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

Copyright (c) 2006-2016, assimp team

All rights reserved.

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with or without modification, are permitted provided that the following
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* 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
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  contributors may be used to endorse or promote products
  derived from this software without specific prior
  written permission of the assimp team.

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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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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,
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*/

/** @file  SIBImporter.cpp
 *  @brief Implementation of the SIB importer class
 *
 *  The Nevercenter Silo SIB format is undocumented.
 *  All details here have been reverse engineered from
 *  studying the binary files output by Silo.
 *
 *  Nevertheless, this implementation is reasonably complete.
 */


#ifndef ASSIMP_BUILD_NO_SIB_IMPORTER

// internal headers
#include "SIBImporter.h"
#include "ByteSwapper.h"
#include "StreamReader.h"
#include "TinyFormatter.h"
#include "../contrib/ConvertUTF/ConvertUTF.h"
#include "../include/assimp/IOSystem.hpp"
#include "../include/assimp/DefaultLogger.hpp"
#include "../include/assimp/scene.h"


using namespace Assimp;

static const aiImporterDesc desc = {
    "Silo SIB Importer",
    "Richard Mitton (http://www.codersnotes.com/about)",
    "",
    "Does not apply subdivision.",
    aiImporterFlags_SupportBinaryFlavour,
    0, 0,
    0, 0,
    "sib"
};

struct SIBChunk
{
    uint32_t    Tag;
    uint32_t    Size;
} PACK_STRUCT;

enum { POS, NRM, UV,    N };

typedef std::pair<uint32_t, uint32_t> SIBPair;
static SIBPair makePair(uint32_t a, uint32_t b) { return (a<b) ? SIBPair(a, b) : SIBPair(b, a); }

struct SIBEdge
{
    uint32_t faceA, faceB;
    bool creased;
};

struct SIBMesh
{
    aiMatrix4x4 axis;
    uint32_t numPts;
    std::vector<aiVector3D> pos, nrm, uv;
    std::vector<uint32_t> idx;
    std::vector<uint32_t> faceStart;
    std::vector<uint32_t> mtls;
    std::vector<SIBEdge> edges;
    std::map<SIBPair, uint32_t> edgeMap;
};

struct SIBObject
{
    aiString name;
    aiMatrix4x4 axis;
    size_t meshIdx, meshCount;
};

struct SIB
{
    std::vector<aiMaterial*> mtls;
    std::vector<aiMesh*> meshes;
    std::vector<aiLight*> lights;
    std::vector<SIBObject> objs, insts;
};

// ------------------------------------------------------------------------------------------------
static SIBEdge& GetEdge(SIBMesh* mesh, uint32_t posA, uint32_t posB)
{
    SIBPair pair = (posA < posB) ? SIBPair(posA, posB) : SIBPair(posB, posA);
    std::map<SIBPair, uint32_t>::iterator it = mesh->edgeMap.find(pair);
    if (it != mesh->edgeMap.end())
        return mesh->edges[it->second];

    SIBEdge edge;
    edge.creased = false;
    edge.faceA = edge.faceB = 0xffffffff;
    mesh->edgeMap[pair] = mesh->edges.size();
    mesh->edges.push_back(edge);
    return mesh->edges.back();
}

// ------------------------------------------------------------------------------------------------
// Helpers for reading chunked data.

#define TAG(A,B,C,D) ((A << 24) | (B << 16) | (C << 8) | D)

static SIBChunk ReadChunk(StreamReaderLE* stream)
{
    SIBChunk chunk;
    chunk.Tag = stream->GetU4();
    chunk.Size = stream->GetU4();
    if (chunk.Size > stream->GetRemainingSizeToLimit())
        DefaultLogger::get()->error("SIB: Chunk overflow");
    ByteSwap::Swap4(&chunk.Tag);
    return chunk;
}

static aiColor3D ReadColor(StreamReaderLE* stream)
{
    float r = stream->GetF4();
    float g = stream->GetF4();
    float b = stream->GetF4();
    stream->GetU4(); // Colors have an unused(?) 4th component.
    return aiColor3D(r, g, b);
}

static void UnknownChunk(StreamReaderLE* stream, const SIBChunk& chunk)
{
    char temp[5] = { 
        static_cast<char>(( chunk.Tag>>24 ) & 0xff),
        static_cast<char>(( chunk.Tag>>16 ) & 0xff),
        static_cast<char>(( chunk.Tag>>8 ) & 0xff),
        static_cast<char>(chunk.Tag & 0xff), '\0'
    };
    
