My old background was 1024x768; my new background is 1366x768 (this is the 16:9 ratio screen of the old 1024 5:4 size).
The transparent map that the .bmp (or some other format) I'm saving in is not the screen size; instead, it's edges are defined by the limits of the walkbehind/whatever
So all exported resources come out a different size, and also, a different proportion... :/ (position is for my purposes, not important).
The purpose of the export operation is to print the actual bitmap as it is stored in the room you
export from. It is only wrong if the result does not match the room
it is exported from. In other words, for the test you should be able to import the same mask back into the
same room and keep the original looks.
Then, if I got it correctly, you are exporting masks from the rooms which had one resolution and then trying to import them into the new rooms that have different resolution (with also different aspect ratio). Is it so, or something else?
If that's the case, correcting proportions is not what the export operation should do, but rather import operation. Because at the time of export the program has no idea what are you going to do with these images (and should not -- that's not its concern to know that).
BTW, you keep saying "screen size", do you actually mean game resolution? I was pretty confused by this earlier.
So all exported resources come out a different size, and also, a different proportion... :/ (position is for my purposes, not important).
When I open them in paint.net, and alter canvas size to be the dimensions of the screen, the eg. hotspot ends up being a different position on-screen (and different proportions).
I don't understand how the proportion problem could have happened; I only increased canvas size, not changed image size.
If you have imported the masks from the 1024x768 room into 1366x768 room without modifying the image size, then it is only logical that proportions do not match the proportions of the background picture. You'd probably need to change mask size, stretching the proportions. But, that really depends on how much your backgrounds have changed. If they are like 1:1 only with different proportions, then stretching original mask should work; maybe will require a bit of adjustment by hand to correct loose pixels.
Could you upload some room (*.crm file) you do export from for me to test it out? Actually - both rooms, a pair of old and new ones.