OpenGL ES 2.0 FrameBuffer gives back a blackscreen

Question

Alright I made an application that uses a FBO to render to a texture and later uses this texture to display it on a quad.

That's the code I am using to initialize the FBO and the texture:

    IntBuffer intBuffer = IntBuffer.allocate(1);
    GLES20.glGenFramebuffers(1, intBuffer);
    fbo = intBuffer.get(0);

    GLES20.glGenTextures(1, intBuffer);
    tex = intBuffer.get(0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, tex);
    GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, width, height, 0, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, null);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_NEAREST);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);

    GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, fbo);

    GLES20.glFramebufferTexture2D(GLES20.GL_FRAMEBUFFER, GLES20.GL_COLOR_ATTACHMENT0, GLES20.GL_TEXTURE_2D, tex, 0);

    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
    GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, 0);

(1. code in onDrawFrame())

The problem is that I don't know where to put the code, so at first I put the code in the onDrawFrame() method. When I do that the texturing works fine and I get the result that I want. But since I am creating a new FBO and texture every frame, after some time The application starts to lag and at the end the emulator crashes.

(2. code in onSurfaceChanged())

After noticing that behaviour I decided to put the code in the onSurfaceChanged() method. This time the application didn't crash but the entire texture is black. I tried to clear the texture or draw a white quad over it but nothing worked. And when I try to get an error from GLES20.glCheckFramebufferStatus(GLES20.GL_FRAMEBUFFER) or GLES20.glGetError() it says that everything is fine.

I also tried to put the code in the onDrawFrame() method surrounded with a if-clause so that it's only executed once. The result is also the black texture.

(3. code in onDrawFrame() and onSurfaceChanged())

The last thing I tried was to put the code in both methods. I wanted to reduce the code in the onDrawFrame() method until I find the codeline that makes the texture work fine. But when I started the application the quad flickered, changing from the black texture to the right texture.

There is no problem with the texture displaying since it works with the one method. I also tried to add a depth-buffer to the code but the result is the same. So since I don't need it in my application I commented it out.

Is there anyone who can say what's going on? If someone has a application that works but doesn't know what's the problem with mine it would be nice if that person could upload the project because I didn't find a tutorial that has a android project up for download.

Answer 1

Alright thanks to Rabbid76 for giving me a checklist to find my problem. I tried to use the fbo as a texture. This is the right binding: GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, tex). In the tutorial I have read the FBO was also bound. I still don't know why it works when I initialize the FBO in the onDrawFrame() method and use it then as texture.