1/** \file mikktspace/mikktspace.h
2 * \ingroup mikktspace
3 */
4/**
5 * Copyright (C) 2011 by Morten S. Mikkelsen
6 *
7 * This software is provided 'as-is', without any express or implied
8 * warranty. In no event will the authors be held liable for any damages
9 * arising from the use of this software.
10 *
11 * Permission is granted to anyone to use this software for any purpose,
12 * including commercial applications, and to alter it and redistribute it
13 * freely, subject to the following restrictions:
14 *
15 * 1. The origin of this software must not be misrepresented; you must not
16 * claim that you wrote the original software. If you use this software
17 * in a product, an acknowledgment in the product documentation would be
18 * appreciated but is not required.
19 * 2. Altered source versions must be plainly marked as such, and must not be
20 * misrepresented as being the original software.
21 * 3. This notice may not be removed or altered from any source distribution.
22 */
23
24#ifndef __MIKKTSPACE_H__
25#define __MIKKTSPACE_H__
26
27
28#ifdef __cplusplus
29extern "C" {
30#endif
31
32/* Author: Morten S. Mikkelsen
33 * Version: 1.0
34 *
35 * The files mikktspace.h and mikktspace.c are designed to be
36 * stand-alone files and it is important that they are kept this way.
37 * Not having dependencies on structures/classes/libraries specific
38 * to the program, in which they are used, allows them to be copied
39 * and used as is into any tool, program or plugin.
40 * The code is designed to consistently generate the same
41 * tangent spaces, for a given mesh, in any tool in which it is used.
42 * This is done by performing an internal welding step and subsequently an order-independent evaluation
43 * of tangent space for meshes consisting of triangles and quads.
44 * This means faces can be received in any order and the same is true for
45 * the order of vertices of each face. The generated result will not be affected
46 * by such reordering. Additionally, whether degenerate (vertices or texture coordinates)
47 * primitives are present or not will not affect the generated results either.
48 * Once tangent space calculation is done the vertices of degenerate primitives will simply
49 * inherit tangent space from neighboring non degenerate primitives.
50 * The analysis behind this implementation can be found in my master's thesis
51 * which is available for download --> http://image.diku.dk/projects/media/morten.mikkelsen.08.pdf
52 * Note that though the tangent spaces at the vertices are generated in an order-independent way,
53 * by this implementation, the interpolated tangent space is still affected by which diagonal is
54 * chosen to split each quad. A sensible solution is to have your tools pipeline always
55 * split quads by the shortest diagonal. This choice is order-independent and works with mirroring.
56 * If these have the same length then compare the diagonals defined by the texture coordinates.
57 * XNormal which is a tool for baking normal maps allows you to write your own tangent space plugin
58 * and also quad triangulator plugin.
59 */
60
61
62typedef int tbool;
63typedef struct SMikkTSpaceContext SMikkTSpaceContext;
64
65typedef struct {
66 // Returns the number of faces (triangles/quads) on the mesh to be processed.
67 int (*m_getNumFaces)(const SMikkTSpaceContext * pContext);
68
69 // Returns the number of vertices on face number iFace
70 // iFace is a number in the range {0, 1, ..., getNumFaces()-1}
71 int (*m_getNumVerticesOfFace)(const SMikkTSpaceContext * pContext, const int iFace);
72
73 // returns the position/normal/texcoord of the referenced face of vertex number iVert.
74 // iVert is in the range {0,1,2} for triangles and {0,1,2,3} for quads.
75 void (*m_getPosition)(const SMikkTSpaceContext * pContext, float fvPosOut[], const int iFace, const int iVert);
76 void (*m_getNormal)(const SMikkTSpaceContext * pContext, float fvNormOut[], const int iFace, const int iVert);
77 void (*m_getTexCoord)(const SMikkTSpaceContext * pContext, float fvTexcOut[], const int iFace, const int iVert);
78
79 // either (or both) of the two setTSpace callbacks can be set.
80 // The call-back m_setTSpaceBasic() is sufficient for basic normal mapping.
81
82 // This function is used to return the tangent and fSign to the application.
