146 lines
8 KiB
C
146 lines
8 KiB
C
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/** \file mikktspace/mikktspace.h
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* \ingroup mikktspace
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*/
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/**
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* Copyright (C) 2011 by Morten S. Mikkelsen
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef __MIKKTSPACE_H__
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#define __MIKKTSPACE_H__
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Author: Morten S. Mikkelsen
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* Version: 1.0
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*
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* The files mikktspace.h and mikktspace.c are designed to be
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* stand-alone files and it is important that they are kept this way.
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* Not having dependencies on structures/classes/libraries specific
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* to the program, in which they are used, allows them to be copied
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* and used as is into any tool, program or plugin.
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* The code is designed to consistently generate the same
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* tangent spaces, for a given mesh, in any tool in which it is used.
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* This is done by performing an internal welding step and subsequently an order-independent evaluation
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* of tangent space for meshes consisting of triangles and quads.
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* This means faces can be received in any order and the same is true for
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* the order of vertices of each face. The generated result will not be affected
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* by such reordering. Additionally, whether degenerate (vertices or texture coordinates)
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* primitives are present or not will not affect the generated results either.
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* Once tangent space calculation is done the vertices of degenerate primitives will simply
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* inherit tangent space from neighboring non degenerate primitives.
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* The analysis behind this implementation can be found in my master's thesis
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* which is available for download --> http://image.diku.dk/projects/media/morten.mikkelsen.08.pdf
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* Note that though the tangent spaces at the vertices are generated in an order-independent way,
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* by this implementation, the interpolated tangent space is still affected by which diagonal is
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* chosen to split each quad. A sensible solution is to have your tools pipeline always
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* split quads by the shortest diagonal. This choice is order-independent and works with mirroring.
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* If these have the same length then compare the diagonals defined by the texture coordinates.
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* XNormal which is a tool for baking normal maps allows you to write your own tangent space plugin
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* and also quad triangulator plugin.
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*/
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typedef int tbool;
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typedef struct SMikkTSpaceContext SMikkTSpaceContext;
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typedef struct {
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// Returns the number of faces (triangles/quads) on the mesh to be processed.
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int (*m_getNumFaces)(const SMikkTSpaceContext * pContext);
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// Returns the number of vertices on face number iFace
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// iFace is a number in the range {0, 1, ..., getNumFaces()-1}
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int (*m_getNumVerticesOfFace)(const SMikkTSpaceContext * pContext, const int iFace);
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// returns the position/normal/texcoord of the referenced face of vertex number iVert.
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// iVert is in the range {0,1,2} for triangles and {0,1,2,3} for quads.
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void (*m_getPosition)(const SMikkTSpaceContext * pContext, float fvPosOut[], const int iFace, const int iVert);
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void (*m_getNormal)(const SMikkTSpaceContext * pContext, float fvNormOut[], const int iFace, const int iVert);
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void (*m_getTexCoord)(const SMikkTSpaceContext * pContext, float fvTexcOut[], const int iFace, const int iVert);
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// either (or both) of the two setTSpace callbacks can be set.
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// The call-back m_setTSpaceBasic() is sufficient for basic normal mapping.
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// This function is used to return the tangent and fSign to the application.
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// fvTangent is a unit length vector.
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// For normal maps it is sufficient to use the following simplified version of the bitangent which is generated at pixel/vertex level.
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// bitangent = fSign * cross(vN, tangent);
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// Note that the results are returned unindexed. It is possible to generate a new index list
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// But averaging/overwriting tangent spaces by using an already existing index list WILL produce INCRORRECT results.
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// DO NOT! use an already existing index list.
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void (*m_setTSpaceBasic)(const SMikkTSpaceContext * pContext, const float fvTangent[], const float fSign, const int iFace, const int iVert);
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// This function is used to return tangent space results to the application.
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// fvTangent and fvBiTangent are unit length vectors and fMagS and fMagT are their
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// true magnitudes which can be used for relief mapping effects.
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// fvBiTangent is the "real" bitangent and thus may not be perpendicular to fvTangent.
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// However, both are perpendicular to the vertex normal.
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// For normal maps it is sufficient to use the following simplified version of the bitangent which is generated at pixel/vertex level.
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// fSign = bIsOrientationPreserving ? 1.0f : (-1.0f);
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// bitangent = fSign * cross(vN, tangent);
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// Note that the results are returned unindexed. It is possible to generate a new index list
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// But averaging/overwriting tangent spaces by using an already existing index list WILL produce INCRORRECT results.
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// DO NOT! use an already existing index list.
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void (*m_setTSpace)(const SMikkTSpaceContext * pContext, const float fvTangent[], const float fvBiTangent[], const float fMagS, const float fMagT,
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const tbool bIsOrientationPreserving, const int iFace, const int iVert);
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} SMikkTSpaceInterface;
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struct SMikkTSpaceContext
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{
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SMikkTSpaceInterface * m_pInterface; // initialized with callback functions
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void * m_pUserData; // pointer to client side mesh data etc. (passed as the first parameter with every interface call)
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};
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// these are both thread safe!
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tbool genTangSpaceDefault(const SMikkTSpaceContext * pContext); // Default (recommended) fAngularThreshold is 180 degrees (which means threshold disabled)
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tbool genTangSpace(const SMikkTSpaceContext * pContext, const float fAngularThreshold);
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// To avoid visual errors (distortions/unwanted hard edges in lighting), when using sampled normal maps, the
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// normal map sampler must use the exact inverse of the pixel shader transformation.
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// The most efficient transformation we can possibly do in the pixel shader is
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// achieved by using, directly, the "unnormalized" interpolated tangent, bitangent and vertex normal: vT, vB and vN.
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// pixel shader (fast transform out)
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// vNout = normalize( vNt.x * vT + vNt.y * vB + vNt.z * vN );
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// where vNt is the tangent space normal. The normal map sampler must likewise use the
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// interpolated and "unnormalized" tangent, bitangent and vertex normal to be compliant with the pixel shader.
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// sampler does (exact inverse of pixel shader):
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// float3 row0 = cross(vB, vN);
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// float3 row1 = cross(vN, vT);
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// float3 row2 = cross(vT, vB);
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// float fSign = dot(vT, row0)<0 ? -1 : 1;
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// vNt = normalize( fSign * float3(dot(vNout,row0), dot(vNout,row1), dot(vNout,row2)) );
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// where vNout is the sampled normal in some chosen 3D space.
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//
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// Should you choose to reconstruct the bitangent in the pixel shader instead
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// of the vertex shader, as explained earlier, then be sure to do this in the normal map sampler also.
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// Finally, beware of quad triangulations. If the normal map sampler doesn't use the same triangulation of
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// quads as your renderer then problems will occur since the interpolated tangent spaces will differ
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// eventhough the vertex level tangent spaces match. This can be solved either by triangulating before
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// sampling/exporting or by using the order-independent choice of diagonal for splitting quads suggested earlier.
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// However, this must be used both by the sampler and your tools/rendering pipeline.
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#ifdef __cplusplus
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}
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#endif
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#endif
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