Concurrency with android GLES glBufferData

Question

I'm trying to use Android and OpenGL 2.0 to create a sort-of desert racing game. At least that's the end goal. For the time being I'm really just working with generating an endless desert, through the use of a Perlin noise algorithm. However, I'm coming across a lot of problems with regard to concurrency and synchronization. The program consists of three threads: a "render" thread, a "geometry" thread which essentially sits in the background generating tiles of perlin noise (eventually sending them through to the render thread to process in its own time) and a "main" thread which updates the camera's position and updates the geometry thread if new perlin noise tiles need to be created.

Aforementioned perlin tiles are stored in VBOs and only rendered when they're within a certain distance of the camera. Buffer initialization always begins immediately.

This all works well, without any noticeable problems.

HOWEVER.

When the tiles are uploaded to the GPU through glBufferData() (after processing by the separate geometry thread), the render thread always appears to block. I presume this is because Android implicitly calls glFinish() before the screen buffer is rendered. Obviously, I'd like the data uploading to be performed in the background while everything else is being drawn - even taking place over multiple frames if necessary.

I've looked on google and the only solution I could find is to use glMapBuffer/glMapBufferRange(), but these two methods aren't supported in GLES2.0. Neither are any of the synchronization objects - glFenceSync etc. so...

....

any help?

P.S. I haven't provided any code as I didn't think it was necessary, as the problem seems more theoretical to me. However I can certainly produce some on request.

A screenshot of the game so far: http://i.stack.imgur.com/Q6S0k.png

Answer 1

Android does not call glFinish() (glFinish() is actually a no-op on IMG's GPUs). The problem is that glBufferData() is not an asynchronous API. What you really want is PBOs which are only available in OpenGL ES 3.0 and do offer the ability to perform asynchronous copies (including texture uploads.)

Are you always using glBufferData()? You should use glBufferSubData() as much as possible to avoid reallocating your VBO every time.