assimp.assimp/code/Pbrt/PbrtExporter.cpp

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

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All rights reserved.

Redistribution and use of this software in source and binary forms,
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following disclaimer.

* Redistributions in binary form must reproduce the above
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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*/

/* TODO:

Material improvements:
- don't export embedded textures that we're not going to use
- diffuse roughness
- what is with the uv mapping, uv transform not coming through??
- metal? glass? mirror?  detect these better?
  - eta/k from RGB?
- emissive textures: warn at least

Other:
- use aiProcess_GenUVCoords if needed to handle spherical/planar uv mapping?
- don't build up a big string in memory but write directly to a file
- aiProcess_Triangulate meshes to get triangles only?
- animation (allow specifying a time)

 */

#ifndef ASSIMP_BUILD_NO_EXPORT
#ifndef ASSIMP_BUILD_NO_PBRT_EXPORTER

#include "PbrtExporter.h"

#include <assimp/version.h>
#include <assimp/DefaultIOSystem.h>
#include <assimp/IOSystem.hpp>
#include <assimp/Exporter.hpp>
#include <assimp/DefaultLogger.hpp>
#include <assimp/StreamWriter.h>
#include <assimp/Exceptional.h>
#include <assimp/material.h>
#include <assimp/scene.h>
#include <assimp/mesh.h>

#include <algorithm>
#include <cctype>
#include <cmath>
#include <fstream>
#include <functional>
#include <iostream>
#include <memory>
#include <sstream>
#include <string>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

using namespace Assimp;

namespace Assimp {

void ExportScenePbrt (
    const char* pFile,
    IOSystem* pIOSystem,
    const aiScene* pScene,
    const ExportProperties* /*pProperties*/
){
    std::string path = DefaultIOSystem::absolutePath(std::string(pFile));
    std::string file = DefaultIOSystem::completeBaseName(std::string(pFile));

    // initialize the exporter
    PbrtExporter exporter(pScene, pIOSystem, path, file);
}

} // end of namespace Assimp

// Constructor
PbrtExporter::PbrtExporter (
    const aiScene* pScene, IOSystem* pIOSystem,
    const std::string path, const std::string file)
: mScene(pScene),
  mIOSystem(pIOSystem),
  mPath(path),
  mFile(file)
{
    // Export embedded textures.
    if (mScene->mNumTextures > 0)
        if (!mIOSystem->CreateDirectory("textures"))
            throw DeadlyExportError("Could not create textures/ directory.");
    for (unsigned int i = 0; i < mScene->mNumTextures; ++i) {
        aiTexture* tex = mScene->mTextures[i];
        std::string fn = CleanTextureFilename(tex->mFilename, false);
        std::cerr << "Writing embedded texture: " << tex->mFilename.C_Str() << " -> "
                  << fn << "\n";

        std::unique_ptr<IOStream> outfile(mIOSystem->Open(fn, "wb"));
        if (!outfile) {
            throw DeadlyExportError("could not open output texture file: " + fn);
        }
        if (tex->mHeight == 0) {
            // It's binary data
            outfile->Write(tex->pcData, tex->mWidth, 1);
        } else {
            std::cerr << fn << ": TODO handle uncompressed embedded textures.\n";
        }
    }

#if 0
    // Debugging: print the full node hierarchy
    std::function<void(aiNode*, int)> visitNode;
    visitNode = [&](aiNode* node, int depth) {
        for (int i = 0; i < depth; ++i) std::cerr << "    ";
        std::cerr << node->mName.C_Str() << "\n";
        for (int i = 0; i < node->mNumChildren; ++i)
            visitNode(node->mChildren[i], depth + 1);
    };
    visitNode(mScene->mRootNode, 0);
#endif

    mOutput.precision(ASSIMP_AI_REAL_TEXT_PRECISION);

    // Write everything out
    WriteMetaData();
    WriteCameras();
    WriteWorldDefinition();

    // And write the file to disk...
    std::unique_ptr<IOStream> outfile(mIOSystem->Open(mPath,"wt"));
    if (!outfile) {
        throw DeadlyExportError("could not open output .pbrt file: " + std::string(mFile));
    }
    outfile->Write(mOutput.str().c_str(), mOutput.str().length(), 1);
}

