How to move the ends of skewed lines to the bleed bounds

Question

Hi all,
I am developing a script that trims page items to the bleed. To achieve this I collect all page items (except text frames) located partially on the pasteboard, create a temporary mask and 'crop' them with Pathfinder's Subtract feature. However this approach doesn't work with graphic lines so I am attempting to move ends of lines to the bounds of bleed box. (I'm assuming that these are simple straight lines consisting of two end points.)
I've figured out how to deal with orthogonal lines -- it's quite easy:
if (theItem.constructor.name == "GraphicLine" && theItem.paths.length === 1) {
     path = theItem.paths[0];
     if (path.pathPoints.length === 2) {
          ep = path.entirePath;
          w = ep[1][0]-ep[0][0];
          h = ep[1][1]-ep[0 ][1];
          if (w > h) {
               newEp = [ [ spreadWithBleedBounds[1], ep[0][1] ], [ spreadWithBleedBounds[3], ep[1][1] ] ];
               path.entirePath = newEp;
          else if (h > w) {
               newEp = [ [ ep[0][0], spreadWithBleedBounds[0] ], [ ep[1][0], spreadWithBleedBounds[2] ] ];
               path.entirePath = newEp;
This moves A1 to A2, B1 to B2, C1 to C2, D1 to D2.
But how to deal with skewed lines? How to calculate coordinates for points E2 and F2? Is there some magic formula? Or can anybody point me to the right direction: e.g. some book to read?
I guess this has something to do with geometry/trigonometry, but I haven't studied this stuff at school. (I graduated an art school -- studied to draw nude models instead.)
If someone is going to answer to my question, please do it on elementary level since I am a total noob in this.
Below is the whole script:
if (Number(String(app.version).split(".")[0]) == 7) ErrorExit("This script can't work with InDesign CS5 so far.", true);
var doc = app.activeDocument;
var spreadBounds, spreadWithBleedBounds, gPartiallyOutOfSpreadItems;
var ungroupErrors = 0;
var originalHorUnits =  doc.viewPreferences.horizontalMeasurementUnits;
var originalVerUnits =  doc.viewPreferences.verticalMeasurementUnits;
doc.viewPreferences.horizontalMeasurementUnits = doc.viewPreferences.verticalMeasurementUnits = MeasurementUnits.INCHES;
doc.viewPreferences.rulerOrigin = RulerOrigin.spreadOrigin;
doc.zeroPoint = [0, 0];
if (doc.layers.itemByName("Temporary Layer") == null ) {
     var tempLayer = doc.layers.add({name:"Temporary Layer"});
else {
     var tempLayer = doc.layers.itemByName("Temporary Layer");
UngroupAllGroups(doc.groups);
DeleteObjectsOnPasteboard();
ProcessSpreads(doc.spreads);
ProcessSpreads(doc.masterSpreads);
tempLayer.remove();
doc.viewPreferences.horizontalMeasurementUnits = originalHorUnits;
doc.viewPreferences.verticalMeasurementUnits = originalVerUnits;
var msg = (ungroupErrors > 0) ? " Failed to ungroup " + ungroupErrors + " groups since they are too large." : "";
alert("Done." + msg, "Trim Pages Script");
//================================== FUNCTONS ===========================================
function ProcessSpreads(spreads) {
     var spread, path, ep, w, h;
     for (var s = 0; s < spreads.length; s++) {
          spread = spreads[s];
          spreadBounds = GetSpreadBound(spread, false);
          spreadWithBleedBounds = GetSpreadBound(spread, true);
          gPartiallyOutOfSpreadItems = GetPartiallyOutOfSpreadItems(spread);
          var theItem, theMask, newItem;
          for (var i = gPartiallyOutOfSpreadItems.length-1; i >= 0; i--) {
               theItem = gPartiallyOutOfSpreadItems[i];
               if (theItem.constructor.name == "GraphicLine" && theItem.paths.length === 1) {
                    path = theItem.paths[0];
                    if (path.pathPoints.length === 2) {
                         ep = path.entirePath;
                         w = ep[1][0]-ep[0][0];
                         h = ep[1][1]-ep[0 ][1];
                         if (w > h) {
                              newEp = [ [ spreadWithBleedBounds[1], ep[0][1] ], [ spreadWithBleedBounds[3], ep[1][1] ] ];
                              path.entirePath = newEp;
                         else if (h > w) {
                              newEp = [ [ ep[0][0], spreadWithBleedBounds[0] ], [ ep[1][0], spreadWithBleedBounds[2] ] ];
                              path.entirePath = newEp;
               else {
