OpenGL screen savers

How to develop a fantastic 3D screen saver with OpenGL 1.1

Environment: VC5.0, Win95/98, NT4.0

This article just gives a description about how to use some
new render functions in OpenGL 1.1 with a fantastic 3D screen
saver. And give a practical method to solve the problem about how to
instance the setting dialogbox successfully from windows
system properties dialogbox both in Win95 and NT. The code also give
a demo to use function pointer.

1. Interleaved arrays and indices array for rendering.
   In OpenGl 1.1, there are some new functions quite different
   from old Version, which make rendering 3D picture faster and easily in
   coding.
2. One of new methods in OpenGl 1.1 is that it can allow the
   developer to set the most important data , such as texture, colors,
   normals, vertexs, in an interleaved data structure body and build one vertex
   array. Besides that, an indices array is necessary for rendering. The two key
   functions in this realization are “glInterleavedArrays” and
   “glDrawArrays”. The definition of vertex structure for “glInterleavedArrays”
   function depends on what format will be used in “glInterleavedArrays”. The
   definition of the indices array also bases on what type of rendering index in
   “glDrawArrays” The following is the vertex structure and indices (with C++
   template) in this demo.

   //Vertex value of the object
   template <class Typeclass vertex
   {
   public:
       Type m_texture[2];
       Type m_normal[3];
       Type m_vertex[3];
   public:
       vertex(){};
       ~vertex(){};
       void SetTexture(Type texture1, Type texture2)
       {
           m_texture[0] = texture1;
           m_texture[1] = texture2;
       };
       void GetTexture(Type* texture1, Type* texture2)
       {
           *texture1 = m_texture[0];
           *texture2 = m_texture[1];
       };
       void SetNormal(Type normal1, Type normal2, Type normal3)
       {
           m_normal[0] = normal1;
           m_normal[1] = normal2;
           m_normal[2] = normal3;
       };
       void GetNormal(Type* normal1, Type* normal2, Type* normal3)
       {
           *normal1 = m_normal[0];
           *normal2 = m_normal[1];
           *normal3 = m_normal[2];
       };
       void SetVertex(Type vertex1, Type vertex2, Type vertex3)
       {
           m_vertex[0] = vertex1;
           m_vertex[1] = vertex2;
           m_vertex[2] = vertex3;
       };
       void GetVertex(Type* vertex1, Type* vertex2, Type* vertex3)
       {
           *vertex1 = m_vertex[0];
           *vertex2 = m_vertex[1];
           *vertex3 = m_vertex[2];
       };
   };
   typedef vertex<float fVertex;
   //Indices value of the object
   template <class Typeclass indices
   {
   public:
       Type m_indice[2];
   public:
       indices(){};
       ~indices(){};
       void SetIndices(Type indice1, Type indice2)
       {
            m_indice[0] = indice1;
            m_indice[1] = indice2;
       };
       void GetIndices(Type* indice1, Type* indice2)
       {
            *indice1 = m_indice[0];
            *indice2 = m_indice[1];
       };
   };
   typedef indices<unsigned int uiIndice;
   The rendering implementation in code is
   class CSGObject : public CObject
   {
   //Attribute
   private:
   …………
       fVertex*    m_vertex;   //vertex array
       uiIndice*   m_indice;   //indices array
   …………
       float       m_x;        //x-coordinate of the center of object
       float       m_y;        //y-coordinate of the center of object
       float       m_z;        //z-coordinate of the center of object
       float       m_sx;       //scale in x-axis
       float       m_sy;       //scale in y-axis
       float       m_sz;       //scale in z-axis
       float       m_rx;       //rotating angle around x-axis
       float       m_ry;       //rotating angle around y-axis
       float       m_rz;       //rotating angle around z-axis
       BOOL        m_bWire;    //flag for showing wireframe or not
   public:
   …………
       void DrawObject(void);
   …………
   };
   void CSGObject::DrawObject(void)
   {
       int k;
       int i;
       if(m_bWire)
       {
            m_dvalue.SetValue(m_dMemvalue.m_dX*4, m_dMemvalue.m_dY*4, m_dMemvalue.m_dZ*4);
            m_size.SetValue((int)(m_Memsize.m_row*2.5), (int)(m_Memsize.m_col*2.5));
           glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
       }
       else
       {
            m_dvalue.SetValue(m_dMemvalue.m_dX, m_dMemvalue.m_dY, m_dMemvalue.m_dZ);
            m_size.SetValue(m_Memsize.m_row*10, m_Memsize.m_col*10);
           glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
       }
       if(m_Oldsize.m_row != m_size.m_row || m_Oldsize.m_col != m_size.m_col)
       {
           if(m_vertex)
                delete []m_vertex;
           if(m_indice)
                delete []m_indice;
           m_vertex = new fVertex[(m_size.m_row+1) * (m_size.m_col+1)];
           m_indice = new uiIndice[m_size.m_row * (m_size.m_col+1)];
           (*FuncIndice)(m_indice, m_size);
           m_Oldsize.m_row = m_size.m_row;
           m_Oldsize.m_col = m_size.m_col;
       }
       (*FuncVertex)(m_vertex, m_size, m_factor, m_dvalue);
       SetTexture();
       glInterleavedArrays(GL_T2F_N3F_V3F, 0, m_vertex);
       glColorMaterial(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE);
       glEnable(GL_COLOR_MATERIAL);
       glMatrixMode(GL_MODELVIEW);
       glTranslatef(m_x, m_y, m_z);
       glScalef(m_sx, m_sy, m_sz);
       glRotatef(m_rx, 1.0, 0.0, 0.0);
       glRotatef(m_ry, 0.0, 1.0, 0.0);
       glRotatef(m_rz, 0.0, 0.0, 1.0);
       for(i=0; i< m_size.m_row; i++)
       {
           k = i*(m_size.m_col+1);
           glDrawElements(GL_TRIANGLE_STRIP, 2*(m_size.m_col+1), GL_UNSIGNED_INT, &m_indice[k]);
       }
       glRotatef((float)(-1.0 * m_rz), 0.0, 0.0, 1.0);
       glRotatef((float)(-1.0 * m_ry), 0.0, 1.0, 0.0);
       glRotatef((float)(-1.0 * m_rx), 1.0, 0.0, 0.0);
       glScalef((float)(1.0f/m_sx), (float)(1.0f/m_sy), (float)(1.0f/m_sz));
       glTranslatef((float)(-1.0 * m_x), (float)(-1.0 * m_y), (float)(-1.0 * m_z));
   }
   

