[tbb-dev] Debugging/Seeing the trace of an execution of WebGL code

[Rishabh Raj]

Hello everyone,

I am working on making some changes to the WebGL part of Tor Browser's
source code. But each WebGL API goes through multiple files and functions
in the browser's source code. So, before I can start changing them, I would
need to know how exactly the transfer of data takes place. To be more
clear, I start with a program which draws a rectangle (vertices have
different colors, so interpolation takes place). Take for example the
function `bufferData()`, which sends the data to the GPU. Once the shader
code or vertices/indices data is sent to the GPU, I am helpless, isn't it?
I need to be able to hook before this and analyze the various function
calls in different source code files and the data parameters that are
circulating through (of course it is not just one API, but a whole bunch of
JavaScript API's that have to be executed before something is drawn).

So, how do I figure this out? Initially, I had tried using a bunch of
fprintf's, but I always get lost after, say `fBufferData()` [I noticed that
many `API()` end up with `fAPI()` in the source code]. In addition, I
couldn't figure out when the ANGLE part comes into the picture since I
tried putting fprintf's in there as well, but nothing got printed.
Basically I am trying to find the right place to hook, just after all
calculations on the data are done and before the control is sent to the
GPU. So, do I have to attach a debugger, say gdb, to a running instance of
tor-browser (incidentally, there are three processes that commence when tor
browser is run). Basically, I need some help figuring out how to put all of
this together. I would really appreciate if you could provide me with some
suggestions.

Warm Regards,
Rishabh
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