Thank you so much Lorfean for the kind words. I'm happy you enjoy vanilla BG. I've played BGT and tried BGEE, and finally made this mod coming to the conclusion that nothing can beat the vanilla experience.
I am not quite sure how pb1866 found the offset values in BG1. I've tried opening the .exe file in a hex editor, and it looks nearly impossible to locate anything. I'm sure there are people that might be able to help, but I don't think it'd be an easy task. I wish I can point you in the right direction, but I can't, if I knew a bit more I would have tried to find them myself. The best suggestion I can offer is if you know somebody who has worked on a trainer or hack for an older game to ask them.
The reason I chose this resolution is two fold. First I tried how the gameplay screen looks in a few 16:9 resolutions. My monitor is 2560x1440, so I tried a few between my max resolution and 800x600. I came to the conclusion that since the visible radius around the characters is only so big, there is not much point to try to zoom out the view too much beyond that. It's just a dark screen when you do. Too close and everything looks too pixelated and you have to move the view around too much, which is also not ideal. The second consideration was I wanted to pick a resolution that is standard. When I played BGT I played at 1366x768, but that's not exactly 16:9. Anything around that to me looked good, so I tried the standard 1280x720, and as soon as I tried it things just looked perfect, with enough view, and still preventing pixelation. So the limitation mostly has to do with the graphics and the format of the game itself, not so much with our monitors anymore. You can test a few resolutions with BG2 and the widescreen mod. If you are still convinced you want to try something else, here is what I used, and how:
- Near Infinity to import/export the .mos files into .gif files that I then changed in Photoshop. I don't remember if it was .gif or .png, but it has to be lossless. This is also where I changed the values of the placement of the interface elements in the .chu files.
- The values that you have to change in both x and y direction are many, but usually they had to be increased by the same number, so in order to automate the process, I used AutoHotKey. I made a few scripts that copy, then increase some value, and then paste it at a certain mouse pointer location.
- The .gif or .png I had to edit into Photoshop. They are all the different user interface elements that had to have different dimensions. In all cases they had to be made bigger, so you have to take some part of the graphic from somewhere else to extend it. In some cases I took parts of some other image that I found used in the game somewhere else in order not to change the theme of the graphics. To make everything look seamless it takes some patience in Photoshop. In the end things seemed to look pretty good, so after I finished with BG1 I looked at the files generated from the widescreen mod in BG2 and found some artifacts that I decided to correct, and upload in a BG2 version of the mod.
- The custom fonts that I made I had to also edit in Photoshop. First I used the bam generator, and then exported each letter into a separate .gif file with Near Infinity that I cropped in Photoshop. I used recorded Actions in Photoshop to automate the process. Then reconstructed the font back in Near Infinity. I did a similar thing with the clock in BG2, which is an animation made of different images that I slightly edited in Photoshop.
All in all, it took quite some time. Zed Nocear (the creator of TWM) probably used a better method, as in his mod he allows couple of different resolutions. You might want to contact him as well before you try this.