Photoshop script: save image in pieces

For my personal project, I started with a map of the world in photoshop. This map was 16384x8192. I exported the map at about half the scale to use in unreal. When I wanted to build the project on my phone, I bumped into an issue with it. My phone could only load images that were maximum 2048x2048px.

To export the map at 2048x2048 would lose too much of the detail. What I did instead, I split up the map (and globe to put the map on) in eight pieces. Now I do iterate on the map quite a lot and it would be a hassle to actually keep seperate photshop files for every piece of the map.

Instead, I wrote a script that will split the map for me, and save the pieces to the correct location. Here is how I did it:

function savePNG(saveFile) {  //1
    var saveOptions = new PNGSaveOptions();  
    saveOptions.compression = 9;  // (level of compression 0 .. 9       0 - without compression)
    saveOptions.interlaced = false;
    app.activeDocument.saveAs(File(saveFile), saveOptions, true, Extension.LOWERCASE);  

var numberOfPieciesHorizontal = 4;
var numberOfPiecesVertical = 2;

var docwidth = app.activeDocument.width; //2
var docheight = app.activeDocument.height; //2
var sizeHorizontal = docwidth / numberOfPieciesHorizontal; //3
var sizeVertical = docheight / numberOfPiecesVertical; //3

for (var i = 0; i < numberOfPieciesHorizontal; ++i) { //4
  for (var j = 0; j < numberOfPiecesVertical; ++j) { //5
    // array is left, top, right, bottom
        Array (
            Array(i * sizeHorizontal, j * sizeVertical),
            Array(i * sizeHorizontal, j * sizeVertical + sizeVertical),
            Array(i * sizeHorizontal + sizeHorizontal, j * sizeVertical + sizeVertical),
            Array(i* sizeHorizontal + sizeHorizontal, j * sizeVertical)
        ), SelectionType.REPLACE, 0, false); //6
    // crop
    var savedStateCrop = app.activeDocument.activeHistoryState; //7
    executeAction(charIDToTypeID('Crop'), new ActionDescriptor(), DialogModes.NO); //8

    // save
    savePNG("C:/map" + i + "_" + j + ".png"); //9
    app.activeDocument.activeHistoryState = savedStateCrop; //10

To start, we get the current height and width of the document (2). Depending on how many pieces, we calculate the width and height of each piece (3). After that, we loop over all the horizontal pieces we will create (4), and immediatly go over the vertical ones (5). Now that we know which piece we are currently trying to export, we create a selection of that specific piece (6). We remember the current state of the document (7), crop the piece (8) and save it to the correct location (9). We save using the function we have used in other scripts before (1). Last but not least we restore the state to before the crop happend and do (6 - 10) over again until all pieces are exported.