    DefaultLogger::get()->warn((Formatter::format(), "SIB: Skipping unknown '",temp,"' chunk."));
}

// Reads a UTF-16LE string and returns it at UTF-8.
static aiString ReadString(StreamReaderLE* stream, uint32_t numWChars)
{
    // Allocate buffers (max expansion is 1 byte -> 4 bytes for UTF-8)
    UTF16* temp = new UTF16[numWChars];
    UTF8* str = new UTF8[numWChars * 4 + 1];
    for (uint32_t n=0;n<numWChars;n++)
        temp[n] = stream->GetU2();

    // Convert it and NUL-terminate.
    const UTF16 *start = temp, *end = temp + numWChars;
    UTF8 *dest = str, *limit = str + numWChars*4;
    ConvertUTF16toUTF8(&start, end, &dest, limit, lenientConversion);
    *dest = '\0';

    // Return the final string.
    aiString result = aiString((const char *)str);
    delete[] str;
    delete[] temp;
    return result;
}

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
SIBImporter::SIBImporter()
{}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
SIBImporter::~SIBImporter()
{}

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file.
bool SIBImporter::CanRead( const std::string& pFile, IOSystem* /*pIOHandler*/, bool /*checkSig*/) const
{
    return SimpleExtensionCheck(pFile, "sib");
}

// ------------------------------------------------------------------------------------------------
const aiImporterDesc* SIBImporter::GetInfo () const
{
    return &desc;
}

// ------------------------------------------------------------------------------------------------
static void ReadVerts(SIBMesh* mesh, StreamReaderLE* stream, uint32_t count)
{
    mesh->pos.resize(count);

    for (uint32_t n=0;n<count;n++) {
        mesh->pos[n].x = stream->GetF4();
        mesh->pos[n].y = stream->GetF4();
        mesh->pos[n].z = stream->GetF4();
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadFaces(SIBMesh* mesh, StreamReaderLE* stream)
{
    uint32_t ptIdx = 0;
    while (stream->GetRemainingSizeToLimit() > 0)
    {
        uint32_t numPoints = stream->GetU4();

        // Store room for the N index channels, plus the point count.
        size_t pos = mesh->idx.size() + 1;
        mesh->idx.resize(pos + numPoints*N);
        mesh->idx[pos-1] = numPoints;
        uint32_t *idx = &mesh->idx[pos];

        mesh->faceStart.push_back(pos-1);
        mesh->mtls.push_back(0);

        // Read all the position data.
        // UV/normals will be supplied later.
        // Positions are supplied indexed already, so we preserve that
        // mapping. UVs are supplied uniquely, so we allocate unique indices.
        for (uint32_t n=0;n<numPoints;n++,idx+=N,ptIdx++)
        {
            uint32_t p = stream->GetU4();
            if (p >= mesh->pos.size())
                throw DeadlyImportError("Vertex index is out of range.");
            idx[POS] = p;
            idx[NRM] = ptIdx;
            idx[UV] = ptIdx;
        }
    }

