assimp/code/CalcTangentsProcess.cpp

/*
---------------------------------------------------------------------------
Open Asset Import Library (ASSIMP)
---------------------------------------------------------------------------

Copyright (c) 2006-2008, ASSIMP Development Team

All rights reserved.

Redistribution and use of this software in source and binary forms, 
with or without modification, are permitted provided that the following 
conditions are met:

* Redistributions of source code must retain the above
  copyright notice, this list of conditions and the
  following disclaimer.

* Redistributions in binary form must reproduce the above
  copyright notice, this list of conditions and the
  following disclaimer in the documentation and/or other
  materials provided with the distribution.

* Neither the name of the ASSIMP team, nor the names of its
  contributors may be used to endorse or promote products
  derived from this software without specific prior
  written permission of the ASSIMP Development Team.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
---------------------------------------------------------------------------
*/

/** @file Implementation of the post processing step to calculate 
 *  tangents and bitangents for all imported meshes
 */

#include <vector>
#include <assert.h>
#include "DefaultLogger.h"
#include "CalcTangentsProcess.h"
#include "SpatialSort.h"
#include "../include/aiPostProcess.h"
#include "../include/aiMesh.h"
#include "../include/aiScene.h"

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
CalcTangentsProcess::CalcTangentsProcess()
{
	// nothing to do here
}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
CalcTangentsProcess::~CalcTangentsProcess()
{
	// nothing to do here
}

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool CalcTangentsProcess::IsActive( unsigned int pFlags) const
{
	return (pFlags & aiProcess_CalcTangentSpace) != 0;
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void CalcTangentsProcess::Execute( aiScene* pScene)
{
	DefaultLogger::get()->debug("CalcTangentsProcess begin");

	bool bHas = false;
	for( unsigned int a = 0; a < pScene->mNumMeshes; a++)
		if(ProcessMesh( pScene->mMeshes[a]))bHas = true;

	if (bHas)DefaultLogger::get()->debug("CalcTangentsProcess finished. There was much work to do ...");
	else DefaultLogger::get()->debug("CalcTangentsProcess finished");
}

// ------------------------------------------------------------------------------------------------
// Calculates tangents and bitangents for the given mesh
bool CalcTangentsProcess::ProcessMesh( aiMesh* pMesh)
{
	// we assume that the mesh is still in the verbose vertex format where each face has its own set
	// of vertices and no vertices are shared between faces. Sadly I don't know any quick test to 
	// assert() it here.
    //assert( must be verbose, dammit);

	// TODO (Aramis)
	// If we had a model format in the lib which has native support for
	// tangents and bitangents, it would be necessary to add a
	// "KillTangentsAndBitangents" flag ...
	if (pMesh->mTangents && pMesh->mBitangents)
	{
		return false;
	}

	// what we can check, though, is if the mesh has normals and texture coord. That's a requirement
	if( pMesh->mNormals == NULL || pMesh->mTextureCoords[0] == NULL)
	{
		DefaultLogger::get()->error("Normal vectors and at least one "
			"texture coordinate set are required to calculate tangents. ");
		return false;
	}

	// calculate the position bounds so we have a reliable epsilon to check position differences against 
	aiVector3D minVec( 1e10f, 1e10f, 1e10f), maxVec( -1e10f, -1e10f, -1e10f);
	for( unsigned int a = 0; a < pMesh->mNumVertices; a++)
	{
		minVec.x = std::min( minVec.x, pMesh->mVertices[a].x);
		minVec.y = std::min( minVec.y, pMesh->mVertices[a].y);
		minVec.z = std::min( minVec.z, pMesh->mVertices[a].z);
		maxVec.x = std::max( maxVec.x, pMesh->mVertices[a].x);
		maxVec.y = std::max( maxVec.y, pMesh->mVertices[a].y);
		maxVec.z = std::max( maxVec.z, pMesh->mVertices[a].z);
	}

	// calculate epsilons border
	const float epsilon = 1e-5f;
	const float posEpsilon = (maxVec - minVec).Length() * epsilon;
	const float angleEpsilon = 0.9999f;

	// create space for the tangents and bitangents
	pMesh->mTangents = new aiVector3D[pMesh->mNumVertices];
	pMesh->mBitangents = new aiVector3D[pMesh->mNumVertices];

	const aiVector3D* meshPos = pMesh->mVertices;
	const aiVector3D* meshNorm = pMesh->mNormals;
	const aiVector3D* meshTex = pMesh->mTextureCoords[0];
	aiVector3D* meshTang = pMesh->mTangents;
	aiVector3D* meshBitang = pMesh->mBitangents;
	
