Question

I’m starting out with the Android NDK and OpenGL. I know I’m doing something (probably a few) things wrong here and since I keep getting a black screen when I test I know the rendering isn’t being sent to the screen.

In the Java I have a GLSurfaceView.Renderer that calls these two native methods. They are being called correctly but not drawing to the device screen.

Could someone point me in the right direction with this?

Here are the native method implementations:

int init()
{
    sendMessage("init()");

    glGenFramebuffersOES(1, &framebuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);

    glGenRenderbuffersOES(1, &colorRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, 854, 480);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer);

    GLuint depthRenderbuffer;
    glGenRenderbuffersOES(1, &depthRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, 854, 480);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);

    GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
    if(status != GL_FRAMEBUFFER_COMPLETE_OES)
        sendMessage("Failed to make complete framebuffer object");

    return 0;
}

void draw()
{
    sendMessage("draw()");

    GLfloat vertices[] = {1,0,0, 0,1,0, -1,0,0};
    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, 0, vertices);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glDisableClientState(GL_VERTEX_ARRAY);

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

    glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
}

The log output is:

init()
draw()
draw()
draw()
etc..

Answer 1

I finally found the problem after MUCH tinkering.

Turns out that because I was calling the code from a GLSurfaceView.Renderer in Java the frame buffer already existed and so by calling:

glGenFramebuffersOES(1, &framebuffer);

I was unintentionally allocating a NEW buffer that was not attached to the target display. By removing this line and replacing it with:

framebuffer = (GLuint) 0;

It now renders to the correct buffer and displays properly on the screen. Note that even though I don’t really use the buffer in this snippet, changing it is what messed up the proper display.