    // Allocate data channels for normals/UVs.
    mesh->nrm.resize(ptIdx, aiVector3D(0,0,0));
    mesh->uv.resize(ptIdx, aiVector3D(0,0,0));

    mesh->numPts = ptIdx;
}

// ------------------------------------------------------------------------------------------------
static void ReadUVs(SIBMesh* mesh, StreamReaderLE* stream)
{
    while (stream->GetRemainingSizeToLimit() > 0)
    {
        uint32_t faceIdx = stream->GetU4();
        uint32_t numPoints = stream->GetU4();

        if (faceIdx >= mesh->faceStart.size())
            throw DeadlyImportError("Invalid face index.");

        uint32_t pos = mesh->faceStart[faceIdx];
        uint32_t *idx = &mesh->idx[pos + 1];

        for (uint32_t n=0;n<numPoints;n++,idx+=N)
        {
            uint32_t id = idx[UV];
            mesh->uv[id].x = stream->GetF4();
            mesh->uv[id].y = stream->GetF4();
        }
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadMtls(SIBMesh* mesh, StreamReaderLE* stream)
{
    // Material assignments are stored run-length encoded.
    // Also, we add 1 to each material so that we can use mtl #0
    // as the default material.
    uint32_t prevFace = stream->GetU4();
    uint32_t prevMtl = stream->GetU4() + 1;
    while (stream->GetRemainingSizeToLimit() > 0)
    {
        uint32_t face = stream->GetU4();
        uint32_t mtl = stream->GetU4() + 1;
        while (prevFace < face)
        {
            if (prevFace >= mesh->mtls.size())
                throw DeadlyImportError("Invalid face index.");
            mesh->mtls[prevFace++] = prevMtl;
        }

        prevFace = face;
        prevMtl = mtl;
    }

    while (prevFace < mesh->mtls.size())
        mesh->mtls[prevFace++] = prevMtl;
}

// ------------------------------------------------------------------------------------------------
static void ReadAxis(aiMatrix4x4& axis, StreamReaderLE* stream)
{
    axis.a4 = stream->GetF4();
    axis.b4 = stream->GetF4();
    axis.c4 = stream->GetF4();
    axis.d4 = 1;
    axis.a1 = stream->GetF4();
    axis.b1 = stream->GetF4();
    axis.c1 = stream->GetF4();
    axis.d1 = 0;
    axis.a2 = stream->GetF4();
    axis.b2 = stream->GetF4();
    axis.c2 = stream->GetF4();
    axis.d2 = 0;
    axis.a3 = stream->GetF4();
    axis.b3 = stream->GetF4();
    axis.c3 = stream->GetF4();
    axis.d3 = 0;
}

// ------------------------------------------------------------------------------------------------
static void ReadEdges(SIBMesh* mesh, StreamReaderLE* stream)
{
    while (stream->GetRemainingSizeToLimit() > 0)
    {
        uint32_t posA = stream->GetU4();
        uint32_t posB = stream->GetU4();
        GetEdge(mesh, posA, posB);
    }
}

// ------------------------------------------------------------------------------------------------
static void ReadCreases(SIBMesh* mesh, StreamReaderLE* stream)
{
    while (stream->GetRemainingSizeToLimit() > 0)
    {
        uint32_t edge = stream->GetU4();
        if (edge >= mesh->edges.size())
            throw DeadlyImportError("SIB: Invalid edge index.");
        mesh->edges[edge].creased = true;
    }
}

// ------------------------------------------------------------------------------------------------
static void ConnectFaces(SIBMesh* mesh)
{
    // Find faces connected to each edge.
    size_t numFaces = mesh->faceStart.size();
    for (size_t faceIdx=0;faceIdx<numFaces;faceIdx++)
    {
        uint32_t *idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;
        uint32_t prev = idx[(numPoints-1)*N+POS];
    
        for (uint32_t i=0;i<numPoints;i++,idx+=N)
        {
            uint32_t next = idx[POS];

            // Find this edge.
            SIBEdge& edge = GetEdge(mesh, prev, next);

