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Asked: 2026-06-01T18:19:04+00:00

I have a test program that programmatically renders a texture and then renders a

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I have a test program that programmatically renders a texture and then renders a simple quad that is skinned with the previously drawn texture. The program is extremely simple and everything is done in 2D. This program works great under linux and everything looks like it should: Running on Linux

However when I run the program on my mac running 10.7 nothing shows up:
Running on Mac

I’m at a complete loss as to why this program isn’t working on my mac.

Here are the relevant bits of the program.

Creating the texture:

void createTextureObject(){
    cout<<"Creating a new texture of size:"<<textureSize<<endl;
    //glDeleteTextures(1, &textureId);
    glGenTextures(1, &textureId);
    glBindTexture(GL_TEXTURE_2D, textureId);
    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap generation included in OpenGL v1.4
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, textureSize, textureSize, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);

    isTextureValid = true;
    createFBObject();
}

Creating the Frame Buffer Object:

void createFBObject(){
    cout<<"Creating a new frame buffer object"<<endl;

    glDeleteFramebuffers(1, &fboId);
    glGenFramebuffersEXT(1, &fboId);

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboId);

    glGenRenderbuffersEXT(1, &rboId);
    glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, rboId);
    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, textureSize, textureSize);
    glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0);

    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, textureId, 0);

    glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, rboId);

    bool status = checkFramebufferStatus();
    if(!status){
        cout<<"FrameBufferObject not created! Quitting!"<<endl;
        exit(1);
        fboUsed = false;
    }

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}

Rendering to the texture:

void drawToTexture(){

    if (!isTextureValid)
        createTextureObject();

    glViewport(0, 0, textureSize, textureSize);
    glLoadIdentity();
    // set the rendering destination to FBO
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboId);
    // clear buffer
    glClearColor(0, 0, 0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   // draw to the texture
    glColor3f(0.0, 1.0, 0.0);

    for (int i=1; i<=5; i++){
        glBegin(GL_LINE_LOOP);
            glVertex2f(-1 * i/5.0f, -1 * i/5.0f);
            glVertex2f( 1 * i/5.0f, -1 * i/5.0f);
            glVertex2f( 1 * i/5.0f,  1 * i/5.0f);
            glVertex2f(-1 * i/5.0f,  1 * i/5.0f);
        glEnd();
    }
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); 
}

Rendering the textured quad:

void drawTexturedQuad(){
    glViewport(50, 50, textureSize, textureSize);
    glLoadIdentity();
    glClearColor(0.2, 0.2, 0.2, 0.2);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glBindTexture(GL_TEXTURE_2D, textureId);

    int size = 1;
    int texS = 1;

    glBegin(GL_QUADS);
        glColor4f(1, 1, 1, 1);
        glTexCoord2f(texS,  texS);  glVertex3f(size,        size,0);
        glTexCoord2f(0,     texS);  glVertex3f(-1 * size ,  size,0);
        glTexCoord2f(0,     0);     glVertex3f(-1 * size,   -1 * size,0);
        glTexCoord2f(texS,  0);     glVertex3f(size,        -1 * size,0);
    glEnd();

    glBindTexture(GL_TEXTURE_2D, 0);
}

I’m using GLUT and my display call back is simply:

void displayCB(){
    drawToTexture();
    drawTexturedQuad();
    glutSwapBuffers();
}

Additionally I have other methods check to see if FrameBufferObjects are supported by OpenGL and if they are not the program quits. Additionally I have other logic that sets textureSize whenever the window is resized.

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1 Answer

  1. Editorial Team
    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap generation included in OpenGL v1.4

    This might be a problem. The GL specification doesn’t say exactly at what point mipmaps should be generated, and of course, this generates problems with render to texture. So the GL_EXT_framebuffer_object (and core versions too) introduced glGenerateMipmapEXT, which you call exactly in the point where you want mipmaps generated (usually after rendering to the texture).

    So, remove the GL_GENERATE_MIPMAP stuff and use glGenerateMipmap manually when needed. You can read more about this problem in the GL_EXT_framebuffer_object specification.

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