Hi,

I am an undergraduate student wiritng a thesis report on pov-ray version 3.6.0.
I have been studying pov-ray source code but since there is no description or
explanation about many parts of the code, I have beem facing lots of
difficulties. I have been trying to figure out the point inside a triangle
test. I understood the plane intersection part, which is simple but cant figure
out the point inside the triangle test. I googled to find out what algorithm was
implemented but didnt find any similarity with any algorithm I have searched.
So, can someone please explain the test to me.

Here is the code ray triangle intersection...

static int Intersect_Triangle(RAY *Ray, TRIANGLE *Triangle, DBL *Depth)
{
  DBL NormalDotOrigin, NormalDotDirection;
  DBL s, t;

  Increase_Counter(stats[Ray_Triangle_Tests]);

  if (Test_Flag(Triangle, DEGENERATE_FLAG))
  {
    return(false);
  }

  VDot(NormalDotDirection, Triangle->Normal_Vector, Ray->Direction);

  if (fabs(NormalDotDirection) < EPSILON)
  {
    return(false);
  }

  VDot(NormalDotOrigin, Triangle->Normal_Vector, Ray->Initial);

  *Depth = -(Triangle->Distance + NormalDotOrigin) / NormalDotDirection;

  if ((*Depth < DEPTH_TOLERANCE) || (*Depth > Max_Distance))
  {
    return(false);
  }

  switch (Triangle->Dominant_Axis)
  {
    case X:

      s = Ray->Initial[Y] + *Depth * Ray->Direction[Y];
      t = Ray->Initial[Z] + *Depth * Ray->Direction[Z];

      if ((Triangle->P2[Y] - s) * (Triangle->P2[Z] - Triangle->P1[Z]) <
          (Triangle->P2[Z] - t) * (Triangle->P2[Y] - Triangle->P1[Y]))
      {
        return(false);
      }

      if ((Triangle->P3[Y] - s) * (Triangle->P3[Z] - Triangle->P2[Z]) <
          (Triangle->P3[Z] - t) * (Triangle->P3[Y] - Triangle->P2[Y]))
      {
        return(false);
      }

      if ((Triangle->P1[Y] - s) * (Triangle->P1[Z] - Triangle->P3[Z]) <
          (Triangle->P1[Z] - t) * (Triangle->P1[Y] - Triangle->P3[Y]))
      {
        return(false);
      }

      Increase_Counter(stats[Ray_Triangle_Tests_Succeeded]);

      return(true);

    case Y:

      s = Ray->Initial[X] + *Depth * Ray->Direction[X];
      t = Ray->Initial[Z] + *Depth * Ray->Direction[Z];

      if ((Triangle->P2[X] - s) * (Triangle->P2[Z] - Triangle->P1[Z]) <
          (Triangle->P2[Z] - t) * (Triangle->P2[X] - Triangle->P1[X]))
      {
        return(false);
      }

      if ((Triangle->P3[X] - s) * (Triangle->P3[Z] - Triangle->P2[Z]) <
          (Triangle->P3[Z] - t) * (Triangle->P3[X] - Triangle->P2[X]))
      {
        return(false);
      }

      if ((Triangle->P1[X] - s) * (Triangle->P1[Z] - Triangle->P3[Z]) <
          (Triangle->P1[Z] - t) * (Triangle->P1[X] - Triangle->P3[X]))
      {
        return(false);
      }

      Increase_Counter(stats[Ray_Triangle_Tests_Succeeded]);

      return(true);

    case Z:

      s = Ray->Initial[X] + *Depth * Ray->Direction[X];
      t = Ray->Initial[Y] + *Depth * Ray->Direction[Y];

      if ((Triangle->P2[X] - s) * (Triangle->P2[Y] - Triangle->P1[Y]) <
          (Triangle->P2[Y] - t) * (Triangle->P2[X] - Triangle->P1[X]))
      {
        return(false);
      }

      if ((Triangle->P3[X] - s) * (Triangle->P3[Y] - Triangle->P2[Y]) <
          (Triangle->P3[Y] - t) * (Triangle->P3[X] - Triangle->P2[X]))
      {
        return(false);
      }

      if ((Triangle->P1[X] - s) * (Triangle->P1[Y] - Triangle->P3[Y]) <
          (Triangle->P1[Y] - t) * (Triangle->P1[X] - Triangle->P3[X]))
      {
        return(false);
      }

      Increase_Counter(stats[Ray_Triangle_Tests_Succeeded]);

      return(true);
  }

  return(false);
}



Thanks in advance.

Post a reply to this message