tri_stripper.cpp

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//
// Copyright (C) 2004 Tanguy Fautré.
// For conditions of distribution and use,
// see copyright notice in tri_stripper.h
//
// SVN: $Id: tri_stripper.cpp 86 2005-06-08 17:47:27Z gpsnoopy $

#include "tri_stripper.h"

#include "detail/connectivity_graph.h"
#include "detail/policy.h"

#include <cassert>




namespace triangle_stripper {

    using namespace detail;




tri_stripper::tri_stripper(const indices & TriIndices)
    : m_Triangles(TriIndices.size() / 3), // Silently ignore extra indices if (Indices.size() % 3 != 0)
      m_StripID(0),
      m_FirstRun(true)
{
    SetCacheSize();
    SetMinStripSize();
    SetBackwardSearch();
    SetPushCacheHits();

    make_connectivity_graph(m_Triangles, TriIndices);
}



void tri_stripper::Strip(primitive_vector * out_pPrimitivesVector)
{
    assert(out_pPrimitivesVector);

    if (! m_FirstRun) {
        unmark_nodes(m_Triangles);
        ResetStripIDs();
        m_Cache.reset();
        m_TriHeap.clear();
        m_Candidates.clear();
        m_StripID = 0;

        m_FirstRun = false;
    }

    out_pPrimitivesVector->clear();

    InitTriHeap();

    Stripify();
    AddLeftTriangles();
    
    std::swap(m_PrimitivesVector, (* out_pPrimitivesVector));
}



void tri_stripper::InitTriHeap()
{
    m_TriHeap.reserve(m_Triangles.size());

    // Set up the triangles priority queue
    // The lower the number of available neighbour triangles, the higher the priority.
    for (size_t i = 0; i < m_Triangles.size(); ++i)
        m_TriHeap.push(m_Triangles[i].out_size());

    // We're not going to add new elements anymore
    m_TriHeap.lock();

    // Remove useless triangles
    // Note: we had to put all of them into the heap before to ensure coherency of the heap_array object
    while ((! m_TriHeap.empty()) && (m_TriHeap.top() == 0))
        m_TriHeap.pop();
}



void tri_stripper::ResetStripIDs()
{
    for (triangle_graph::node_iterator it = m_Triangles.begin(); it != m_Triangles.end(); ++it)
        (**it).ResetStripID();
}



void tri_stripper::Stripify()
{
    while (! m_TriHeap.empty()) {

        // There is no triangle in the candidates list, refill it with the loneliest triangle
        const size_t HeapTop = m_TriHeap.position(0);
        m_Candidates.push_back(HeapTop);

        while (! m_Candidates.empty()) {

            // Note: FindBestStrip empties the candidate list, while BuildStrip refills it
            const strip TriStrip = FindBestStrip();

            if (TriStrip.Size() >= m_MinStripSize)
                BuildStrip(TriStrip);
        }

        if (! m_TriHeap.removed(HeapTop))
            m_TriHeap.erase(HeapTop);

        // Eliminate all the triangles that have now become useless
        while ((! m_TriHeap.empty()) && (m_TriHeap.top() == 0))
            m_TriHeap.pop();
    }
}



inline strip tri_stripper::FindBestStrip()
{
    // Allow to restore the cache (modified by ExtendTriToStrip) and implicitly reset the cache hit count
    const cache_simulator CacheBackup = m_Cache;

    policy Policy(m_MinStripSize, Cache());

    while (! m_Candidates.empty()) {

        const size_t Candidate = m_Candidates.back();
        m_Candidates.pop_back();

        // Discard useless triangles from the candidate list
        if ((m_Triangles[Candidate].marked()) || (m_TriHeap[Candidate] == 0))
            continue;       

