What is a good way to load textures dynamically in OpenGL?

Question

Currently I am loading an image in to memory on a 2nd thread, and then during the display loop (if there is a texture load required), load the texture.

I discovered that I could not load the texture on the 2nd thread because OpenGL didn't like that; perhaps this is possible but I did something wrong - so please correct me if this is actually possible.

On the other hand, if my failure was valid - how do I load a texture without disrupting the rendering loop? Currently the textures take around 1 second to load from memory, and although this isn't a major issue, it can be slightly irritating for the user.

Answer 1

You can load a texture from disk to memory on any thread you like, using any tool you wish for reading the files.

However, when you bind it to OpenGL, it's going to need to be handled on the same thread as the rendering for that OpenGL context. That being said, this discussion suggests that using a PBO in a second thread is an option, and can speed up the process.

Answer 2

You can certainly load the texture from disk into RAM in any number of threads you like, but OpenGL won't upload to VRAM in multiple threads for the reason mentioned in Reed's answer.

Given the loading from disk is the slowest part, thats the bit you'll probably want to thread. The loading thread(s) build up a queue of textures to be uploaded, then this queue is consumed by the thread that owns the GL context (mind your access to that queue by the various threads however). You could also consider a non-threaded approach of uploading N textures per frame, where N is a number that doesn't slow the rendering down too much.