Question

I am trying to start using framebuffers in my app. I fallowed Apple tutorial Using a Framebuffer Object as a Texture. And my code looks like this:

Somewhere in header file:

GLuint framebuffer, texture;
GLenum status;

And .m file:

-(void)initFBO {
    glGenFramebuffersEXT(1, &framebuffer);
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer);
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0,
                 GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
                              GL_TEXTURE_2D, texture, 0);
    status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
    if (status != GL_FRAMEBUFFER_COMPLETE_EXT) {
        NSLog(@"failed");
    } else {
        NSLog(@"success");
    }
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}

-(void)someDrawingFunc {
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer);
glClearColor(0.0, 0.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
    glEnable(GL_BLEND);
    glBlendFunc(GL_ONE, GL_ZERO);
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, someTexture);
    glBegin(GL_QUADS);
    glTexCoord2f(0.0f, 0.0f);
    glVertex2f(0.0, height);
    glTexCoord2f(0.0f, 1.0f);;
    glVertex2f(0.0, 0.0);
    glTexCoord2f(1.0f, 1.0f);
    glVertex2f(width, 0.0);
    glTexCoord2f(1.0f, 0.0f);
    glVertex2f(width, height);
    glEnd();
glFlush();
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

    [self drawFBO];
}

-(void)drawFBO {
glClearColor(1.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glColor4f(1.0, 1.0, 1.0, 1.0);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex2f(0.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f); glVertex2f(0.0f, 1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex2f(1.0f, 1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex2f(1.0f, 0.0f);
glEnd();
glFlush();
glBindTexture(GL_TEXTURE_2D, 0);
}

In console I see "success", but in my app window I see:

And when I do glReadPixels and save them to image I get:

The size of saved image is as it should be, everything is OK, but I just get the glClearColor filled image with mysterious black line, and not what I have drawn to framebuffer

While with same code just without using framebuffer at all, in my app I see:

And when I save then, I see:

What am I doing wrong?

---

So, framebuffer refuses textured GL_QUAD, that I am trying to draw, for some reason. So I guess problem has to be somewhere at framebuffer usage.

---

EDIT

Strange thing. When drawing fbo to screen now I see only red color (glClearColor where drawing FBO to screen), but when I do glReadPixels it reads pixels good. It saves image with my texture.

Default image (texture image, drawn to FBO):

What I see in my app window:

glReadPixels result image (texture readed from FBO and saved to file):

Yes, its upside down. Its normal for reading pixels from OpenGL. I updated code in question with that how my code looks like now

Answer 1

I have solved it. The problem was with my glTranslatef. I done glPushMatrix() and setted needed matrix parameters when rendering to FBO, and everything works fine now.