problem with updating VBO

OpenGL OpenGL: Basic Coding
1

Hey,

I’m tryin’ to rotate a texture by changing the UV coords. It’s a cube model, that contains 6 faces (intern: materials). I want to rotate the texture of the ground face. All polygons can only be seen from the inside (face culling), so that i can use it as a skybox.


// Function Call

pApp->mdl3d_rotate_texture_inner_cube(MDL_SKYBOX, CUBE_MAT_GROUND, ROTATE_LEFT);

/////////////////////////////////////
// Definition A
/////////////////////////////////////

int CApp::mdl3d_rotate_texture_inner_cube(int ID, int cube_side, int rot_flag)
{
  int exit_code = ERR_EN_NO_ERROR; 
  Elem_3D_Mdl * pElem = this->mdl3d_get_elem(ID);

  if(pElem != NULL)
    {exit_code = pElem->pModel->rotate_texture_inner_cube(cube_side, rot_flag);}
  else
    {exit_code = ERR_EN_MDL_NOEXIST;}

  return exit_code;
}

/////////////////////////////////////
// Definition B
/////////////////////////////////////

int CModel_3D::rotate_texture_inner_cube(int cube_side, int rot_flag)
{
  int exit_code = ERR_EN_NO_ERROR;
  Material * pMaterial = NULL;

  switch(cube_side)
  {
    case CUBE_MAT_FRONT:
    {
      pMaterial = this->get_material("Cube Front");
    } break;
    case CUBE_MAT_LEFT:
    {
      pMaterial = this->get_material("Cube Left");
    } break;
    case CUBE_MAT_RIGHT:
    {
      pMaterial = this->get_material("Cube Right");
    } break;
    case CUBE_MAT_BACK:
    {
      pMaterial = this->get_material("Cube Back");
    } break;
    case CUBE_MAT_TOP:
    {
      pMaterial = this->get_material("Cube Top");
    } break;
    case CUBE_MAT_GROUND:
    {
      pMaterial = this->get_material("Cube Ground");
    } break; 
  };

  // UV leeren

  if(pMaterial != NULL)
    {this->clear_UV(pMaterial);}
  else
    {exit_code = ERR_EN_MAT_NOEXIST;}

  // neue UV ground

  if(exit_code == ERR_EN_NO_ERROR && cube_side == CUBE_MAT_GROUND)
  {
    switch(rot_flag)
    {
      case ROTATE_LEFT:
      {		
        this->add_face_UV(pMaterial, 3);  // (1 | 1) , that Vertex is (-x, -y, -z)
        this->add_face_UV(pMaterial, 1);  // (0 | 0) , that Vertex is (x, -y, z)
        this->add_face_UV(pMaterial, 4);  // (1 | 0) , that Vertex is (x, -y, -z)
        this->add_face_UV(pMaterial, 1);  // (0 | 0) , that Vertex is (x, -y, z)
        this->add_face_UV(pMaterial, 3);  // (1 | 1) , that Vertex is (-x, -y, -z)
        this->add_face_UV(pMaterial, 2);  // (0 | 1) , that Vertex is (-x, -y, z)
        exit_code = this->update_UV(pMaterial);
      } break;
    };
  }

  return exit_code;
}

/////////////////////////////////////
// Definition C
/////////////////////////////////////

int CModel_3D::update_UV(Material * pElem)
{
  int exit_code = ERR_EN_NO_ERROR;
  glm::vec2 * pUV = new glm::vec2[pElem->number_vertexes];

  glBindBuffer(GL_ARRAY_BUFFER, pElem->pVBO[INDEX_UV]);
								
  if(glGetError() == GL_NO_ERROR)
  {
    glBufferSubData(GL_ARRAY_BUFFER, 0, (sizeof(glm::vec2) * pElem->number_vertexes), pUV); // pElem->number_vertexes = 6!
	
    if(glGetError() != GL_NO_ERROR)
      {exit_code = ERR_EN_MDL_VBO_SUB_DATA;}
  }
  else
    {exit_code = ERR_EN_MDL_BIND_VBO;}

  // Speicher freigeben

  if(pUV != NULL)
    {delete [] pUV;}

  return exit_code;
}

So when I try that, the ground cube face just has a single color. I failed to rotate the texture to the left. Why is that?
No error is returned by any of my functions. When I skip the rotation function mentioned at the very top, the texture is shown correctly.

U can see the image, so you can see what I mean:

Image Of SkyBox

2

Okay… sorry… I came up with the solution the moment I clicked on “post” ^^
pUV was empty… sorry

3

This, by the way, is an awful, awful, awful, awful way of doing what you want.

You can use a texture matrix instead. That way you don’t need to change the VBO data.