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Compute ParametricGeometry normals from tangent vectors #11056

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merged 3 commits into from Mar 26, 2017
Merged

Compute ParametricGeometry normals from tangent vectors #11056

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63e9628
Compute ParametricGeometry normals from derivative
Mar 25, 2017
1dc0ce6
ParametricGeometry: normalize normal vectors directly
Mar 25, 2017
387e82d
ParametricGeometry: use forward/backward differences restricted to uv…
Mar 25, 2017
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22 changes: 18 additions & 4 deletions src/geometries/ParametricGeometry.js
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Expand Up @@ -36,6 +36,7 @@ ParametricGeometry.prototype.constructor = ParametricGeometry;

import { BufferGeometry } from '../core/BufferGeometry';
import { Float32BufferAttribute } from '../core/BufferAttribute';
import { Vector3 } from '../math/Vector3';

function ParametricBufferGeometry( func, slices, stacks ) {

Expand All @@ -53,11 +54,15 @@ function ParametricBufferGeometry( func, slices, stacks ) {

var indices = [];
var vertices = [];
var normals = [];
var uvs = [];

var EPS = 0.00001;
var pu = new Vector3(), pv = new Vector3(), normal = new Vector3();

var i, j;

// generate vertices and uvs
// generate vertices, normals and uvs

var sliceCount = slices + 1;

Expand All @@ -72,6 +77,16 @@ function ParametricBufferGeometry( func, slices, stacks ) {
var p = func( u, v );
vertices.push( p.x, p.y, p.z );

// approximate tangent plane vectors via central difference

pu.subVectors( func( u + EPS, v ), func( u - EPS, v ) );
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Is func( u, v ) guaranteed to be well-defined for values of u, v outside [ 0, 1 ] ?

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@Mugen87 Mugen87 Mar 25, 2017 •
edited

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That's a good point! According to the implementation of func(), values outside [ 0, 1 ] can be problematic.

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Then, use non-centered differences with a special case for the edge. By reusing p, only two additional calls are needed.

pv.subVectors( func( u, v + EPS ), func( u, v - EPS ) );
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@jaxry jaxry Mar 25, 2017 •
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Should the Vector3s returned by func be .cloneed here in case the Vector3s actually reference the same object? Or is there a better way to do this?

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func normally returns a new instance of Vector3, see https://github.com/mrdoob/three.js/blob/dev/examples/js/ParametricGeometries.js

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@Mugen87 Actually, there should be no reason to instantiate 4 * slices * stacks Vector3's when using central differences. We could add an optionalTarget to func() and reuse just two instances.

var result = optionalTarget || new THREE.Vector3();
...
return result.set( x, y, z );

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Sounds reasonable. We can also adjust some entities in THREE.ParametricGeometries so they use the optionalTarget. But let's do this in a separate PR, okay?

@jaxry Are you interested in doing this 😉 ?

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Yes. Separate PR.


// cross product of tangent plane vectors returns surface normal

normal.crossVectors( pu, pv );
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normal.crossVectors( pu, pv ).normalize();

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👍

normals.push( normal.x, normal.y, normal.z );

uvs.push( u, v );

}
Expand Down Expand Up @@ -102,11 +117,10 @@ function ParametricBufferGeometry( func, slices, stacks ) {

this.setIndex( indices );
this.addAttribute( 'position', new Float32BufferAttribute( vertices, 3 ) );
this.addAttribute( 'normal', new Float32BufferAttribute( normals, 3 ) );
this.addAttribute( 'uv', new Float32BufferAttribute( uvs, 2 ) );

// generate normals

this.computeVertexNormals();
this.normalizeNormals();
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not needed


}

Expand Down