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A small VRML viewer using OpenGL and MFC

, 30 Nov 1999
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    FIG. 1. You can easily display a wrl-based terrain using OpenGL and MFC.
     

    This contribution is a small MFC sample to learn how to :

    • display a VRML file
    • use OpenGL display lists
    • superimpose wireframe on a flat or smoothly shaded mesh
    • smoothly subdivide a 3D triangular mesh (from Charles Loop)
    • implement mouse interaction (rotation and translation)
    • build a scene graph from a vrml 2.0 file (hand-made and not lex-based)

    DISPLAY LIST

    Using display lists is a nice way to accelerate your rendering application. A display list compiles a sequence of gl drawings using standard OpenGL calls, then can be recalled later using a simple list id number. The resulting list is thus resident in the main memory in a precompilated mode, the which greatly accelerates rendering loops. A good command sequence to build a display list may be :
    int list = ::glGenLists(1); <font color="#009900">// ask for a free id number</font> 
    ::glNewList(list,GL_COMPILE_AND_EXECUTE); 
      ::glBegin(GL_TRIANGLES); 
      <font color="#009900">// std gl calls here... fill vertices, normals, colors</font> 
      ::glEnd(); 
    ::glEndList();
    A good command sequence to use a display list may be :
    if(::glIsList(list) == GL_TRUE)
      ::glCallList(m_ListOpenGL);
    The sample builds a scene graph from a vrml 2.0 file (exported via 3D Studio Max only), then uses display lists. Each 3D mesh contains a list number, and use a glCallList command instead of standards glBegin(GL_TRIANGLES) commands when its list is built. A flag m_Modified permits to rebuild the list when the mesh is modified.
    //******************************************** 
    // The 3D mesh class definition 
    //******************************************** 
    class CMesh2d : public CObject3d 
    { 
    private : 
    
     // Std datas 
     CArray<CVertex3d> m_ArrayVertex; 
     CArray<CFace3d>   m_ArrayFace; 
    
     // OpenGL-specific 
     unsigned int m_ListOpenGL; 
     BOOL m_ListDone; 
     BOOL m_Modified; 
     .../... 
    
    public : 
     BOOL glDraw(); 
     .../... 
    } 
    
    //******************************************** 
    // Mesh drawing 
    //******************************************** 
    BOOL CMesh2d::glDraw() 
    { 
     // Build list at first 
     if(!m_ListDone || m_Modified) 
      glBuildList(); 
    
     // Is the list valid ? 
     if(::glIsList(m_ListOpenGL)==GL_TRUE) 
     { 
       ::glCallList(m_ListOpenGL); 
      return TRUE; 
     } 
     return FALSE; 
    }

    SUPERIMPOSING WIREFRAME

    Sometime you would like to view the wireframe superimposing the flat or smooth shaded mesh. A good way to do this is to use the glPolygonOffset command, which creates a z-buffer offset. The following code shows the RenderScene function of the document, if one resumes two rendering passes are necessary, the first render the mesh using lighted flat mode, the second cut off the light, set the line mode, set a z-buffer offset, then draw the mesh again.
    <font color="#009900">//*********************************************** 
    // RenderScene 
    //***********************************************</font> 
    void CMeshDoc::RenderScene() 
    { 
     // Main drawing 
     m_SceneGraph.glDraw(); 
    
     // Add wireframe (no light, and line mode) 
     if(m_AddWireframe) 
     { 
      // Set state 
      ::glDisable(GL_LIGHTING); 
      ::glPolygonMode(GL_FRONT_AND_BACK,GL_LINE); 
      ::glEnable(GL_POLYGON_OFFSET_LINE); 
      ::glPolygonOffset(m_PolygonOffset,-1.0f); 
    
      // Draw again... 
      m_SceneGraph.glDraw(TYPE_MESh2D); 
    
      // Restore light and mode 
      ::glDisable(GL_POLYGON_OFFSET_LINE); 
      ::glPolygonMode(GL_FRONT_AND_BACK,GL_FILL); 
      ::glEnable(GL_LIGHTING); 
     } 
    
     ::glFlush(); 
    }

    FIG. 2. You can superimpose a wireframe on a flat-rendered mesh, using a second rendering loop with the line option.

    SMOOTH SUBDIVISION

    From a given 3D mesh, how can we improve the geometric appearence on smooth models ? The Charles Loop smooth subdivision comes here to help us. Each triangle is divided in four triangles (see figure 3), and a filtering function permits the mesh to be smoothed. The command is easy-to-use in the document, and I let you discover the details in the mesh's code.
    <img SRC="wrl_viewer/wrl_viewer3.jpg" height=191 width=600>
    FIG.3. The one-to-four triangle subdivision scheme used by method.
    <font color="#006600">//*********************************************** 
    // Smooth subdivision 
    </font><font color="#009900">//***********************************************</font> 
    void CMeshDoc::OnMeshLoop() 
    { 
     BeginWaitCursor(); 
     int NbObject = m_SceneGraph.NbObject(); 
     for(int i=0;i<NbObject;i++) 
     { 
       CObject3d *pObject3d = m_SceneGraph[i]; 
       if(pObject3d->GetType() == TYPE_MESh2D) 
      { 
       CMesh2d *pMesh  = (CMesh2d *)pObject3d; 
       pMesh->SubdivisionLoop(); 
      } 
     } 
     UpdateAllViews(NULL); 
     EndWaitCursor(); 
    }

    FIG.4. Two successives iterations of one-to-four subdivision scheme.

