three.js/src/math/Matrix2.js

export class Matrix2 {

	constructor( n11, n12, n21, n22 ) {

		Matrix2.prototype.isMatrix2 = true;

		this.elements = [
			1, 0,
			0, 1,
		];

		if ( n11 !== undefined ) {

			this.set( n11, n12, n21, n22 );

		}

	}

	identity() {

		this.set(
			1, 0,
			0, 1,
		);

		return this;

	}

	fromArray( array, offset = 0 ) {

		for ( let i = 0; i < 4; i ++ ) {

			this.elements[ i ] = array[ i + offset ];

		}

		return this;

	}

	set( n11, n12, n21, n22 ) {

		const te = this.elements;

		te[ 0 ] = n11; te[ 2 ] = n12;
		te[ 1 ] = n21; te[ 3 ] = n22;

		return this;

	}

}