CreateHorizontalMenu.jsx

#target photoshop
app.bringToFront();

(function(global) {

  if (!documents.length) return;

  function getSelectedLayers() {
    var layers, gL, desc11, ref9, ref10;
    layers = [];
    desc11 = new ActionDescriptor();
    ref9 = new ActionReference();
    ref10 = new ActionReference();
    ref9.putClass(stringIDToTypeID('layerSection'));
    desc11.putReference(charIDToTypeID('null'), ref9);
    ref10.putEnumerated(charIDToTypeID('Lyr '), charIDToTypeID('Ordn'), charIDToTypeID('Trgt'));
    desc11.putReference(charIDToTypeID('From'), ref10);
    executeAction(charIDToTypeID('Mk  '), desc11, DialogModes.NO);
    gL = activeDocument.activeLayer.layers;
    for (var i = 0; i < gL.length; i++) {
      layers.push(gL[i]);
    }
    undo();
    return layers;
  }

  function undo() {
    executeAction(charIDToTypeID('undo'), undefined, DialogModes.NO);
  }

  function unitBounds(a, b) {
    return [
      a[0] < b[0] ? a[0] : b[0],
      a[1] < b[1] ? a[1] : b[1],
      a[2] > b[2] ? a[2] : b[2],
      a[3] > b[3] ? a[3] : b[3]
    ];
  }

  function getBounds(layer) {
    var bounds;
    switch(layer.typename) {
      case "ArtLayer":
        layer.rasterize(RasterizeType.ENTIRELAYER);
        bounds = layer.bounds;
        undo();
      break;
      case "LayerSet":
        bounds = getBounds(layer.layers[0]);
        for(var i = 1, iz = layer.layers.length; i < iz; i++) {
          bounds = unitBounds(bounds, getBounds(layer.layers[i]));
        }
      break;
      default:
        bounds = layer.bounds;
      break;
    }
    return bounds;
  }

  function LayerObject(layer) {
    this.layer = layer;
    this.bounds = getBounds(layer);
    this.left = parseInt(this.bounds[0]);
    this.top = parseInt(this.bounds[1]);
    this.right = parseInt(this.bounds[2]);
    this.bottom = parseInt(this.bounds[3]);
    this.width = this.right - this.left;
    this.height = this.bottom - this.top;
    this.translate = function() {
      layer.translate.apply(layer, arguments);
    };
  }

  function align(rl) {
    var baseGap, gaps, selectedLayers, layers, selectionBounds, totalWidth, maxHeight, startPoint, offset, gapNum;
    selectedLayers = getSelectedLayers();
    if (selectedLayers.length <= 1) return false;

    selectionBounds = {
      left: parseInt(activeDocument.selection.bounds[0]),
      top: parseInt(activeDocument.selection.bounds[1]),
      right: parseInt(activeDocument.selection.bounds[2]),
      bottom: parseInt(activeDocument.selection.bounds[3])
    };
    selectionBounds.width = selectionBounds.right - selectionBounds.left;
    selectionBounds.height = selectionBounds.bottom - selectionBounds.top;

    layers = new Array(selectedLayers.length);
    totalWidth = 0;
    maxHeight = 0;
    for (var i = 0, iz = selectedLayers.length; i < iz; i++) {
      layers[i] = new LayerObject(selectedLayers[i]);
      totalWidth += layers[i].width;
      maxHeight = Math.max(maxHeight, layers[i].height);
    }

    if (totalWidth > selectionBounds.width || maxHeight > selectionBounds.height) {
      alert("The selection is too small!");
      return;
    }

    baseGap = parseInt((selectionBounds.width - totalWidth) / layers.length);
    notmuchGap = selectionBounds.width - (baseGap * layers.length + totalWidth);

    gaps = new Array(layers.length+1);
    for(var i = 0; i < layers.length; i++) {
      gaps[i] = baseGap;
    }

    var index = 0;
    while(notmuchGap > 0) {
      gaps[index] += 1;
      notmuchGap--;
      index = (index + 1) % layers.length;
    }
    gaps[layers.length] = parseInt(gaps[0]/2);
    gaps[0] -= gaps[layers.length];

    startPoint = selectionBounds.left + gaps[0];

    activeDocument.selection.deselect();
    activeDocument.guides.add(Direction.VERTICAL, UnitValue(selectionBounds.left, "px"));
    activeDocument.guides.add(Direction.VERTICAL, UnitValue(selectionBounds.right, "px"));
    activeDocument.guides.add(Direction.HORIZONTAL, UnitValue(selectionBounds.top, "px"));
    activeDocument.guides.add(Direction.HORIZONTAL, UnitValue(selectionBounds.bottom, "px"));

    for(var i = 0, iz = layers.length; i < iz; i++) {
      var layer, offsetX, offsetY;
      layer = layers[i];
      if (i != 0) {
        activeDocument.guides.add(Direction.VERTICAL, startPoint - Math.round(gaps[i] / 2));
      }
      offsetX = startPoint - layer.left;
      offsetY = selectionBounds.top - layer.top + parseInt((selectionBounds.height - layer.height)/2);
      layer.translate(offsetX, offsetY);
      startPoint += layer.width + gaps[i + 1];
    }
  }

  activeDocument.suspendHistory("Create horizontal menu", "align(2)");
  refresh();

})(this);