linalg.ts

interface Matrix3x3 {
  v: number[];
}

function c(a: Matrix3x3, col: number): number[] {
  return [a.v[col], a.v[col + 3], a.v[col + 6]];
}

function r(a: Matrix3x3, row: number): number[] {
  return [a.v[row*3+0], a.v[row*3+1], a.v[row*3+2]];
}

function dot(a: number[], b: number[]): number {
  return a[0]*b[0] + a[1]*b[1] + a[2]*b[2];
}

function ident(): Matrix3x3 {
  return {
    v: [
      1, 0, 0,
      0, 1, 0,
      0, 0, 1
    ]
  }
}

function mult(a: Matrix3x3, b: Matrix3x3) {
  return {
    v: [
      dot(r(a,0), c(b,0)),  dot(r(a,0), c(b,1)), dot(r(a,0), c(b,2)),
      dot(r(a,1), c(b,0)),  dot(r(a,1), c(b,1)), dot(r(a,1), c(b,2)),
      dot(r(a,2), c(b,0)),  dot(r(a,2), c(b,1)), dot(r(a,2), c(b,2))
    ]
  }
}

// a c tx
// b d ty
// 0 0 1
// ->
// [a b c d tx ty]
function toCss(a: Matrix3x3) {
  const v = a.v;
  return `matrix(${v[0]}, ${v[3]}, ${v[1]}, ${v[4]}, ${v[2]}, ${v[5]})`;
}

function mkScale(s: number): Matrix3x3 {
  const m = ident();
  m.v[0] = s;
  m.v[4] = s;
  return m;
}

function mkTranslate(x: number, y: number): Matrix3x3 {
  const m = ident();
  m.v[2] = x;
  m.v[5] = y;
  return m;
}