glDeleteBuffers slower than glBufferData

Question

I'm having a bit of performance issue in my iOS/Android game where several VBO's have to be updated every once in a while. After profiling my game it turns out that glDeleteBuffers() takes up to 7ms per VBO update. This of course results in a hiccup when frames normally take only 4 ms to render.

Here's the part where I update my VBO:

Chunk* chunk;
pthread_join(constructionThread, (void**)&chunk);
building = false;

if (vboID)
{
    //takes 7 milliseconds
    glDeleteBuffers(1, &vboID); 
    vboID = 0;
}
if (offset)
{
    glGenBuffers(1, &vboID);
    glBindBuffer(GL_ARRAY_BUFFER, vboID);

    //takes about 1-2 milliseconds, which is acceptable
    glBufferData(GL_ARRAY_BUFFER, offset * 4, constructionBuffer, GL_STATIC_DRAW);
}

where offset is an instance variable is basically the size of the new VBO, which is quite variable. vboID speaks for itself, I guess ;)

Answer 1

glGenBuffers and glDeleteBuffers are designed to only be run on initialization and cleanup, respectively. Calling them during runtime is bad.

glBufferData replaces the current buffer data with a new set of data, which automatically changes the size of the buffer. You can safely remove the whole glGenBuffers/glDeleteBuffers thing and move it into initialization and cleanup.

Additionally, you are creating the buffer as a static buffer. This is telling OpenGL that you will almost never change it so it stores it in a way that's quicker to access on the GPU but slower to access from the rest of the system. Try changing GL_STATIC_DRAW to GL_DYNAMIC_DRAW or GL_STREAM_DRAW. More on this here: http://www.opengl.org/wiki/Buffer_Objects#Buffer_Object_Usage