SOURCE CODE: Uize.Widget.ImagePort.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.ImagePort.Draggable Class
|   /    / /    |
|  /    / /  /| |    ONLINE : http://www.uize.com
| /____/ /__/_| | COPYRIGHT : (c)2005-2016 UIZE
|          /___ |   LICENSE : Available under MIT License or GNU General Public License
|_______________|             http://www.uize.com/license.html
*/

/* Module Meta Data
  type: Class
  importance: 3
  codeCompleteness: 90
  docCompleteness: 2
*/

/*?
  Introduction
    The =Uize.Widget.ImagePort.Draggable= class extends its superclass by letting the user change logical sizing and positioning by clicking and dragging.

    *DEVELOPERS:* `Chris van Rensburg`
*/

Uize.module ({
  name:'Uize.Widget.ImagePort.Draggable',
  required:'Uize.Widget.Drag',
  builder:function (_superclass) {
    'use strict';

    var
      /*** Variables for Scruncher Optimization ***/
        _true = true,
        _false = false
    ;

    return _superclass.subclass ({
      omegastructor:function () {
        var m = this;

        /*** add drag child widget ***/
          var
            _drag = m.addChild ('drag',Uize.Widget.Drag,{idPrefixConstruction:'same as parent'}),
            _dragStartAlign = [],
            _dragStartSizingValue, _dragMode
          ;
          _drag.wire ({
            'Drag Start':
              function (_event) {
                _dragMode = _event.domEvent.ctrlKey ? 'sizing' : 'alignment';
                m.set ({_inDrag:_true});
                _dragStartSizingValue = m.get ('sizingValue');
                _dragStartAlign [0] = m.get ('alignX');
                _dragStartAlign [1] = m.get ('alignY');
              },
            'Drag Update':
              function (_event) {
                if (_dragMode == 'sizing') {
                  m.set ({
                    sizingValue:Uize.constrain (
                      _dragStartSizingValue + (0 - _drag.eventDeltaPos [1]) / 100,
                      m._minSizingValue,
                      m._maxSizingValue
                    )
                  });
                } else {
                  var _calculateNewAlignValue = function (_axis) {
                    return (
                      Uize.constrain (
                        _dragStartAlign [_axis] + _drag.eventDeltaPos [_axis] *
                          (
                            m.portVsScaledDelta [_axis]
                              ? (1 / m.portVsScaledDelta [_axis])
                              : 0
                          ),
                        0,
                        1
                      )
                    );
                  };
                  m.set ({
                    alignX:_calculateNewAlignValue (0),
                    alignY:_calculateNewAlignValue (1)
                  });
                }
              },
            'Drag Done':
              function () {m.set ({_inDrag:_false})}
          });

        /*** manage cursor state ***/
          function _updateUiCursor () {
            var
              _alignApplicableX = m.get ('alignApplicableX'),
              _alignApplicableY = m.get ('alignApplicableY')
            ;
            m.children.drag.set ({
              cursor:
                m._inZoomMode
                  ? 'n-resize'
                  : _alignApplicableX && _alignApplicableY
                    ? 'move'
                    : _alignApplicableX
                      ? 'w-resize'
                      : _alignApplicableY
                        ? 'n-resize'
                        : 'not-allowed'
            });
          }
          m.wire ({
            'Changed.alignApplicableX':_updateUiCursor,
            'Changed.alignApplicableY':_updateUiCursor,
            'Changed.inZoomMode':_updateUiCursor
          });
      },

      instanceMethods:{
        wireUi:function () {
          var m = this;
          if (!m.isWired) {
            /*** maintain inZoomMode state ***/
              /* NOTE:
                - Unfortunately, must watch for ctrl pressed at document level (can't do it at the root node level).
                - There are issues with some browsers and how they reflect (or don't reflect) changes in the cursor style property of an element that the mouse is already over.
                  - Safari seems to only reflect a cursor change on the next mousemove.
                  - Opera seems to only reflect a cursor change on a more radical repaint / re-render (not sure exactly what it's logic is).
                  - None of the browsers can pick up the key events if the document isn't focused (e.g. the location field is focused instead).
              */
              m.wireNode (
                document,
                {
                  keydown:function (_event) {_event.ctrlKey && m.set ({_inZoomMode:_true})},
                  keyup:function () {m.set ({_inZoomMode:_false})}
                }
              );

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

      stateProperties:{
        _inDrag:{
          name:'inDrag',
          value:_false
        },
        _inZoomMode:{
          name:'inZoomMode',
          value:_false
        },
        _maxSizingValue:{
          name:'maxSizingValue',
          value:Infinity
        },
        _minSizingValue:{
          name:'minSizingValue',
          value:0
        }
      }
    });
  }
});