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/** @file Implementation of the post processing step to improve the cache locality of a mesh.
 * <br>
 * The algorithm is roughly basing on this paper:
 * http://www.cs.princeton.edu/gfx/pubs/Sander_2007_%3ETR/tipsy.pdf
 *   .. although overdraw reduction isn't implemented yet ...
 */

// internal headers
#include "PostProcessing/ImproveCacheLocality.h"
#include "Common/VertexTriangleAdjacency.h"

#include <assimp/StringUtils.h>
#include <assimp/postprocess.h>
#include <assimp/scene.h>
#include <assimp/DefaultLogger.hpp>
#include <stdio.h>
#include <stack>

namespace Assimp {

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
ImproveCacheLocalityProcess::ImproveCacheLocalityProcess() :
        mConfigCacheDepth(PP_ICL_PTCACHE_SIZE) {
    // empty
}

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

// ------------------------------------------------------------------------------------------------
// Setup configuration
void ImproveCacheLocalityProcess::SetupProperties(const Importer *pImp) {
    // AI_CONFIG_PP_ICL_PTCACHE_SIZE controls the target cache size for the optimizer
    mConfigCacheDepth = pImp->GetPropertyInteger(AI_CONFIG_PP_ICL_PTCACHE_SIZE, PP_ICL_PTCACHE_SIZE);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void ImproveCacheLocalityProcess::Execute(aiScene *pScene) {
    if (!pScene->mNumMeshes) {
        ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess skipped; there are no meshes");
        return;
    }

    ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess begin");

    float out = 0.f;
    unsigned int numf = 0, numm = 0;
    for (unsigned int a = 0; a < pScene->mNumMeshes; ++a) {
        const float res = ProcessMesh(pScene->mMeshes[a], a);
        if (res) {
            numf += pScene->mMeshes[a]->mNumFaces;
            out += res;
            ++numm;
        }
    }
    if (!DefaultLogger::isNullLogger()) {
        if (numf > 0) {
            ASSIMP_LOG_INFO("Cache relevant are ", numm, " meshes (", numf, " faces). Average output ACMR is ", out / numf);
        }
        ASSIMP_LOG_DEBUG("ImproveCacheLocalityProcess finished. ");
    }
}

// ------------------------------------------------------------------------------------------------
static ai_real calculateInputACMR(aiMesh *pMesh, const aiFace *const pcEnd,
        unsigned int configCacheDepth, unsigned int meshNum) {
    ai_real fACMR = 0.0f;
    unsigned int *piFIFOStack = new unsigned int[configCacheDepth];
    memset(piFIFOStack, 0xff, configCacheDepth * sizeof(unsigned int));
    unsigned int *piCur = piFIFOStack;
    const unsigned int *const piCurEnd = piFIFOStack + configCacheDepth;

    // count the number of cache misses
    unsigned int iCacheMisses = 0;
    for (const aiFace *pcFace = pMesh->mFaces; pcFace != pcEnd; ++pcFace) {
        for (unsigned int qq = 0; qq < 3; ++qq) {
            bool bInCache = false;
            for (unsigned int *pp = piFIFOStack; pp < piCurEnd; ++pp) {
                if (*pp == pcFace->mIndices[qq]) {
                    // the vertex is in cache
                    bInCache = true;
                    break;
                }
            }
            if (!bInCache) {
                ++iCacheMisses;
                if (piCurEnd == piCur) {
                    piCur = piFIFOStack;
                }
                *piCur++ = pcFace->mIndices[qq];
            }
        }
    }
    delete[] piFIFOStack;
    fACMR = (ai_real)iCacheMisses / pMesh->mNumFaces;
    if (3.0 == fACMR) {
        char szBuff[128]; // should be sufficiently large in every case

        // the JoinIdenticalVertices process has not been executed on this
        // mesh, otherwise this value would normally be at least minimally
        // smaller than 3.0 ...
        ai_snprintf(szBuff, 128, "Mesh %u: Not suitable for vcache optimization", meshNum);
        ASSIMP_LOG_WARN(szBuff);
        return static_cast<ai_real>(0.f);
    }
    return fACMR;
}

// ------------------------------------------------------------------------------------------------
// Improves the cache coherency of a specific mesh
ai_real ImproveCacheLocalityProcess::ProcessMesh(aiMesh *pMesh, unsigned int meshNum) {
    // TODO: rewrite this to use std::vector or boost::shared_array
    ai_assert(nullptr != pMesh);

