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Open Asset Import Library (assimp)
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/** @file Implementation of the post processing step to invert
 * all normals in meshes with infacing normals.
 */

#include "AssimpPCH.h"

// internal headers
#include "FixNormalsStep.h"
#include "System/FastMath.h"

using namespace Assimp;


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

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

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

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

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

	if (bHas)
		 DefaultLogger::get()->debug("FixInfacingNormalsProcess finished. Found issues.");
	else DefaultLogger::get()->debug("FixInfacingNormalsProcess finished. No changes to the scene.");
}

// ------------------------------------------------------------------------------------------------
// Apply the step to the mesh
bool FixInfacingNormalsProcess::ProcessMesh( aiMesh* pcMesh, unsigned int index)
{
	ai_assert(NULL != pcMesh);

	// Nothing to do if there are no model normals
	if (!pcMesh->HasNormals())return false;

	// Compute the bounding box of both the model vertices + normals and
	// the umodified model vertices. Then check whether the first BB
	// is smaller than the second. In this case we can assume that the
	// normals need to be flipped, although there are a few special cases ..
	// convex, concave, planar models ...

	aiVector3D vMin0 (1e10f,1e10f,1e10f);
	aiVector3D vMin1 (1e10f,1e10f,1e10f);
	aiVector3D vMax0 (-1e10f,-1e10f,-1e10f);
	aiVector3D vMax1 (-1e10f,-1e10f,-1e10f);

	for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
	{
		vMin1.x = std::min(vMin1.x,pcMesh->mVertices[i].x);
		vMin1.y = std::min(vMin1.y,pcMesh->mVertices[i].y);
		vMin1.z = std::min(vMin1.z,pcMesh->mVertices[i].z);

		vMax1.x = std::max(vMax1.x,pcMesh->mVertices[i].x);
		vMax1.y = std::max(vMax1.y,pcMesh->mVertices[i].y);
		vMax1.z = std::max(vMax1.z,pcMesh->mVertices[i].z);

		const aiVector3D vWithNormal = pcMesh->mVertices[i] + pcMesh->mNormals[i];

		vMin0.x = std::min(vMin0.x,vWithNormal.x);
		vMin0.y = std::min(vMin0.y,vWithNormal.y);
		vMin0.z = std::min(vMin0.z,vWithNormal.z);

		vMax0.x = std::max(vMax0.x,vWithNormal.x);
		vMax0.y = std::max(vMax0.y,vWithNormal.y);
		vMax0.z = std::max(vMax0.z,vWithNormal.z);
	}

	const float fDelta0_x = (vMax0.x - vMin0.x);
	const float fDelta0_y = (vMax0.y - vMin0.y);
	const float fDelta0_z = (vMax0.z - vMin0.z);

	const float fDelta1_x = (vMax1.x - vMin1.x);
	const float fDelta1_y = (vMax1.y - vMin1.y);
	const float fDelta1_z = (vMax1.z - vMin1.z);

	// Check whether the boxes are overlapping
	if ((fDelta0_x > 0.0f) != (fDelta1_x > 0.0f))return false;
	if ((fDelta0_y > 0.0f) != (fDelta1_y > 0.0f))return false;
	if ((fDelta0_z > 0.0f) != (fDelta1_z > 0.0f))return false;

	// Check whether this is a planar surface
	const float fDelta1_yz = fDelta1_y * fDelta1_z;

	if (fDelta1_x < 0.05f * math::sqrtf( fDelta1_yz ))return false;
	if (fDelta1_y < 0.05f * math::sqrtf( fDelta1_z * fDelta1_x ))return false;
	if (fDelta1_z < 0.05f * math::sqrtf( fDelta1_y * fDelta1_x ))return false;

	// now compare the volumes of the bounding boxes
	if (math::fabsf(fDelta0_x * fDelta1_yz) <
		math::fabsf(fDelta1_x * fDelta1_y * fDelta1_z))
	{
		if (!DefaultLogger::isNullLogger())
		{
			char buffer[128]; // should be sufficiently large
			::sprintf(buffer,"Mesh %i: Normals are facing inwards (or the mesh is planar)",index);
			DefaultLogger::get()->info(buffer);
		}

		// Invert normals
		for (unsigned int i = 0; i < pcMesh->mNumVertices;++i)
			pcMesh->mNormals[i] *= -1.0f;

		// ... and flip faces
		for (unsigned int i = 0; i < pcMesh->mNumFaces;++i)
		{
			aiFace& face = pcMesh->mFaces[i];
			for( unsigned int b = 0; b < face.mNumIndices / 2; b++)
				std::swap( face.mIndices[b], face.mIndices[ face.mNumIndices - 1 - b]);
		}
		return true;
	}
	return false;
}
