FrameBuffers with GLSurfaceView pattern in OpenGLES 1.1 on android ndk

Question

in Android NDK, is it possible to make OpenGL ES 1.1 work with the typical java-side GLSurfaceView pattern (overriding methods from GLSurfaceView.Renderer onDrawFrame, onSurfaceCreated, etc.) while using in the C++ side the frame, color and depth buffers, and VBO?

I am trying to create them using this:

void ES1Renderer::on_surface_created() {
    // Create default framebuffer object. The backing will be allocated for the current layer in -resizeFromLayer
    glGenFramebuffersOES(1, &defaultFramebuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, defaultFramebuffer);

    // Create color renderbuffer object.
    glGenRenderbuffersOES(1, &colorRenderbuffer); 
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer);

    // create depth renderbuffer object.
    glGenRenderbuffersOES(1, &depthRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
}

However, it seems that this does not get the context appropriately, which is I think created when the GLSurfaceView and renderer are initialized (java side).

I am no expert either on NDK nor OpenGLES, but I have to port an iOS app which is using OpenGL ES 1.1, and i aim to reuse as much code as i can. Since the app is also leveraging the platform-specific UI components (buttons, lists, etc.), while drawing GL graphics, I thought this would be the best way to go. However, I am now considering using a native activity, though I am not sure about what will be the relationship with the other java components.

Answer 1

Absolutely, yes. The standard approach is that you create a GLSurfaceView like you would when using OpenGL from Java, create and hook up your GLSurfaceView.Renderer implementation, and let the rendering thread start up.

From your Renderer methods, like onSurfaceCreated() and onDrawFrame(), you can now call the JNI functions that invoke functions in your native code. In those native functions, you can make any OpenGL API calls your heart desires. For example, in the function you call from onSurfaceCreated() you might create some objects and set up some initial state. In the function you call from onSurfaceChanged(), you might set up your viewport and projection. In the function you call from onDrawFrame(), you do your rendering.

You can even make OpenGL calls from both Java and native code. The Java OpenGL API is just a very thin layer around the native functions. It doesn't make a difference if the functions are called from native code or through the Java API.

The only thing you need to watch out for is that you invoke all your native code that makes OpenGL API calls from the GLSurfaceView.Renderer implementations of onSurfaceCreated(), onSurfaceChanged() and onDrawFrame(). When these methods are called, you are in the rendering thread, and have a current OpenGL context. If native OpenGL code is invoked from anywhere else, chances are that you are in the wrong thread and/or you do not have a current OpenGL context.

There are of course more complex setups where you create your own OpenGL contexts, make them current explicitly, etc. But I would strongly recommend to stick with the simple approach above unless you have a very good reason why you need something more. For most standard OpenGL rendering, what I described should be perfectly sufficient.