            // Link this face onto it.
            // This gives potentially undesirable normals when used
            // with non-2-manifold surfaces, but then so does Silo to begin with.
            if (edge.faceA == 0xffffffff)
                edge.faceA = faceIdx;
            else
                edge.faceB = faceIdx;

            prev = next;
        }
    }
}

// ------------------------------------------------------------------------------------------------
static aiVector3D CalculateVertexNormal(SIBMesh* mesh, uint32_t faceIdx, uint32_t pos,
                                        const std::vector<aiVector3D>& faceNormals)
{
    // Creased edges complicate this. We need to find the start/end range of the 
    // ring of faces that touch this position.
    // We do this in two passes. The first pass is to find the end of the range,
    // the second is to work backwards to the start and calculate the final normal.
    aiVector3D vtxNormal;
    for (int pass=0;pass<2;pass++)
    {
        vtxNormal = aiVector3D(0, 0, 0);
        uint32_t startFaceIdx = faceIdx;
        uint32_t prevFaceIdx = faceIdx;

        // Process each connected face.
        while (true)
        {
            // Accumulate the face normal.
            vtxNormal += faceNormals[faceIdx];

            uint32_t nextFaceIdx = 0xffffffff;

            // Move to the next edge sharing this position.
            uint32_t* idx = &mesh->idx[mesh->faceStart[faceIdx]];
            uint32_t numPoints = *idx++;
            uint32_t posA = idx[(numPoints-1)*N+POS];
            for (uint32_t n=0;n<numPoints;n++,idx+=N)
            {
                uint32_t posB = idx[POS];

                // Test if this edge shares our target position.
                if (posA == pos || posB == pos)
                {
                    SIBEdge& edge = GetEdge(mesh, posA, posB);

                    // Move to whichever side we didn't just come from.
                    if (!edge.creased) {
                        if (edge.faceA != prevFaceIdx && edge.faceA != faceIdx)
                            nextFaceIdx = edge.faceA;
                        else if (edge.faceB != prevFaceIdx && edge.faceB != faceIdx)
                            nextFaceIdx = edge.faceB;
                    }
                }

                posA = posB;
            }

            // Stop once we hit either an creased/unconnected edge, or we
            // wrapped around and hit our start point.
            if (nextFaceIdx == 0xffffffff || nextFaceIdx == startFaceIdx)
                break;

            prevFaceIdx = faceIdx;
            faceIdx = nextFaceIdx;
        }       
    }

    // Normalize it.
    float len = vtxNormal.Length();
    if (len > 0.000000001f)
        vtxNormal /= len;
    return vtxNormal;
}

// ------------------------------------------------------------------------------------------------
static void CalculateNormals(SIBMesh* mesh)
{
    size_t numFaces = mesh->faceStart.size();

    // Calculate face normals.
    std::vector<aiVector3D> faceNormals(numFaces);
    for (size_t faceIdx=0;faceIdx<numFaces;faceIdx++)
    {
        uint32_t* idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;

        aiVector3D faceNormal(0, 0, 0);

        uint32_t *prev = &idx[(numPoints-1)*N];

        for (uint32_t i=0;i<numPoints;i++)
        {
            uint32_t *next = &idx[i*N];

            faceNormal += mesh->pos[prev[POS]] ^ mesh->pos[next[POS]];
            prev = next;
        }

        faceNormals[faceIdx] = faceNormal;
    }

    // Calculate vertex normals.
    for (size_t faceIdx=0;faceIdx<numFaces;faceIdx++)
    {
        uint32_t* idx = &mesh->idx[mesh->faceStart[faceIdx]];
        uint32_t numPoints = *idx++;

        for (uint32_t i=0;i<numPoints;i++)
        {
            uint32_t pos = idx[i*N+POS];
            uint32_t nrm = idx[i*N+NRM];
            aiVector3D vtxNorm = CalculateVertexNormal(mesh, faceIdx, pos, faceNormals);
            mesh->nrm[nrm] = vtxNorm;
        }
    }
}

// ------------------------------------------------------------------------------------------------
struct TempMesh
{
    std::vector<aiVector3D> vtx;
    std::vector<aiVector3D> nrm;
    std::vector<aiVector3D> uv;
    std::vector<aiFace> faces;
};

static void ReadShape(SIB* sib, StreamReaderLE* stream)
{
    SIBMesh smesh;
    aiString name;