    FIG.5. See the visual enhancement obtained by a smooth subdivsion scheme..
     

    MOUSE INTERACTION

    A few variables and commands inserted in the view permit mouse interaction.
    <font color="#009900">//*********************************************** 
    // Left button -> x/y translation 
    //*********************************************** 
    </font>void CMeshView::OnLButtonDown(UINT nFlags, CPoint point) 
    { 
     m_LeftButtonDown = TRUE; 
     m_LeftDownPos = point; 
     SetCapture(); 
     CView::OnLButtonDown(nFlags, point); 
    } 
    void CMeshView::OnLButtonUp(UINT nFlags, CPoint point) 
    { 
     m_RightButtonDown = FALSE; 
     m_LeftButtonDown = FALSE; 
     ReleaseCapture(); 
     CView::OnLButtonUp(nFlags, point); 
    } 
    
    <font color="#009900">//*********************************************** 
    // Right button : z translation 
    //*********************************************** 
    </font>void CMeshView::OnRButtonDown(UINT nFlags, CPoint point) 
    { 
     m_RightButtonDown = TRUE; 
     m_RightDownPos = point; 
     SetCapture(); 
     CView::OnRButtonDown(nFlags, point); 
    } 
    void CMeshView::OnRButtonUp(UINT nFlags, CPoint point) 
    { 
     m_RightButtonDown = FALSE; 
     m_LeftButtonDown = FALSE; 
     ReleaseCapture(); 
     CView::OnRButtonUp(nFlags, point); 
    } 
    
    <font color="#009900">//*********************************************** 
    // Mouse move 
    // Both : rotation 
    // Left : x / y translation 
    // Right : z translation 
    //*********************************************** 
    </font>void CMeshView::OnMouseMove(UINT nFlags, CPoint point) 
    { 
     // Both : rotation 
     if(m_LeftButtonDown && m_RightButtonDown) 
     { 
      if(m_xyRotation) 
      { 
       m_yRotation -= (float)(m_LeftDownPos.x - point.x) * m_SpeedRotation; 
       m_xRotation -= (float)(m_LeftDownPos.y - point.y) * m_SpeedRotation; 
      } 
      else 
      { 
       m_zRotation -= (float)(m_LeftDownPos.x - point.x) * m_SpeedRotation; 
       m_xRotation -= (float)(m_LeftDownPos.y - point.y) * m_SpeedRotation; 
      } 
      m_LeftDownPos = point; 
      m_RightDownPos = point; 
      InvalidateRect(NULL,FALSE); 
     } 
    
     else 
    
     // Left : x / y translation 
     if(m_LeftButtonDown) 
     { 
      m_xTranslation -= (float)(m_LeftDownPos.x - point.x) * m_SpeedTranslation; 
      m_yTranslation += (float)(m_LeftDownPos.y - point.y) * m_SpeedTranslation; 
      m_LeftDownPos = point; 
      InvalidateRect(NULL,FALSE); 
     } 
    
     else 
    
     // Right : z translation 
     if(m_RightButtonDown) 
     { 
      m_zTranslation += (float)(m_RightDownPos.y - point.y) * m_SpeedTranslation; 
      m_RightDownPos = point; 
      InvalidateRect(NULL,FALSE); 
     } 
    
