Randomize textures from variants.

[will-ca]

Pretend the letters are slightly different textures:

Adds ImageGetter.getRandomImageVariant(baseFileName: String, seed: Int? = null): String, which randomly chooses an image variant from all available, following the pattern: {"baseName", "baseName-A", "baseName-B", …, "baseName-Z"}.

Short-circuits quickly and should add only minimal overhead if there are no variants available.

Returned result is a new image path String, so it can further be used in other image-getting functions, like getLayeredImageColored. (Note the nation-coloured letters above.) (#3231 is also partly inspiration for this.)

Used in all invocations of .getImage in TileGroup, and only in TileGroup.

Hashcode of tile position Vector2 is used as seed for terrain-y images to make sure the map doesn't change during gameplay.

Added a var randomnessSeed: Int to MapUnit that is set on construction and preserved on .clone() for the same purpose. Currently @Transient, deciding a visual effect isn't worth a save file field. I could see myself getting attached to a special Frigate and getting sad when it's changed on a save reload or something, though.

I actually skimmed through all 118 invocations of .getImage(), and TileGroup was really the only place where it made sense to use random variants. It's just as well to have such a clearly defined scope.

Test files in above screenshot are available as example mod: https://github.com/will-ca/Unciv-Tileset-Variants-Example. If you fork it and tag the fork, I'll delete my repo to keep all the examples consolidated.

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Why? Abstract reasons: Perfectly repeating patterns are very unnatural and jarring in textures. Randomly mixing just two or three variants is often enough to break up large-scale patterns a lot. Likewise clones don't exist, so slightly different units are always a really cool touch IMO.

Direct reason/Example: I was experimenting with breaking up coastlines/biomes with fractal and blended boundaries (#5835). Some results looked fairly natural. But repeating textures and patterns are still a big immersion breaker— What are the odds of there being fifty of the exact same, very distinctive mountain?

FantasyHex does a really good job hiding the repetition where possible and working it into the visual style otherwise. That gets harder with more realistic tilesets. I notice a lot more repetition with 5Hex. Contemplated CGI-generating a "photorealistic" tileset— Repetition would be a nightmare unless variants are possible.

[ravignir]

It does not solve the issue for 5Hex without introducing new problems, that is forest/jungle tiles. When these tiles are improved, some trees stay on the same position (for example, compare lumber mill tiles with forest tiles, the trees would be misplaced if the game were to choose completely random texture from the available list).

[will-ca]

…So, there's an Ancient ruins.png and an Ancient ruins2.png, both of which get used… Which means that somewhere, in some way, some kind of functionality something like this is already in the game…

4fd869d

0c06237

I did search both the code and wiki for keywords… Evidently not thoroughly enough.

Well, compare and contrast, I guess. The code looks basically the same, just moved and used in more places. …IMO Letters would be a clearer convention since unit colours already use numbers, and I guess only one texture would have to be renamed…

[will-ca]

@ravignir I'm not sure I understand. This PR doesn't change how images are retrieved for improvements, though. It just adds more places where different variants can be provided by the tileset.

[yairm210]

We already have this - see TileGroup:254