A Photoshop script to snap all path points on selected shape layers to nearest pixels.

Snap to Pixels.jsx

// Based on Adobe Community Forums member BlipAdobe's script:
// http://forums.adobe.com/message/3908198#3908198

#target photoshop
 
// Constants
var QUANTIZE_PIXELS = 1;    // The number of whole pixels we wish the path points to be quantized to
var PIXEL_RATIO = app.activeDocument.resolution / 72; // Standardize pixels and points
 
// Some helpers
function cTID(s) { return charIDToTypeID(s); };
function sTID(s) { return stringIDToTypeID(s); };
 
 
app.bringToFront();
 
app.activeDocument.suspendHistory("Snap To Pixel", "main();");
 
 
// Quantizes all points in the active layers' vector masks to the value specified by QUANTIZE_PIXELS.
function main()
{    
    // Work in pixels
    var OrigRulerUnits = app.preferences.rulerUnits;
    var OrigTypeUnits = app.preferences.typeUnits;
    app.preferences.rulerUnits = Units.PIXELS;
    app.preferences.typeUnits = TypeUnits.PIXELS;
 
    // Obtain the action manager indices of all the selected layers
    var SelIndices = GetSelectedLayersIdx();
    if (SelIndices.length == 1)
    {
        // Only a single layer is selected
        QuantizeVectorMaskForActiveLayer(QUANTIZE_PIXELS);
    }
    else
    { 
        // More than one layer is selected
        for (var i = 0; i < SelIndices.length; ++i)
        {
            if (MakeActiveByIndex(SelIndices[i], false) != -1)
            {
                QuantizeVectorMaskForActiveLayer(QUANTIZE_PIXELS);
            }
        }
    }
    
    // Restore original ruler units
    app.preferences.rulerUnits = OrigRulerUnits;
    app.preferences.typeUnits = OrigTypeUnits;
}
 
 
function QuantizeVectorMaskForActiveLayer(zQuantizeUnits)
{
    var doc = app.activeDocument;
    var PathItems = doc.pathItems;
 
    // Nothing to do if the active layer has no path
    if (PathItems.length == 0)
        return;
        
    var QuantizedPathInfo = null;
    
    for (var i = 0; i < PathItems.length; ++i)
    {
        var Path = PathItems[i];
        
        // It would appear that the path for the selected layer is of kind VECTORMASK.  If so, when does WORKPATH come into play?
        if (Path.kind == PathKind.VECTORMASK)
        {
            // Build a path info structure by copying the properties of this path, quantizing all anchor and left/right points
            var QuantizedPathInfo = BuildPathInfoFromPath(Path, zQuantizeUnits);
            if (QuantizedPathInfo.length > 0)
            {
                // We've now finished with the original path so it can go
                Path.remove();
 
                // Add our new path to the doc
                var TempQuantizedPath = doc.pathItems.add("TempQuantizedPath", QuantizedPathInfo);
                
                // Convert the new path to a vector mask on the active layer
                PathtoVectorMask();
 
                // Finished with the path
                TempQuantizedPath.remove();
            }
        }
    }
}
 
 
// Copies the specified path to a new path info structure, which is then returned.  The function will
// optionally quantize all points to the specified number of whole units.  Specify zQuantizeUnits = 0
// if you do not wish to quantize the points.
function BuildPathInfoFromPath(zInputPath, zQuantizeUnits)
{
    // The output path will be an array of SubPathInfo objects
    var OutputPathInfo = [];
    
    // For each subpath in the input path
    for (var SubPathIndex = 0; SubPathIndex < zInputPath.subPathItems.length; ++SubPathIndex)
    {
        var InputSubPath = zInputPath.subPathItems[SubPathIndex];
 
        var OutputPointInfo = [];    
        
        // For each point in the input subpath
        var NumPoints = InputSubPath.pathPoints.length;
        for (var PointIndex = 0; PointIndex < NumPoints; ++PointIndex)
        {
            var InputPoint = InputSubPath.pathPoints[PointIndex];
            
            var InputAnchor = InputPoint.anchor;
            var InputAnchorQ = QuantizePoint(InputAnchor, zQuantizeUnits);
            
