Can't subtract one var from another in js

[davidgordon]

I have a script which I'm modifying, it resizes an image, adds a black border then adds white borders to replicate the look of a 10x8 inch print.

This line is giving me trouble and I can't seee why!

     docRef.resizeCanvas ( docRef.width + (portraitPrintW - docRef.width), docRef.height, AnchorPosition.MIDDLECENTER);

I've already set

     var docRef = activeDocument; var portraitPrintW = 576;

The script has resized the image to 72ppi and to fit 676ppi long side. Its then added a 2px black border all around. At this point the image should be 454px wide. I want to add a white border to the left and right to give a total width of 576. So the above line should be 454 + (576-454) which is 454+126=576 therefore I'm doing a Resize Canvas 576, 680 (the current height) middle centre (with a white background - set as a var earlier).

What actually happens is the canvas is resized to be 334 wide (height is correct) - how did that happen?

Replacing a couple or vars with real number allows the script to work as expected

     docRef.resizeCanvas ( (docRef.width + (576 - 450) ), docRef.height, AnchorPosition.MIDDLECENTER);

and

     docRef.resizeCanvas ( (docRef.width + (portraitPrintW - 450) ), docRef.height, AnchorPosition.MIDDLECENTER);

also works as expected

Maybe I can't use the same var twice in a calculation, no because even this doesn't work

     var currentWidth = docRef.width;

     docRef.resizeCanvas ( (docRef.width + (portraitPrintW - currentWidth) ), docRef.height, AnchorPosition.MIDDLECENTER);

So why does ( docRef.width + (portraitPrintW - docRef.width) return 334, not 676?

Thanks for any clues.

[davidgordon]

There's a typo in my maths,  454+126=576 should read  454+122=576. So that's not the problem!

[c.pfaffenbichler]

Huh?

docRef.width + (portraitPrintW - docRef.width) = portraitPrintW

So what are you trying to achieve?

[davidgordon]

I'm trying to take an image which is 454px wide and use resize canvas to make it 576px wide. So that calculation makes sence to me, but if there's a better way!

Er, or are you saying why don't I just use portraitPrintW as that will always be the answer? That might be a better way but it still doesn't explain why the calclation returns 334, not (as you say, portraitPrintW) 576.

Thanks, its a helpful answer as its making me look from a different angle.

[Michael_L_Hale]

I think that part of the problem is that you are adding UnitValue objects and Number objects.

One fix would be

var docRef = activeDocument; var portraitPrintW = New UnitValue(576,'px');

Another way would to use

docRef.resizeCanvas ( new UnitValue(docRef.width.as('px') + (576 - 450) ),'px'), docRef.height, AnchorPosition.MIDDLECENTER);

Or set your ruler to pixels and just use Numbers.

[davidgordon]

I think I'm already setting the ruler units to pixels, here I'm saving them to a var in order to reset them after the scrip is finished.

        var strtRulerUnits = preferences.rulerUnits;

        var strtTypeUnits = preferences.typeUnits;

        preferences.rulerUnits = Units.PIXELS;

        preferences.typeUnits = TypeUnits.PIXELS;

and that appears to be working. The calculation returns the expected answer when using numeric values in place of some vars, as I say:

     docRef.resizeCanvas ( docRef.width + (portraitPrintW - docRef.width), docRef.height, AnchorPosition.MIDDLECENTER);

returns a different answer from

      docRef.resizeCanvas ( (docRef.width + (576 - 450) ), docRef.height, AnchorPosition.MIDDLECENTER);

even though var portraitPrintW is set to 576 and docRef.width (should) be 450.

Thanks again.

[Chuck Uebele]

When you get values such as docRef.width, it adds the unit values ie: px.  Sometimes it's best to strip out all the unit values and just work with numbers, so use parseFloat() or parseInt().