3. Texture
   By the way of calling glEnable(GL_TEXTURE_2D),
   glTexImage2D(………) and
   glInterleavedArrays(………), the texture map can be
   realized.
4. Fogs
   The fogs in rendering is implemented by the functions of glFog
   and glEnable(GL_FOG).
5. Function pointer
   In this code, there is only one universal geometry object
   class. In this class, there is a pointer of geometry data calculation
   function. Signing different 3D geometry data generating
   function to this function pointer can create different geometry object.
6. About triggering setting dialogbox from Windows properties
   dialog box.
   This sample gives a practical method to solve the problem of
   instancing the setting dialogbox. The key point is that the message for
   clicking setting button in Windows system properties dialogbox in Win95
   is different from in NT. In Win95, command line __argv[1] for clicking
   setting dialogbox is “/c”, but in NT, is “/c XXXXXX”, XXXXXX is a number, may be
   the system dialogbox window handle or other window handle (I am not sure).
   So parsing the __argv[1] should be in single character not
   string. This part of code is shown following:

   BOOL CGlsaverApp::InitInstance()
   {
       // Standard initialization
       // If you are not using these features and wish to reduce the size
       //  of your final executable, you should remove from the following
       //  the specific initialization routines you do not need.
       Enable3dControls();
       enmCMDline cmdLine;
       cmdLine = getCMDline(__argv[1]);
       if (__argc == 1 || getCMDline(__argv[1]) == CMD_SETTING)
            DoSaverSetting();
       else if(getCMDline(__argv[1]) == CMD_PREVIEW)
       {
            DoSaverPreview();
            return TRUE;
       }
       else if(getCMDline(__argv[1]) == CMD_SAVER)
       {
            DoScreenSaver();
            return TRUE;
       }
       // Nothing happened, return FALSE so that we exit the
       //  application, rather than start the application’s message pump.
       return FALSE;
   }
   enmCMDline CGlsaverApp::getCMDline(LPTSTR pszCmd)
   {
       if (pszCmd[0] == _T(‘-‘) || pszCmd[0] == _T(‘/’))
            pszCmd++;
       LPTSTR  pszChar = pszCmd;
       switch(*pszChar)
       {
           case _T(‘c’):
                 return CMD_SETTING;
           case _T(‘C’):
                 return CMD_SETTING;
           case _T(‘p’):
                 return CMD_PREVIEW;
           case _T(‘P’):
                 return CMD_PREVIEW;
           case _T(‘s’):
                 return CMD_SAVER;
           case _T(‘S’):
                 return CMD_SAVER;
           default:
                 return CMD_NONE;
       }
   }

Download source – 48KB

Date Posted: 03/17/99