    // Check whether the input data is valid
    // - there must be vertices and faces
    // - all faces must be triangulated or we can't operate on them
    if (!pMesh->HasFaces() || !pMesh->HasPositions())
        return static_cast<ai_real>(0.f);

    if (pMesh->mPrimitiveTypes != aiPrimitiveType_TRIANGLE) {
        ASSIMP_LOG_ERROR("This algorithm works on triangle meshes only");
        return static_cast<ai_real>(0.f);
    }

    if (pMesh->mNumVertices <= mConfigCacheDepth) {
        return static_cast<ai_real>(0.f);
    }

    ai_real fACMR = 3.f;
    const aiFace *const pcEnd = pMesh->mFaces + pMesh->mNumFaces;

    // Input ACMR is for logging purposes only
    if (!DefaultLogger::isNullLogger()) {
        fACMR = calculateInputACMR(pMesh, pcEnd, mConfigCacheDepth, meshNum);
    }

    // first we need to build a vertex-triangle adjacency list
    VertexTriangleAdjacency adj(pMesh->mFaces, pMesh->mNumFaces, pMesh->mNumVertices, true);

    // build a list to store per-vertex caching time stamps
    std::vector<unsigned int> piCachingStamps;
    piCachingStamps.resize(pMesh->mNumVertices);
    memset(&piCachingStamps[0], 0x0, pMesh->mNumVertices * sizeof(unsigned int));

    // allocate an empty output index buffer. We store the output indices in one large array.
    // Since the number of triangles won't change the input faces can be reused. This is how
    // we save thousands of redundant mini allocations for aiFace::mIndices
    const unsigned int iIdxCnt = pMesh->mNumFaces * 3;
    std::vector<unsigned int> piIBOutput;
    piIBOutput.resize(iIdxCnt);
    std::vector<unsigned int>::iterator piCSIter = piIBOutput.begin();

    // allocate the flag array to hold the information
    // whether a face has already been emitted or not
    std::vector<bool> abEmitted(pMesh->mNumFaces, false);

    // dead-end vertex index stack
    std::stack<unsigned int, std::vector<unsigned int>> sDeadEndVStack;

    // create a copy of the piNumTriPtr buffer
    unsigned int *const piNumTriPtr = adj.mLiveTriangles;
    const std::vector<unsigned int> piNumTriPtrNoModify(piNumTriPtr, piNumTriPtr + pMesh->mNumVertices);

    // get the largest number of referenced triangles and allocate the "candidate buffer"
    unsigned int iMaxRefTris = 0;
    {
        const unsigned int *piCur = adj.mLiveTriangles;
        const unsigned int *const piCurEnd = adj.mLiveTriangles + pMesh->mNumVertices;
        for (; piCur != piCurEnd; ++piCur) {
            iMaxRefTris = std::max(iMaxRefTris, *piCur);
        }
    }
    ai_assert(iMaxRefTris > 0);
    std::vector<unsigned int> piCandidates;
    piCandidates.resize(iMaxRefTris * 3);
    unsigned int iCacheMisses = 0;

    // ...................................................................................
    /** PSEUDOCODE for the algorithm

        A = Build-Adjacency(I) Vertex-triangle adjacency
        L = Get-Triangle-Counts(A) Per-vertex live triangle counts
        C = Zero(Vertex-Count(I)) Per-vertex caching time stamps
        D = Empty-Stack() Dead-end vertex stack
        E = False(Triangle-Count(I)) Per triangle emitted flag
        O = Empty-Index-Buffer() Empty output buffer
        f = 0 Arbitrary starting vertex
        s = k+1, i = 1 Time stamp and cursor
        while f >= 0 For all valid fanning vertices
            N = Empty-Set() 1-ring of next candidates
            for each Triangle t in Neighbors(A, f)
                if !Emitted(E,t)
                    for each Vertex v in t
                        Append(O,v) Output vertex
                        Push(D,v) Add to dead-end stack
                        Insert(N,v) Register as candidate
                        L[v] = L[v]-1 Decrease live triangle count
                        if s-C[v] > k If not in cache
                            C[v] = s Set time stamp
                            s = s+1 Increment time stamp
                    E[t] = true Flag triangle as emitted
            Select next fanning vertex
            f = Get-Next-Vertex(I,i,k,N,C,s,L,D)
        return O
        */
    // ...................................................................................

