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/** @file Implementation of the Terragen importer class */

#ifndef ASSIMP_BUILD_NO_TERRAGEN_IMPORTER

#include "TerragenLoader.h"
#include <assimp/StreamReader.h>
#include <assimp/importerdesc.h>
#include <assimp/scene.h>
#include <assimp/DefaultLogger.hpp>
#include <assimp/IOSystem.hpp>
#include <assimp/Importer.hpp>

using namespace Assimp;

static const aiImporterDesc desc = {
    "Terragen Heightmap Importer",
    "",
    "",
    "http://www.planetside.co.uk/",
    aiImporterFlags_SupportBinaryFlavour,
    0,
    0,
    0,
    0,
    "ter"
};

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
TerragenImporter::TerragenImporter() :
        configComputeUVs(false) {
    // empty
}

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

// ------------------------------------------------------------------------------------------------
// Returns whether the class can handle the format of the given file.
bool TerragenImporter::CanRead(const std::string &pFile, IOSystem *pIOHandler, bool /*checkSig*/) const {
    static const char *tokens[] = { "terragen" };
    return SearchFileHeaderForToken(pIOHandler, pFile, tokens, AI_COUNT_OF(tokens));
}

// ------------------------------------------------------------------------------------------------
// Build a string of all file extensions supported
const aiImporterDesc *TerragenImporter::GetInfo() const {
    return &desc;
}

// ------------------------------------------------------------------------------------------------
// Setup import properties
void TerragenImporter::SetupProperties(const Importer *pImp) {
    // AI_CONFIG_IMPORT_TER_MAKE_UVS
    configComputeUVs = (0 != pImp->GetPropertyInteger(AI_CONFIG_IMPORT_TER_MAKE_UVS, 0));
}

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

    // Check whether we can read from the file
    if (file == nullptr)
        throw DeadlyImportError("Failed to open TERRAGEN TERRAIN file ", pFile, ".");

    // Construct a stream reader to read all data in the correct endianness
    StreamReaderLE reader(file);
    if (reader.GetRemainingSize() < 16)
        throw DeadlyImportError("TER: file is too small");

    // Check for the existence of the two magic strings 'TERRAGEN' and 'TERRAIN '
    if (::strncmp((const char *)reader.GetPtr(), AI_TERR_BASE_STRING, 8))
        throw DeadlyImportError("TER: Magic string \'TERRAGEN\' not found");

    if (::strncmp((const char *)reader.GetPtr() + 8, AI_TERR_TERRAIN_STRING, 8))
        throw DeadlyImportError("TER: Magic string \'TERRAIN\' not found");

    unsigned int x = 0, y = 0, mode = 0;

    aiNode *root = pScene->mRootNode = new aiNode();
    root->mName.Set("<TERRAGEN.TERRAIN>");

    // Default scaling is 30
    root->mTransformation.a1 = root->mTransformation.b2 = root->mTransformation.c3 = 30.f;

    // Now read all chunks until we're finished or an EOF marker is encountered
    reader.IncPtr(16);
    while (reader.GetRemainingSize() >= 4) {
        const char *head = (const char *)reader.GetPtr();
        reader.IncPtr(4);

        // EOF, break in every case
        if (!::strncmp(head, AI_TERR_EOF_STRING, 4))
            break;

        // Number of x-data points
        if (!::strncmp(head, AI_TERR_CHUNK_XPTS, 4)) {
            x = (uint16_t)reader.GetI2();
        }
        // Number of y-data points
        else if (!::strncmp(head, AI_TERR_CHUNK_YPTS, 4)) {
            y = (uint16_t)reader.GetI2();
        }
        // Squared terrains width-1.
        else if (!::strncmp(head, AI_TERR_CHUNK_SIZE, 4)) {
            x = y = (uint16_t)reader.GetI2() + 1;
        }
        // terrain scaling
        else if (!::strncmp(head, AI_TERR_CHUNK_SCAL, 4)) {
            root->mTransformation.a1 = reader.GetF4();
            root->mTransformation.b2 = reader.GetF4();
            root->mTransformation.c3 = reader.GetF4();
        }
        // mapping == 1: earth radius
        else if (!::strncmp(head, AI_TERR_CHUNK_CRAD, 4)) {
            reader.GetF4();
        }
        // mapping mode
        else if (!::strncmp(head, AI_TERR_CHUNK_CRVM, 4)) {
            mode = reader.GetI1();
            if (0 != mode)
                ASSIMP_LOG_ERROR("TER: Unsupported mapping mode, a flat terrain is returned");
        }
        // actual terrain data
        else if (!::strncmp(head, AI_TERR_CHUNK_ALTW, 4)) {
            float hscale = (float)reader.GetI2() / 65536;
            float bheight = (float)reader.GetI2();

