Create WGPU widget similar to Gtk.GLArea

[nixigaj]

I've been wanting to create a GUI app using WGPU and use GTK for window decorations on Linux/BSD. Using OpenGL this can be done using GLArea covering the entire window with the widget. I have seen requests for this but not seen any implementation.

[sdroege]

That's certainly possible but it would probably make sense for this to either a) be just an example in this repo, or b) an external crate that provides such a widget in a general way.

Do you intend to work on this?

[i509VCB]

It would be possible to use the gles backend quite easily for this (wgpu-hal has a way to create an Adapter from a glGetProcAddress like function). But there are limitations with the gles backend and the Vulkan backend would be preferred. However the Vulkan backend would either force gtk to initialize with Vulkan or share memory objects between apis.

For a minimum viable product using the gles backend would be fine, but long term some work will be needed in wgpu (or an auxillary crate) to import memory objects from other apis.

[bilelmoussaoui]

If someone wants to work on this, we could potentially have a crate that has useful "integration" widgets with the rest of the rust ecosystem. See also #1163

[ThrashAbaddon]

I'm interested in this for Linux and Windows.

[Doublonmousse]

I was thinking that using the gtk webkit would get us some of the way there (even if not necessarily ideal).

Epiphany (gnome's web browser) is using gtk4 as the ui toolkit and some of the demos of wgpu.rs work (only webgl2 though, not WebGPU).

So using WebKitGTK inside a gtk4 app would allow for webgl2-based wgpu applications to run. And maybe WebGPU later if support is added in the future.

[Doublonmousse]

I think there's a working implementation (at least on the architecture side) here : https://github.com/BartBM/wgpu-dma-buf
that we could adapt for gtk.

What it does is
wgpu -> dma-buf -> glcontext -> slint window
or
wgpu -> dma-buf -> glutin -> winit window
Using dma-buf to go from wgpu to gl.

As gtk 4.14 and gtk-rs 0.9 exposes the dma-buf graphics offloading on linux, it should be possible to make the same thing work on linux with wgpu -> dma-buf -> gtk using the graphics offload feature.

Though that's linux-only for the moment (although it may come to windows in the future : https://gitlab.gnome.org/GNOME/gtk/-/issues/6869)

Maybe it's possible to adapt the other part and do
wgpu -> dma-buf -> glutin -> glcontext (gtk) -> gtk window.

Now there are probably some things to adapt between OS to have this work on all platforms (with or without graphics offload) but it seems doable given that the same trick works with slint and glutin and it doesn't seem like there's too much conceptual difference between these and gtk.

[Doublonmousse]

Looking back at what we tried (https://github.com/flxzt/gtk-wgpu-area) using the gles backend, it didn't work yet.

Though doing comparison with what was done on with the femtovg-area example in this repo, the expoxy loading function was done

https://github.com/flxzt/gtk-wgpu-area/blob/038ca27ecc7330a3ba09eb8ae2f06769c21d25f0/src/wgpuarea.rs#L12-L16

coinciding with

gtk4-rs/examples/femtovg_area/femtovg_area/imp.rs

Line 154 in 99fa8ed

let ctx = glow::Context::from_loader_function(LOAD_FN);

But what we didn't do is this

        // SAFETY: Need to get the framebuffer id that gtk expects us to draw into, so
        // femtovg knows which framebuffer to bind. This is safe as long as we
        // call attach_buffers beforehand. Also unbind it here just in case,
        // since this can be called outside render.

from

gtk4-rs/examples/femtovg_area/femtovg_area/imp.rs

Lines 147 to 150 in 99fa8ed

	// SAFETY: Need to get the framebuffer id that gtk expects us to draw into, so
	// femtovg knows which framebuffer to bind. This is safe as long as we
	// call attach_buffers beforehand. Also unbind it here just in case,
	// since this can be called outside render.

and the next lines

So we'd need to do the same with wgpu but I haven't found a way to do that yet (and also if this is at all supported)

[Doublonmousse]

I have a first working example here: flxzt/gtk-wgpu-area#1
For now it seems to only work well on linux and windows (I'm yet to see how to setup wgpu to use gles on mac as it needs an angle feature flag + installing ANGLE)

This work on all 3 major platforms (with the need for the ANGLE library on mac os to be installed)

The catch is that I'm using a patched version of wgpu to do the aforementioned framebuffer binding

[flxzt]

wgpu now has the ability to bind to an external gl framebuffer! (see gfx-rs/wgpu#7671)

[bilelmoussaoui]

Nice! @flxzt wanna add this as an example to the gtk4-rs repo?