBufferGeometry();
geometry2.index = bufferGeometry.index;
geometry2.attributes.position = bufferGeometry.attributes.position;
geometry2.attributes.uv = bufferGeometry.attributes.uv;
//Now with instancing
geometry2.addAttribute( 'center', new THREE.InstancedBufferAttribute( fnGetFloat32ArrayCenters( geometry2 ), 3 ) );
var material_2 = new THREE.ShaderMaterial( {
uniforms: {},
vertexShader: document.getElementById( 'vertexShader' ).textContent,
fragmentShader: document.getElementById( 'fragmentShader' ).textContent
} );
material_2.extensions.derivatives = true;
mesh2 = new THREE.Mesh( geometry2, material_2 );
mesh2.position.x = 100;
scene.add( mesh2 );
// renderer
renderer = new THREE.WebGLRenderer( { antialias: true } );
renderer.setPixelRatio( window.devicePixelRatio );
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );
// events
window.addEventListener( 'resize', onWindowResize, false );
function fnGetFloat32ArrayCenters( geometry ) {
var vectors = [
new THREE.Vector3( 1, 0, 0 ),
new THREE.Vector3( 0, 1, 0 ),
new THREE.Vector3( 0, 0, 1 )
];
var position = geometry.attributes.position;
var centers = new Float32Array( position.count * 3 );
for ( var i = 0, l = position.count; i < l; i ++ ) {
vectors[ i % 3 ].toArray( centers, i * 3 );
}
return centers;
} //fnGetFloat32ArrayCenters
} //init
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize( window.innerWidth, window.innerHeight );
}
</script>
</body>
</html>【问题讨论】：