# llafuente developer diary, important notes, links, notes...
# maybe don't worth reading ^.^


Physics
* http://www.metanetsoftware.com/technique/tutorialB.html
* http://www.metanetsoftware.com/technique/tutorialA.html
* http://buildnewgames.com/gamephysics/


* Algorithm
  * Backtracking
  * A*

* IK
  * FABRIK

vec2 distances (minkowski distance, euclidean, Manhattan)
https://github.com/abeja-inc/vector-algebra/blob/master/lib/vectorAlgebra.js

http://www.ryanjuckett.com/programming/constraint-relaxation-ik-in-2d/
http://www.dhteumeuleu.com/dhtml/robot-arm-ik.html
http://www.gvh.co.za/basic-inverse-kinematics/


http://arifudin.com/view.php?id=andreasaristidou.com/publications/FABRIK.pdf&k=gmod%20rating
https://github.com/RGBboy/fabrik-2d


Input: The joint positions pi for i = 1,...,n, the target position t and the distances between each joint
di = jpi+1 А
pij for i = 1,...,n А 1.
Output: The new joint positions pi for i = 1,...,n.


% The distance between root and target
dist = jp1 А tj
% Check whether the target is within reach
if dist > d1 + d2 +...+ dnА1 then
  % The target is unreachable
  for i = 1,...,n А 1 do
  % Find the distance ri between the target t and the joint position pi
  ri = jt А pij
  ki = di/ri
  % Find the new joint positions pi.
  pi+1 = (1 А ki) pi + kit
end
else
  % The target is reachable; thus, set as b the initial position of the joint p1
  b = p1
  % Check whether the distance between the end effector pn and the target t is greater than a tolerance.
  difA = jpn А tj

  while difA > tol do
    % STAGE 1: FORWARD REACHING
    % Set the end effector pn as target t
    pn = t
    for i = n А 1,...,1 do
      % Find the distance ri between the new joint position pi+1 and the joint pi
      ri = jpi+1 А pij
      ki = di/ri
      % Find the new joint positions pi.
      pi = (1 А ki) pi+1 + kipi
    end

    % STAGE 2: BACKWARD REACHING
    % Set the root p1 its initial position.
    p1 = b
    for i = 1,...,n А 1 do
      % Find the distance ri between the new joint position pi and the joint pi+1
      ri = jpi+1 А pij
      ki = di/ri
      % Find the new joint positions pi.
      pi+1 = (1 А ki)pi + kipi+1
    end
  difA = jpn А tj
  end
end


/**
* closestPointToBezier Find the closest point on a quadratic or cubic Bezier curve to an arbitrary point
*
* @param _curve:Geometry reference that must be a quadratic or cubic Bezier3
* @param _p:Point reference to <code>Point</code> to which the closest point on the Bezier curve is desired
*
* @return Number t-parameter of the closest point on the parametric curve. Returns 0 if inputs are <code>null</code> or not a valid reference to a Bezier curve.
*
* This code is derived from the Graphic Gem, "Solving the Nearest-Point-On-Curve Problem", by P.J. Schneider, published in 'Graphic Gems',
* A.S. Glassner, ed., Academic Press, Boston, 1990, pp. 607-611.
*
* @since 1.0
*
*/
function closestPoint (out_vec2, curve, vec2) {
  // record distances from point to endpoints
  var p:Point = _curve.pointAt(0);
  var deltaX:Number = p.x-_p.x;
  var deltaY:Number = p.y-_p.y;
  var d0:Number = Math.sqrt(deltaX*deltaX + deltaY*deltaY);

  p = _curve.pointAt(1);
  deltaX = p.x-_p.x;
  deltaY = p.y-_p.y;
  var d1:Number = Math.sqrt(deltaX*deltaX + deltaY*deltaY);

  var n:uint = (_curve is QuadraticBezier) ? 2 : 3; // degree of input Bezier curve

  // array of control points
  var v:Array = new Array();
  if( n == 2 )
  {
    var quad:QuadraticBezier = _curve as QuadraticBezier;
    v[0] = new Point(quad.x0, quad.y0);
    v[1] = new Point(quad.cx, quad.cy);
    v[2] = new Point(quad.x1, quad.y1);
  }
  else
  {
    var cubic:CubicBezier = _curve as CubicBezier;
    v[0] = new Point(cubic.x0 , cubic.y0 );
    v[1] = new Point(cubic.cx , cubic.cy );
    v[2] = new Point(cubic.cx1, cubic.cy1);
    v[3] = new Point(cubic.x1 , cubic.y1 );
  }

  // instaead of power form, convert the function whose zeros are required to Bezier form
  var w:Array = toBezierForm(_p, v);

  // Find roots of the Bezier curve with control points stored in 'w' (algorithm is recursive, this is root depth of 0)
  var roots:Array = findRoots(w, 2*n-1, 0);

  // compare the candidate distances to the endpoints and declare a winner :)
  if( d0 < d1 )
  {
   var tMinimum:Number = 0;
   __dMinimum = d0;
  }
  else
  {
   tMinimum = 1;
   __dMinimum = d1;
  }

  // tbd - compare 2-norm squared
  for( var i:uint=0; i<roots.length; ++i )
  {
   var t:Number = roots[i];
   if( t >= 0 && t <= 1 )
   {
   p = _curve.pointAt(t);
   deltaX = p.x - _p.x;
   deltaY = p.y - _p.y;
   var d:Number = Math.sqrt(deltaX*deltaX + deltaY*deltaY);

   if( d < __dMinimum )
   {
   tMinimum = t;
   __dMinimum = d;
   }
   }
  }

  // tbd - alternate optima.
  return tMinimum;
}


* Posts and links you should have read
  http://realtimecollisiondetection.net/blog/?p=80

* How Valve Connects Art Direction to Gameplay
  http://www.microsoft.com/en-us/download/details.aspx?id=18638

* Bringing Characters to Life: Using Physics to Enhance Animation
  http://www.microsoft.com/en-us/download/details.aspx?id=3507

* Bit Twiddling Hacks
  http://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2