            // Copy all the input point's properties to the output point info
            OutputPointInfo[PointIndex] = new PathPointInfo();
            OutputPointInfo[PointIndex].kind = InputPoint.kind;
            OutputPointInfo[PointIndex].anchor = QuantizePoint(InputPoint.anchor, zQuantizeUnits);
            OutputPointInfo[PointIndex].leftDirection = QuantizePoint(InputPoint.leftDirection, zQuantizeUnits);
            OutputPointInfo[PointIndex].rightDirection = QuantizePoint(InputPoint.rightDirection, zQuantizeUnits);
        }
 
        // Create the SubPathInfo for our output path, and copy properties from the input sub path
        OutputPathInfo[SubPathIndex] = new SubPathInfo();
        OutputPathInfo[SubPathIndex].closed = InputSubPath.closed;
        OutputPathInfo[SubPathIndex].operation = InputSubPath.operation;
        OutputPathInfo[SubPathIndex].entireSubPath = OutputPointInfo;    
    }
 
    return OutputPathInfo;
}
 
 
// Quantizes the specified point to the specified number of whole units
function QuantizePoint(zPoint, zQuantizeUnits)
{
    // Check for divide by zero (if zQuantizeUnits == 0 we don't quantize)
    if (zQuantizeUnits == 0)
        return [ zPoint[0]/PIXEL_RATIO, zPoint[1]/PIXEL_RATIO ];
    else
        return [ Math.round(zPoint[0] / zQuantizeUnits)/PIXEL_RATIO * zQuantizeUnits, Math.round(zPoint[1] / zQuantizeUnits)/PIXEL_RATIO * zQuantizeUnits ];
}
 
 
// Converts the current working path to a vector mask on the active layer.  This function will fail
// if the active layer already has a vector mask, so you should remove it beforehand.
function PathtoVectorMask()
{
    var desc11 = new ActionDescriptor();
    var ref8 = new ActionReference();
    ref8.putClass( cTID("Path") );
    desc11.putReference( cTID("null"), ref8);
    var ref9 = new ActionReference();
    ref9.putEnumerated(cTID("Path"), cTID("Path"), sTID("vectorMask"));
    desc11.putReference(cTID("At  "), ref9);
    var ref10 = new ActionReference();
    ref10.putEnumerated(cTID("Path"), cTID("Ordn"), cTID("Trgt"));
    desc11.putReference(cTID("Usng"), ref10);
    executeAction(cTID("Mk  "), desc11, DialogModes.NO );
}
 
 
// Make a layer active by its action manager index
function MakeActiveByIndex(zIndex, zVisible)
{
    var desc = new ActionDescriptor();
    var ref = new ActionReference();
    ref.putIndex(cTID("Lyr "), zIndex)
    desc.putReference(cTID( "null"), ref );
    desc.putBoolean(cTID( "MkVs"), zVisible );
    executeAction(cTID( "slct"), desc, DialogModes.NO );
}
 
 
// Returns the AM index of the selected layers
function GetSelectedLayersIdx()
{
    var selectedLayers = new Array;
    var ref = new ActionReference();
    ref.putEnumerated(cTID('Dcmn'), cTID('Ordn'), cTID('Trgt') );
    var desc = executeActionGet(ref);
 
    if (desc.hasKey(sTID('targetLayers')))
    {
        desc = desc.getList(sTID('targetLayers'));
        var c = desc.count 
        var selectedLayers = new Array();
        for(var i = 0; i < c; ++i)
        {
            selectedLayers.push(desc.getReference(i).getIndex());
        }
    }
    else
    {
        var ref = new ActionReference(); 
        ref.putProperty(cTID('Prpr'), cTID('ItmI')); 
        ref.putEnumerated(cTID('Lyr '), cTID('Ordn'), cTID('Trgt'));
        selectedLayers.push(executeActionGet(ref).getInteger(cTID('ItmI')));
    }
 
    return selectedLayers;
}

When multiple layers are selected, it would make sense to re-select the same layers before exiting the script.

I'm not sure why this keeps shifting the selection by one index - but here's the general idea:

    // Select layers by their action manager indices
    function SelectByIndices(indices)
    {
        var ref = new ActionReference();
        var c = indices.length;
        for(var i = 0; i < c; ++i)
        {
            ref.putIdentifier(cTID('Lyr '), indices[i]);
        }
        var desc = new ActionDescriptor();
        desc.putReference(cTID('null'), ref);
        desc.putBoolean(cTID('MkVs'), false);
        executeAction(cTID('slct'), desc, DialogModes.NO);
   }