How to load VBO and render it on separate Java threads?
To create a virtual world I am using Lightweight Java Game Library (LWJGL) (Java + OpenGL). I want to load my terrains into graphics card memory on worker thread, while on main thread I want to take these, already loaded terrains, and render them. In order to do that I have to create Vertex Array Object (VAO), create Vertex Buffer Object (VBO), add VBO into VAO attribute list and finally render everything. This works perfectly on single-threaded system, however I am having problems implementing it on multi-threaded system. I know that VBO can be shared between OpenGL contexts, while VAO cannot be shared (reference1; reference2). Therefore to accomplish my goal I:
create VBO on worker tread by using these methods:
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, ID); int ID = GL15.glGenBuffers(); GL15.glBufferData(GL15.GL_ARRAY_BUFFER, buffer, GL15.GL_STATIC_DRAW); GL20.glVertexAttribPointer(attributeNr, coordSize, GL11.GL_FLOAT, false, 0, 0); GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
render it on main thread, however I get this exception:
Exception in thread "main" org.lwjgl.opengl.OpenGLException: Cannot use offsets when Element Array Buffer Object is disabled
I am sure that I do not render not loaded terrains, because I load terrains when they are outside render scope. I have read many articles, questions and blogs about OpenGL shared contexts and concurrency, but did not managed to find a solution. I would be very grateful for any help.
As you already stated, VAOs are NOT shared between contexts, so it is also impossible to modify them from multiple threads.
GL20.glVertexAttribPointer(attributeNr, coordSize, GL11.GL_FLOAT, false, 0, 0);
is modifying the VAO state, thus it has to be called from the main thread.
It is perfectly fine to have the data upload ( glBufferData ) in a separate thread, but constructing the VAO can only be done from the main thread.