jquery-menu.aim.js

//jQuery menu.aim.js

(function($) {

  $.fn.menuAim = function(opts) {
    // Initialize menu-aim for all elements in jQuery collection
    this.each(function() {
      init.call(this, opts);
    });

    return this;
  };

  function init(opts) {
    var $menu = $(this),
      activeRow = null,
      mouseLocs = [],
      lastDelayLoc = null,
      timeoutId = null,
      options = $.extend({
        rowSelector: "> li",
        submenuSelector: "*",
        submenuDirection: "right",
        tolerance: 75, // bigger = more forgivey when entering submenu
        enter: $.noop,
        exit: $.noop,
        activate: $.noop,
        deactivate: $.noop,
        exitMenu: $.noop
      }, opts);

    var MOUSE_LOCS_TRACKED = 3, // number of past mouse locations to track
      DELAY = 300; // ms delay when user appears to be entering submenu

    /**
     * Keep track of the last few locations of the mouse.
     */
    var mousemoveDocument = function(e) {
      mouseLocs.push({
        x: e.pageX,
        y: e.pageY
      });

      if (mouseLocs.length > MOUSE_LOCS_TRACKED) {
        mouseLocs.shift();
      }
    };

    /**
     * Cancel possible row activations when leaving the menu entirely
     */
    var mouseleaveMenu = function() {
      if (timeoutId) {
        clearTimeout(timeoutId);
      }

      // If exitMenu is supplied and returns true, deactivate the
      // currently active row on menu exit.
      if (options.exitMenu(this)) {
        if (activeRow) {
          options.deactivate(activeRow);
        }

        activeRow = null;
      }
    };

    /**
     * Trigger a possible row activation whenever entering a new row.
     */
    var mouseenterRow = function() {
        if (timeoutId) {
          // Cancel any previous activation delays
          clearTimeout(timeoutId);
        }

        options.enter(this);
        possiblyActivate(this);
      },
      mouseleaveRow = function() {
        options.exit(this);
      };

    /*
     * Immediately activate a row if the user clicks on it.
     */
    var clickRow = function() {
      activate(this);
    };

    /**
     * Activate a menu row.
     */
    var activate = function(row) {
      if (row == activeRow) {
        return;
      }

      if (activeRow) {
        options.deactivate(activeRow);
      }

      options.activate(row);
      activeRow = row;
    };

    /**
     * Possibly activate a menu row. If mouse movement indicates that we
     * shouldn't activate yet because user may be trying to enter
     * a submenu's content, then delay and check again later.
     */
    var possiblyActivate = function(row) {
      var delay = activationDelay();

      if (delay) {
        timeoutId = setTimeout(function() {
          possiblyActivate(row);
        }, delay);
      } else {
        activate(row);
      }
    };

    /**
     * Return the amount of time that should be used as a delay before the
     * currently hovered row is activated.
     *
     * Returns 0 if the activation should happen immediately. Otherwise,
     * returns the number of milliseconds that should be delayed before
     * checking again to see if the row should be activated.
     */
    var activationDelay = function() {
      if (!activeRow || !$(activeRow).is(options.submenuSelector)) {
        // If there is no other submenu row already active, then
        // go ahead and activate immediately.
        return 0;
      }

      var offset = $menu.offset(),
        upperLeft = {
          x: offset.left,
          y: offset.top - options.tolerance
        },
        upperRight = {
          x: offset.left + $menu.outerWidth(),
          y: upperLeft.y
        },
        lowerLeft = {
          x: offset.left,
          y: offset.top + $menu.outerHeight() + options.tolerance
        },
        lowerRight = {
          x: offset.left + $menu.outerWidth(),
          y: lowerLeft.y
        },
        loc = mouseLocs[mouseLocs.length - 1],
        prevLoc = mouseLocs[0];

      if (!loc) {
        return 0;
      }

      if (!prevLoc) {
        prevLoc = loc;
      }

      if (prevLoc.x < offset.left || prevLoc.x > lowerRight.x ||
        prevLoc.y < offset.top || prevLoc.y > lowerRight.y) {
        // If the previous mouse location was outside of the entire
        // menu's bounds, immediately activate.
        return 0;
      }

      if (lastDelayLoc &&
        loc.x == lastDelayLoc.x && loc.y == lastDelayLoc.y) {
        // If the mouse hasn't moved since the last time we checked
        // for activation status, immediately activate.
        return 0;
      }

      // Detect if the user is moving towards the currently activated
      // submenu.
      //
      // If the mouse is heading relatively clearly towards
      // the submenu's content, we should wait and give the user more
      // time before activating a new row. If the mouse is heading
      // elsewhere, we can immediately activate a new row.
      //
      // We detect this by calculating the slope formed between the
      // current mouse location and the upper/lower right points of
      // the menu. We do the same for the previous mouse location.
      // If the current mouse location's slopes are
      // increasing/decreasing appropriately compared to the
      // previous's, we know the user is moving toward the submenu.
      //
      // Note that since the y-axis increases as the cursor moves
      // down the screen, we are looking for the slope between the
      // cursor and the upper right corner to decrease over time, not
      // increase (somewhat counterintuitively).
      function slope(a, b) {
        return (b.y - a.y) / (b.x - a.x);
      };

      var decreasingCorner = upperRight,
        increasingCorner = lowerRight;

      // Our expectations for decreasing or increasing slope values
      // depends on which direction the submenu opens relative to the
      // main menu. By default, if the menu opens on the right, we
      // expect the slope between the cursor and the upper right
      // corner to decrease over time, as explained above. If the
      // submenu opens in a different direction, we change our slope
      // expectations.
      if (options.submenuDirection == "left") {
        decreasingCorner = lowerLeft;
        increasingCorner = upperLeft;
      } else if (options.submenuDirection == "below") {
        decreasingCorner = lowerRight;
        increasingCorner = lowerLeft;
      } else if (options.submenuDirection == "above") {
        decreasingCorner = upperLeft;
        increasingCorner = upperRight;
      }

      var decreasingSlope = slope(loc, decreasingCorner),
        increasingSlope = slope(loc, increasingCorner),
        prevDecreasingSlope = slope(prevLoc, decreasingCorner),
        prevIncreasingSlope = slope(prevLoc, increasingCorner);

      if (decreasingSlope < prevDecreasingSlope &&
        increasingSlope > prevIncreasingSlope) {
        // Mouse is moving from previous location towards the
        // currently activated submenu. Delay before activating a
        // new menu row, because user may be moving into submenu.
        lastDelayLoc = loc;
        return DELAY;
      }

      lastDelayLoc = null;
      return 0;
    };

    /**
     * Hook up initial menu events
     */
    $menu
      .mouseleave(mouseleaveMenu)
      .find(options.rowSelector)
      .mouseenter(mouseenterRow)
      .mouseleave(mouseleaveRow)
      .click(clickRow);

    $(document).mousemove(mousemoveDocument);

  };
})(jQuery);