                    theMask = CreateMask(spread);
                    try {
                         newItem = theMask.subtractPath(theItem);
                    catch (err) {
                         $.writeln("2 - " + err);
                         theMask.remove();
function IsPartiallyOutOfSpread(pageItem) {
     var result = false;
     if (pageItem.constructor.name == "TextFrame" ||
          pageItem.constructor.name == "Group" ||
          pageItem.parent.constructor.name == "Group")
          return result;
     var visBounds = pageItem.visibleBounds;
     if (visBounds[0] < spreadBounds[0] && visBounds[2] > spreadBounds[0] ||
          visBounds[1] < spreadBounds[1] && visBounds[3] > spreadBounds[1] ||
          visBounds[2] > spreadBounds[2] && visBounds[0] < spreadBounds[2] ||
          visBounds[3] > spreadBounds[3] && visBounds[1] < spreadBounds[3]  ) {
          result = true;
     return result;
function GetSpreadBound(spread, bleed) { // including bleed -boolean
     if (bleed == undefined) bleed = false;
     with (doc.documentPreferences) {
          var topBleed = documentBleedTopOffset
          var leftBleed = documentBleedInsideOrLeftOffset;
          var bottomBleed = documentBleedBottomOffset;
          var rightBleed = documentBleedOutsideOrRightOffset;
     var bFirst = spread.pages.item(0).bounds; // bounds of the first page
     var bLast = spread.pages.item(-1).bounds; // bounds of the last page
     return [     ((bleed) ? bFirst[0]-topBleed : bFirst[0]),
                    ((bleed) ? bFirst[1]-leftBleed : bFirst[1]),
                    ((bleed) ? bLast[2]+bottomBleed : bFirst[2]),
                    ((bleed) ? bLast[3]+rightBleed : bLast[3])
function CreateMask(spread) {
     var unitValue = new UnitValue (app.pasteboardPreferences.minimumSpaceAboveAndBelow, "mm");
     var unitValueAsInch = unitValue.as("in");
     var outerRectangleBounds = [spreadWithBleedBounds[0]-unitValueAsInch,
                                                            spreadWithBleedBounds[1]-8.07,
                                                            spreadWithBleedBounds[2]+unitValueAsInch,
                                                            spreadWithBleedBounds[3]+8.07
     var outerRectangle = spread.rectangles.add(tempLayer, undefined, undefined, {geometricBounds:outerRectangleBounds});
     var innerRectangle = spread.rectangles.add(tempLayer, undefined, undefined, {geometricBounds:spreadWithBleedBounds, fillColor:doc.swatches.item("Black"), fillTint:30});
     var mask = outerRectangle.excludeOverlapPath(innerRectangle);
     return mask;
function GetPartiallyOutOfSpreadItems(spread) {
     var allPageItems = spread.allPageItems;
     var partiallyOutOfSpreadItems = [];
     var currentItem;
     for (var i = 0; i < allPageItems.length; i++) {
          currentItem = allPageItems[i];
          if (IsPartiallyOutOfSpread(currentItem)) partiallyOutOfSpreadItems.push(currentItem);
     return partiallyOutOfSpreadItems;
function DeleteObjectsOnPasteboard() {
     var objs = app.documents[0].pageItems.everyItem().getElements();
     while (obj=objs.pop()) {
          try {
               if(obj.parent instanceof Spread || obj.parent instanceof MasterSpread){ obj.remove() }
          catch(err) {
               //$.writeln("2 - " + err);
function ErrorExit(myMessage, myIcon) {
     alert(myMessage, "Trim Pages Script", myIcon);
     exit();
function UngroupAllGroups(groups) {
     for (var i = groups.length-1; i >= 0; i--) {
          var gr = groups[i];
          if (gr.groups.length > 0) {
               var subGroups = [];
               for (var j = gr.groups.length-1; j >= 0; j--) {
                    subGroups.push(gr.groups[j].id);
               try {
                    gr.ungroup();
               catch(err) {
                    //$.writeln("1 - " + err);
                    ungroupErrors++;
               for (var k = subGroups.length-1; k >= 0; k--) {
                    try {
                         doc.groups.itemByID(subGroups[k]).ungroup();
                    catch(err) {
                         //$.writeln("2 - " + err);
                         ungroupErrors++;
          else {
               try {
                    gr.ungroup();
               catch(err) {
                    //$.writeln("1 - " + err);
                    ungroupErrors++;
Thanks in advance.