// Destructor
PbrtExporter::~PbrtExporter() {
    // Empty
}

void PbrtExporter::WriteMetaData() {
    mOutput << "#############################\n";
    mOutput << "# Scene metadata:\n";

    aiMetadata* pMetaData = mScene->mMetaData;
    for (unsigned int i = 0; i < pMetaData->mNumProperties; i++) {
        mOutput << "# - ";
        mOutput << pMetaData->mKeys[i].C_Str() << " :";
        switch(pMetaData->mValues[i].mType) {
            case AI_BOOL : {
                mOutput << " ";
                if (*static_cast<bool*>(pMetaData->mValues[i].mData))
                    mOutput << "TRUE\n";
                else
                    mOutput << "FALSE\n";
                break;
            }
            case AI_INT32 : {
                mOutput << " " <<
                    *static_cast<int32_t*>(pMetaData->mValues[i].mData) <<
                    std::endl;
                break;
            }
            case AI_UINT64 :
                mOutput << " " <<
                    *static_cast<uint64_t*>(pMetaData->mValues[i].mData) <<
                    std::endl;
                break;
            case AI_FLOAT :
                mOutput << " " <<
                    *static_cast<float*>(pMetaData->mValues[i].mData) <<
                    std::endl;
                break;
            case AI_DOUBLE :
                mOutput << " " <<
                    *static_cast<double*>(pMetaData->mValues[i].mData) <<
                    std::endl;
                break;
            case AI_AISTRING : {
                aiString* value =
                    static_cast<aiString*>(pMetaData->mValues[i].mData);
                std::string svalue = value->C_Str();
                std::size_t found = svalue.find_first_of("\n");
                mOutput << "\n";
                while (found != std::string::npos) {
                    mOutput << "#     " << svalue.substr(0, found) << "\n";
                    svalue = svalue.substr(found + 1);
                    found = svalue.find_first_of("\n");
                }
                mOutput << "#     " << svalue << "\n";
                break;
            }
            case AI_AIVECTOR3D :
                // TODO
                mOutput << " Vector3D (unable to print)\n";
                break;
            default:
                // AI_META_MAX and FORCE_32BIT
                mOutput << " META_MAX or FORCE_32Bit (unable to print)\n";
                break;
        }
    }
}

void PbrtExporter::WriteCameras() {
    mOutput << "\n";
    mOutput << "###############################\n";
    mOutput << "# Cameras (" << mScene->mNumCameras << ") total\n\n";

    if (mScene->mNumCameras == 0) {
        std::cerr << "Warning: No cameras found in scene file.\n";
        return;
    }

    if (mScene->mNumCameras > 1) {
        std::cerr << "Multiple cameras found in scene file; defaulting to first one specified.\n";
    }

    for (unsigned int i = 0; i < mScene->mNumCameras; i++) {
        WriteCamera(i);
    }
}

aiMatrix4x4 PbrtExporter::GetNodeTransform(const aiString &name) const {
    aiMatrix4x4 m;
    auto node = mScene->mRootNode->FindNode(name);
    if (!node) {
        std::cerr << '"' << name.C_Str() << "\": node not found in scene tree.\n";
        throw DeadlyExportError("Could not find node");
    }
    else {
        while (node) {
            m = node->mTransformation * m;
            node = node->mParent;
        }
    }
    return m;
}

std::string PbrtExporter::TransformAsString(const aiMatrix4x4 &m) {
    // Transpose on the way out to match pbrt's expected layout (sanity
    // check: the translation component should be the last 3 entries
    // before a '1' as the final entry in the matrix, assuming it's
    // non-projective.)
    std::stringstream s;
    s << m.a1 << " " << m.b1 << " " << m.c1 << " " << m.d1 << " "
      << m.a2 << " " << m.b2 << " " << m.c2 << " " << m.d2 << " "
      << m.a3 << " " << m.b3 << " " << m.c3 << " " << m.d3 << " "
      << m.a4 << " " << m.b4 << " " << m.c4 << " " << m.d4;
    return s.str();
}

void PbrtExporter::WriteCamera(int i) {
    auto camera = mScene->mCameras[i];
    bool cameraActive = i == 0;

    mOutput << "# - Camera " << i+1 <<  ": "
        << camera->mName.C_Str() << "\n";

    // Get camera aspect ratio
    float aspect = camera->mAspect;
    if (aspect == 0) {
        aspect = 4.f/3.f;
        mOutput << "#   - Aspect ratio : 1.33333 (no aspect found, defaulting to 4/3)\n";
    } else {
        mOutput << "#   - Aspect ratio : " << aspect << "\n";
    }

    // Get Film xres and yres
    int xres = 1920;
    int yres = (int)round(xres/aspect);

    // Print Film for this camera
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "Film \"rgb\" \"string filename\" \"" << mFile << ".exr\"\n";
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "    \"integer xresolution\" [" << xres << "]\n";
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "    \"integer yresolution\" [" << yres << "]\n";

