Follow ImGui binding examples a bit more closely

[eliasdaler]

So, currently we have this: ImGui::SFML::Render(target) which calls ImGui::Render internally, while in other ImGui binding examples it should be more like this:

ImGui::Render(); // prepare render data
ImGui::SFML::Render(target);

Note that this will be a breaking change, so I'll release v3.0 if we agree on this.
This is needed to save future users from just calling ImGui::Render instead of ImGui::SFML::Render and being confused.

There's another good thing: if ImGui will have nothing to draw, resetGLStates won't be called on RenderTarget, while now it's called every time.

So, thoughts?

[eliasdaler]

Also, following other conventions, we should do

ImGui::SFML::Update(...);
ImGui::NewFrame();

instead of calling ImGui::NewFrame inside "Update". Yeah, it'll not be as automatic as now, but it's explicit.

[ocornut]

There's another good thing: if ImGui will have nothing to draw, resetGLStates won't be called on RenderTarget, while now it's called every time.

You can make this change right away, that's orthogonal to changing the api. Just move the resetGLStates in the drawing function.

ImGui::SFML::Update(...);

Calling this NewFrame() would be consistent with other back-ends.

[Rosme]

I see nothing wrong with that. A major version can (and is somewhat supposed) to have breaking changes. Having a binding that follow the most common practice is for the best. I definitely vote for making this breaking change.

[pinam45]

I think it is worth it to make a breaking change to be more consistent with the other back-ends.