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk))
	{
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag)
        {
        case TAG('M','I','R','P'): break; // mirror plane maybe?
        case TAG('I','M','R','P'): break; // instance mirror? (not supported here yet)
        case TAG('D','I','N','F'): break; // display info, not needed
        case TAG('P','I','N','F'): break; // ?
        case TAG('V','M','I','R'): break; // ?
        case TAG('F','M','I','R'): break; // ?
        case TAG('T','X','S','M'): break; // ?
        case TAG('F','A','H','S'): break; // ?
        case TAG('V','R','T','S'): ReadVerts(&smesh, stream, chunk.Size/12); break;
        case TAG('F','A','C','S'): ReadFaces(&smesh, stream); break;
        case TAG('F','T','V','S'): ReadUVs(&smesh, stream); break;
        case TAG('S','N','A','M'): name = ReadString(stream, chunk.Size/2); break;
        case TAG('F','A','M','A'): ReadMtls(&smesh, stream); break;
        case TAG('A','X','I','S'): ReadAxis(smesh.axis, stream); break;
        case TAG('E','D','G','S'): ReadEdges(&smesh, stream); break;
        case TAG('E','C','R','S'): ReadCreases(&smesh, stream); break;
        default:                   UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    assert(smesh.faceStart.size() == smesh.mtls.size()); // sanity check

    // Silo doesn't store any normals in the file - we need to compute
    // them ourselves. We can't let AssImp handle it as AssImp doesn't
    // know about our creased edges.
    ConnectFaces(&smesh);
    CalculateNormals(&smesh);

    // Construct the transforms.
    aiMatrix4x4 worldToLocal = smesh.axis;
    worldToLocal.Inverse();
    aiMatrix4x4 worldToLocalN = worldToLocal;
    worldToLocalN.a4 = worldToLocalN.b4 = worldToLocalN.c4 = 0.0f;
    worldToLocalN.Inverse().Transpose();

    // Allocate final mesh data.
    // We'll allocate one mesh for each material. (we'll strip unused ones after)
    std::vector<TempMesh> meshes(sib->mtls.size());

    // Un-index the source data and apply to each vertex.
    for (unsigned fi=0;fi<smesh.faceStart.size();fi++)
    {
        uint32_t start = smesh.faceStart[fi];
        uint32_t mtl = smesh.mtls[fi];
        uint32_t *idx = &smesh.idx[start];

        if (mtl >= meshes.size())
        {
            DefaultLogger::get()->error("SIB: Face material index is invalid.");
            mtl = 0;
        }

        TempMesh& dest = meshes[mtl];

        aiFace face;
        face.mNumIndices = *idx++;
        face.mIndices = new unsigned[face.mNumIndices];
        for (unsigned pt=0;pt<face.mNumIndices;pt++,idx+=N)
        {
            size_t vtxIdx = dest.vtx.size();
            face.mIndices[pt] = vtxIdx;

            // De-index it. We don't need to validate here as
            // we did it when creating the data.
            aiVector3D pos = smesh.pos[idx[POS]];
            aiVector3D nrm = smesh.nrm[idx[NRM]];
            aiVector3D uv  = smesh.uv[idx[UV]];

            // The verts are supplied in world-space, so let's
            // transform them back into the local space of this mesh:
            pos = worldToLocal * pos;
            nrm = worldToLocalN * nrm;

            dest.vtx.push_back(pos);
            dest.nrm.push_back(nrm);
            dest.uv.push_back(uv);
        }
        dest.faces.push_back(face);
    }

    SIBObject obj;
    obj.name = name;
    obj.axis = smesh.axis;
    obj.meshIdx = sib->meshes.size();
    