    int ivdx = 0;
    int ics = 1;
    int iStampCnt = mConfigCacheDepth + 1;
    while (ivdx >= 0) {

        unsigned int icnt = piNumTriPtrNoModify[ivdx];
        unsigned int *piList = adj.GetAdjacentTriangles(ivdx);
        std::vector<unsigned int>::iterator piCurCandidate = piCandidates.begin();

        // get all triangles in the neighborhood
        for (unsigned int tri = 0; tri < icnt; ++tri) {

            // if they have not yet been emitted, add them to the output IB
            const unsigned int fidx = *piList++;
            if (!abEmitted[fidx]) {

                // so iterate through all vertices of the current triangle
                const aiFace *pcFace = &pMesh->mFaces[fidx];
                const unsigned nind = pcFace->mNumIndices;
                for (unsigned ind = 0; ind < nind; ind++) {
                    unsigned dp = pcFace->mIndices[ind];

                    // the current vertex won't have any free triangles after this step
                    if (ivdx != (int)dp) {
                        // append the vertex to the dead-end stack
                        sDeadEndVStack.push(dp);

                        // register as candidate for the next step
                        *piCurCandidate++ = dp;

                        // decrease the per-vertex triangle counts
                        piNumTriPtr[dp]--;
                    }

                    // append the vertex to the output index buffer
                    *piCSIter++ = dp;

                    // if the vertex is not yet in cache, set its cache count
                    if (iStampCnt - piCachingStamps[dp] > mConfigCacheDepth) {
                        piCachingStamps[dp] = iStampCnt++;
                        ++iCacheMisses;
                    }
                }
                // flag triangle as emitted
                abEmitted[fidx] = true;
            }
        }

        // the vertex has now no living adjacent triangles anymore
        piNumTriPtr[ivdx] = 0;

        // get next fanning vertex
        ivdx = -1;
        int max_priority = -1;
        for (std::vector<unsigned int>::iterator piCur = piCandidates.begin(); piCur != piCurCandidate; ++piCur) {
            const unsigned int dp = *piCur;

            // must have live triangles
            if (piNumTriPtr[dp] > 0) {
                int priority = 0;

                // will the vertex be in cache, even after fanning occurs?
                unsigned int tmp;
                if ((tmp = iStampCnt - piCachingStamps[dp]) + 2 * piNumTriPtr[dp] <= mConfigCacheDepth) {
                    priority = tmp;
                }

                // keep best candidate
                if (priority > max_priority) {
                    max_priority = priority;
                    ivdx = dp;
                }
            }
        }
        // did we reach a dead end?
        if (-1 == ivdx) {
            // need to get a non-local vertex for which we have a good chance that it is still
            // in the cache ...
            while (!sDeadEndVStack.empty()) {
                unsigned int iCachedIdx = sDeadEndVStack.top();
                sDeadEndVStack.pop();
                if (piNumTriPtr[iCachedIdx] > 0) {
                    ivdx = iCachedIdx;
                    break;
                }
            }

            if (-1 == ivdx) {
                // well, there isn't such a vertex. Simply get the next vertex in input order and
                // hope it is not too bad ...
                while (ics < (int)pMesh->mNumVertices) {
                    ++ics;
                    if (piNumTriPtr[ics] > 0) {
                        ivdx = ics;
                        break;
                    }
                }
            }
        }
    }
    ai_real fACMR2 = 0.0f;
    if (!DefaultLogger::isNullLogger()) {
        fACMR2 = static_cast<ai_real>(iCacheMisses / pMesh->mNumFaces);
        const ai_real averageACMR = ((fACMR - fACMR2) / fACMR) * 100.f;
        // very intense verbose logging ... prepare for much text if there are many meshes
        if (DefaultLogger::get()->getLogSeverity() == Logger::VERBOSE) {
            ASSIMP_LOG_VERBOSE_DEBUG("Mesh ", meshNum, "| ACMR in: ", fACMR, " out: ", fACMR2, " | average ACMR ", averageACMR);
        }
        fACMR2 *= pMesh->mNumFaces;
    }

    // sort the output index buffer back to the input array
    piCSIter = piIBOutput.begin();
    for (aiFace *pcFace = pMesh->mFaces; pcFace != pcEnd; ++pcFace) {
        unsigned nind = pcFace->mNumIndices;
        unsigned *ind = pcFace->mIndices;
        if (nind > 0)
            ind[0] = *piCSIter++;
        if (nind > 1)
            ind[1] = *piCSIter++;
        if (nind > 2)
            ind[2] = *piCSIter++;
    }

    return fACMR2;
}

} // namespace Assimp

