//---------------------------------------------------------------
#endregion
//---------------------------------------------------------------
//---------------------------------------------------------------
#region Methods
//---------------------------------------------------------------
/// <summary>
/// Creates a deep-copy of the current <see cref="IGraphicsStream"/>.
/// </summary>
/// <returns>A deep-copy of the current <see cref="IGraphicsStream"/>.</returns>
public override IGraphicsStream Clone()
{
IGraphicsStream stream = new TangentStream(this.Size);
stream.Copy(this);
return(stream);
}
/// <summary>
/// calculate tangent, normal and binormal stream
/// Triangle list is assumed for indices format
/// there will be a more sophisticated version of this functions for SubSets, which will
/// have much similiarity to NVidias MeshMender
/// </summary>
/// <param name="positions">stream containing vertex positions</param>
/// <param name="textures">stream containing texture coordinates</param>
/// <param name="indices">stream containing indices</param>
/// <returns></returns>
public static IGraphicsStream[] CalcTangentSpaceStreams(VertexStreams.PositionStream positions,
VertexStreams.TextureStream textures,
VertexStreams.IndexStream indices)
{
// create ret streams
VertexStreams.NormalStream normal = new VertexStreams.NormalStream(positions.Size);
VertexStreams.TangentStream tangent = new VertexStreams.TangentStream(positions.Size);
VertexStreams.BinormalStream binormal = new VertexStreams.BinormalStream(positions.Size);
for (int i = 0; i < indices.Size / 3; i++)
{
// prepare data
Vector3 s = Vector3.Zero;
Vector3 t = Vector3.Zero;
Triangle tri = indices.GetTriangle(i);
// calculate s.X and t.X
Vector3 a = new Vector3(positions[tri.B].X - positions[tri.A].X,
textures[tri.B].X - textures[tri.A].X,
textures[tri.B].Y - textures[tri.A].Y);
Vector3 b = new Vector3(positions[tri.C].X - positions[tri.A].X,
textures[tri.C].X - textures[tri.A].X,
textures[tri.C].Y - textures[tri.A].Y);
Vector3 axb = Vector3.Cross(a, b);
if (Basic.Abs(axb.X) > float.Epsilon)
{
s.X = -axb.Y / axb.X;
t.X = -axb.Z / axb.X;
}
// calculate s.Y and t.Y
a.X = positions[tri.B].Y - positions[tri.A].Y;
b.X = positions[tri.C].Y - positions[tri.A].Y;
axb = Vector3.Cross(a, b);
if (Basic.Abs(axb.X) > float.Epsilon)
{
s.Y = -axb.Y / axb.X;
t.Y = -axb.Z / axb.X;
}
// calculate s.Z and t.Z
a.X = positions[tri.B].Z - positions[tri.A].Z;
b.X = positions[tri.C].Z - positions[tri.A].Z;
axb = Vector3.Cross(a, b);
if (Basic.Abs(axb.X) > float.Epsilon)
{
s.Z = -axb.Y / axb.X;
t.Z = -axb.Z / axb.X;
}
// normalize and calculate normal vector
s.Normalize();
t.Normalize();
// swap t if normal vector of texture space triangle has a negative z direction
if (axb.X < float.Epsilon)
{
t = -t;
}
Vector3 sxt = Vector3.Unit(Vector3.Cross(s, t));
// add s, t, sxt into the streams
// to get the average value - in a later version I will add functionality
// to duplicate vertices if the results for one vertex are too different
// (like the NVidia MeshMender does ...)
tangent[tri.A] += s;
tangent[tri.B] += s;
tangent[tri.C] += s;
binormal[tri.A] += t;
binormal[tri.B] += t;
binormal[tri.C] += t;
normal[tri.A] += sxt;
normal[tri.B] += sxt;
normal[tri.C] += sxt;
}
// so last but not least renormalize the summed vectors
for (int i = 0; i < positions.Size; i++)
{
tangent[i].Normalize();
binormal[i].Normalize();
normal[i].Normalize();
}
return(new IGraphicsStream[] { tangent, binormal, normal });
}