在ogre中进行精细射线检测

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原创最新推荐文章于 2026-07-24 16:11:08 发布 2.6k 阅读 AI 写同款· GEO 优化 ›

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ogre有一个RaySceneQuery的类，在默认场景管理器下，这个类返回一组RaySceneQueryResultEntry，他们都是通过包围盒进行的检测，由于包围盒过于简陋，我们可以再进行更精细的基于面的射线碰撞检测。

主要注意的就是mesh的构造方式，是否用了index，index是16位还是32位，其他的没什么了，射线到三角的检测函数取自dx例子，ogre自己也提供了，不过我感觉不太好用。

另外，mesh的顶点格式还要注意，position不一定独享其所在的source段，可能包含其它信息比如顶点色。所以我们必须计算一个偏移量。

废话少说，看代码。

bool IntersectMesh( const Ogre::Ray &ray, const Entity *pEntity, int *SubEntityIndex, Vector3 *IntersectTriangleA, Vector3 *IntersectTriangleB, Vector3 *IntersectTriangleC, float *t, float *u, float *v )
{
int numSubEntities = pEntity->getNumSubEntities();

for ( int i = 0; i<numSubEntities; i++ )
{
  //get VertexData and IndexData
  Ogre::SubEntity *pSubEntity = pEntity->getSubEntity( i );
  Ogre::VertexData *pSubEntityVertexData = pSubEntity->getVertexDataForBinding();
  Ogre::SubMesh *pSubMesh = pSubEntity->getSubMesh();
  Ogre::IndexData *pSubEntityIndexData = pSubMesh->indexData;

  //read buffer
  Ogre::VertexBufferBinding::VertexBufferBindingMap ghm_VBBM = pSubEntityVertexData->vertexBufferBinding->getBindings();
  int iPositonIndex = -1;
  //find position buffer
  DWORD ElementCount = (DWORD)pSubEntityVertexData->vertexDeclaration->getElementCount();
  for ( DWORD k = 0; k < ElementCount; i++)
  {
   const VertexElement *ghm_VE = pSubEntityVertexData->vertexDeclaration->getElement( k );
   if ( ghm_VE->getSemantic() == VES_POSITION )  //we are just interested in position
   {
    //bingo,get it
    iPositonIndex = k;
    break;
   }
  }

if ( iPositonIndex == -1 ) //can't find position buffer
return false;

  //read vertex buffer
  Ogre::VertexBufferBinding::VertexBufferBindingMap::iterator vbbm_interator = ghm_VBBM.find( iPositonIndex );
  size_t vertexbuffersize = vbbm_interator->second->getNumVertices() * vbbm_interator->second->getVertexSize(); //buffer size
  BYTE *VertexBuffer = new BYTE[vertexbuffersize];                //build vertex buffer
  vbbm_interator->second->readData( 0, vertexbuffersize, VertexBuffer );

  //float *fVertexBuffer = (float*)VertexBuffer;

  size_t PositionElementOffset = vbbm_interator->second->getVertexSize() - 12;  //得到顶点之外的字节数
  //check index
  Ogre::RenderOperation roSub;
  pSubMesh->_getRenderOperation( roSub );
  if ( roSub.useIndexes )  //使用index
  {

   //read index buffer
   size_t indexbuffersize = pSubEntityIndexData->indexBuffer->getNumIndexes() * pSubEntityIndexData->indexBuffer->getIndexSize(); //buffer size
   BYTE *IndexBuffer = new BYTE[indexbuffersize];                 //build index buffer

   //read data
   pSubEntityIndexData->indexBuffer->readData( 0, indexbuffersize, IndexBuffer );

size_t numfaces = pSubEntityIndexData->indexBuffer->getNumIndexes() / 3;

   //进行射线碰撞检测，很慢啊。。。。。。55555
   //check index type
   if ( pSubEntityIndexData->indexBuffer->getType() == Ogre::HardwareIndexBuffer::IT_16BIT )
   {
    short *iIndexBuffer = (short*)IndexBuffer;
    for ( size_t j = 0; j<numfaces; j++ )
    {
     float fa,fb,fc;
     memcpy( &fa, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fb, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + sizeof(float) + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fc, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + sizeof(float) * 2 + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     Vector3 t1 = Vector3( fa, fb, fc );

     memcpy( &fa, &VertexBuffer[ iIndexBuffer[ j * 3 + 1 ] * sizeof(float) * 3 + ( iIndexBuffer[ j * 3 + 1 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fb, &VertexBuffer[ iIndexBuffer[ j * 3 + 1 ] * sizeof(float) * 3 + sizeof(float) + ( iIndexBuffer[ j * 3 + 1 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fc, &VertexBuffer[ iIndexBuffer[ j * 3 + 1 ] * sizeof(float) * 3 + sizeof(float) * 2 + ( iIndexBuffer[ j * 3 + 1 ] * PositionElementOffset ) ], sizeof(float) );
     Vector3 t2 = Vector3( fa, fb, fc );

