js matrix math

matrix_math.js

function makeMatrixFromVec2(x, y) {
  return [
    x, 0, 0,
    0, y, 0,
    0, 0, 0
  ];
}

function makeVec2FromMatrix3(mat3) {
  return {
    x: mat3[0],
    y: mat3[4]
  };
}

function makeTranslation(tx, ty) {
  return [
    1,  0,  0,
    0,  1,  0,
    tx, ty, 1
  ];
}

function makeRotation(angleInRadians) {
  var c = Math.cos(angleInRadians);
  var s = Math.sin(angleInRadians);
  return [
    c, -s,  0,
    s,  c,  0,
    0,  0,  1
  ];
}

function makeScale(sx, sy) {
  return [
    sx, 0,  0,
    0,  sy, 0,
    0,  0,  1
  ];
}

function matrixMultiply(a, b) {
  var a00 = a[0*3+0];
  var a01 = a[0*3+1];
  var a02 = a[0*3+2];
  var a10 = a[1*3+0];
  var a11 = a[1*3+1];
  var a12 = a[1*3+2];
  var a20 = a[2*3+0];
  var a21 = a[2*3+1];
  var a22 = a[2*3+2];
  var b00 = b[0*3+0];
  var b01 = b[0*3+1];
  var b02 = b[0*3+2];
  var b10 = b[1*3+0];
  var b11 = b[1*3+1];
  var b12 = b[1*3+2];
  var b20 = b[2*3+0];
  var b21 = b[2*3+1];
  var b22 = b[2*3+2];
  return [a00 * b00 + a01 * b10 + a02 * b20,
          a00 * b01 + a01 * b11 + a02 * b21,
          a00 * b02 + a01 * b12 + a02 * b22,
          a10 * b00 + a11 * b10 + a12 * b20,
          a10 * b01 + a11 * b11 + a12 * b21,
          a10 * b02 + a11 * b12 + a12 * b22,
          a20 * b00 + a21 * b10 + a22 * b20,
          a20 * b01 + a21 * b11 + a22 * b21,
          a20 * b02 + a21 * b12 + a22 * b22];
}