How to lock canvas resizing

The following script provides an interactive square crop, based on the selection size entered in pixels.

Only two user interactions are required:

1) Entering a desired square selection size in pixel values (an integer)

2) Don't resize the transform selection edges, just move the entire selection to where the crop should be performed, then press the enter/return key or press the "tick" in the options bar for "Commit transform", then the script will continue to automatically crop the image.

/*
Interactive square canvas crop.jsx
Stephen Marsh, v1.0 - 5th January 2022
https://community.adobe.com/t5/photoshop-ecosystem-discussions/how-to-lock-canvas-resizing/m-p/12634283
*/

#target photoshop

function main() {

    var savedRuler = app.preferences.rulerUnits;

    app.preferences.rulerUnits = Units.PIXELS;

    var inputSelection;
    while (isNaN(inputSelection = prompt("Enter a square selection size (pixels):", "")));

    if (inputSelection === null) {
        alert('Script cancelled!');
        return;
    }

    while (inputSelection.length === 0) {
        inputSelection = prompt("Blank value not accepted! Enter a square selection size (pixels):", "");
    }

    var finalSelection = parseInt(inputSelection);

    app.activeDocument.selection.select( [ [0,0], [0,finalSelection], [finalSelection,finalSelection], [finalSelection,0] ] );

    centerSelectionHack();

    interactiveTransformSelection();

    cropToSelection();

    app.preferences.rulerUnits = savedRuler;

}

app.activeDocument.suspendHistory("Square canvas crop", "main()");


// Functions

function interactiveTransformSelection() {
    var idtransform = stringIDToTypeID("transform");
    var desc2058 = new ActionDescriptor();
    var idnull = stringIDToTypeID("null");
    var ref311 = new ActionReference();
    var idchannel = stringIDToTypeID("channel");
    var idselection = stringIDToTypeID("selection");
    ref311.putProperty(idchannel, idselection);
    desc2058.putReference(idnull, ref311);
    var idfreeTransformCenterState = stringIDToTypeID("freeTransformCenterState");
    var idquadCenterState = stringIDToTypeID("quadCenterState");
    var idQCSAverage = stringIDToTypeID("QCSAverage");
    desc2058.putEnumerated(idfreeTransformCenterState, idquadCenterState, idQCSAverage);
    var idoffset = stringIDToTypeID("offset");
    var desc2059 = new ActionDescriptor();
    var idhorizontal = stringIDToTypeID("horizontal");
    var idpixelsUnit = stringIDToTypeID("pixelsUnit");
    desc2059.putUnitDouble(idhorizontal, idpixelsUnit, 0);
    var idvertical = stringIDToTypeID("vertical");
    var idpixelsUnit = stringIDToTypeID("pixelsUnit");
    desc2059.putUnitDouble(idvertical, idpixelsUnit, 0);
    var idoffset = stringIDToTypeID("offset");
    desc2058.putObject(idoffset, idoffset, desc2059);
    var idinterfaceIconFrameDimmed = stringIDToTypeID("interfaceIconFrameDimmed");
    var idinterpolationType = stringIDToTypeID("interpolationType");
    var idnearestNeighbor = stringIDToTypeID("nearestNeighbor");
    desc2058.putEnumerated(idinterfaceIconFrameDimmed, idinterpolationType, idnearestNeighbor);
    executeAction(idtransform, desc2058, DialogModes.ALL);
}

function centerSelectionHack() {
    
    /* It gets the job done, but surely there is a more elegant way...
    I couldn't get selection.translate() to work as intended */

