Does anyone understand what LayerScope actually does?

[athenian200]

I stumbled upon it while looking at things in our codebase that use protobuf, and I got curious as to what it does. I discovered the following things:

1. To use it, first you have to flip gfx.layerscope.enabled. This opens a WebSocket at ws://localhost:23456

2. The main UI for this feature is not in the browser at all, it's on GitHub: http://mozilla.github.io/layerscope/

3. The project is no longer active: https://github.com/mozilla/layerscope

4. The code has been removed by Mozilla upstream, without comment: https://bugzilla.mozilla.org/show_bug.cgi?id=1728193

I've looked at it, and I can't figure out what precisely this does or how to use the frame/layer data collected... is this anything that would actually help us with developing the CSS parser or debugging WebGL, or is it just some weird leftover from b2g that was primarily used for remote debugging?

Not a pressing priority, but I'm wondering if this is dead code that's just bloating the binary size, or a hidden feature we have yet to make use of.

[Moonchild]

I've looked at it, and I can't figure out what precisely this does

It seems to dump ordering and texture data for from the layer manager

how to use the frame/layer data collected

No idea.

is this anything that would actually help us with developing the CSS parser or debugging WebGL

Very unlikely. the layer manager deals with layer composition, that's like 2 levels deeper than either CSS or WebGL.
It would only be useful to debug issues with the underpinnings of HWA acceleration and the likes.

is it just some weird leftover from b2g that was primarily used for remote debugging?

No, this would apply to all OSes with accelerated compositing.
And the fact it uses a websocket doesn't mean it's remote debugging It's regularly simpler to dump debugging data over a network port to whatever client than it is to display in the application itself. Especially if it touches very low-level stuff.

I'm wondering if this is dead code

Certainly doesn't seem like we'll ever use this in our development.