    // Get camera fov
    float hfov = AI_RAD_TO_DEG(camera->mHorizontalFOV);
    float fov = (aspect >= 1.0) ? hfov : (hfov * aspect);
    if (fov < 5) {
        std::cerr << fov << ": suspiciously low field of view specified by camera. Setting to 45 degrees.\n";
        fov = 45;
    }

    // Get camera transform
    aiMatrix4x4 worldFromCamera = GetNodeTransform(camera->mName);

    // Print Camera LookAt
    auto position = worldFromCamera * camera->mPosition;
    auto lookAt = worldFromCamera * (camera->mPosition + camera->mLookAt);
    aiMatrix3x3 worldFromCamera3(worldFromCamera);
    auto up = worldFromCamera3 * camera->mUp;
    up.Normalize();

    if (!cameraActive)
        mOutput << "# ";
    mOutput << "Scale -1 1 1\n";  // right handed -> left handed
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "LookAt "
        << position.x << " " << position.y << " " << position.z << "\n";
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "       "
        << lookAt.x << " " << lookAt.y << " " << lookAt.z << "\n";
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "       "
        << up.x << " " << up.y << " " << up.z << "\n";

    // Print camera descriptor
    if (!cameraActive)
        mOutput << "# ";
    mOutput << "Camera \"perspective\" \"float fov\" " << "[" << fov << "]\n\n";
}

void PbrtExporter::WriteWorldDefinition() {
    // Figure out which meshes are referenced multiple times; those will be
    // emitted as object instances and the rest will be emitted directly.
    std::map<int, int> meshUses;
    std::function<void(aiNode*)> visitNode;
    visitNode = [&](aiNode* node) {
        for (unsigned int i = 0; i < node->mNumMeshes; ++i)
            ++meshUses[node->mMeshes[i]];
        for (unsigned int i = 0; i < node->mNumChildren; ++i)
            visitNode(node->mChildren[i]);
    };
    visitNode(mScene->mRootNode);
    int nInstanced = 0, nUnused = 0;
    for (const auto &u : meshUses) {
        if (u.second == 0) ++nUnused;
        else if (u.second > 1) ++nInstanced;
    }
    std::cerr << nInstanced << " / " << mScene->mNumMeshes << " meshes instanced.\n";
    if (nUnused)
        std::cerr << nUnused << " meshes defined but not used in scene.\n";

    mOutput << "WorldBegin\n";

    WriteLights();
    WriteTextures();
    WriteMaterials();

    // Object instance definitions
    mOutput << "# Object instance definitions\n\n";
    for (const auto &mu : meshUses) {
        if (mu.second > 1) {
            WriteInstanceDefinition(mu.first);
        }
    }

    mOutput << "# Geometry\n\n";
    aiMatrix4x4 worldFromObject;
    WriteGeometricObjects(mScene->mRootNode, worldFromObject, meshUses);
}

void PbrtExporter::WriteTextures() {
    mOutput << "###################\n";
    mOutput << "# Textures\n\n";

    C_STRUCT aiString path;
    aiTextureMapping mapping;
    unsigned int uvIndex;
    ai_real blend;
    aiTextureOp op;
    aiTextureMapMode mapMode[3];

    // For every material in the scene,
    for (unsigned int m = 0 ; m < mScene->mNumMaterials; m++) {
        auto material = mScene->mMaterials[m];
        // Parse through all texture types,
        for (int tt = 1; tt <= aiTextureType_UNKNOWN; tt++) {
            int ttCount = material->GetTextureCount(aiTextureType(tt));
            // ... and get every texture
            for (int t = 0; t < ttCount; t++) {
                // TODO write out texture specifics
                // TODO UV transforms may be material specific
                //        so those may need to be baked into unique tex name
                if (material->GetTexture(aiTextureType(tt), t, &path, &mapping,
                                         &uvIndex, &blend, &op, mapMode) != AI_SUCCESS) {
                    std::cerr << "Error getting texture! " << m << " " << tt << " " << t << "\n";
                    continue;
                }

                std::string filename = CleanTextureFilename(path);

                if (uvIndex != 0)
                    std::cerr << "Warning: texture \"" << filename << "\" uses uv set #" <<
                        uvIndex << " but the pbrt converter only exports uv set 0.\n";
#if 0
                if (op != aiTextureOp_Multiply)
                    std::cerr << "Warning: unexpected texture op " << (int)op <<
                        " encountered for texture \"" <<
                        filename << "\". The resulting scene may have issues...\n";
                if (blend != 1)
                    std::cerr << "Blend value of " << blend << " found for texture \"" << filename
                              << "\" but not handled in converter.\n";
#endif

