sokol_imgui.h: Automatically re-build sokol-gfx resources when Dear ImGui font data has changed.

[elloramir]

Every time you invoke the io->AddFontXXX functions, imgui invalidates the default atlas texture, as it rebuilds the texture packer and needs to reload the new atlas on the GPU.

[floooh]

Hmm... that change would leak textures and samplers because they wouldn't be destroyed anywhere.

I think the intention is to call the newly exposed functions simgui_create_fonts_texture() and simgui_destroy_fonts_texture() functions around the ImGui AddTexture...() calls, e.g.

    simgui_destroy_fonts_texture();
    // ...
    io.Fonts->AddFontFromMemoryTTF(dump_font, sizeof(dump_font), 16.0f, &fontCfg)
    simgui_create_fonts_texture(...);

...apart from that, it would probably be a good idea though if simgui_create_fonts_texture() either destroys the previous texture and samplers, or at least asserts that there currently is no sampler and texture.

I think I'll add the assert, otherwise it's to easy to accidentially leak textures.

@Dvad do you have an opinion on this PR?

[floooh]

I have added a couple of assert to protect from textures leaking in when simgui_create_fonts_texture() is called when the texture already exists: dd00e4d

...I'm tending towards requiring the user to call those functions explicitly around AddFontXXX() instead of automatically in the simgui_new_frame() though, but I'm open for discussion ;)

[elloramir]

Oh, it did not come to mind that kind of leak 😅.
I think the automatic way is more aligned with other official implementations present in the DearImgui project, but calling it explicitly is also a fair choice. I do prefer the implicit one because the way DearImgui presents the API suggests that the implementation might know how to handle these cases, but any choice for me sounds totally okay.

[Dvad]

@Dvad do you have an opinion on this PR?

I think this PR is a good idea!

[floooh]

I think this PR is a good idea!

Ok noted :) Then we should come up with a solution that works both implicitly during simgui_new_frame() (how this PR implements it), or by manually calling the simgui_create/destroy_fonts_texture()

@elloramir: I'm going to add a couple of minor change requests

[elloramir]

done!

[floooh]

Looks good, thanks! I'll try to do a bit of testing and the merge by tomorrow evening.

[floooh]

Ok merged! I tested with imgui-highdpi-sapp by removing the explicit call to simgui_create_fonts_texture() and it works as expected. I also added a changelog item.

Thanks for the PR!