Multithreading in BGFX

[Delvix000]

I am writing a small 2D game framework just for fun and I'm implementing the core game loop. I am considering switching from pure OpenGL to bgfx because I want to be able to target multiple rendering backends easily, so I'm a beginner and sorry for the noob question.

I need some clarification on how threads are working in bgfx and if my idea can be implemented in bgfx. I'll explain what I mean.

Right now my application is single threaded and consists of 150k bunnies (a 2d texture) that move and bounce inside a 800x450 rectangle. The game loop goes like this:

• iterate over all 150kbunnies
• for each one, update its position and velocity according to some rules, and fill a dynamic vertex buffer with two tris (will represent the quad texture)
• call glDrawElements on the vertex buffer to draw all bunnies in one go (this is still a costly operation because the buffer is big)
• flush to screen
• repeat

The two costly operations are the bunny update logic and rendering. What I want to do is to parallelize those operations in two different threads like this:

• on the logic thread, all bunnies are updated and a vertex buffer is filled
• the logic thread tells the render thread to glDrawElements and flush screen, then proceeds to update bunnies again without waiting
• the render thread draws the bunnies, flushes to screen and tells the logic thread that he's done. The logic thread in the meantime has computed and filled another bunny buffer, so the render thread can immediately get to work again

So basically, both render and logic threads run independently, but they sync when the logic has produced a new vertex buffer or the render tells the logic he's done (depending on who completes its task first)

Of course I won't create a new vertex buffer for the bunnies every frame, I was thinking like swapping between two preallocated buffers and use only one at a time.

Is something like this feasible in bgfx? If so, how?

[bkaradzic]

Is something like this feasible in bgfx? If so, how?

It already works like this. See: https://bkaradzic.github.io/bgfx/internals.html

bgfx API is declarative, when you call it, it just records what needs to be done. Once you call bgfx::frame work is getting done on other thread.

If you want to submit from multiple threads you need to use bgfx::Encoder API: https://bkaradzic.github.io/bgfx/bgfx.html#encoder

[Delvix000]

Thanks! This was exactly what I was looking for. So, If I get this correctly, I should cal bgfx::init and bgfx::frame from the thread I want to use as logic thread (the API thread), and bgfx::renderFrame from the thread I want to use as render thread, am I right?

Also, I don't think I understood if the render thread is created automatically by bgfx::init (in which case i suppose I don't have to use bgfx::renderFrame at all) or I should manage both threads manually, making the "main" thread the render thread

[bkaradzic]

Also, I don't think I understood if the render thread is created automatically by bgfx::init (in which case i suppose I don't have to use bgfx::renderFrame at all) or I should manage both threads manually, making the "main" thread the render thread

It's created automatically if you don't call bgfx::renderFrame before bgfx::init.

[bkaradzic]

The best way to get familiar with bgfx is to start experimenting with provided examples.

[Delvix000]

Thanks! Will do