                std::string mappingString;
#if 0
                if (mapMode[0] != mapMode[1])
                    std::cerr << "Different texture boundary mode for u and v for texture \"" <<
                        filename << "\". Using u for both.\n";
                switch (mapMode[0]) {
                case aiTextureMapMode_Wrap:
                    // pbrt's default
                    break;
                case aiTextureMapMode_Clamp:
                    mappingString = "\"string wrap\" \"clamp\"";
                    break;
                case aiTextureMapMode_Decal:
                    std::cerr << "Decal texture boundary mode not supported by pbrt for texture \"" <<
                        filename << "\"\n";
                    break;
                case aiTextureMapMode_Mirror:
                    std::cerr << "Mirror texture boundary mode not supported by pbrt for texture \"" <<
                        filename << "\"\n";
                    break;
                default:
                    std::cerr << "Unexpected map mode " << (int)mapMode[0] << " for texture \"" <<
                        filename << "\"\n";
                    //throw DeadlyExportError("Unexpected aiTextureMapMode");
                }
#endif

#if 0
                aiUVTransform uvTransform;
                if (material->Get(AI_MATKEY_TEXTURE(tt, t), uvTransform) == AI_SUCCESS) {
                    mOutput << "# UV transform " << uvTransform.mTranslation.x << " "
                            << uvTransform.mTranslation.y << " " << uvTransform.mScaling.x << " "
                            << uvTransform.mScaling.y << " " << uvTransform.mRotation << "\n";
                }
#endif

                std::string texName, texType, texOptions;
                if (aiTextureType(tt) == aiTextureType_SHININESS ||
                    aiTextureType(tt) == aiTextureType_OPACITY ||
                    aiTextureType(tt) == aiTextureType_HEIGHT ||
                    aiTextureType(tt) == aiTextureType_DISPLACEMENT ||
                    aiTextureType(tt) == aiTextureType_METALNESS ||
                    aiTextureType(tt) == aiTextureType_DIFFUSE_ROUGHNESS) {
                    texType = "float";
                    texName = std::string("float:") + RemoveSuffix(filename);

                    if (aiTextureType(tt) == aiTextureType_SHININESS) {
                        texOptions = "    \"bool invert\" true\n";
                        texName += "_Roughness";
                    }
                } else if (aiTextureType(tt) == aiTextureType_DIFFUSE ||
                           aiTextureType(tt) == aiTextureType_BASE_COLOR) {
                    texType = "spectrum";
                    texName = std::string("rgb:") + RemoveSuffix(filename);
                }

                // Don't export textures we're not actually going to use...
                if (texName.empty())
                    continue;

                if (mTextureSet.find(texName) == mTextureSet.end()) {
                    mOutput << "Texture \"" << texName << "\" \"" << texType << "\" \"imagemap\"\n"
                            << texOptions
                            << "    \"string filename\" \"" << filename << "\" " << mappingString << '\n';
                    mTextureSet.insert(texName);
                }

                // Also emit a float version for use with alpha testing...
                if ((aiTextureType(tt) == aiTextureType_DIFFUSE ||
                     aiTextureType(tt) == aiTextureType_BASE_COLOR) &&
                    TextureHasAlphaMask(filename)) {
                    texType = "float";
                    texName = std::string("alpha:") + filename;
                    if (mTextureSet.find(texName) == mTextureSet.end()) {
                        mOutput << "Texture \"" << texName << "\" \"" << texType << "\" \"imagemap\"\n"
                                << "    \"string filename\" \"" << filename << "\" " << mappingString << '\n';
                        mTextureSet.insert(texName);
                    }
                }
            }
        }
    }
}

bool PbrtExporter::TextureHasAlphaMask(const std::string &filename) {
    // TODO: STBIDEF int      stbi_info               (char const *filename,     int *x, int *y, int *comp);
    // quick return if it's 3

    int xSize, ySize, nComponents;
    unsigned char *data = stbi_load(filename.c_str(), &xSize, &ySize, &nComponents, 0);
    if (!data) {
        std::cerr << filename << ": unable to load texture and check for alpha mask in texture. "
        "Geometry will not be alpha masked with this texture.\n";
        return false;
    }

    bool hasMask = false;
    switch (nComponents) {
    case 1:
        for (int i = 0; i < xSize * ySize; ++i)
            if (data[i] != 255) {
                hasMask = true;
                break;
            }
        break;
    case 2:
          for (int y = 0; y < ySize; ++y)
              for (int x = 0; x < xSize; ++x)
                  if (data[2 * (x + y * xSize) + 1] != 255) {
                      hasMask = true;
                      break;
                  }
        break;
    case 3:
        break;
    case 4:
          for (int y = 0; y < ySize; ++y)
              for (int x = 0; x < xSize; ++x)
                  if (data[4 * (x + y * xSize) + 3] != 255) {
                      hasMask = true;
                      break;
                  }
          break;
    default:
        std::cerr << filename << ": unexpected number of image channels, " <<
            nComponents << ".\n";
    }

