I got inspired by Raph Levien's talk on Rust and GUI layout [0] and realized that a simple flexbox layout algorithm can be implemented really efficiently.

So I started making a prototype in C (also a small proto in Rust), using a densely packed array to implement a DOM-like tree. The tree nodes have short strings, boxes (with border, padding, etc), images (texture coordinates in an atlas), layout constraints, containers, etc. Flexbox layout is applied to the tree in linear time (and constant memory!) and then the tree is traversed to output an ordered list of axis aligned rectangles.

The output list can be fed to the GPU, where a special (but simple) shader draws clipped triangles that get applied with textures, msdf font, etc. The whole GUI gets rendered with a single draw call.

This all can be done with very fast performance (sub-millisecond for layout and rendering, excluding GPU latency). There are other implementation details that make it efficient for cache (sizeof(node) == cache line), no recursion, no memory allocation, no unbounded loops, no system calls, etc.

I'm fairly convinced that this approach should be enough to cover 80% of modern GUI paradigms. However I don't have the time or the interest to build a complete widget set GUI library.

Right now I'm sporadically working on the project with a goal to make a game UI with clickable, scrollable and scalable text and images with a modern layout. Right now all I have to show is some ugly text and rectangles (but with a very nice layout), but it's a start for a project with potential.

[0] https://youtu.be/4YTfxresvS8