            if (!hscale) hscale = 1;

            // Ensure we have enough data
            if (reader.GetRemainingSize() < x * y * 2)
                throw DeadlyImportError("TER: ALTW chunk is too small");

            if (x <= 1 || y <= 1)
                throw DeadlyImportError("TER: Invalid terrain size");

            // Allocate the output mesh
            pScene->mMeshes = new aiMesh *[pScene->mNumMeshes = 1];
            aiMesh *m = pScene->mMeshes[0] = new aiMesh();

            // We return quads
            aiFace *f = m->mFaces = new aiFace[m->mNumFaces = (x - 1) * (y - 1)];
            aiVector3D *pv = m->mVertices = new aiVector3D[m->mNumVertices = m->mNumFaces * 4];

            aiVector3D *uv(nullptr);
            float step_y(0.0f), step_x(0.0f);
            if (configComputeUVs) {
                uv = m->mTextureCoords[0] = new aiVector3D[m->mNumVertices];
                step_y = 1.f / y;
                step_x = 1.f / x;
            }
            const int16_t *data = (const int16_t *)reader.GetPtr();

            for (unsigned int yy = 0, t = 0; yy < y - 1; ++yy) {
                for (unsigned int xx = 0; xx < x - 1; ++xx, ++f) {

                    // make verts
                    const float fy = (float)yy, fx = (float)xx;
                    unsigned tmp, tmp2;
                    *pv++ = aiVector3D(fx, fy, (float)data[(tmp2 = x * yy) + xx] * hscale + bheight);
                    *pv++ = aiVector3D(fx, fy + 1, (float)data[(tmp = x * (yy + 1)) + xx] * hscale + bheight);
                    *pv++ = aiVector3D(fx + 1, fy + 1, (float)data[tmp + xx + 1] * hscale + bheight);
                    *pv++ = aiVector3D(fx + 1, fy, (float)data[tmp2 + xx + 1] * hscale + bheight);

                    // also make texture coordinates, if necessary
                    if (configComputeUVs) {
                        *uv++ = aiVector3D(step_x * xx, step_y * yy, 0.f);
                        *uv++ = aiVector3D(step_x * xx, step_y * (yy + 1), 0.f);
                        *uv++ = aiVector3D(step_x * (xx + 1), step_y * (yy + 1), 0.f);
                        *uv++ = aiVector3D(step_x * (xx + 1), step_y * yy, 0.f);
                    }

                    // make indices
                    f->mIndices = new unsigned int[f->mNumIndices = 4];
                    for (unsigned int i = 0; i < 4; ++i) {
                        f->mIndices[i] = t;
                        t++;
                    }
                }
            }

            // Add the mesh to the root node
            root->mMeshes = new unsigned int[root->mNumMeshes = 1];
            root->mMeshes[0] = 0;
        }

        // Get to the next chunk (4 byte aligned)
        unsigned dtt = reader.GetCurrentPos() & 0x3;
        if (dtt) {
            reader.IncPtr(4 - dtt);
        }
    }

    // Check whether we have a mesh now
    if (pScene->mNumMeshes != 1)
        throw DeadlyImportError("TER: Unable to load terrain");

    // Set the AI_SCENE_FLAGS_TERRAIN bit
    pScene->mFlags |= AI_SCENE_FLAGS_TERRAIN;
}

#endif // !! ASSIMP_BUILD_NO_TERRAGEN_IMPORTER
