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/** @file Implementation of the post processing step to invert
 * all normals in meshes with infacing normals.
 */

// internal headers
#include "FixNormalsStep.h"
#include <assimp/StringUtils.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/postprocess.h>
#include <assimp/scene.h>
#include <stdio.h>


using namespace Assimp;


// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
FixInfacingNormalsProcess::FixInfacingNormalsProcess() = default;

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
FixInfacingNormalsProcess::~FixInfacingNormalsProcess() = default;

// ------------------------------------------------------------------------------------------------
// 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)
{
    ASSIMP_LOG_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) {
        ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. Found issues.");
    } else {
        ASSIMP_LOG_DEBUG("FixInfacingNormalsProcess finished. No changes to the scene.");
    }
}

// ------------------------------------------------------------------------------------------------
// Apply the step to the mesh
bool FixInfacingNormalsProcess::ProcessMesh( aiMesh* pcMesh, unsigned int index)
{
    ai_assert(nullptr != 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 unmodified 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 * std::sqrt( fDelta1_yz ))return false;
    if (fDelta1_y < 0.05f * std::sqrt( fDelta1_z * fDelta1_x ))return false;
    if (fDelta1_z < 0.05f * std::sqrt( fDelta1_y * fDelta1_x ))return false;

    // now compare the volumes of the bounding boxes
    if (std::fabs(fDelta0_x * fDelta0_y * fDelta0_z) < std::fabs(fDelta1_x * fDelta1_yz)) {
        if (!DefaultLogger::isNullLogger()) {
            ASSIMP_LOG_INFO("Mesh ", index, ": Normals are facing inwards (or the mesh is planar)", index);
        }

        // 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;
}