3DS轉換矩陣

經過半天的勞力，終於成功載入轉換矩陣 (0x4160 trunk)，全靠 lib3ds 的原碼。

// Trunk 0x4160 comes before 0x4120,
// during the loading of 0x4160 we got the information to
// change the clockwise/anti-clockwise triangle winding or not
// and apply this information during the loading of 0x4120
bool invertTriangleWinding = false;

// ...

// Loading the local coordinates chunk
// It's base from lib3ds: http://www.lib3ds.org
case 0x4160:
{
 // We are using row major matrix
 Mat44f matrix = Mat44f::cIdentity;
 for(size_t i=0; i<4; ++i)
  mStream->read(matrix.row[i], sizeof(float) * 3);

 // Flip X coordinate of vertices if mesh matrix has negative determinant
 if((invertWinding = (matrix.determinant() < 0)) == true) {
  Mat44f inv = matrix.inverse();

  matrix.m00 = -matrix.m00;
  matrix.m01 = -matrix.m01;
  matrix.m02 = -matrix.m02;
  matrix.m03 = -matrix.m03;

  matrix = (inv * matrix).transpose();

  size_t vertexCount = getVertexCount();
  Vec3f* vertex = getVertexPointer();

  for(size_t i=0; i<vertexCount; ++i) {
   // Transform tmp using matrix, where matrix[3] holds the translation
#ifdef FLIP_YZ_AXIS
   Vec4f tmp(vertex[i].x, -vertex[i].z, vertex[i].y, 0);
   tmp = (matrix * tmp) + matrix[3];
   vertex[i] = Vec3f(tmp.x, tmp.z, -tmp.y);
#else
   Vec4f tmp(vertex[i].x, vertex[i].y, vertex[i].z, 0);
   tmp = (matrix * tmp) + matrix[3];
   vertex[i] = Vec3f(tmp.x, tmp.y, tmp.z);
#endif
  }
 }
}  break;

// ...

// Loading the face description (index values) trunk
case 0x4120:
{
 uint16_t faceCount = 0;
 uint16_t* indexArray = nullptr;

 // ...

 if(invertTriangleWinding) {
  for(size_t i=0; i<faceCount*3; i+=3)
   std::swap(indexArray[i], indexArray[i+2]);
 }
}  break;