ITangentsComputationCallback Class Reference

This class is a callback for computing bump basis vectors on a given set of triangle/quad faces. More...

#include <gutil.h>

Public Member Functions
virtual int	GetNumberOfFaces () const =0
	Get the number of faces to be computed. More...
virtual int	GetNumberVerticesOfFace (const int faceIndex) const =0
	Get the number of vertices for the given index of face. More...
virtual void	GetVertex (Point3 &vertex, const int faceIndex, const int vertexIndex)=0
	Get the vertex coordinates for the given index of face and index of vertex. More...
virtual void	GetNormal (Point3 &normal, const int faceIndex, const int vertexIndex)=0
	Get the normal coordinates for the given index of face and index of vertex. More...
virtual void	GetTexture (Point2 &texture, const int faceIndex, const int vertexIndex)=0
	Get the texture coordinates for the given index of face and index of vertex. More...
virtual void	SetTangent (const Point3 &tangent, const Point3 &binormal, const float handedness, const int faceIndex, const int vertexIndex)=0
	Set the tangent and binormal(bitangent) coordinates for the given index of face and index of vertex. More...

Protected Member Functions
virtual	~ITangentsComputationCallback ()

Detailed Description

This class is a callback for computing bump basis vectors on a given set of triangle/quad faces.

The callback could be used as an input parameter of the method ComputeMikkTangents to compute the tangent and binormal(bitangent). The Plug-ins need to implement GetNumberOfFaces, GetNumberVerticesOfFace, GetVertex, GetNormal and GetTexture methods to input all required data to be computed, and SetTangent method to output the computation results. Usage: The following code demostrates how to compute the MikkT tangents for a given triangle face.

// Derive from ITangentsComputationCallback to fill the input data and receive the output results
class TangentsComputationCallback : public ITangentsComputationCallback
{
public:
    // Return 1 for the case with only one face
    virtual int GetNumberOfFaces() const override
    {
        return 1;
    }
    // Return the vertex number for the given face, 3 for triangle face, 4 for quad face
    virtual int GetNumberVerticesOfFace(const int faceIdx) const override
    {
        return 3;
    }
    // Input the position coordinates for the given vertex specified by the index of face and vertex
    virtual void GetVertex(Point3& position, const int faceIdx, const int vertIdx) override
    {
        if (vertIdx ==0) {
            position = { 0.0f, 0.0f, 0.0f };
        }
        else if (vertIdx==1) {
            position = { 0.0f, 1.0f, 0.0f };
        }
        else if (vertIdx==2) {
            position = { 1.0f, 0.0f, 0.0f };
        }
    }
    // Input the normal coordinates for the given vertex specified by the index of face and vertex
    virtual void GetNormal(Point3& normal, const int faceIdx, const int vertIdx) override
    {
        // Use the same normal coordinates { 0.0f, 0.0f, 1.0f } for all three vertices for simplicity
        if (vertIdx == 0) {
            normal = { 0.0f, 0.0f, 1.0f };
        }
        else if (vertIdx == 1) {
            normal = { 0.0f, 0.0f, 1.0f };
        }
        else if (vertIdx == 2) {
            normal = { 0.0f, 0.0f, 1.0f };
        }
    }
    // Input the texture coordinates for the given vertex specified by the index of face and vertex
    virtual void GetTexture(Point2& texture, const int faceIdx, const int vertIdx) override
    {
        if (vertIdx == 0) {
            texture = { 0.0f, 0.0f };
        }
        else if (vertIdx == 1) {
            texture = { 0.0f, 1.0f };
        }
        else if (vertIdx == 2) {
            texture = { 1.0f, 0.0f };
        }
    }
    // Ouput the tangent, bitangent and handedness for the given vertex specified by the index of face and vertex
    virtual void SetTangent(const Point3& tangent, const Point3& binormal,
        const float handedness, const int faceIdx, const int vertIdx) override
    {
        // Set tangent
        Point3 tan = tangent;
        outputTangents.Append(1, &tan);
 
        // Set binormal
        Point3 binml = binormal;
        outputBinormals.Append(1, &binml);
 
        // Set handedness
        float hand = handedness;
        outputHandednesses.Append(1, &hand);
    }
 
    // Return the computation result of Tangents
    Tab<Point3> GetTangentsResult() {
        return outputTangents;
    }
 
    // Return the computation result of Binormals
    Tab<Point3> GetBinormalsResult() {
        return outputBinormals;
    }
 
    // Return the computation result of Handednesses
    Tab<float> GetHandednessesResult() {
        return outputHandednesses;
    }
 
    private:
        // Output tangent/binormal data
        Tab<Point3> outputTangents;
        Tab<Point3> outputBinormals;
        Tab<float> outputHandednesses;
};
 
// Compute tangent basis
TangentsComputationCallback cb;
ComputeMikkTangents(&cb);
// Get the computation results
Tab<Point3> tangents = cb.GetTangentsResult();
Tab<Point3> binormals = cb.GetBinormalsResult();
Tab<float> handednesses = cb.GetHandednessesResult();

Constructor & Destructor Documentation

~ITangentsComputationCallback()

virtual ~ITangentsComputationCallback ( )

inlineprotectedvirtual

    {
    }

Member Function Documentation

GetNumberOfFaces()

virtual int GetNumberOfFaces ( ) const

pure virtual

Get the number of faces to be computed.

Returns

The the number of faces to be computed.

GetNumberVerticesOfFace()

virtual int GetNumberVerticesOfFace ( const int  faceIndex ) const

pure virtual

Get the number of vertices for the given index of face.

Parameters

faceIndex

The index of the face.

Returns

The number of vertices for the given index of face.

GetVertex()

virtual void GetVertex ( Point3 &  vertex, const int  faceIndex, const int  vertexIndex  )

pure virtual

Get the vertex coordinates for the given index of face and index of vertex.

Parameters

[out]	vertex	The vertex coordinates for the given index of face and index of vertex.
	faceIndex	The index of the face.
	vertexIndex	The index of the vertex based on the face.

GetNormal()

virtual void GetNormal ( Point3 &  normal, const int  faceIndex, const int  vertexIndex  )

pure virtual

Get the normal coordinates for the given index of face and index of vertex.

Parameters

[out]	normal	The normal coordinates for the given index of face and index of vertex.
	faceIndex	The index of the face.
	vertexIndex	The index of the vertex based on the face.

GetTexture()

virtual void GetTexture ( Point2 &  texture, const int  faceIndex, const int  vertexIndex  )

pure virtual

Get the texture coordinates for the given index of face and index of vertex.

Parameters

[out]	texture	The texture coordinates for the given index of face and index of vertex.
	faceIndex	The index of the face.
	vertexIndex	The index of the vertex based on the face.

SetTangent()

virtual void SetTangent ( const Point3 &  tangent, const Point3 &  binormal, const float  handedness, const int  faceIndex, const int  vertexIndex  )

pure virtual

Set the tangent and binormal(bitangent) coordinates for the given index of face and index of vertex.

Parameters

tangent	The tangent coordinates for the given index of face and index of vertex.
binormal	The binormal(bitangent) coordinates for the given index of face and index of vertex.
handedness	The handedness of tangent basis, either 1.0f or -1.0f. the handedness can be used to determine the direction of the binormal(bitangent), callers can use normal, tangent and handedness to re-calculate the binormal(bitangent) in pixel level, binormal(bitangent) = handedness * CrossProd(normal, tangent);
faceIndex	The index of the face.
vertexIndex	The index of the vertex based on the face.