matrix.ts

// Translated from https://github.com/leeoniya/transformation-matrix-js/blob/master/src/matrix.js

export class Matrix {
  public constructor(
    private readonly a: number,
    private readonly b: number,
    private readonly c: number,
    private readonly d: number,
    private readonly e: number,
    private readonly f: number
  ) {}

  public static identity = new Matrix(1, 0, 0, 1, 0, 0);

  public transform(
    a2: number,
    b2: number,
    c2: number,
    d2: number,
    e2: number,
    f2: number
  ): Matrix {
    return new Matrix(
      this.a * a2 + this.c * b2,
      this.b * a2 + this.d * b2,
      this.a * c2 + this.c * d2,
      this.b * c2 + this.d * d2,
      this.a * e2 + this.c + f2 + this.e,
      this.b * e2 + this.d * f2 + this.f
    );
  }

  public flipX(): Matrix {
    return this.transform(-1, 0, 0, 1, 0, 0);
  }

  public flipY(): Matrix {
    return this.transform(1, 0, 0, -1, 0, 0);
  }

  public rotate(angle: number): Matrix {
    const cos = Math.cos(angle),
      sin = Math.sin(angle);
    return this.transform(cos, sin, -sin, cos, 0, 0);
  }

  public rotateDeg(angle: number): Matrix {
    return this.rotate(angle * 0.017453292519943295);
  }

  public scale(sx: number, sy: number): Matrix {
    return this.transform(sx, 0, 0, sy, 0, 0);
  }

  public skew(sx: number, sy: number): Matrix {
    return this.transform(1, sy, sx, 1, 0, 0);
  }

  public translate(tx: number, ty: number): Matrix {
    return this.transform(1, 0, 0, 1, tx, ty);
  }

  public inverse(): Matrix {
    const dt = this.a * this.d - this.b * this.c;
    return new Matrix(
      this.d / dt,
      -this.b / dt,
      -this.c / dt,
      this.a / dt,
      (this.c * this.f - this.d * this.e) / dt,
      -(this.a * this.f - this.b * this.e) / dt
    );
  }

  public applyTo(x: number, y: number): [number, number] {
    return [x * this.a + y * this.c + this.e, x * this.b + y * this.d + this.f];
  }
}