Advice on creating a backend not using vertex buffers.

[Convery]

Greetings fellow humans, quick question on backends that I couldn't find in the docs:

Consider a system where there's no viable API for drawing with vertices / triangles. A system where you pass a structure in the form of { DRAW_LINE, x0, y0, x1, y1, colour } to a device and it does the rendering on its own.

Is there any proper customization-point to capture the calls or is the only option to replace ImDrawList or modify AddPolyline() and friends in imgui_draw.cpp?

Somewhat related to #2724 which could probably benefit from the advice.

[thedmd]

There is no customization point where you can capture individual draw commands.

Only way is to do as you suggested and replace AddXXX function implementations.

[ocornut]

I think you'd want to #ifdef out the ImDrawList header and implementation and create your own in another file.

I don't mind supporting this for experiments such as https://github.com/ggerganov/imtui etc. but I'd only do this with an actual implementation lined up. Aka if you have something useful working, I would take the PR to add an official way to ifdef the default implementation out. But I suspect it's going to be more subtle than that. So first I suggest you hack imgui with the minimum amount of change (only new #ifdef blocks) and add the rest in separate code.

[Convery]

So far the least intrusive implementation has been to create a define in imconfig to select between the original ImDrawList and one that inherits and extends. Seems to be the minimum amount of change, added a PR for that alone. #3185

[MouriNaruto]

It's a good idea for the pull request created by myself. (#2724)

I am agree with that "Probably a better idea to allow passing a custom drawlist to context creation." in #3185 (comment).

[englercj]

The ability to configure this part of ImGui is more interesting to me than the various PRs/Issues about improved font rendering. I don't mind writing the things necessary to do better font handling (maybe Slug) or rendering (maybe Primitive Buffers), but don't have a good hook for it right now. Even a compile-time one would be nice.