Android OpenGL queueEvent why?

Question

What is different between this:

queueEvent(new Runnable(){

@Override
public void run() {
 mRenderer.method();
}});

And this:

mRenderer.method();

And what is better for OpenGL FPS?

Answer 1

GLSurfaceView creates a separate rendering thread. In OpenGL, you need a current context for making any OpenGL calls. The "current context" state is per thread. GLSurfaceView creates an OpenGL context for you, and makes it current for any of the GLSurfaceView.Renderer overrides you implement. So as long as you make OpenGL calls in those methods, you don't have to worry about any of that, it just works like pure magic (well, it's not really magic, but hides a lot of complexity).

Based on this, you can't make OpenGL calls from the UI thread without jumping through hoops. So simply calling a method on the Renderer in something that is e.g. triggered by user input, and then making OpenGL calls in that method, will fail. Beyond that, even if you don't make OpenGL calls in the method, you have to worry about thread safety if the method accesses/modifies member variables of the Renderer that are also used by the rendering thread.

Using queueEvent() provides a convenient way of executing a method in the rendering thread. So you don't have to worry about thread safety of Renderer member variables, because all access will happen in the rendering thread.

I believe you might also be able to make OpenGL calls in that method if you submit it through queueEvent(). But I'm not totally sure if the OpenGL context is always current in the rendering thread, or if that's only guaranteed while the Renderer method overrides are called. It's much more typically to just change state in the Renderer in response to user input, and then use that new state in your override of Renderer.onDrawFrame().