affine.js

var divider, mappedCoords, an, bn, cn, dn, en, fn;

var ref0 = [0, 0]; // upper left corner
var ref1 = [0, 1024]; // lower left corner
var ref2 = [1280, 0]; // upper right corner
var ref3 = [1280, 1024]; // lower right corner

// Tomap -> which are mapped to [ref0, ref1, ref2, ref3, ref4]
var tomap0 = [0, 0]; // upper left corner
var tomap1 = [0, 768]; // lower left corner
var tomap2 = [1024, 0]; // upper right corner
var tomap3 = [1024, 768]; // lower right corner

// testpoint
var testpoint = testpoint = [1280, 1024];

function calculateDivider() {
  var result = ((tomap0[0] - tomap2[0]) * (tomap1[1] - tomap2[1])) - ((tomap1[0] - tomap2[0]) * (tomap0[1] - tomap2[1]));
  if (result == 0.0) {
    console.log("Divider is ZERO - check your coords");
  } else {
    divider = result;
    console.log("Divider is:" + divider);
    calculateAn();
    calculateBn();
    calculateCn();
    calculateDn();
    calculateEn();
    calculateFn();
  }
  return result;
}
function calculateAn() {
  var result = ((ref0[0] - ref2[0]) * (tomap1[1] - tomap2[1])) - ((ref1[0] - ref2[0]) * (tomap0[1] - tomap2[1]));
  an = result;
  console.log("An derived " + an);
  return result;
}
function calculateBn() {
  var result = ((tomap0[0] - tomap2[0]) * (ref1[0] - ref2[0])) - ((ref0[0] - ref2[0]) * (tomap1[0] - tomap2[0]));
  bn = result;
  console.log("Bn derived " + bn);
  return result;
}
function calculateCn() {
  var result = (tomap2[0] * ref1[0] - tomap1[0] * ref2[0]) * tomap0[1] + (tomap0[0] * ref2[0] - tomap2[0] * ref0[0]) * tomap1[1] + (tomap1[0] * ref0[0] - tomap0[0] * ref1[0]) * tomap2[1];
  cn = result;
  console.log("Cn derived " + cn);
  return result;
}
function calculateDn() {
  var result = ((ref0[1] - ref2[1]) * (tomap1[1] - tomap2[1])) - ((ref1[1] - ref2[1]) * (tomap0[1] - tomap2[1]));
  dn = result;
  console.log("Dn derived " + dn);
  return result;
}
function calculateEn() {
  var result = ((tomap0[0] - tomap2[0]) * (ref1[1] - ref2[1])) - ((ref0[1] - ref2[1]) * (tomap1[0] - tomap2[0]));
  en = result;
  console.log("En derived " + en);
  return result;
}
function calculateFn() {
  var result = (tomap2[0] * ref1[1] - tomap1[0] * ref2[1]) * tomap0[1] + (tomap0[0] * ref2[1] - tomap2[0] * ref0[1]) * tomap1[1] + (tomap1[0] * ref0[1] - tomap0[0] * ref1[1]) * tomap2[1];
  fn = result;
  console.log("Fn derived " + fn);
  return result;
}

// Use this method in test case
function deriveMappingCoords(point) {
  console.log(divider)
  if (divider != 0) {
    var x = ((an * point[0]) + (bn * point[1]) + cn) / divider;
    var y = ((dn * point[0]) + (en * point[1]) + fn) / divider;
    console.log("Test: " + " " + "X mapped to: " + x + " / " + "Y mapped to: " + y + "\n");
  }
}

calculateDivider();
deriveMappingCoords(testpoint);