	// calculate the tangent and bitangent for every face
	for( unsigned int a = 0; a < pMesh->mNumFaces; a++)
	{
		const aiFace& face = pMesh->mFaces[a];

		// triangle or polygon... we always use only the first three indices. A polygon
		// is supposed to be planar anyways....
		// FIXME: (thom) create correct calculation for multi-vertex polygons maybe?
		const unsigned int p0 = face.mIndices[0], p1 = face.mIndices[1], p2 = face.mIndices[2];

		// position differences p1->p2 and p1->p3
		aiVector3D v = meshPos[p1] - meshPos[p0], w = meshPos[p2] - meshPos[p0];

		// texture offset p1->p2 and p1->p3
		float sx = meshTex[p1].x - meshTex[p0].x, sy = meshTex[p1].y - meshTex[p0].y;
        float tx = meshTex[p2].x - meshTex[p0].x, ty = meshTex[p2].y - meshTex[p0].y;
		float dirCorrection = (tx * sy - ty * sx) < 0.0f ? -1.0f : 1.0f;

		// tangent points in the direction where to positive X axis of the texture coords would point in model space
		// bitangents points along the positive Y axis of the texture coords, respectively
		aiVector3D tangent, bitangent;
		tangent.x = (w.x * sy - v.x * ty) * dirCorrection;
        tangent.y = (w.y * sy - v.y * ty) * dirCorrection;
        tangent.z = (w.z * sy - v.z * ty) * dirCorrection;
        bitangent.x = (w.x * sx - v.x * tx) * dirCorrection;
        bitangent.y = (w.y * sx - v.y * tx) * dirCorrection;
        bitangent.z = (w.z * sx - v.z * tx) * dirCorrection;

		// store for every vertex of that face
		for( unsigned int b = 0; b < face.mNumIndices; b++)
		{
			unsigned int p = face.mIndices[b];

			// project tangent and bitangent into the plane formed by the vertex' normal
			aiVector3D localTangent = tangent - meshNorm[p] * (tangent * meshNorm[p]);
			aiVector3D localBitangent = bitangent - meshNorm[p] * (bitangent * meshNorm[p]);
			localTangent.Normalize(); localBitangent.Normalize();

			// and write it into the mesh.
			meshTang[p] = localTangent;
			meshBitang[p] = localBitangent;
		}
    }

	// create a helper to quickly find locally close vertices among the vertex array
	SpatialSort vertexFinder( meshPos, pMesh->mNumVertices, sizeof( aiVector3D));
	std::vector<unsigned int> verticesFound;

	// in the second pass we now smooth out all tangents and bitangents at the same local position 
	// if they are not too far off.
	std::vector<bool> vertexDone( pMesh->mNumVertices, false);
	for( unsigned int a = 0; a < pMesh->mNumVertices; a++)
	{
		if( vertexDone[a])
			continue;

		const aiVector3D& origPos = pMesh->mVertices[a];
		const aiVector3D& origNorm = pMesh->mNormals[a];
		const aiVector3D& origTang = pMesh->mTangents[a];
		const aiVector3D& origBitang = pMesh->mBitangents[a];
		std::vector<unsigned int> closeVertices;
		closeVertices.push_back( a);

		// find all vertices close to that position
		vertexFinder.FindPositions( origPos, posEpsilon, verticesFound);

		// look among them for other vertices sharing the same normal and a close-enough tangent/bitangent
		static const float MAX_DIFF_ANGLE = 0.701f;
		for( unsigned int b = 0; b < verticesFound.size(); b++)
		{
			unsigned int idx = verticesFound[b];
			if( vertexDone[idx])
				continue;
			if( meshNorm[idx] * origNorm < angleEpsilon)
				continue;
			if( meshTang[idx] * origTang < MAX_DIFF_ANGLE)
				continue;
			if( meshBitang[idx] * origBitang < MAX_DIFF_ANGLE)
				continue;

			// it's similar enough -> add it to the smoothing group
			closeVertices.push_back( idx);
			vertexDone[idx] = true;
		}

		// smooth the tangents and bitangents of all vertices that were found to be close enough
		aiVector3D smoothTangent( 0, 0, 0), smoothBitangent( 0, 0, 0);
		for( unsigned int b = 0; b < closeVertices.size(); b++)
		{
			smoothTangent += meshTang[ closeVertices[b] ];
			smoothBitangent += meshBitang[ closeVertices[b] ];
		}
		smoothTangent.Normalize();
		smoothBitangent.Normalize();

		// and write it back into all affected tangents
		for( unsigned int b = 0; b < closeVertices.size(); b++)
		{
			meshTang[ closeVertices[b] ] = smoothTangent;
			meshBitang[ closeVertices[b] ] = smoothBitangent;
		}
	}
	return true;
}