    // Now that we know the size of everything,
    // we can build the final one-material-per-mesh data.
    for (size_t n=0;n<meshes.size();n++)
    {
        TempMesh& src = meshes[n];
        if (src.faces.empty())
            continue;

        aiMesh* mesh = new aiMesh;
        mesh->mName = name;
        mesh->mNumFaces = src.faces.size();
        mesh->mFaces = new aiFace[mesh->mNumFaces];
        mesh->mNumVertices = src.vtx.size();
        mesh->mVertices = new aiVector3D[mesh->mNumVertices];
        mesh->mNormals = new aiVector3D[mesh->mNumVertices];
        mesh->mTextureCoords[0] = new aiVector3D[mesh->mNumVertices];
        mesh->mNumUVComponents[0] = 2;
        mesh->mMaterialIndex = n;

        for (unsigned i=0;i<mesh->mNumVertices;i++)
        {
            mesh->mVertices[i] = src.vtx[i];
            mesh->mNormals[i] = src.nrm[i];
            mesh->mTextureCoords[0][i] = src.uv[i];
        }
        for (unsigned i=0;i<mesh->mNumFaces;i++)
        {
            mesh->mFaces[i] = src.faces[i];
        }

        sib->meshes.push_back(mesh);
    }

    obj.meshCount = sib->meshes.size() - obj.meshIdx;
    sib->objs.push_back(obj);
}

// ------------------------------------------------------------------------------------------------
static void ReadMaterial(SIB* sib, StreamReaderLE* stream)
{
    aiColor3D diff = ReadColor(stream);
    aiColor3D ambi = ReadColor(stream);
    aiColor3D spec = ReadColor(stream);
    aiColor3D emis = ReadColor(stream);
    float shiny = (float)stream->GetU4();

    uint32_t nameLen = stream->GetU4();
    aiString name = ReadString(stream, nameLen/2);
    uint32_t texLen = stream->GetU4();
    aiString tex = ReadString(stream, texLen/2);

    aiMaterial* mtl = new aiMaterial();
    mtl->AddProperty(&diff, 1, AI_MATKEY_COLOR_DIFFUSE);
    mtl->AddProperty(&ambi, 1, AI_MATKEY_COLOR_AMBIENT);
    mtl->AddProperty(&spec, 1, AI_MATKEY_COLOR_SPECULAR);
    mtl->AddProperty(&emis, 1, AI_MATKEY_COLOR_EMISSIVE);
    mtl->AddProperty(&shiny, 1, AI_MATKEY_SHININESS);
    mtl->AddProperty(&name, AI_MATKEY_NAME);
    if (tex.length > 0) {
        mtl->AddProperty(&tex, AI_MATKEY_TEXTURE_DIFFUSE(0));
        mtl->AddProperty(&tex, AI_MATKEY_TEXTURE_AMBIENT(0));
    }

    sib->mtls.push_back(mtl);
}

// ------------------------------------------------------------------------------------------------
static void ReadLightInfo(aiLight* light, StreamReaderLE* stream)
{
    uint32_t type = stream->GetU4();
    switch (type) {
    case 0: light->mType = aiLightSource_POINT; break;
    case 1: light->mType = aiLightSource_SPOT; break;
    case 2: light->mType = aiLightSource_DIRECTIONAL; break;
    default: light->mType = aiLightSource_UNDEFINED; break;
    }

    light->mPosition.x = stream->GetF4();
    light->mPosition.y = stream->GetF4();
    light->mPosition.z = stream->GetF4();
    light->mDirection.x = stream->GetF4();
    light->mDirection.y = stream->GetF4();
    light->mDirection.z = stream->GetF4();
    light->mColorDiffuse = ReadColor(stream);
    light->mColorAmbient = ReadColor(stream);
    light->mColorSpecular = ReadColor(stream);
    float spotExponent = stream->GetF4();
    float spotCutoff = stream->GetF4();
    light->mAttenuationConstant = stream->GetF4();
    light->mAttenuationLinear = stream->GetF4();
    light->mAttenuationQuadratic = stream->GetF4();

