Best Walnut/ImGui alternative?

What is the best GUI library alternative to C++ librarues like ImGui or its wrapper Walnut. I need to be able have dockable windows and a canvas sort of thing where i can specify each pixel. I'm building a ray-tracer

There's egui which is an immediate-mode GUI inspired by Dear ImGui.

See the online demo at egui – An immediate mode GUI written in Rust