Add repeat fit mode to image decorator

[viseztrance]

I needed the ability to repeat a texture, and stumbled onto this issue.

We could also add an image-fit: repeat property value to the image decorator, I'd happily take a PR for that.

The caveat is that this won't work using spritesheets, though I imagine you can still use atlases for repeating on a single axis, provided there are no gaps at the edges for that specific direction.

I haven't seen any regression anywhere by switching to GL_REPEAT but please double check.

[mikke89]

Very good! Thanks for the PR.

I think it would be helpful to add a warning and stop it from making the decorator when using a sprite together with the repeat modes. Could you implement that?

Perhaps we could name the new image something a bit more descriptive, e.g. alien_small.tga?

[viseztrance]

I made the changes. I don't know if there's a better way of checking if we're within a spritesheet or not, but it works.

As long as the it fills the entire texture, you can still use these in a spritesheet with a single element and no warning will appear. So you can still have control over the size of the texture by using the resolution (magnification) field.

[mikke89]

Looks great! Thanks again for the pull request :)

If you want to, it would be helpful if you could add this feature to the documentation: https://mikke89.github.io/RmlUiDoc/pages/rcss/decorators/image.html