    // Silo uses the OpenGL default lighting model for it's
    // spot cutoff/exponent. AssImp unfortunately, does not.
    // Let's try and approximate it by solving for the
    // 99% and 1% percentiles.
    //    OpenGL: I = cos(angle)^E
    //   Solving: angle = acos(I^(1/E))
    float E = 1.0f / std::max(spotExponent, 0.00001f);
    float inner = acosf(powf(0.99f, E));
    float outer = acosf(powf(0.01f, E));

    // Apply the cutoff.
    outer = std::min(outer, AI_DEG_TO_RAD(spotCutoff));

    light->mAngleInnerCone = std::min(inner, outer);
    light->mAngleOuterCone = outer;
}

static void ReadLight(SIB* sib, StreamReaderLE* stream)
{
    aiLight* light = new aiLight();

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk))
	{
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag)
        {
        case TAG('L','N','F','O'): ReadLightInfo(light, stream); break;
        case TAG('S','N','A','M'): light->mName = ReadString(stream, chunk.Size/2); break;
        default:                   UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    sib->lights.push_back(light);
}

// ------------------------------------------------------------------------------------------------
static void ReadScale(aiMatrix4x4& axis, StreamReaderLE* stream)
{
    aiMatrix4x4 scale;
    scale.a1 = stream->GetF4();
    scale.b1 = stream->GetF4();
    scale.c1 = stream->GetF4();
    scale.d1 = stream->GetF4();
    scale.a2 = stream->GetF4();
    scale.b2 = stream->GetF4();
    scale.c2 = stream->GetF4();
    scale.d2 = stream->GetF4();
    scale.a3 = stream->GetF4();
    scale.b3 = stream->GetF4();
    scale.c3 = stream->GetF4();
    scale.d3 = stream->GetF4();
    scale.a4 = stream->GetF4();
    scale.b4 = stream->GetF4();
    scale.c4 = stream->GetF4();
    scale.d4 = stream->GetF4();

    axis = axis * scale;
}

static void ReadInstance(SIB* sib, StreamReaderLE* stream)
{
    SIBObject inst;
    uint32_t shapeIndex = 0;

    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk))
	{
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag)
        {
		case TAG('D','I','N','F'): break; // display info, not needed
		case TAG('P','I','N','F'): break; // ?
        case TAG('A','X','I','S'): ReadAxis(inst.axis, stream); break;
		case TAG('I','N','S','I'): shapeIndex = stream->GetU4(); break;
		case TAG('S','M','T','X'): ReadScale(inst.axis, stream); break;
		case TAG('S','N','A','M'): inst.name = ReadString(stream, chunk.Size/2); break;
        default:                   UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }

    if (shapeIndex >= sib->objs.size())
        throw DeadlyImportError("SIB: Invalid shape index.");

    const SIBObject& src = sib->objs[shapeIndex];
    inst.meshIdx = src.meshIdx;
    inst.meshCount = src.meshCount;
    sib->insts.push_back(inst);
}

// ------------------------------------------------------------------------------------------------
static void CheckVersion(StreamReaderLE* stream)
{
    uint32_t version = stream->GetU4();
    if (version != 1)
        throw DeadlyImportError("SIB: Unsupported file version.");
}

static void ReadScene(SIB* sib, StreamReaderLE* stream)
{
    // Parse each chunk in turn.
    while (stream->GetRemainingSizeToLimit() >= sizeof(SIBChunk))
	{
        SIBChunk chunk = ReadChunk(stream);
        unsigned oldLimit = stream->SetReadLimit(stream->GetCurrentPos() + chunk.Size);

        switch (chunk.Tag)
        {
        case TAG('H','E','A','D'): CheckVersion(stream); break;
        case TAG('S','H','A','P'): ReadShape(sib, stream); break;
        case TAG('G','R','P','S'): break; // group assignment, we don't import this
        case TAG('T','E','X','P'): break; // ?
        case TAG('I','N','S','T'): ReadInstance(sib, stream); break;
        case TAG('M','A','T','R'): ReadMaterial(sib, stream); break;
        case TAG('L','G','H','T'): ReadLight(sib, stream); break;
        default:                   UnknownChunk(stream, chunk); break;
        }

        stream->SetCurrentPos(stream->GetReadLimit());
        stream->SetReadLimit(oldLimit);
    }
}

