jquery-ui draggable(1.12.1) 重なりを考慮した処理に変更

(function($){

	$.extend($.ui.ddmanager, {

		// ドロップ処理
		drop: function( draggable, event ) {

			var dropped = false;
			var max_z = -1;
			var _that, z, trgt, pos;

			// Create a copy of the droppables in case the list changes during the drop (#9116)
			$.each( ( $.ui.ddmanager.droppables[ draggable.options.scope ] || [] ).slice(), function() {

				if ( !this.options ) {
					return;
				}

				if ( !this.options.disabled && this.visible &&
						$.ui.intersect( draggable, this, this.options.tolerance, event ) ) {	// ドラッグ位置に掛かっているドロップ範囲のもののみ

					// get z-index
					trgt = this.element;
					z = ( ( trgt.css('zIndex') == 'auto' ) ? 0 : trgt.css('zIndex') ) || 0;

					// 最大z-indexのものを処理対象にする
					if (z > max_z) {
						_that = this;
						max_z = z;
					}
				}

				if ( !this.options.disabled && this.visible && this.accept.call( this.element[ 0 ],
						( draggable.currentItem || draggable.element ) ) ) {
					this.isout = true;
					this.isover = false;
					this._deactivate.call( this, event );
				}

			} );
			
			return (_that) ? _that._drop.call(_that, event) : false;

		},
		
		drag: function( draggable, event ) {

			// If you have a highly dynamic page, you might try this option. It renders positions
			// every time you move the mouse.
			if ( draggable.options.refreshPositions ) {
				$.ui.ddmanager.prepareOffsets( draggable, event );
			}
			
			var dropped = false
				,max_z = -1
				,_that, z, trgt, pos, _c
			;

			// Run through all droppables and check their positions based on specific tolerance options
			$.each( $.ui.ddmanager.droppables[ draggable.options.scope ] || [], function() {

				if ( this.options.disabled || this.greedyChild || !this.visible ) {
					return;
				}

				// ドラッグ位置に掛かっているドロップ範囲のものの中からz-indexが最大のものを見つける
				var intersects = $.ui.intersect( draggable, this, this.options.tolerance, event );
				if (intersects) {

					// get z-index
					trgt = this.element;
					z = ( ( trgt.css('zIndex') == 'auto' ) ? 0 : trgt.css('zIndex') ) || 0;

					// 最大z-indexのものを処理対象にする
					if ( z > max_z ){

						var c = !intersects && this.isover ?
							"isout" :
							( intersects && !this.isover ? "isover" : null );

						_that = this;
						max_z = z;
						_c = c;

					}

				}
			} );

			$.each( $.ui.ddmanager.droppables[ draggable.options.scope ] || [], function() {
				if ( this.options.disabled || this.greedyChild || !this.visible ) {
					return;
				}

				var c;
				if ( _that === this ) {				// 手前のものは通常通りover,outを処理
					c = _c;
				} else {							// 手前それ以外はoutのみ処理
					c = this.isover ? "isout" : null;
				}

				if ( !c ) {							// 変わりないものは処理しない
					return;
				}
				
				var parentInstance, scope, parent;

				if ( this.options.greedy ) {

					// find droppable parents with same scope
					scope = this.options.scope;
					parent = this.element.parents( ":data(ui-droppable)" ).filter( function() {
						return $( this ).droppable( "instance" ).options.scope === scope;
					} );

					if ( parent.length ) {
						parentInstance = $( parent[ 0 ] ).droppable( "instance" );
						parentInstance.greedyChild = ( c === "isover" );
					}
				}

				// We just moved into a greedy child
				if ( parentInstance && c === "isover" ) {
					parentInstance.isover = false;
					parentInstance.isout = true;
					parentInstance._out.call( parentInstance, event );
				}

				this[ c ] = true;
				this[ c === "isout" ? "isover" : "isout" ] = false;
				this[ c === "isover" ? "_over" : "_out" ].call( this, event );

				// We just moved out of a greedy child
				if ( parentInstance && c === "isout" ) {
					parentInstance.isout = false;
					parentInstance.isover = true;
					parentInstance._over.call( parentInstance, event );
				}
			} );

		}
	});

})(jQuery);