CODEWITHSUNDEEP
c++multithreadingopengl
tower120
tower120

Reputation: 5255

OpenGL multithreading/shared context and glGenBuffers

If I plan to use multithreading in OpenGL, should I have separate buffers (from glGenBuffers) for each context?

I do not know much about OpenGL multithreading yet (for now I work in "single" thread). I need to know if I can share buffers already pushed to Video Memory (with glBufferData/glBufferSubData), or I have to keep copy of buffer for another thread.

Upvotes: 6

Views: 5440

Answers (2)

Damon
Damon

Reputation: 70136

You do not want to use several contexts with several threads. You really don't.

While this sounds like a good idea, in practice muli-context-multi-thread is complicated, troublesome, and badly supported on the driver side, and it only marginally improves (possibly even reduces!) performance.

What you really want is to have only one thread talk to OpenGL (with one context, obviously), map a buffer, and pass the memory pointer to another thread, preferrably using 3 buffers (3 subbuffers of a 3x sized buffer) with immutable storage and persistent mapping, if this is available.
That, and doing indirect render calls, where a second thread feeds the buffers the indirect call reads from.

Further info on the persistent mapping topic: See in particular slides 22-25 of this GDC2014 presentation, which is basically a remake of Cass Everitt's 2013 SIGGRAPH talk.
See also Everitt's original talk: Beyond porting.

Upvotes: 8

bvs
bvs

Reputation: 350

Vaos aren't shared so you'll need to generate a new vao for each object per context or else the behavior will become unpredictable and incorrect upon deletion / creation of a new one. This can be a major source of error. Vbos can be shared, so you just need one vbo per object.

Upvotes: 6

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