// ------------------------------------------------------------------------------------------------
// Imports the given file into the given scene structure.
void SIBImporter::InternReadFile(const std::string& pFile,
    aiScene* pScene, IOSystem* pIOHandler)
{
    StreamReaderLE stream(pIOHandler->Open(pFile, "rb"));

    // We should have at least one chunk
    if (stream.GetRemainingSize() < 16)
        throw DeadlyImportError("SIB file is either empty or corrupt: " + pFile);

    SIB sib;

    // Default material.
    aiMaterial* defmtl = new aiMaterial;
    aiString defname = aiString(AI_DEFAULT_MATERIAL_NAME);
    defmtl->AddProperty(&defname, AI_MATKEY_NAME);
    sib.mtls.push_back(defmtl);

    // Read it all.
    ReadScene(&sib, &stream);

    // Join the instances and objects together.
    size_t firstInst = sib.objs.size();
    sib.objs.insert(sib.objs.end(), sib.insts.begin(), sib.insts.end());
    sib.insts.clear();

    // Transfer to the aiScene.
    pScene->mNumMaterials = sib.mtls.size();
    pScene->mNumMeshes = sib.meshes.size();
    pScene->mNumLights = sib.lights.size();
    pScene->mMaterials = new aiMaterial* [pScene->mNumMaterials];
    pScene->mMeshes = new aiMesh* [pScene->mNumMeshes];
    pScene->mLights = new aiLight* [pScene->mNumLights];
    if (pScene->mNumMaterials)
        memcpy(pScene->mMaterials, &sib.mtls[0], sizeof(aiMaterial*) * pScene->mNumMaterials);
    if (pScene->mNumMeshes)
        memcpy(pScene->mMeshes, &sib.meshes[0], sizeof(aiMesh*) * pScene->mNumMeshes);
    if (pScene->mNumLights)
        memcpy(pScene->mLights, &sib.lights[0], sizeof(aiLight*) * pScene->mNumLights);

    // Construct the root node.
    size_t childIdx = 0;
    aiNode *root = new aiNode();
    root->mName.Set("<SIBRoot>");
    root->mNumChildren = sib.objs.size() + sib.lights.size();
    root->mChildren = new aiNode* [root->mNumChildren];
    pScene->mRootNode = root;

    // Add nodes for each object.
    for (size_t n=0;n<sib.objs.size();n++)
    {
        SIBObject& obj = sib.objs[n];
        aiNode* node = new aiNode;
        root->mChildren[childIdx++] = node;
        node->mName = obj.name;
        node->mParent = root;
        node->mTransformation = obj.axis;

        node->mNumMeshes = obj.meshCount;
        node->mMeshes = new unsigned[node->mNumMeshes];
        for (unsigned i=0;i<node->mNumMeshes;i++)
            node->mMeshes[i] = obj.meshIdx + i;

        // Mark instanced objects as being so.
        if (n >= firstInst)
        {
            node->mMetaData = new aiMetadata;
            node->mMetaData->mNumProperties = 1;
            node->mMetaData->mKeys = new aiString[1];
            node->mMetaData->mValues = new aiMetadataEntry[1];
            node->mMetaData->Set(0, "IsInstance", true);
        }
    }

    // Add nodes for each light.
    // (no transformation as the light is already in world space)
    for (size_t n=0;n<sib.lights.size();n++)
    {
        aiLight* light = sib.lights[n];
        aiNode* node = new aiNode;
        root->mChildren[childIdx++] = node;
        node->mName = light->mName;
        node->mParent = root;
    }
}

#endif // !! ASSIMP_BUILD_NO_SIB_IMPORTER