    stbi_image_free(data);
    return hasMask;
}

void PbrtExporter::WriteMaterials() {
    mOutput << "\n";
    mOutput << "####################\n";
    mOutput << "# Materials (" << mScene->mNumMaterials << ") total\n\n";

    for (unsigned int i = 0; i < mScene->mNumMaterials; i++) {
        WriteMaterial(i);
    }
    mOutput << "\n\n";
}

void PbrtExporter::WriteMaterial(int m) {
    aiMaterial* material = mScene->mMaterials[m];

    // get material name
    auto materialName = material->GetName();
    mOutput << std::endl << "# - Material " << m+1 <<  ": " << materialName.C_Str() << "\n";

    // Print out number of properties
    mOutput << "#   - Number of Material Properties: " << material->mNumProperties << "\n";

    // Print out texture type counts
    mOutput << "#   - Non-Zero Texture Type Counts: ";
    for (int i = 1; i <= aiTextureType_UNKNOWN; i++) {
        int count = material->GetTextureCount(aiTextureType(i));
        if (count > 0)
            mOutput << TextureTypeToString(aiTextureType(i)) << ": " <<  count << " ";
    }
    mOutput << "\n";

    auto White = [](aiColor3D c) { return c.r == 1 && c.g == 1 && c.b == 1; };
    auto Black = [](aiColor3D c) { return c.r == 0 && c.g == 0 && c.b == 0; };

    aiColor3D diffuse, specular, transparency;
    bool constantDiffuse = (material->Get(AI_MATKEY_COLOR_DIFFUSE, diffuse) == AI_SUCCESS &&
                            !White(diffuse));
    bool constantSpecular = (material->Get(AI_MATKEY_COLOR_SPECULAR, specular) == AI_SUCCESS &&
                             !White(specular));
    bool constantTransparency = (material->Get(AI_MATKEY_COLOR_TRANSPARENT, transparency) == AI_SUCCESS &&
                                 !Black(transparency));

    float opacity, shininess, shininessStrength, eta;
    bool constantOpacity = (material->Get(AI_MATKEY_OPACITY, opacity) == AI_SUCCESS &&
                            opacity != 0);
    bool constantShininess = material->Get(AI_MATKEY_SHININESS, shininess) == AI_SUCCESS;
    bool constantShininessStrength = material->Get(AI_MATKEY_SHININESS_STRENGTH, shininessStrength) == AI_SUCCESS;
    bool constantEta = (material->Get(AI_MATKEY_REFRACTI, eta) == AI_SUCCESS &&
                        eta != 1);

    mOutput << "#    - Constants: diffuse " << constantDiffuse << " specular " << constantSpecular <<
        " transprency " << constantTransparency << " opacity " << constantOpacity <<
        " shininess " << constantShininess << " shininess strength " << constantShininessStrength <<
        " eta " << constantEta << "\n";

    aiString roughnessMap;
    if (material->Get(AI_MATKEY_TEXTURE_SHININESS(0), roughnessMap) == AI_SUCCESS) {
        std::string roughnessTexture = std::string("float:") +
            RemoveSuffix(CleanTextureFilename(roughnessMap)) + "_Roughness";
        mOutput << "MakeNamedMaterial \"" << materialName.C_Str() << "\""
                << " \"string type\" \"coateddiffuse\"\n"
                << "    \"texture roughness\" \"" << roughnessTexture << "\"\n";
    } else if (constantShininess) {
        // Assume plastic for now at least
        float roughness = std::max(0.f, 1.f - shininess);
        mOutput << "MakeNamedMaterial \"" << materialName.C_Str() << "\""
                << " \"string type\" \"coateddiffuse\"\n"
                << "    \"float roughness\" " << roughness << "\n";
    } else
        // Diffuse
        mOutput << "MakeNamedMaterial \"" << materialName.C_Str() << "\""
                << " \"string type\" \"diffuse\"\n";

    aiString diffuseTexture;
    if (material->Get(AI_MATKEY_TEXTURE_DIFFUSE(0), diffuseTexture) == AI_SUCCESS)
        mOutput << "    \"texture reflectance\" \"rgb:" << RemoveSuffix(CleanTextureFilename(diffuseTexture)) << "\"\n";
    else
        mOutput << "    \"rgb reflectance\" [ " << diffuse.r << " " << diffuse.g <<
            " " << diffuse.b << " ]\n";