     memcpy( &fa, &VertexBuffer[ iIndexBuffer[ j * 3 + 2 ] * sizeof(float) * 3 + ( iIndexBuffer[ j * 3 + 2 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fb, &VertexBuffer[ iIndexBuffer[ j * 3 + 2 ] * sizeof(float) * 3 + sizeof(float) + ( iIndexBuffer[ j * 3 + 2 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fc, &VertexBuffer[ iIndexBuffer[ j * 3 + 2 ] * sizeof(float) * 3 + sizeof(float) * 2 + ( iIndexBuffer[ j * 3 + 2 ] * PositionElementOffset ) ], sizeof(float) );
     Vector3 t3 = Vector3( fa, fb, fc );

bool rt = IntersectTriangle( ray.getOrigin(), ray.getDirection(), t1, t2, t3, t, u, v );

     if ( rt )
     {
      SAFE_DELETE_ARRAY( VertexBuffer );
      SAFE_DELETE_ARRAY( IndexBuffer );

      if ( SubEntityIndex )
      {
       *SubEntityIndex = i;
      }
      if ( IntersectTriangleA && IntersectTriangleB && IntersectTriangleC )
      {
       *IntersectTriangleA = t1;
       *IntersectTriangleB = t2;
       *IntersectTriangleC = t3;
      }
      return true;
     }
    }

   }
   else   //this is 32 bit index
   {
    long *iIndexBuffer = (long*)IndexBuffer;
    for ( size_t j = 0; j<numfaces; j++ )
    {
     float fa,fb,fc;
     memcpy( &fa, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fb, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + sizeof(float) + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     memcpy( &fc, &VertexBuffer[ iIndexBuffer[ j * 3 ] * sizeof(float) * 3 + sizeof(float) * 2 + ( iIndexBuffer[ j * 3 ] * PositionElementOffset ) ], sizeof(float) );
     Vector3 t1 = Vector3( fa, fb, fc );

     bool rt = IntersectTriangle( ray.getOrigin(), ray.getDirection(), t1, t2, t3, t, u, v );
     if ( rt )
     {
      SAFE_DELETE_ARRAY( VertexBuffer );
      SAFE_DELETE_ARRAY( IndexBuffer );

   SAFE_DELETE_ARRAY( VertexBuffer );
   SAFE_DELETE_ARRAY( IndexBuffer );
  }
  else //don't use index
  {
   //get face number
   size_t numfaces = vbbm_interator->second->getNumVertices() / 3;
   for ( size_t j = 0; j<numfaces; j++ )
   {
    float fa,fb,fc;
    memcpy( &fa, &VertexBuffer[ j * 9 + j * 9 * PositionElementOffset ], sizeof(float) );
    memcpy( &fb, &VertexBuffer[ j * 9 + sizeof(float) + ( j * 9 + sizeof(float) ) * PositionElementOffset ], sizeof(float) );
    memcpy( &fc, &VertexBuffer[ j * 9 + sizeof(float) * 2 + ( j * 9 + sizeof(float) * 2 ) * PositionElementOffset ], sizeof(float) );
    Vector3 t1 = Vector3( fa, fb, fc );

    memcpy( &fb, &VertexBuffer[ j * 9 + sizeof(float) * 3 + ( j * 9 + sizeof(float) * 3 ) * PositionElementOffset ], sizeof(float) );
    memcpy( &fb, &VertexBuffer[ j * 9 + sizeof(float) * 4 + ( j * 9 + sizeof(float) * 4 ) * PositionElementOffset ], sizeof(float) );
    memcpy( &fc, &VertexBuffer[ j * 9 + sizeof(float) * 5 + ( j * 9 + sizeof(float) * 5 ) * PositionElementOffset ], sizeof(float) );
    Vector3 t2 = Vector3( fa, fb, fc );

    memcpy( &fb, &VertexBuffer[ j * 9 + sizeof(float) * 6 + ( j * 9 + sizeof(float) * 6 ) * PositionElementOffset ], sizeof(float) );
    memcpy( &fb, &VertexBuffer[ j * 9 + sizeof(float) * 7 + ( j * 9 + sizeof(float) * 7 ) * PositionElementOffset ], sizeof(float) );
    memcpy( &fc, &VertexBuffer[ j * 9 + sizeof(float) * 8 + ( j * 9 + sizeof(float) * 8 ) * PositionElementOffset ], sizeof(float) );
    Vector3 t3 = Vector3( fa, fb, fc );

    bool rt = IntersectTriangle( ray.getOrigin(), ray.getDirection(), t1, t2, t3, t, u, v );
    if ( rt )
    {
     SAFE_DELETE_ARRAY( VertexBuffer );

     if ( SubEntityIndex )
     {
      *SubEntityIndex = i;
     }
     if ( IntersectTriangleA && IntersectTriangleB && IntersectTriangleC )
     {
      *IntersectTriangleA = t1;
      *IntersectTriangleB = t2;
      *IntersectTriangleC = t3;
     }
     return true;
    }
   }
  }

}

return false;
}

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