Introduce mikktshape

code/PostProcessing/GenerateMikkTSpaceTangents.cpp

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+#include "GenerateMikkTSpaceTangents.h"
+
+namespace Assimp {
+
+bool GenerateMikkTSpaceTangents::IsActive(unsigned int pFlags) const {
+
+}
+
+void GenerateMikkTSpaceTangents::Execute(aiScene* pScene) {
+
+}
+
+}

code/PostProcessing/GenerateMikkTSpaceTangents.h

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+#pragma once
+
+#include "Common/BaseProcess.h"
+
+namespace Assimp {
+
+class GenerateMikkTSpaceTangents : public BaseProcess {
+public:
+    GenerateMikkTSpaceTangents() = default;
+    ~GenerateMikkTSpaceTangents() override = default;
+    bool IsActive(unsigned int pFlags) const override;
+    void Execute(aiScene* pScene) override;
+
+};
+
+}
+

contrib/MikkTSpace/mikktspace.h

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