A small VRML viewer using OpenGL and MFC

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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); // ask for a free id number 

::glNewList(list,GL_COMPILE_AND_EXECUTE); 
  ::glBegin(GL_TRIANGLES); 
  // std gl calls here... fill vertices, normals, colors 

  ::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.

//*********************************************** 

// RenderScene 

//*********************************************** 

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.

"wrl_viewer/wrl_viewer3.jpg" height=191 width=600>

FIG.3. The one-to-four triangle subdivision scheme used by method.

//*********************************************** 

// Smooth subdivision 

//*********************************************** 

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.

//*********************************************** 

// Left button -> x/y translation 

//*********************************************** 

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); 
} 

//*********************************************** 

// Right button : z translation 

//*********************************************** 

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); 
} 

//*********************************************** 

// Mouse move 

// Both : rotation 

// Left : x / y translation 

// Right : z translation 

//*********************************************** 

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); 
}

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thank you woshisiguigui 7hrs 29mins ago  your code is very useful. Sign In·View Thread·PermaLink mouse interaction.. how to make each obkect "clickable" (or selectable)? mimosa 10:20 24 Jun '08   nice work! I'd like to have some nice effect when I hoover the mouse over eash mesh, that the specific mesh the mouse is hoovering over, the mesh boundary will become highlighted (changed color, line thickness) and that I will know which triangle it is (number is fine), so I can keep track of a user selection.. Mat Sign In·View Thread·PermaLink 5.00/5 (1 vote) unable to render other .wrl files Rajani Kamath 0:13 29 Apr '08   hi, excellent program, but when I tried same program with other vrml files it is not working. can any body suggest me? thank u Sign In·View Thread·PermaLink 2.00/5 (5 votes) Wont compile in VisStudio 2005 Member 4600014 15:31 13 Mar '08   I get heaps & heaps of errors. What compiler has it been compiled in ? Sign In·View Thread·PermaLink 1.67/5 (2 votes) Re: Wont compile in VisStudio 2005 CDO 23:35 18 Mar '08   Same here, but was easy to fix. Problem comes from change in c++ standard scoping rules in for loop: solution: replace all for(int i; ,,,,, for(int j=0;,, with int i=0,j=0,k=0; for(i=0,..... HTH CDO Sign In·View Thread·PermaLink updating surface Olaf Petersen 4:43 25 Oct '07   Hi I'm searching for a ActiveX or other Libary to draw 3d surfaces with Color from high, like you have done. I want to draw 3d Images i get from an Camera and display them with min 12Hz. Is this possible by using this aktiveX, and how shoud i do this? best greating Olaf Sign In·View Thread·PermaLink 1.00/5 (1 vote) how's that supposed to work? Quarkette 9:19 20 Aug '07        for(int i=0;i<NbVertex;i++)      {           // Get distance to set of faces           distance = MAX_FLOAT;           for(int j=0;j<NbFace;j++)           {                double d = ::SquareDistanceVertexToFace(pArrayVertex->GetAt(i),                                                                              pArrayFace->GetAt(j),&v);                if(d < distance)                     distance = d;           }           // Get max for each vertex         if(distance > max)           {                max = distance;                if(ppFace != NULL && ppVertex != NULL)                {                     *ppFace = pArrayFace->GetAt(j); // how can j be accessible here?                     *ppVertex = pArrayVertex->GetAt(i);                }           }      } error: d:\c++\projects\wrl_viewer\lib3d\utils3d.cpp(582) : error C2065: 'j' : undeclared identifier why am i not able to compile the project? (using vs2005) q. Sign In·View Thread·PermaLink 1.00/5 (2 votes) Re: how's that supposed to work? DucThanh 21:49 8 Oct '07   Vs2005 compiler treat the variable "j" in those lines of code as the local one which can be used within the loop "for". To fix this problem, just declare it before the loop: // Get distance to set of faces distance = MAX_FLOAT; int j=0; for(j=0;j Nguyen Duc Thanh Sign In·View Thread·PermaLink Change Alpha Value Digvijay Gupta 0:16 26 May '07   I am implementing Transparency in Mesh Viewer. For that i have to change Alpha value. But when i change alpha value OF CCOLOR Class it hardly makes any difference. In that class Only m_Green,m_Red & m_Blue value been set.Even i m confused how thesse colors are transfered to OpenGl libraries or mesh. If anybody have any idea on this PLEASE help me. Thanks & Regards Digvijay Gupta Research Engineer Sign In·View Thread·PermaLink thank you! kru_pl 2:13 9 Jan '07   neat, tidy, beautiful thank you for your effort in writing the article! very usefull cheers kru Sign In·View Thread·PermaLink can not draw dapson.dps 23:27 7 Sep '06   i use IndexFaceSet format wrl file for test. when i debug it,i got the following erros: Face [4b8caf0] has the same vertices Face [4b8e770] has invalid reciproc. neighboring Face [4b90d70] has invalid reciproc. neighboring ok Calculate normal per vertex (522 faces, 261 vertices)...ok Build list.ok CMesh3d::Draw : unable to draw list 1 The thread 'Win32 Thread' (0xadc) has exited with code 0 (0x0). The thread 'Win32 Thread' (0xb9c) has exited with code 0 (0x0). The thread 'Win32 Thread' (0xa34) has exited with code 0 (0x0). can you give any help? thanks! daipeishan@163.com Sign In·View Thread·PermaLink 2.00/5 (2 votes) Some suggest Papyna 21:09 11 Mar '06   First Of all, admire your program I suggets you changed the gl_Vertex to to glEnableClientState,it will takes less time on calling-driver to draw vertexs Sign In·View Thread·PermaLink 1.00/5 (1 vote) nothing happens when i upload .wrl in openGL vijethas 14:09 20 Nov '05   Hey, I have a VRML 2.0 file where i am giving the object a scale, and sound. when i run it in cosmo player it works perfectly, just the way i want it but when i run it in openGL, only the graphic is showing up. It doesn't play the sound and the scale doen'st work.Is there any way to make it work? am i missing any include file?? In the code file, i have gstSeparator *rootSep; gstSeparator *vrmlSep = new gstSeparator(); vrmlSep = gstReadVRMLFile("heart2.wrl"); won't the other things that i have in VRML file work? This is partially what i have in my VRML file. DEF CLOCK TimeSensor { cycleInterval 1.0 loop TRUE } DEF heartSIZE PositionInterpolator { key [ 0.0, 0.2, 0.65, 1.0 ] keyValue [ 1.0 1.0 1.0, 1.5 1.5 1.5, 1.1 1.1 1.1, 1.0 1.0 1.0, ] } Sound{ Sound DEF Mysound AudioClip{ url [ "heartbeat3.wav" "http://www.a1freesoundeffects.com/popular1/heartbeat2.wav" ] } } ] } ROUTE CLOCK.fraction_changed TO heartSIZE.set_fraction ROUTE heartSIZE.value_changed TO heartTransform.set_scale ROUTE CLOCK.value_changed TO Mysound .set_scale Please help me. Thank you Sign In·View Thread·PermaLink 1.75/5 (4 votes) Thanks coder@coder.gr 10:42 6 Apr '05   Awesome code thank you for sharing it with the rest of us Sign In·View Thread·PermaLink 3.00/5 (2 votes) Specifying a texture image onto the mesh surface? TBiker 12:33 24 Feb '05   Great work! Is there any demo that shows a texture image