sokol_gfx.h: WebGL performance issues in Chrome due to calls to glGetError

[mgerdes]

In my app I've been having some performance issues with WebGL in Chrome. After some debugging I've found out it's because of this call to glGetError that happens very frequently:

https://github.com/floooh/sokol/blob/5f569027afa6fe6e5a5b6060aad612d8ee976b79/sokol_gfx.h#L2486

If I define SOKOL_ASSERT to just do nothing, then my application goes from about 10fps to 60fps just from removing the calls to glGetError, nothing else. So defining SOKOL_ASSERT to do nothing is currently my workaround, but I'm wondering if these checks shouldn't be made if SOKOL_DEBUG is not defined? The other call to glGetError doesn't happen if SOKOL_DEBUG is not defined so maybe this should be the same?

Anyways, I figured this is a potential performance issue for people and wanted to bring it to your attention as it can be a little tricky to debug. It's also interesting that in FireFox there there seems to be no performance decrease with all the calls to glGetError, only in Chrome.

[floooh]

Hmm, looks like there are different levels to this... first: release-mode builds using the sokol headers for WASM should definitely be compiled with assert-checks removed, this happens automatically in assert.h when NDEBUG is defined (see here: https://en.cppreference.com/w/cpp/error/assert), or alternatively if you redefine SOKOL_ASSERT() to be empty.

SOKOL_DEBUG also depends on NDEBUG, but SOKOL_ASSERT and SOKOL_DEBUG are not related to each other.

In sokol_gfx.h, SOKOL_DEBUG is mainly used to enable or disable the validation layer, but the validation layer is independent from glGetError() checks.

So basically: make sure that your release-mode builds are compiled with -DNDEBUG (most build systems should add this automatically though for a release-mode build).

That glGetError() drastically reduces WebGL performance is also expected, because this most likely causes a pipeline flush and render-process roundtrip each time it is called.

I'm not sure how the current situation could be improved. We'd need a warning (ideally during the build, but a runtime message would also work) when a "release build" is compiled without NDEBUG. Trouble is, how to actually detect a release build from inside the sokol headers (since that's not clearly defined, is it the absence of debug info, or the presence of optimization flags?).

[mgerdes]

Ok. Yea, I just needed to compile with -DNDEBUG. That fixes the issue for me. Thanks!