[GUI] SFML backend for ImGui

[Verra]

The example at the top of the page is outdated as well as the instructions for how to set it up. The repository shows that you've split a lot of stuff into seperate files. I also noticed in imgui-rendering-SFML there is a reference to ImImpl_fontTex which doesn't exist anywhere as far as I can tell. It'd be nice to see you include an example in the repository.

[Aster]

I've updated the repository and main post.
The usage has slightly changed, but everything works now.

Sorry for my absence and lack of response, thanks for your patience.

[bock]

> What isn't implemented:
>  Stencils. If the horizontal ImGui window size is too small, you'll still see transparent rectangles, as SFML does not provide support for clipping, and I haven't gotten around to working on a solution.

Note that you want scissoring and not stencil. Scissoring is a cheaper operation than stenciling which rely on a buffer.

- For some reason it's not supported in sf::RenderStates. It's a rather rarely used feature but it's also trivial to implement so perhaps it could be added to SFML.

- Otherwise you can do the scissoring in a shader (which is possibly what a graphics card driver would do for do when enabling scissoring anyway). Pass the float4 cliprect as a uniform to your shader and do a clipping in the pixel shader/

( - Or last resort you might be able to use sf::View::setViewport() as a workaround for the clipping, but I don't know how SFML behave in term of performance when changing the viewport. but adding it to the shader would be more sane. )