method skew

Source

void skew(num skewX, num skewY) {

  var sinX = sin(skewX);
  var cosX = cos(skewX);
  var sinY = sin(skewY);
  var cosY = cos(skewY);

  var a =  this.a;
  var b =  this.b;
  var c =  this.c;
  var d =  this.d;
  var tx = this.tx;
  var ty = this.ty;

  _data[0] = a * cosY - b * sinX;
  _data[1] = a * sinY + b * cosX;
  _data[2] = c * cosY - d * sinX;
  _data[3] = c * sinY + d * cosX;
  _data[4] = tx * cosY - ty * sinX;
  _data[5] = tx * sinY + ty * cosX;
}