Hi,

Is the following function for a support vector correct?

class Vector2
{
     public Vector2 SupportVector()
     {
         if (Math.Abs(X) > Math.Abs(Y))
             return new Vector2(X, 0);
         else
             return new Vector2(0, Y);
     }
}

Oh right, so I'm working on a physics engine ... contact normals. I've read about support vectors, but I can't find a definition, or code. I'm assuming a support vector is the orthogonal projection with greatest influence on V.

I think you mean the support vertex, which is the max dot product of a particular direction vector with the vertices of a (convex) polygon A.

Look at Dirk Gregorius 2013 slides, he explains it well.

https://code.google.com/p/box2d/downloads/list

The support point is the furthest (extreme) point in a given direction:

int Support( const std::vector< vector2 >& vertices, const vector2& vDirection )
{
  float flBestDistance = -FLT_MAX;
  int nBestVertex = -1;

  for ( int nVertex = 0; nVertex < nVertexCount; ++nVertex )
  {
    float flDistance = DotProduct( vertices[ nVertex ], vDirection );
    if ( flDistance > flBestDistance )
    {
      flBestDistance = flDistance;
      nBestVertex = nVertex;
    }
  }

  return nBestVertex;
}

@Javier - The X and Y are the x and y ordinates of a Vector2, this is c#, not c++, so a Vector is a geometric vector, not an array, or anything like that.

I wanted to make sure that i was using the right terminology, but it seems from the mixed responses that there is no single definition, and it can mean any number of things. I'll just call it a support vector for now.

Thanks all.

In a Vector2, X and Y seem fairly obvious. Support Vector, the definition seems a bit different than how Dirk defined it (I kinda love that someone mentions the GDC slides of someone, and then that someone then replies to the thread). If you're looking for the vector orthogonal, that's not right.

Vector2 perpVector = new Vector2(-Y, X); (or the negative of that for the other direction, and I'd have to double check, but that first one is the 'left' vector, the negative is the 'right' vector, if you consider the existing vector to be 'forward')