Pivot/center point in x.file

Pivot/center point in x.file

• MarcoL

  You can use this function:
  
  D3DXComputeBoundingSphere( (D3DXVECTOR3*)pData, numVertices, fvfSize, &center, &m_boundingRadius );

  It will tell you the center of your mesh and it will tell you the radius of the smallest sphere around your mesh...with this information you can treat your entire mesh has if it was a sphere...you remove the center point value to put your mesh at 0,0,0 (move it with a translation matrix in World Matrix with negative value of the center coordinate)and after that you can rotate it and move it back where you want it's center in the 3D world

  This demo is also in Managed code on their site

  void CMeshInstance::SetMesh( CMesh* pMesh )
  {

  Release();
  m_pMesh = pMesh;
  
  // Compute bounding sphere
  if ( m_pMesh )
  {

  D3DXVECTOR3 center;
  LPD3DXMESH pD3DXMesh = m_pMesh->GetMesh();
  DWORD numVertices = pD3DXMesh->GetNumVertices();
  DWORD fvfSize = D3DXGetFVFVertexSize( pD3DXMesh->GetFVF() );
  char* pData = NULL;
  if ( FAILED( pD3DXMesh->LockVertexBuffer( 0, (void**)&pData ) ) )
  {

  SHOWERROR( "Failed to lock mesh vertex buffer.", __FILE__, __LINE__ );
  return;
  

  }
  D3DXComputeBoundingSphere( (D3DXVECTOR3*)pData, numVertices, fvfSize, &center, &m_boundingRadius );
  if ( FAILED( pD3DXMesh->UnlockVertexBuffer() ) )
  {

  SHOWERROR( "Failed to unlock mesh vertex buffer.", __FILE__, __LINE__ );
  return;
  

  }
  

  }
  

  }

  http://www.c-unit.com/tutorials/directx/ t=24

  
  

• Mumshelp

  Can you explain in more detail I know how I can calculate the bounding sphere of the mesh, but I don't understand how I can use that information to change my center/pivot point. I don't understand what you mean by this "you remove the center point value to put your mesh at 0,0,0 (move it with a translation matrix in World Matrix with negative value of the center coordinate)and after that you can rotate it and move it back where you want it's center in the 3D world"

  I'm using managed directx

  
  

• Soaring Skies

  Thank you both of you:) I finaly understand. The point I have been missig is that rotations always happen about 0,0,0.
  

• xlthim

  or load the model into the modelling package and center it on the origin

  
  
  

• lchristensen

  You are setting the world matrix to a rotation and rotations always happen about 0,0,0. So if you 'move' your mesh such that what used to be a,b,c (where a,b,c is the center point from getboundingspehere) is now 0,0,0 then do the rotation, then move the mesh bak so that 0,0,0 is now a,b,c again then you will get the effect you want.

  The easiest way is to set your world matrix to do all 3 of these things

  world = translate(-a,-b,-c) * rotate(your original rotation) * translate(a,b,c)

  
  
  
• Pivot/center point in x.file