125 lines
2.9 KiB
JavaScript
125 lines
2.9 KiB
JavaScript
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/**
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* Represents a 2x2 matrix.
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*
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* A Note on Row-Major and Column-Major Ordering:
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*
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* The constructor and {@link Matrix2#set} method take arguments in
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* [row-major]{@link https://en.wikipedia.org/wiki/Row-_and_column-major_order#Column-major_order}
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* order, while internally they are stored in the {@link Matrix2#elements} array in column-major order.
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* This means that calling:
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* ```js
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* const m = new THREE.Matrix2();
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* m.set( 11, 12,
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* 21, 22 );
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* ```
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* will result in the elements array containing:
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* ```js
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* m.elements = [ 11, 21,
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* 12, 22 ];
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* ```
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* and internally all calculations are performed using column-major ordering.
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* However, as the actual ordering makes no difference mathematically and
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* most people are used to thinking about matrices in row-major order, the
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* three.js documentation shows matrices in row-major order. Just bear in
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* mind that if you are reading the source code, you'll have to take the
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* transpose of any matrices outlined here to make sense of the calculations.
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*/
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export class Matrix2 {
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/**
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* Constructs a new 2x2 matrix. The arguments are supposed to be
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* in row-major order. If no arguments are provided, the constructor
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* initializes the matrix as an identity matrix.
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*
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* @param {number} [n11] - 1-1 matrix element.
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* @param {number} [n12] - 1-2 matrix element.
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* @param {number} [n21] - 2-1 matrix element.
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* @param {number} [n22] - 2-2 matrix element.
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*/
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constructor( n11, n12, n21, n22 ) {
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/**
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* This flag can be used for type testing.
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*
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* @type {boolean}
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* @readonly
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* @default true
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*/
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Matrix2.prototype.isMatrix2 = true;
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/**
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* A column-major list of matrix values.
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*
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* @type {Array<number>}
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*/
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this.elements = [
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1, 0,
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0, 1,
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];
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if ( n11 !== undefined ) {
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this.set( n11, n12, n21, n22 );
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}
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}
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/**
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* Sets this matrix to the 2x2 identity matrix.
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*
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* @return {Matrix2} A reference to this matrix.
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*/
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identity() {
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this.set(
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1, 0,
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0, 1,
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);
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return this;
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}
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/**
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* Sets the elements of the matrix from the given array.
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*
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* @param {Array<number>} array - The matrix elements in column-major order.
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* @param {number} [offset=0] - Index of the first element in the array.
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* @return {Matrix2} A reference to this matrix.
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*/
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fromArray( array, offset = 0 ) {
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for ( let i = 0; i < 4; i ++ ) {
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this.elements[ i ] = array[ i + offset ];
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}
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return this;
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}
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/**
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* Sets the elements of the matrix.The arguments are supposed to be
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* in row-major order.
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*
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* @param {number} n11 - 1-1 matrix element.
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* @param {number} n12 - 1-2 matrix element.
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* @param {number} n21 - 2-1 matrix element.
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* @param {number} n22 - 2-2 matrix element.
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* @return {Matrix2} A reference to this matrix.
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*/
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set( n11, n12, n21, n22 ) {
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const te = this.elements;
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te[ 0 ] = n11; te[ 2 ] = n12;
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te[ 1 ] = n21; te[ 3 ] = n22;
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return this;
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}
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}
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