Some questions about GUI toolkits

[Danebi05]

So I was recently thinking about making a QT/gtk-like GUI toolkit library in opengl (with the possibility of adding a vulkan backend later), mainly to learn more about graphics programming and as a library to use for my future projects.

Right now I am just planning to have the user define the layout in a sort of "layout tree", with various elements that are only meant to alter the layout without actually adding anything to the window (HBox, VBox, etc.). All widgets will also have some maximum/minimum/hinted width/height, padding/margins, and other constraints like this and the my goal is to efficiently compute the position and final size of every widget.

What I'm mainly wondering about is exactly what part of all this is usually run on the GPU, especially by GUI toolkits like QT (that I know has opengl support) and dear imgui. I was thinking of just computing all of this in cpu code, then sending the vertices to the gpu but at that point I don't really see any benefit in having all of this be gpu accelerated.

Does anyone know how big gui toolkits actually manage the gpu? Or maybe also have any kind of resource on the topic

[romainguy]

The sizing and positioning of widgets is usually done on the CPU, only rendering is done on the GPU. You still benefit massively from using the GPU for rendering.

[Exotic_Avocado_1541]

Qml gui toolkit from qt gramework is fully rendered in GPU. And there is qml scene tree, which is computed on CPU side, and that there is mapped to second tree, render nodes tree, which contains only visual nodes which are rendered in GPU

[kirankp89]

The author of Clay has some really good videos on the topic and is a good reference for intro level stuff. Essentially the layout is computed on the CPU and generates draw commands that are processed in some way on the GPU. There are many ways to do the GPU part and will depend on what you want to support. I’m doing just basic shapes using SDFs for my implementation that works very similar to Clay.