83 // fvTangent is a unit length vector.
84 // For normal maps it is sufficient to use the following simplified version of the bitangent which is generated at pixel/vertex level.
85 // bitangent = fSign * cross(vN, tangent);
86 // Note that the results are returned unindexed. It is possible to generate a new index list
87 // But averaging/overwriting tangent spaces by using an already existing index list WILL produce INCRORRECT results.
88 // DO NOT! use an already existing index list.
89 void (*m_setTSpaceBasic)(const SMikkTSpaceContext * pContext, const float fvTangent[], const float fSign, const int iFace, const int iVert);
90
91 // This function is used to return tangent space results to the application.
92 // fvTangent and fvBiTangent are unit length vectors and fMagS and fMagT are their
93 // true magnitudes which can be used for relief mapping effects.
94 // fvBiTangent is the "real" bitangent and thus may not be perpendicular to fvTangent.
95 // However, both are perpendicular to the vertex normal.
96 // For normal maps it is sufficient to use the following simplified version of the bitangent which is generated at pixel/vertex level.
97 // fSign = bIsOrientationPreserving ? 1.0f : (-1.0f);
98 // bitangent = fSign * cross(vN, tangent);
99 // Note that the results are returned unindexed. It is possible to generate a new index list
100 // But averaging/overwriting tangent spaces by using an already existing index list WILL produce INCRORRECT results.
101 // DO NOT! use an already existing index list.
102 void (*m_setTSpace)(const SMikkTSpaceContext * pContext, const float fvTangent[], const float fvBiTangent[], const float fMagS, const float fMagT,
103 const tbool bIsOrientationPreserving, const int iFace, const int iVert);
104} SMikkTSpaceInterface;
105
106struct SMikkTSpaceContext
107{
108 SMikkTSpaceInterface * m_pInterface; // initialized with callback functions
109 void * m_pUserData; // pointer to client side mesh data etc. (passed as the first parameter with every interface call)
110};
111
112// these are both thread safe!
113tbool genTangSpaceDefault(const SMikkTSpaceContext * pContext); // Default (recommended) fAngularThreshold is 180 degrees (which means threshold disabled)
114tbool genTangSpace(const SMikkTSpaceContext * pContext, const float fAngularThreshold);
115
116
117// To avoid visual errors (distortions/unwanted hard edges in lighting), when using sampled normal maps, the
118// normal map sampler must use the exact inverse of the pixel shader transformation.
119// The most efficient transformation we can possibly do in the pixel shader is
120// achieved by using, directly, the "unnormalized" interpolated tangent, bitangent and vertex normal: vT, vB and vN.
121// pixel shader (fast transform out)
122// vNout = normalize( vNt.x * vT + vNt.y * vB + vNt.z * vN );
123// where vNt is the tangent space normal. The normal map sampler must likewise use the
124// interpolated and "unnormalized" tangent, bitangent and vertex normal to be compliant with the pixel shader.
125// sampler does (exact inverse of pixel shader):
126// float3 row0 = cross(vB, vN);
127// float3 row1 = cross(vN, vT);
128// float3 row2 = cross(vT, vB);
129// float fSign = dot(vT, row0)<0 ? -1 : 1;
130// vNt = normalize( fSign * float3(dot(vNout,row0), dot(vNout,row1), dot(vNout,row2)) );
131// where vNout is the sampled normal in some chosen 3D space.
132//
133// Should you choose to reconstruct the bitangent in the pixel shader instead
134// of the vertex shader, as explained earlier, then be sure to do this in the normal map sampler also.
135// Finally, beware of quad triangulations. If the normal map sampler doesn't use the same triangulation of
136// quads as your renderer then problems will occur since the interpolated tangent spaces will differ
137// eventhough the vertex level tangent spaces match. This can be solved either by triangulating before
138// sampling/exporting or by using the order-independent choice of diagonal for splitting quads suggested earlier.
139// However, this must be used both by the sampler and your tools/rendering pipeline.
140
141#ifdef __cplusplus
142}
143#endif
144
145#endif
146