You plug it into your project and it can be rendered on anything that can push pixels and/or triangles to the screen. Events from windowing system go in, list of triangles comes out.
This is intended to be used with OpenGL, Vulkan, D3D and other graphics environment and used in cases where integrating a "real" GUI toolkit would be more trouble than it's worth.
Other popular libs like Dear Imgui or Egui work the same way.
Like a debug UI in a game engine, or in an embedded device that doesn't even have input for a13y.
Dear ImGui [0] is without a doubt the most prevalent immediate mode UI library. It does not have native accessibility features, but that hasn't stopped companies such as Intel, Meta, IKEA and Google from shipping products built upon it. It's also used in a ton of games.
Calling Dear ImGui a toy project at this point would be like calling Unreal Engine a toy project.
It's a shame accessibility support is not more widespread, and furthermore it's a shame that it is so laborious to add it.
I will mention, however, it's kinda abandonware at this point. There is some bug with the draw call iterator which does a misaligned pointer access, which, if your environment is set up to catch that, can get annoying (Zig for example panics on it). There's a github issue that some have used as reason to fork it but all the forks I tried were subtly wrong, for what that's worth.
In the MicroUI example here, there are buttons and text labels and other kinds of controls, but no ability for an outside process to enumerate or interact with the controls. Any program will just set a single giant window with no text and no controls inside. Accessibility software can still hook text output APIs, but not if it also uses custom font rendering.
Anyway, the Windows accessibility API is just implementing a few COM objects, and COM (other than the specific ABI used for storing the vtable and function call convention) is not necessarily specific to Win32.
Really insane comment TBH
peter_d_sherman•2h ago
o Tiny: around 1100 sloc of ANSI C
o Works within a fixed-sized memory region: no additional memory is allocated
o Built-in controls: window, scrollable panel, button, slider, textbox, label, checkbox, wordwrapped text
o Works with any rendering system that can draw rectangles and text
o Designed to allow the user to easily add custom controls
o Simple layout system"