渲染到纹理，读取像素的结果大部分是黑色的

Question

我正在尝试修改一个现有的科学程序，该程序目前渲染到屏幕上，也渲染到纹理，这样我就可以渲染一个比屏幕大得多的图像。我遇到的问题是，虽然我看到渲染到屏幕图像ok，但当我在matlab中打开时保存的纹理几乎都是黑色的，有一些红线。我按照教程http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-14-render-to-texture/有人能看到我做错了什么?对于测试，我有TEXTURE_SIZE = 512

    glGenFramebuffers(1, &FramebufferName);
    glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
    // The texture we're going to render to
    glGenTextures(1, &renderedTexture);
    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, renderedTexture);
    // Give an empty image to OpenGL ( the last "0" means "empty" )
    glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, TEXTURE_SIZE, TEXTURE_SIZE, 0,GL_RGB, GL_UNSIGNED_BYTE, 0);
    // Poor filtering
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

// The depth buffer
GLuint depthrenderbuffer;
glGenRenderbuffers(1, &depthrenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, TEXTURE_SIZE, TEXTURE_SIZE);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer);
    // Set "renderedTexture" as our colour attachement #0
    glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);
    GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
    glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers
    // check OpenGL error
    for (GLenum err; (err = glGetError()) != GL_NO_ERROR; ) {
      std::cerr << "OpenGL error: " << err << std::endl;
    }
    // Always check that our framebuffer is ok
    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    {
      std::cerr << "OpenGL error: " << std::endl;
      return;
    }
    }
    // Switch to new framebuffer 
    glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
    // Clear the screen
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // Rendering Code - Lots of code so I have removed some of it.
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(CommonDefinitions::PANEL_FOV_VERT_DEG, ASPECT_RATIO, mnNearClip, mnFarClip);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(...);
    // background = black
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glShadeModel(GL_SMOOTH);
    glDisable(GL_DITHER);
    glDisable(GL_TEXTURE);
    glDisable(GL_FOG);
    ...
    // Enable graphics card state
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_NORMAL_ARRAY);
    ...
     glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, laDiffuse);
      glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, laSpecular);
      int32 lnShininess = lpObject->GetShininess(tcObject::FLS);
      glMateriali(GL_FRONT_AND_BACK, GL_SHININESS, lnShininess);
      ...
      // Inform the graphics card which vertex VBO is active
      glBindBuffer(GL_ARRAY_BUFFER, lpObject->GetVertexId());
      // Enable the vertex pointer on the graphics card
      glVertexPointer(3, GL_FLOAT, 0, NULL);
      // Set the normal VBO on the graphics card
      glBindBuffer(GL_ARRAY_BUFFER, lpObject->GetNormalId());
      glNormalPointer(GL_FLOAT, 0, NULL);
      //Move object into position
      glPushMatrix(); //Save state
      glMultMatrixf((GLfloat*)(lpObject->GetTransform()));
      glMultMatrixf((GLfloat*)(lpObject->GetAttitude()));
      GLfloat lnScale = lpObject->GetScale();
      glScalef(lnScale, lnScale, lnScale);
      // Render - magic number 3 = vertices per triangle
      glDrawArrays(GL_TRIANGLES, 0, lpObject->GetVertexBufferSize()/3);
      glPopMatrix(); //Restore state
      ...
    // Disable graphics card state
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
    glGetTexImage(GL_TEXTURE_2D,0,GL_RGB,GL_UNSIGNED_BYTE,maColorTest);
    // switch back to window-system-provided framebuffer
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    // check OpenGL error
    for (GLenum err; (err = glGetError()) != GL_NO_ERROR; ) {
      std::cerr << "OpenGL error: " << err << std::endl;
    }
  ofstream fout("image.dat",ios::out | ios::binary);
  fout.write((const char *)maColorTest,TEXTURE_SIZE * TEXTURE_SIZE * 3);
  fout.close();

Answer 1

正如@Reto提到的，我在上面的代码中遗漏了glViewport()调用。谢谢。