Fixes #1671 and Fixes #1139.

[mcourteaux]

Flush the nanovg draw commands whenever the next draw would overflow the uint16_t index type.
Additionally added a bunch of BX_ASSERT (which don't get compiled into release builds) to prevent more bugs along these lines.

I think that, at least given the way things work, this should be a nanovg-bgfx-specific patch, and not a nanovg patch. Nanovg takes a different approach, without index buffers:
https://github.com/memononen/nanovg/blob/f93799c078fa11ed61c078c65a53914c8782c00b/src/nanovg_gl.h#L1029-L1030:

	for (i = 0; i < npaths; i++)
		glDrawArrays(GL_TRIANGLE_FAN, paths[i].fillOffset, paths[i].fillCount);

Therefore, nanovg never suffered this issue, as there were no indices to overflow.

---

Demo with a lot of content (example code not modified in this PR):

Whoop whoop! It took 6 years since opening #1139 for someone to actually investigate and fix this. 😂
(Fixes #1671, which is a duplicate)

[mcourteaux]

Just confirmed this in SilverNode, that all the glitches are gone.

[bkaradzic]

Whoop whoop! It took 6 years since opening #1139 for someone to actually investigate and fix this. 😂
(Fixes #1671, which is a duplicate)

You need to understand that NanoVG in scope of bgfx is just to demonstrate porting from GL to bgfx, and whatever 20-nanovg needs. It never meant to be complete, robust, performant, etc.

[mcourteaux]

Yeah yeah, I fully understand. I was just surprised it took so long, as NanoVG seems so useful. For me, in SilverNode, it's part of the technology stack that makes it fully crossplatform: C++ < SDL2 < bgfx < nanovg < my own widget library. I thought many more people would use bgfx+nanovg to build cross platform user interfaces. That's why it seemed surprising.

However, I just found jdryg/vg-renderer, thanks to some comment you made somewhere. Maybe people use that more. If I understood correctly, you'd also recommend vg-renderer over nanovg, for robustness and speed?

[bkaradzic]

I was just surprised it took so long, as NanoVG seems so useful.

20-nanovg never broke during those years, so from my POV wasn't an issue.

you'd also recommend vg-renderer over nanovg, for robustness and speed?

I haven't used it, but it exist to solve issues with nanovg performance. And I think it's more robust since it has larger software shipped with it.

[bkaradzic]

For me, in SilverNode, it's part of the technology stack that makes it fully crossplatform

This?
https://silvernode.io/

Can you add something about it in "Who is using bgfx" section of README.md?

[mcourteaux]

Yes, that's it! 😄 You asked me more than a year ago for the same, but I wanted to wait, before drawing attention, as I didn't have time to work on it, and I would just disappoint excited people, because there was nothing going on. Luckily, I'll quit my job at new years, and work on SilverNode full time soon! 🥳 Thanks for asking! I'll make work of it one of these weeks. When I do, is there a place in the README you'd want this to be? Bottom, or somewhere higher (as it's an application, rather than a game)?

[bkaradzic]

Bottom, or somewhere higher (as it's an application, rather than a game)?

Bottom. It's chronological based on time when it's added.