    // Create solid colour layer from active selection
    var idmake = stringIDToTypeID("make");
    var desc2180 = new ActionDescriptor();
    var idnull = stringIDToTypeID("null");
    var ref365 = new ActionReference();
    var idcontentLayer = stringIDToTypeID("contentLayer");
    ref365.putClass(idcontentLayer);
    desc2180.putReference(idnull, ref365);
    var idusing = stringIDToTypeID("using");
    var desc2181 = new ActionDescriptor();
    var idtype = stringIDToTypeID("type");
    var desc2182 = new ActionDescriptor();
    var idcolor = stringIDToTypeID("color");
    var desc2183 = new ActionDescriptor();
    var idred = stringIDToTypeID("red");
    desc2183.putDouble(idred, 255.000000);
    var idgrain = stringIDToTypeID("grain");
    desc2183.putDouble(idgrain, 255.000000);
    var idblue = stringIDToTypeID("blue");
    desc2183.putDouble(idblue, 255.000000);
    var idRGBColor = stringIDToTypeID("RGBColor");
    desc2182.putObject(idcolor, idRGBColor, desc2183);
    var idsolidColorLayer = stringIDToTypeID("solidColorLayer");
    desc2181.putObject(idtype, idsolidColorLayer, desc2182);
    var idcontentLayer = stringIDToTypeID("contentLayer");
    desc2180.putObject(idusing, idcontentLayer, desc2181);
    executeAction(idmake, desc2180, DialogModes.NO);
    // Fill opacity to 0%
    app.activeDocument.activeLayer.fillOpacity = 0;
    // Centre active layer on canvas
    app.activeDocument.activeLayer.translate(app.activeDocument.width / 2 - (app.activeDocument.activeLayer.bounds[0] + app.activeDocument.activeLayer.bounds[2]) / 2,
    app.activeDocument.height / 2 - (app.activeDocument.activeLayer.bounds[1] + app.activeDocument.activeLayer.bounds[3]) / 2);
    // Set selection to mask channel
    var idset = stringIDToTypeID("set");
    var desc2554 = new ActionDescriptor();
    var idnull = stringIDToTypeID("null");
    var ref429 = new ActionReference();
    var idchannel = stringIDToTypeID("channel");
    var idselection = stringIDToTypeID("selection");
    ref429.putProperty(idchannel, idselection);
    desc2554.putReference(idnull, ref429);
    var idto = stringIDToTypeID("to");
    var ref430 = new ActionReference();
    var idchannel = stringIDToTypeID("channel");
    var idchannel = stringIDToTypeID("channel");
    var idmask = stringIDToTypeID("mask");
    ref430.putEnumerated(idchannel, idchannel, idmask);
    desc2554.putReference(idto, ref430);
    executeAction(idset, desc2554, DialogModes.NO);
    // Remove temp solid colour layer
    app.activeDocument.activeLayer.remove();
}

function cropToSelection() {
    var idcrop = stringIDToTypeID("crop");
    executeAction(idcrop, undefined, DialogModes.NO);
    // Deselect
    app.activeDocument.selection.deselect();
}

1. Copy the code text to the clipboard
2. Open a new blank file in a plain-text editor (not word-processor)
3. Paste the code in
4. Save the text file as .txt
5. Rename the text .txt to .jsx
6. Install or browse to the .jsx file to run

If these simple instructions are too abbreviated, you may need to read on...

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html

Here is a script to resize the canvas height using the width value from middle centre:

/*
Square canvas resize.jsx
Stephen Marsh, v1.0 - 5th January 2022
https://community.adobe.com/t5/photoshop-ecosystem-discussions/how-to-lock-canvas-resizing/m-p/12634283
*/

#target photoshop

function main() {

    var savedRuler = app.preferences.rulerUnits;
    app.preferences.rulerUnits = Units.PIXELS;
    var doc = app.activeDocument;

    while (isNaN(squareCanvasSize = prompt("Square canvas size from middle center (px):", "")));

    if (squareCanvasSize === null) {
        //alert('Script cancelled!');
        return
    }

    while (squareCanvasSize.length === 0) {
        squareCanvasSize = prompt("Blank value not accepted! Square canvas size from middle center (px):", "");
    }

    var squareInteger = parseInt(squareCanvasSize);

    doc.resizeCanvas(squareInteger, squareInteger, AnchorPosition.MIDDLECENTER);
    app.preferences.rulerUnits = savedRuler;
}

app.activeDocument.suspendHistory("Square canvas resize", "main()");

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html

You can post a feature request in below link 

https://www.adobe.com/products/wishform.html

Hi Mike!

I'm not aware of a function in that window pane to make both inputs the same when you type in one. By chance, are you cropping the images from the same anchor point and the same size each time? If so you could turn that step into an recorded action and make it a one button click rather than opening up the menu each time. There may be a way to do a similar option through the crop tool and actions as well.

That is what the link icon does in Image > Image Size. 

Canvas size crops if a lesser value is entered, the width and height fields are independent by design.

This could be scripted if you really wish to crop content from 800px to 700px square rather than resize.