mapped to a surface and displayed with this project? For example, I want to map an arbitrary image onto the mountain surface dataset. How is that done? Sign In·View Thread·PermaLink 1.10/5 (7 votes) wow Yves 18:38 5 Oct '04   Very, very, very interesting. Sign In·View Thread·PermaLink 2.00/5 (1 vote) How to save GDI+ bmp file as PDF File Format. pubba 21:03 13 Jul '04   Hi everybody, I want to export GDI+ bmp files as PDF File format. I have created GDI+ bmp Objects like this. Bitmap bmp7(L"myImage.jpg"); Now I want to save this bmp7 Object as PDF File format. u please help me if any one know this.:( Thanks. Sign In·View Thread·PermaLink 1.60/5 (6 votes) Re: How to save GDI+ bmp file as PDF File Format. azonenberg 5:09 4 Mar '08   On way to do this is to get a PDF virtual printer, and print the bitmap to the printer. You could also try to find a PDF-generation library somewhere. Off the top of my head, the first is likely to be a bit easier for testing but the second is preferred for production apps. Sign In·View Thread·PermaLink how to display following files using opengl and mfc? buaa2003 16:39 10 May '04   IGES(*.igs),Neutral(*.neu),STEP(*.stp),STL(*.stl),Inventor(*.iv), WaveFront(*.obj),Render(*.slp),ACIS File(*.sat),Assembly(*.asm). Please give me some examples like the above "A small VRML viewer",thank you very much! Sign In·View Thread·PermaLink 1.33/5 (12 votes) How to run 2 different(or same) OpenGL objects in one DialogBox? werter1 22:09 3 May '04   How to run 2 different(or same) OpenGL objects in one DialogBox? IDC_STATIC1 is a first OpenGL objects Scene window. IDC_STATIC2 is a second OpenGL objects Scene window. IDC_STATIC1 and IDC_STATIC2 ,they are placed on IDD_DIALOG1. code: pclStatic = (CStatic *)GetDlgItem(IDC_OpenGL_Window); pclGlView = new CGlView(pclStatic); pclGlView->OnCreate(); pclGlView->InitGL(); pclGlView->DrawGLScene(); pclStatic1 = (CStatic *)GetDlgItem(IDC_OpenGL_Window); pclGlView1 = new CGlView(pclStatic1); pclGlView1->OnCreate(); pclGlView1->InitGL(); pclGlView1->DrawGLScene(); Will not involve both windows (IDC_STATIC2,IDC_STATIC1) Sign In·View Thread·PermaLink 2.00/5 (1 vote) problem of runing the program freeman18 18:22 25 Mar '04   when i load a .wrl file which attached with the program, the program will hand, why this problem exit? Sign In·View Thread·PermaLink 1.50/5 (2 votes) Reverse sub-division? GernotFrisch 11:01 4 Nov '03   Er, nice, but my files have way to much triangles. Is there any way of un-subdividing them and make them still look good? Thank you, Gernot Sign In·View Thread·PermaLink 4x4 Matrix macmac38 11:13 8 Oct '03   Hi all, i found this article because i looked for a 4x4 matrix class. I ve started up with a small company this year to offer some 3d laserscan services. What i am looking for is some code to registrate the data from my scanner which comes in a x,y,z points coordinates ascii-file format. To registrate a number of scans i like to transform these x,y,z coordinates with a 4x4 (translation-rotation) matrix. If someone can help me with code, sources etc. please contact me. If someone like to program this for me i can also donate some money for that. Thanks, Mark Sign In·View Thread·PermaLink 2.00/5 (1 vote) Re: 4x4 Matrix pxp 1:28 13 Feb '05   Hi Mark, i was wondering if your search regarding point-coordinates transformation came up with some interesting stuff? Looking for the same myself. Something like a 'best-fit' or 'least-squares' algorithm would be needed there. Thank, Jan Sign In·View Thread·PermaLink Memory allocation error Frontman 6:44 2 Oct '03   There is "Direct3D9: (ERROR) :Memory still allocated!" in output window when terminate the program. What's up? Who knows? Sign In·View Thread·PermaLink 1.00/5 (1 vote)

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