Me gustaría hacer renderizado fuera de pantalla (en un entorno de consola sin WS) con FBO. Sé que es necesario crear un contexto OpenGL, y al menos una ventana ficticia para cualquier operación, por lo tanto hice la siguiente inicialización:

// Step 1 - Get the default display.
eglDisplay = eglGetDisplay((EGLNativeDisplayType)0);

// Step 2 - Initialize EGL.
EGLint iMajorVersion, iMinorVersion;
if (!eglInitialize(eglDisplay, &iMajorVersion, &iMinorVersion))
{
    printf("Error: eglInitialize() failed.\n");
    goto cleanup;
}

// Step 3 - Make OpenGL ES the current API.
eglBindAPI(EGL_OPENGL_ES_API);
if (!TestEGLError("eglBindAPI"))
{
    goto cleanup;
}

// Step 4 - Specify the required configuration attributes.
EGLint pi32ConfigAttribs[5];
pi32ConfigAttribs[0] = EGL_SURFACE_TYPE;
pi32ConfigAttribs[1] = EGL_WINDOW_BIT;
pi32ConfigAttribs[2] = EGL_RENDERABLE_TYPE;
pi32ConfigAttribs[3] = EGL_OPENGL_ES2_BIT;
pi32ConfigAttribs[4] = EGL_NONE;

// Step 5 - Find a config that matches all requirements.
int iConfigs;
if (!eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs) || (iConfigs != 1))
{
    printf("Error: eglChooseConfig() failed.\n");
    goto cleanup;
}

// Step 6 - Create a surface to draw to.
EGLSurface eglSurface;
eglSurface = eglCreateWindowSurface(eglDisplay, eglConfig, (EGLNativeWindowType)NULL, NULL);
if (!TestEGLError("eglCreateWindowSurface")) goto cleanup;

// Step 7 - Create a context.
eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, ai32ContextAttribs);
if (!TestEGLError("eglCreateContext")) goto cleanup;

// Step 8 - Bind the context to the current thread
eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);
if (!TestEGLError("eglMakeCurrent")) goto cleanup;

Este tipo de inicialización funciona en el sistema de destino, pero si dibujo algo en el FBO, y después de leerlo (getReadPixels) siempre aparece una imagen en negro. He intentado el mismo código anterior a X11, donde (ya) falla en eglCreateWindowSurface call con error: EGL_BAD_NATIVE_WINDOW FUNCIONA, PERO FUNCIONA si paso a esta llamada un controlador de ventana nativo de X11window real (este caso puedo leer la imagen representada válida además)

¿Me aclaran qué tipo de superficie debo usar para la representación FBO? o que hago mal ??

El resto del código de dibujo: // inicie e inicie opengl es shanders Shaders_Init ();

{
    // create a framebuffer object
    glGenFramebuffers(1, &fboId);
    glBindFramebuffer(GL_FRAMEBUFFER, fboId);

    // create a texture object
    GLuint textureId;
    glGenTextures(1, &textureId);
    glBindTexture(GL_TEXTURE_2D, textureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); //GL_LINEAR_MIPMAP_LINEAR
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    //glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_HINT, GL_TRUE); // automatic mipmap
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, renderBufferWidth, renderBufferHeight, 0,
                    GL_RGB, GL_UNSIGNED_BYTE, 0);
    //glBindTexture(GL_TEXTURE_2D, 0);


    // attach the texture to FBO color attachment point
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                           GL_TEXTURE_2D, textureId, 0);

    // check FBO status
    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE) {
        printf("Problem with OpenGL framebuffer after specifying color render buffer: \n%x\n", status);
    } else {
        printf("FBO creation succedded\n");
    }
}





// Sets the clear color.
// The colours are passed per channel (red,green,blue,alpha) as float values from 0.0 to 1.0
glClearColor(0.6f, 0.8f, 1.0f, 1.0f); // clear blue

// We're going to draw a triangle to the screen so create a vertex buffer object for our triangle
{
    // Interleaved vertex data
    GLfloat afVertices[] = {    -0.4f,-0.4f,0.0f, // Position
                            0.4f ,-0.4f,0.0f,
                            0.0f ,0.4f ,0.0f};
    // Generate the vertex buffer object (VBO)
    glGenBuffers(1, &ui32Vbo);

    // Bind the VBO so we can fill it with data
    glBindBuffer(GL_ARRAY_BUFFER, ui32Vbo);

    // Set the buffer's data
    unsigned int uiSize = 3 * (sizeof(GLfloat) * 3); // Calc afVertices size (3 vertices * stride (3 GLfloats per vertex))
    glBufferData(GL_ARRAY_BUFFER, uiSize, afVertices, GL_STATIC_DRAW);
}

// Draw a triangle
{
    glClear(GL_COLOR_BUFFER_BIT);
    if (!TestEGLError("glClear")) goto cleanup;



    // First gets the location of that variable in the shader using its name
    int i32Location = glGetUniformLocation(uiProgramObject, "myPMVMatrix");

    // Then passes the matrix to that variable
    glUniformMatrix4fv( i32Location, 1, GL_FALSE, pfIdentity);

    /*
        Enable the custom vertex attribute at index VERTEX_ARRAY.
        We previously binded that index to the variable in our shader "vec4 MyVertex;"
    */
    glEnableVertexAttribArray(VERTEX_ARRAY);

    // Sets the vertex data to this attribute index
    glVertexAttribPointer(VERTEX_ARRAY, 3, GL_FLOAT, GL_FALSE, 0, 0);

    /*
        Draws a non-indexed triangle array from the pointers previously given.
        This function allows the use of other primitive types : triangle strips, lines, ...
        For indexed geometry, use the function glDrawElements() with an index list.
    */
    glDrawArrays(GL_TRIANGLES, 0, 3);
    if (!TestEGLError("glDrawArrays")) goto cleanup;

        // get the image data
        long imageSize = x * y * 3;
        unsigned char *data = new unsigned char[imageSize];
        glReadPixels(0,0,x,y,GL_RGB,GL_UNSIGNED_BYTE,data);

¡¡¡¡¡Gracias por adelantado!!!!! Saludos, Geza