[engine] Support/favor XCF (instead PNG)

[MetalKing]

B4W uses Lib SDL which support afaics the native ImageFormat of GIMP XCF which support most Features an ImagdFormat can have, RGBA, Layers and Animations. Therefor XCF offers several Advantages. With that Format we enable Designers of ArtWork to contribute their ArtWork in a better editable Format as well as get a single File for a whole AnimationSequence simplifying their Handling. If we write/get a Lib to acces single Layers (e.g. to enable/disable) we can store most Informations inside the Image like "OverLaps"/CrossOvers. Due to reduced Amount of Images the ImageFolders get clearer.
AFAICS it doesn't take alot Work to implement that.
- regardr, MK

*edit* add

[Dugi]

It might be very helpful, multiple layers are extremely useful when making animations. The .xcf files are very large in size, but the creator might change these pictures to .png after that he decides that the edits are done and that it works well together.

[artisticdude]

I'm not by any means an expert on the ins-and-outs of image formats, but I believe XCF is more or less GIMP-specific (with a few exceptions, like Paint.Net and a smattering of GIMP forks). Which means you'd be pretty much forced to use GIMP in order to create/edit those files. The PNG format, on the other hand, is a much more universal format. PNG files can be created/edited by the vast majority of even the most basic image editors.

Speaking as an artist who uses Photoshop primarily, I think this would not be a good idea, because it would scare away potential contributors by forcing them to work with an image format that they may never have heard of before, let alone used before. And even if they weren't scared away by that, now they'd be forced to either convert every XCF image to another format in order to work with it in their image editor of choice (and that conversion process, besides being arduous and annoying, could also introduce other issues, like missing transparency information, compression, artefacts, etc. ). Or they could just give up their favorite image editor and use GIMP, which most non-Gimp users probably won't be willing to do.

There's also the matter of file size (is a layered XCF larger than multiple .png's?). As I said, I've not used XCF much, so I can't comment on that. But it's another important point to consider.

Honestly, I very much doubt that XCF support will be added to Wesnoth any time in the foreseeable future. But if it ever is, I would think that it would be in addition to the PNG format, not in place of it.

[Iris]

Wesnoth doesn’t support reading any image format by itself. Instead, it uses a generic interface provided by the SDL_image library to load the file pointed by whatever path is provided and retrieve the actual pixmap.

SDL_image’s documentation has the following to say about its XCF support:

This format is always changing, and since there's no library supplied by the GIMP project to load XCF, the loader may frequently fail to load much of any image from an XCF file. It's better to load this in GIMP and convert to a better supported image format.

In practice, the latest version in Debian fails to load a trivial XCF produced by the GIMP version 2.6.12 here. Regardless, even if it did have full and reliable support for XCF files, using them for distribution would be a notable waste of space.

As for using XCF or PSD files for storing more complicated art in a more versatile format, we already do that with some stuff in the resources branch as we and individual artists see fit.