    aiString displacementTexture, normalMap;
    if (material->Get(AI_MATKEY_TEXTURE_NORMALS(0), displacementTexture) == AI_SUCCESS)
        mOutput << "    \"string normalmap\" \"" << CleanTextureFilename(displacementTexture) << "\"\n";
    else if (material->Get(AI_MATKEY_TEXTURE_HEIGHT(0), displacementTexture) == AI_SUCCESS)
        mOutput << "    \"texture displacement\" \"float:" <<
            RemoveSuffix(CleanTextureFilename(displacementTexture)) << "\"\n";
    else if (material->Get(AI_MATKEY_TEXTURE_DISPLACEMENT(0), displacementTexture) == AI_SUCCESS)
        mOutput << "    \"texture displacement\" \"float:" <<
            RemoveSuffix(CleanTextureFilename(displacementTexture)) << "\"\n";
}

std::string PbrtExporter::CleanTextureFilename(const aiString &f, bool rewriteExtension) const {
    std::string fn = f.C_Str();
    // Remove directory name
    size_t offset = fn.find_last_of("/\\");
    if (offset != std::string::npos) {
        fn.erase(0, offset + 1);
    }

    // Expect all textures in textures
    fn = std::string("textures") + mIOSystem->getOsSeparator() + fn;

    // Rewrite extension for unsupported file formats.
    if (rewriteExtension) {
        offset = fn.rfind('.');
        if (offset != std::string::npos) {
            std::string extension = fn;
            extension.erase(0, offset + 1);
            std::transform(extension.begin(), extension.end(), extension.begin(),
                           [](unsigned char c) { return (char)std::tolower(c); });

            if (extension != "tga" && extension != "exr" && extension != "png" &&
                extension != "pfm" && extension != "hdr") {
                std::string orig = fn;
                fn.erase(offset + 1);
                fn += "png";

                // Does it already exist? Warn if not.
                std::ifstream filestream(fn);
                if (!filestream.good())
                    std::cerr << orig << ": must convert this texture to PNG.\n";
            }
        }
    }

    return fn;
}

std::string PbrtExporter::RemoveSuffix(std::string filename) {
    size_t offset = filename.rfind('.');
    if (offset != std::string::npos)
        filename.erase(offset);
    return filename;
}

void PbrtExporter::WriteLights() {
    mOutput << "\n";
    mOutput << "#################\n";
    mOutput << "# Lights\n\n";
    if (mScene->mNumLights == 0) {
        // Skip the default light if no cameras and this is flat up geometry
        if (mScene->mNumCameras > 0) {
            std::cerr << "No lights specified. Using default infinite light.\n";

            mOutput << "AttributeBegin\n";
            mOutput << "    # default light\n";
            mOutput << "    LightSource \"infinite\" \"blackbody L\" [6000 1]\n";

            mOutput << "AttributeEnd\n\n";
        }
    } else {
        for (unsigned int i = 0; i < mScene->mNumLights; ++i) {
            const aiLight *light = mScene->mLights[i];

            mOutput << "# Light " << light->mName.C_Str() << "\n";
            mOutput << "AttributeBegin\n";

            aiMatrix4x4 worldFromLight = GetNodeTransform(light->mName);
            mOutput << "    Transform [ " << TransformAsString(worldFromLight) << " ]\n";

            aiColor3D color = light->mColorDiffuse + light->mColorSpecular;
            if (light->mAttenuationConstant != 0)
                color = color * (ai_real)(1. / light->mAttenuationConstant);

