import { Vector3 } from './Vector3.js';
/**
* Primary reference:
* https://graphics.stanford.edu/papers/envmap/envmap.pdf
*
* Secondary reference:
* https://www.ppsloan.org/publications/StupidSH36.pdf
*/
// 3-band SH defined by 9 coefficients
class SphericalHarmonics3 {
constructor() {
this.isSphericalHarmonics3 = true;
this.coefficients = [];
for ( let i = 0; i < 9; i ++ ) {
this.coefficients.push( new Vector3() );
}
}
set( coefficients ) {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].copy( coefficients[ i ] );
}
return this;
}
zero() {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].set( 0, 0, 0 );
}
return this;
}
// get the radiance in the direction of the normal
// target is a Vector3
getAt( normal, target ) {
// normal is assumed to be unit length
const x = normal.x, y = normal.y, z = normal.z;
const coeff = this.coefficients;
// band 0
target.copy( coeff[ 0 ] ).multiplyScalar( 0.282095 );
// band 1
target.addScaledVector( coeff[ 1 ], 0.488603 * y );
target.addScaledVector( coeff[ 2 ], 0.488603 * z );
target.addScaledVector( coeff[ 3 ], 0.488603 * x );
// band 2
target.addScaledVector( coeff[ 4 ], 1.092548 * ( x * y ) );
target.addScaledVector( coeff[ 5 ], 1.092548 * ( y * z ) );
target.addScaledVector( coeff[ 6 ], 0.315392 * ( 3.0 * z * z - 1.0 ) );
target.addScaledVector( coeff[ 7 ], 1.092548 * ( x * z ) );
target.addScaledVector( coeff[ 8 ], 0.546274 * ( x * x - y * y ) );
return target;
}
// get the irradiance (radiance convolved with cosine lobe) in the direction of the normal
// target is a Vector3
// https://graphics.stanford.edu/papers/envmap/envmap.pdf
getIrradianceAt( normal, target ) {
// normal is assumed to be unit length
const x = normal.x, y = normal.y, z = normal.z;
const coeff = this.coefficients;
// band 0
target.copy( coeff[ 0 ] ).multiplyScalar( 0.886227 ); // π * 0.282095
// band 1
target.addScaledVector( coeff[ 1 ], 2.0 * 0.511664 * y ); // ( 2 * π / 3 ) * 0.488603
target.addScaledVector( coeff[ 2 ], 2.0 * 0.511664 * z );
target.addScaledVector( coeff[ 3 ], 2.0 * 0.511664 * x );
// band 2
target.addScaledVector( coeff[ 4 ], 2.0 * 0.429043 * x * y ); // ( π / 4 ) * 1.092548
target.addScaledVector( coeff[ 5 ], 2.0 * 0.429043 * y * z );
target.addScaledVector( coeff[ 6 ], 0.743125 * z * z - 0.247708 ); // ( π / 4 ) * 0.315392 * 3
target.addScaledVector( coeff[ 7 ], 2.0 * 0.429043 * x * z );
target.addScaledVector( coeff[ 8 ], 0.429043 * ( x * x - y * y ) ); // ( π / 4 ) * 0.546274
return target;
}
add( sh ) {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].add( sh.coefficients[ i ] );
}
return this;
}
addScaledSH( sh, s ) {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].addScaledVector( sh.coefficients[ i ], s );
}
return this;
}
scale( s ) {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].multiplyScalar( s );
}
return this;
}
lerp( sh, alpha ) {
for ( let i = 0; i < 9; i ++ ) {
this.coefficients[ i ].lerp( sh.coefficients[ i ], alpha );
}
return this;
}
equals( sh ) {
for ( let i = 0; i < 9; i ++ ) {
if ( ! this.coefficients[ i ].equals( sh.coefficients[ i ] ) ) {
return false;
}
}
return true;
}
copy( sh ) {
return this.set( sh.coefficients );
}
clone() {
return new this.constructor().copy( this );
}
fromArray( array, offset = 0 ) {
const coefficients = this.coefficients;
for ( let i = 0; i < 9; i ++ ) {
coefficients[ i ].fromArray( array, offset + ( i * 3 ) );
}
return this;
}
toArray( array = [], offset = 0 ) {
const coefficients = this.coefficients;
for ( let i = 0; i < 9; i ++ ) {
coefficients[ i ].toArray( array, offset + ( i * 3 ) );
}
return array;
}
// evaluate the basis functions
// shBasis is an Array[ 9 ]
static getBasisAt( normal, shBasis ) {
// normal is assumed to be unit length
const x = normal.x, y = normal.y, z = normal.z;
// band 0
shBasis[ 0 ] = 0.282095;
// band 1
shBasis[ 1 ] = 0.488603 * y;
shBasis[ 2 ] = 0.488603 * z;
shBasis[ 3 ] = 0.488603 * x;
// band 2
shBasis[ 4 ] = 1.092548 * x * y;
shBasis[ 5 ] = 1.092548 * y * z;
shBasis[ 6 ] = 0.315392 * ( 3 * z * z - 1 );
shBasis[ 7 ] = 1.092548 * x * z;
shBasis[ 8 ] = 0.546274 * ( x * x - y * y );
}
}
export { SphericalHarmonics3 };
