layersToSprite.js

// Put this file in Program Files\Adobe\Photoshop\Presets\Scripts\layersToSprite.js
// Run in PhotoShop: File > Automate > Scripts: layersToSprite.js

// Arrange layers into a sprite sheet.

// Set up UI.
var title = "Layers to Spritesheet";

var dlg = new Window('dialog', title, [100,100,320,155]);
dlg.scTxt = dlg.add('statictext',[10,17,45,35],"Cells X");
dlg.CellX = dlg.add('edittext',[55,15,77,35],'3');
dlg.okayBtn = dlg.add('button', [155,17,215,35],'Okay', {name:'ok'});
dlg.show();

    if (documents.length > 0)
    {
        var cols = parseInt(dlg.CellX.text);

        // --------------------------
        docRef = activeDocument;
        var activeLayer = docRef.activeLayer;

        numLayers = docRef.artLayers.length;

        var rows = Math.ceil(numLayers/cols);

         var spriteX = docRef.width;
         var spriteY = docRef.height;

        // put things in order
        app.preferences.rulerUnits = Units.PIXELS;

        // resize the canvas
         newX = spriteX * cols;
         newY = spriteY * rows;

         docRef.resizeCanvas( newX, newY, AnchorPosition.TOPLEFT );

        // move the layers around
         var rowi = 0;
         var coli = 0;

         for (i=(numLayers - 1); i >= 0; i--)
         {
             docRef.artLayers[i].visible = 1;

              var movX = spriteX*coli;
              var movY = spriteY*rowi;

             docRef.artLayers[i].translate(movX, movY);

             coli++;
             if (coli > (cols - 1))
             {
                 rowi++;
                 coli = 0;
             }
         }
    }