SOURCE CODE: Uize.Widget.ColorGrid.Draggable (view docs)

/*______________
|       ______  |   U I Z E    J A V A S C R I P T    F R A M E W O R K
|     /      /  |   ---------------------------------------------------
|    /    O /   |    MODULE : Uize.Widget.ColorGrid.Draggable Class
|   /    / /    |
|  /    / /  /| |    ONLINE : http://www.uize.com
| /____/ /__/_| | COPYRIGHT : (c)2006-2016 UIZE
|          /___ |   LICENSE : Available under MIT License or GNU General Public License
|_______________|             http://www.uize.com/license.html
*/

/* Module Meta Data
  type: Class
  importance: 1
  codeCompleteness: 100
  docCompleteness: 2
*/

/*?
  Introduction
    The =Uize.Widget.ColorGrid.Draggable= class extends its superclass by adding the ability to stretch the grid's color gradient by clicking and dragging.

    *DEVELOPERS:* `Chris van Rensburg`
*/

Uize.module ({
  name:'Uize.Widget.ColorGrid.Draggable',
  required:[
    'Uize.Dom.Util',
    'Uize.Dom.Pos',
    'Uize.Widget.Drag',
    'Uize.Color'
  ],
  builder:function (_superclass) {
    'use strict';

    var
      /*** Variables for Scruncher Optimization ***/
        _blendValues = Uize.blendValues,

      /*** General Variables ***/
        _dummyColor = Uize.Color ()
    ;

    /*** Utility Functions ***/
      function _getColorAtRelativePoint (_cornerColors,_blendX,_blendY) {
        /* IMPORTANT:
          this code is very similar to code inside the superclass, so maybe refactor the superclass to provide a service that can be used in this class
        */
        var
          _colorTopLeftTuple = _cornerColors.colorTopLeft.tuple,
          _colorTopRightTuple = _cornerColors.colorTopRight.tuple,
          _colorBottomLeftTuple = _cornerColors.colorBottomLeft.tuple,
          _colorBottomRightTuple = _cornerColors.colorBottomRight.tuple
        ;
        function _blendColorComponent (_componentNo) {
          return (
            _blendValues (
              _blendValues (_colorTopLeftTuple [_componentNo],_colorTopRightTuple [_componentNo],_blendX),
              _blendValues (_colorBottomLeftTuple [_componentNo],_colorBottomRightTuple [_componentNo],_blendX),
              _blendY
            )
          );
        }
        _dummyColor.encoding = _cornerColors.colorTopLeft.encoding;
        Uize.Color.setTuple (
          _dummyColor.tuple,
          _blendColorComponent (0),_blendColorComponent (1),_blendColorComponent (2)
        );
        return _dummyColor.to ();
      }

    return _superclass.subclass ({
      instanceMethods:{
        wireUi:function () {
          var m = this;
          if (!m.isWired) {
            var
              _shell = m.getNode (),
              _drag = Uize.Widget.Drag ({node:_shell}),
              _xSideNames = ['Left','Right'],
              _ySideNames = ['Top','Bottom'],
              _eventStartPos = _drag.eventStartPos,
              _eventDeltaPos = _drag.eventDeltaPos,
              _eventPos = _drag.eventPos,
              _cubeCoords, _cubeCoordsArray,
              _cornerColorsAtDragStart = {}
            ;
            Uize.Dom.Util.showClickable (_shell);
            _drag.wire ({
              'Drag Start':
                function (_event) {
                  m.set ({_inDrag:true});
                  _cubeCoords = Uize.Dom.Pos.getCoords (_shell);
                  _cubeCoordsArray = [_cubeCoords.left,_cubeCoords.top,_cubeCoords.right,_cubeCoords.bottom];
                  function _initCornerColorAtDragStart (_cornerName) {
                    (
                      _cornerColorsAtDragStart [_cornerName] ||
                      (_cornerColorsAtDragStart [_cornerName] = Uize.Color ())
                    ).from (m.get (_cornerName));
                  }
                  _initCornerColorAtDragStart ('colorTopLeft');
                  _initCornerColorAtDragStart ('colorTopRight');
                  _initCornerColorAtDragStart ('colorBottomLeft');
                  _initCornerColorAtDragStart ('colorBottomRight');
                },
              'Drag Update':
                function (_event) {
                  var
                    _scaledCornerSides = [],
                    _newPropertyValues = {},
                    _newPropertyPoints = {},
                    _fixedCornerSides = []
                  ;
                  function _setScaledCornerSides (_axisNo) {
                    _fixedCornerSides [_axisNo] = _eventDeltaPos [_axisNo] > 0 ? 0 : 1;
                    var
                      _fixedCornerPos = _cubeCoordsArray [_fixedCornerSides [_axisNo] * 2 + _axisNo],
                      _fixedCornerSide = _fixedCornerSides [_axisNo],
                      _fluidCornerSide = 1 - _fixedCornerSide
                    ;
                    _scaledCornerSides [_fixedCornerSide * 2 + _axisNo] = _fixedCornerSide;
                    _scaledCornerSides [_fluidCornerSide * 2 + _axisNo] = _fixedCornerSide + (_fluidCornerSide - _fixedCornerSide) * (_eventPos [_axisNo] - _fixedCornerPos) / (_eventStartPos [_axisNo] - _fixedCornerPos);
                  }
                  _setScaledCornerSides (0);
                  _setScaledCornerSides (1);
                  function _setCornerColor (_xSide,_ySide) {
                    var _propertyName = 'color' + _ySideNames [_ySide] + _xSideNames [_xSide];
                    _newPropertyValues [_propertyName] =
                      _xSide == _fixedCornerSides [0] && _ySide == _fixedCornerSides [1]
                        ? _cornerColorsAtDragStart [_propertyName].to ()
                        : _getColorAtRelativePoint (
                          _cornerColorsAtDragStart,
                          (_xSide - _scaledCornerSides [0]) / (_scaledCornerSides [2] - _scaledCornerSides [0]),
                          (_ySide - _scaledCornerSides [1]) / (_scaledCornerSides [3] - _scaledCornerSides [1])
                        )
                    ;
                  }
                  _setCornerColor (0,0);
                  _setCornerColor (0,1);
                  _setCornerColor (1,0);
                  _setCornerColor (1,1);
                  m.set (_newPropertyValues);
                  m.fire ('Colors Changed');
                },
              'Drag Done':
                function () {m.set ({_inDrag:false})}
            });
            m.addChild ('drag',_drag);

            _superclass.doMy (m,'wireUi');
          }
        }
      },

      stateProperties:{
        _inDrag:{
          name:'inDrag',
          value:false
        }
      }
    });
  }
});