Kasyan

Answer 1

Hi Kasyan!
I didn't try to integrate this into your script, so you might have to adjust it a little bit. The trick is to define a function that finds the intersection point of two lines --- and, obviously, you should only call it for the lines that are sure to cross the page border! (Otherwise, it would simply extend *any* line up and over the border.)
I think it would be wise to allow for a tiny error for lines that appear to run "up to" the page edge -- I tested a line for "x <= 0" on a line that appeared to start on 0; the control panel told me so. However, I didn't type that 0 in; I dragged the line to the edge. Apparently, it was *NOT* at precisely "0mm", but something like "0.001mm", because the script simply didn't "see" the line.
My function comes from this page: http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/ and I didn't test what it does to orthogonal lines
(but of course you could add this as an exception), and this is my line-extending script, with a little wrapper to set things up.
The function tests *any* line against *any* other line, so if one crosses the page bounding box, I get the intersection with the bleed box on the side where it crosses the page bbox.
line = app.selection[0];
// pg size in "regular" [y1,x1, y2,x2] format
pagebbox = [0,0, app.activeDocument.documentPreferences.pageHeight,app.activeDocument.documentPreferences.pageWidth ];
bleedDist = 5; //
bleedbbox = [ pagebbox[0] - bleedDist, pagebbox[1] - bleedDist, pagebbox[2] + bleedDist, pagebbox[3] + bleedDist ];
pt1 = line.paths[0].pathPoints[0].anchor;
pt2 = line.paths[0].pathPoints.lastItem().anchor;
// Start point:
if (pt1[0] <= pagebbox[1] || pt1[0] >= pagebbox[3] ||
pt1[1] <= pagebbox[0] || pt1[1] >= pagebbox[2])
if (pt1[0] <= pagebbox[1])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[0]], [bleedbbox[1], bleedbbox[2] ] ] );
if (pt1[0] >= pagebbox[3])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[3], bleedbbox[0]], [bleedbbox[3], bleedbbox[2] ] ] );
if (pt1[1] <= pagebbox[0])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[0]], [bleedbbox[3], bleedbbox[0] ] ] );
if (pt1[1] >= pagebbox[2])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[2]], [bleedbbox[3], bleedbbox[2] ] ] );
line.paths[0].pathPoints[0].anchor = intersectPt;
// End point:
if (pt2[0] <= pagebbox[1] || pt2[0] >= pagebbox[3] ||
pt2[1] <= pagebbox[0] || pt2[1] >= pagebbox[2])
if (pt2[0] <= pagebbox[1])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[0]], [bleedbbox[1], bleedbbox[2] ] ] );
if (pt2[0] >= pagebbox[3])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[3], bleedbbox[0]], [bleedbbox[3], bleedbbox[2] ] ] );
if (pt2[1] <= pagebbox[0])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[0]], [bleedbbox[3], bleedbbox[0] ] ] );
if (pt2[1] >= pagebbox[2])
  intersectPt = IntersectionPt ( [pt1, pt2], [ [ bleedbbox[1], bleedbbox[2]], [bleedbbox[3], bleedbbox[2] ] ] );
line.paths[0].pathPoints.lastItem().anchor = intersectPt;
function IntersectionPt (ln1, ln2)
var ua;
var x1 = ln1[0][0], x2 = ln1[1][0], x3 = ln2[0][0], x4 = ln2[1][0];
var y1 = ln1[0][1], y2 = ln1[1][1], y3 = ln2[0][1], y4 = ln2[1][1];
ua = ((x4 - x3)*(y1 - y3) - (y4 - y3)*(x1 - x3))/((y4 - y3)*(x2 - x1) - (x4 - x3)*(y2 - y1));
return [ x1 + ua*(x2-x1), y1 + ua*(y2-y1) ];