     CView::OnMouseMove(nFlags, point); 
    }

    License

    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here

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    About the Author

    Pierre Alliez

    France France
    No Biography provided

    Comments and Discussions

     
    Generalupdating surface Pin
    Olaf Petersen at 25-Oct-07 4:43
    memberOlaf Petersen25-Oct-07 4:43 
    Questionhow's that supposed to work? Pin
    Quarkette at 20-Aug-07 9:19
    memberQuarkette20-Aug-07 9:19 
    AnswerRe: how's that supposed to work? Pin
    DucThanh at 8-Oct-07 21:49
    memberDucThanh8-Oct-07 21:49 
    GeneralChange Alpha Value Pin
    Digvijay Gupta at 26-May-07 0:16
    memberDigvijay Gupta26-May-07 0:16 
    Generalthank you! Pin
    kru_pl at 9-Jan-07 2:13
    memberkru_pl9-Jan-07 2:13 
    Questioncan not draw Pin
    dapson.dps at 7-Sep-06 23:27
    memberdapson.dps7-Sep-06 23:27 
    GeneralSome suggest Pin
    Papyna at 11-Mar-06 21:09
    memberPapyna11-Mar-06 21:09 
    Generalnothing happens when i upload .wrl in openGL Pin
    vijethas at 20-Nov-05 14:09
    membervijethas20-Nov-05 14:09 
    GeneralThanks Pin
    coder@coder.gr at 6-Apr-05 10:42
    membercoder@coder.gr6-Apr-05 10:42 
    QuestionSpecifying a texture image onto the mesh surface? Pin
    TBiker at 24-Feb-05 12:33
    memberTBiker24-Feb-05 12:33 
    Generalwow Pin
    Yves at 5-Oct-04 18:38
    memberYves5-Oct-04 18:38 
    QuestionHow to save GDI+ bmp file as PDF File Format. Pin
    pubba at 13-Jul-04 21:03
    susspubba13-Jul-04 21:03 
    AnswerRe: How to save GDI+ bmp file as PDF File Format. Pin
    azonenberg at 4-Mar-08 5:09
    memberazonenberg4-Mar-08 5:09 
    Questionhow to display following files using opengl and mfc? Pin
    buaa2003 at 10-May-04 16:39
    memberbuaa200310-May-04 16:39 
    QuestionHow to run 2 different(or same) OpenGL objects in one DialogBox? Pin
    werter1 at 3-May-04 22:09
    memberwerter13-May-04 22:09 
    Generalproblem of runing the program Pin
    freeman18 at 25-Mar-04 18:22
    memberfreeman1825-Mar-04 18:22 
    QuestionReverse sub-division? Pin
    GernotFrisch at 4-Nov-03 11:01
    sussGernotFrisch4-Nov-03 11:01 
    General4x4 Matrix Pin
    macmac38 at 8-Oct-03 11:13
    membermacmac388-Oct-03 11:13 
    GeneralRe: 4x4 Matrix Pin
    pxp at 13-Feb-05 1:28
    memberpxp13-Feb-05 1:28 
    GeneralMemory allocation error Pin
    Frontman at 2-Oct-03 6:44
    memberFrontman2-Oct-03 6:44 
    GeneralOpengl Color and select Pin
    mcalves@coc.ufrj.br at 7-Apr-03 7:07
    membermcalves@coc.ufrj.br7-Apr-03 7:07 
    GeneralRe: Opengl Color and select Pin
    differ1 at 21-May-03 19:25
    memberdiffer121-May-03 19:25 
    GeneralRe: Opengl Color and select Pin
    mcalves@coc.ufrj.br at 22-May-03 3:26
    membermcalves@coc.ufrj.br22-May-03 3:26 
    GeneralRe: Opengl Color and select Pin
    differ1 at 22-May-03 18:12
    memberdiffer122-May-03 18:12 
    GeneralBad to da bone Pin
    Jeffrey Dutschke at 3-Apr-03 20:53
    memberJeffrey Dutschke3-Apr-03 20:53 
    GeneralNothing show if i load other .wrl files Pin
    Man at 6-Nov-01 1:15
    memberMan6-Nov-01 1:15 
    GeneralRe: Nothing show if i load other .wrl files Pin
    mattie at 10-Dec-01 11:49
    membermattie10-Dec-01 11:49 
    GeneralRe: Nothing show if i load other .wrl files Pin
    Anonymous at 10-Oct-02 22:45
    sussAnonymous10-Oct-02 22:45 
    GeneralRe: Nothing show if i load other .wrl files Pin
    Anonymous at 3-Apr-02 0:44
    memberAnonymous3-Apr-02 0:44 
    GeneralRe: Nothing show if i load other .wrl files Pin
    powerdigital at 29-May-02 18:55
    memberpowerdigital29-May-02 18:55 
    GeneralRe: Nothing show if i load other .wrl files Pin
    Anonymous at 31-May-02 1:38
    memberAnonymous31-May-02 1:38 
    GeneralRe: Nothing show if i load other .wrl files Pin
    Anonymous at 24-Jul-02 5:26
    sussAnonymous24-Jul-02 5:26 
    GeneralRe: Nothing show if i load other .wrl files Pin
    John Ulvr at 15-Nov-06 16:09
    memberJohn Ulvr15-Nov-06 16:09 
    GeneralRe: Nothing show if i load other .wrl files Pin
    garaber at 9-Mar-05 7:39
    membergaraber9-Mar-05 7:39 
    GeneralRe: Nothing show if i load other .wrl files Pin
    Huy Le Xuan at 20-Feb-06 0:44
    memberHuy Le Xuan20-Feb-06 0:44 
    GeneralRe: Nothing show if i load other .wrl files Pin
    scupid at 1-Mar-06 19:49
    memberscupid1-Mar-06 19:49 
    GeneralRe: Nothing show if i load other .wrl files Pin
    zhodj at 14-Nov-11 22:47
    memberzhodj14-Nov-11 22:47 
    GeneralCrashes on vertex/line/face changes Pin
    Jason Douglas at 6-Jul-01 9:47
    memberJason Douglas6-Jul-01 9:47 

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