            switch (light->mType) {
            case aiLightSource_DIRECTIONAL: {
                mOutput << "    LightSource \"distant\"\n";
                mOutput << "        \"point3 from\" [ " << light->mPosition.x << " " <<
                    light->mPosition.y << " " << light->mPosition.z << " ]\n";
                aiVector3D to = light->mPosition + light->mDirection;
                mOutput << "        \"point3 to\" [ " << to.x << " " << to.y << " " << to.z << " ]\n";
                mOutput << "        \"rgb L\" [ " << color.r << " " << color.g << " " << color.b << " ]\n";
                break;
            } case aiLightSource_POINT:
                mOutput << "    LightSource \"distant\"\n";
                mOutput << "        \"point3 from\" [ " << light->mPosition.x << " " <<
                    light->mPosition.y << " " << light->mPosition.z << " ]\n";
                mOutput << "        \"rgb L\" [ " << color.r << " " << color.g << " " << color.b << " ]\n";
                break;
            case aiLightSource_SPOT: {
                mOutput << "    LightSource \"spot\"\n";
                mOutput << "        \"point3 from\" [ " << light->mPosition.x << " " <<
                    light->mPosition.y << " " << light->mPosition.z << " ]\n";
                aiVector3D to = light->mPosition + light->mDirection;
                mOutput << "        \"point3 to\" [ " << to.x << " " << to.y << " " << to.z << " ]\n";
                mOutput << "        \"rgb L\" [ " << color.r << " " << color.g << " " << color.b << " ]\n";
                mOutput << "        \"float coneangle\" [ " << AI_RAD_TO_DEG(light->mAngleOuterCone) << " ]\n";
                mOutput << "        \"float conedeltaangle\" [ " << AI_RAD_TO_DEG(light->mAngleOuterCone -
                                                                                  light->mAngleInnerCone) << " ]\n";
                break;
            } case aiLightSource_AMBIENT:
                mOutput << "# ignored ambient light source\n";
                break;
            case aiLightSource_AREA: {
                aiVector3D left = light->mDirection ^ light->mUp;
                // rectangle. center at position, direction is normal vector
                float dLeft = light->mSize.x / 2, dUp = light->mSize.y / 2;
                aiVector3D vertices[4] = {
                     light->mPosition - dLeft * left - dUp * light->mUp,
                     light->mPosition + dLeft * left - dUp * light->mUp,
                     light->mPosition - dLeft * left + dUp * light->mUp,
                     light->mPosition + dLeft * left + dUp * light->mUp };
                mOutput << "    AreaLightSource \"diffuse\"\n";
                mOutput << "        \"rgb L\" [ " << color.r << " " << color.g << " " << color.b << " ]\n";
                mOutput << "    Shape \"bilinearmesh\"\n";
                mOutput << "        \"point3 p\" [ ";
                for (int j = 0; j < 4; ++j)
                    mOutput << vertices[j].x << " " << vertices[j].y << " " << vertices[j].z;
                mOutput << " ]\n";
                mOutput << "        \"integer indices\" [ 0 1 2 3 ]\n";
                break;
            } default:
                mOutput << "# ignored undefined light source type\n";
                break;
            }
            mOutput << "AttributeEnd\n\n";
        }
    }
}

void PbrtExporter::WriteMesh(aiMesh* mesh) {
    mOutput << "# - Mesh: ";
    if (mesh->mName == aiString(""))
        mOutput << "<No Name>\n";
    else
        mOutput << mesh->mName.C_Str() << "\n";

    mOutput << "AttributeBegin\n";
    aiMaterial* material = mScene->mMaterials[mesh->mMaterialIndex];
    mOutput << "    NamedMaterial \"" << material->GetName().C_Str() << "\"\n";

    // Handle area lights
    aiColor3D emission;
    if (material->Get(AI_MATKEY_COLOR_EMISSIVE, emission) == AI_SUCCESS &&
        (emission.r > 0 || emission.g > 0 || emission.b > 0))
        mOutput << "    AreaLightSource \"diffuse\" \"rgb L\" [ " << emission.r <<
            " " << emission.g << " " << emission.b << " ]\n";

    // Check if any types other than tri
    if (   (mesh->mPrimitiveTypes & aiPrimitiveType_POINT)
        || (mesh->mPrimitiveTypes & aiPrimitiveType_LINE)
        || (mesh->mPrimitiveTypes & aiPrimitiveType_POLYGON)) {
        std::cerr << "Error: ignoring point / line / polygon mesh " << mesh->mName.C_Str() << ".\n";
        return;
    }

    // Alpha mask
    std::string alpha;
    aiString opacityTexture;
    if (material->Get(AI_MATKEY_TEXTURE_OPACITY(0), opacityTexture) == AI_SUCCESS ||
        material->Get(AI_MATKEY_TEXTURE_DIFFUSE(0), opacityTexture) == AI_SUCCESS) {
        // material->Get(AI_MATKEY_TEXTURE_BASE_COLOR(0), opacityTexture) == AI_SUCCESS)
        std::string texName = std::string("alpha:") + CleanTextureFilename(opacityTexture);
        if (mTextureSet.find(texName) != mTextureSet.end())
            alpha = std::string("    \"texture alpha\" \"") + texName + "\"\n";
    } else {
        float opacity = 1;
        if (material->Get(AI_MATKEY_OPACITY, opacity) == AI_SUCCESS && opacity < 1)
            alpha = std::string("    \"float alpha\" [ ") + std::to_string(opacity) + " ]\n";
    }

    // Output the shape specification
    mOutput << "Shape \"trianglemesh\"\n" <<
        alpha <<
        "    \"integer indices\" [";

    // Start with faces (which hold indices)
    for (unsigned int i = 0; i < mesh->mNumFaces; i++) {
        auto face = mesh->mFaces[i];
        if (face.mNumIndices != 3) throw DeadlyExportError("oh no not a tri!");

        for (unsigned int j = 0; j < face.mNumIndices; j++) {
            mOutput << face.mIndices[j] << " ";
        }
        if ((i % 7) == 6) mOutput << "\n    ";
    }
    mOutput << "]\n";

    // Then go to vertices
    mOutput << "    \"point3 P\" [";
    for (unsigned int i = 0; i < mesh->mNumVertices; i++) {
        auto vector = mesh->mVertices[i];
        mOutput << vector.x << " " << vector.y << " " << vector.z << "  ";
        if ((i % 4) == 3) mOutput << "\n    ";
    }
    mOutput << "]\n";

    // Normals (if present)
    if (mesh->mNormals) {
        mOutput << "    \"normal N\" [";
        for (unsigned int i = 0; i < mesh->mNumVertices; i++) {
            auto normal = mesh->mNormals[i];
            mOutput << normal.x << " " << normal.y << " " << normal.z << "  ";
            if ((i % 4) == 3) mOutput << "\n    ";
        }
        mOutput << "]\n";
    }

    // Tangents (if present)
    if (mesh->mTangents) {
        mOutput << "    \"vector3 S\" [";
        for (unsigned int i = 0; i < mesh->mNumVertices; i++) {
            auto tangent = mesh->mTangents[i];
            mOutput << tangent.x << " " << tangent.y << " " << tangent.z << "  ";
            if ((i % 4) == 3) mOutput << "\n    ";
        }
        mOutput << "]\n";
    }

    // Texture Coords (if present)
    // Find the first set of 2D texture coordinates..
    for (int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; ++i) {
        if (mesh->mNumUVComponents[i] == 2) {
            // assert(mesh->mTextureCoords[i] != nullptr);
            aiVector3D* uv = mesh->mTextureCoords[i];
            mOutput << "    \"point2 uv\" [";
            for (unsigned int j = 0; j < mesh->mNumVertices; ++j) {
                mOutput << uv[j].x << " " << uv[j].y << " ";
                if ((j % 6) == 5) mOutput << "\n    ";
            }
            mOutput << "]\n";
            break;
        }
    }
    // TODO: issue warning if there are additional UV sets?

    mOutput << "AttributeEnd\n";
}

void PbrtExporter::WriteInstanceDefinition(int i) {
    aiMesh* mesh = mScene->mMeshes[i];

    mOutput << "ObjectBegin \"";
    if (mesh->mName == aiString(""))
        mOutput << "mesh_" << i+1 << "\"\n";
    else
        mOutput << mesh->mName.C_Str() << "_" << i+1 << "\"\n";

    WriteMesh(mesh);

    mOutput << "ObjectEnd\n";
}

void PbrtExporter::WriteGeometricObjects(aiNode* node, aiMatrix4x4 worldFromObject,
                                         std::map<int, int> &meshUses) {
    // Sometimes interior nodes have degenerate matrices??
    if (node->mTransformation.Determinant() != 0)
        worldFromObject = worldFromObject * node->mTransformation;

    if (node->mNumMeshes > 0) {
        mOutput << "AttributeBegin\n";

        mOutput << "  Transform [ " << TransformAsString(worldFromObject) << "]\n";

        for (unsigned int i = 0; i < node->mNumMeshes; i++) {
            aiMesh* mesh = mScene->mMeshes[node->mMeshes[i]];
            if (meshUses[node->mMeshes[i]] == 1) {
                // If it's only used once in the scene, emit it directly as
                // a triangle mesh.
                mOutput << "  # " << mesh->mName.C_Str();
                WriteMesh(mesh);
            } else {
                // If it's used multiple times, there will be an object
                // instance for it, so emit a reference to that.
                mOutput << "  ObjectInstance \"";
                if (mesh->mName == aiString(""))
                    mOutput << "mesh_" << node->mMeshes[i] + 1 << "\"\n";
                else
                    mOutput << mesh->mName.C_Str() << "_" << node->mMeshes[i] + 1 << "\"\n";
            }
        }
        mOutput << "AttributeEnd\n\n";
    }

    // Recurse through children
    for (unsigned int i = 0; i < node->mNumChildren; i++) {
        WriteGeometricObjects(node->mChildren[i], worldFromObject, meshUses);
    }
}

#endif // ASSIMP_BUILD_NO_PBRT_EXPORTER
#endif // ASSIMP_BUILD_NO_EXPORT