        // Try to extend the triangle in the 3 possible forward directions
        for (size_t i = 0; i < 3; ++i) {

            const strip Strip = ExtendToStrip(Candidate, triangle_order(i));
            Policy.Challenge(Strip, m_TriHeap[Strip.Start()], m_Cache.hitcount());
            
            m_Cache = CacheBackup;
        }

        // Try to extend the triangle in the 6 possible backward directions
        if (m_BackwardSearch) {

            for (size_t i = 0; i < 3; ++i) {

                const strip Strip = BackExtendToStrip(Candidate, triangle_order(i), false);
                Policy.Challenge(Strip, m_TriHeap[Strip.Start()], m_Cache.hitcount());
            
                m_Cache = CacheBackup;
            }

            for (size_t i = 0; i < 3; ++i) {

                const strip Strip = BackExtendToStrip(Candidate, triangle_order(i), true);
                Policy.Challenge(Strip, m_TriHeap[Strip.Start()], m_Cache.hitcount());
            
                m_Cache = CacheBackup;
            }
        }

    }

    return Policy.BestStrip();
}



strip tri_stripper::ExtendToStrip(const size_t Start, triangle_order Order)
{
    const triangle_order StartOrder = Order;
    
    // Begin a new strip
    m_Triangles[Start]->SetStripID(++m_StripID);
    AddTriangle(* m_Triangles[Start], Order, false);

    size_t Size = 1;
    bool ClockWise = false;

    // Loop while we can further extend the strip
    for (tri_iterator Node = (m_Triangles.begin() + Start); 
        (Node != m_Triangles.end()) && (!Cache() || ((Size + 2) < CacheSize()));
        ++Size) {

        const const_link_iterator Link = LinkToNeighbour(Node, ClockWise, Order, false);

        // Is it the end of the strip?
        if (Link == Node->out_end()) {

            Node = m_Triangles.end();
            --Size;

        } else {

            Node = Link->terminal();
            (* Node)->SetStripID(m_StripID);
            ClockWise = ! ClockWise;

        }
    }

    return strip(Start, StartOrder, Size);
}



strip tri_stripper::BackExtendToStrip(size_t Start, triangle_order Order, bool ClockWise)
{
    // Begin a new strip
    m_Triangles[Start]->SetStripID(++m_StripID);
    BackAddIndex(LastEdge(* m_Triangles[Start], Order).B());
    size_t Size = 1;

    tri_iterator Node;

    // Loop while we can further extend the strip
    for (Node = (m_Triangles.begin() + Start); 
        !Cache() || ((Size + 2) < CacheSize());
        ++Size) {

        const const_link_iterator Link = BackLinkToNeighbour(Node, ClockWise, Order);

        // Is it the end of the strip?
        if (Link == Node->out_end())
            break;

        else {
            Node = Link->terminal();
            (* Node)->SetStripID(m_StripID);
            ClockWise = ! ClockWise;
        }
    }

    // We have to start from a counterclockwise triangle.
    // Simply return an empty strip in the case where the first triangle is clockwise.
    // Even though we could discard the first triangle and start from the next counterclockwise triangle,
    // this often leads to more lonely triangles afterward.
    if (ClockWise)
        return strip();

    if (Cache()) {
        m_Cache.merge(m_BackCache, Size);
        m_BackCache.reset();
    }

    return strip(Node - m_Triangles.begin(), Order, Size);
}



void tri_stripper::BuildStrip(const strip Strip)
{
    const size_t Start = Strip.Start();

    bool ClockWise = false;
    triangle_order Order = Strip.Order();

    // Create a new strip
    m_PrimitivesVector.push_back(primitive_group());
    m_PrimitivesVector.back().Type = TRIANGLE_STRIP;
    AddTriangle(* m_Triangles[Start], Order, true);
    MarkTriAsTaken(Start);

    // Loop while we can further extend the strip
    tri_iterator Node = (m_Triangles.begin() + Start);

    for (size_t Size = 1; Size < Strip.Size(); ++Size) {

        const const_link_iterator Link = LinkToNeighbour(Node, ClockWise, Order, true);

        assert(Link != Node->out_end());

        // Go to the next triangle
        Node = Link->terminal();
        MarkTriAsTaken(Node - m_Triangles.begin());
        ClockWise = ! ClockWise;
    }
}



inline tri_stripper::const_link_iterator tri_stripper::LinkToNeighbour(const const_tri_iterator Node, const bool ClockWise, triangle_order & Order, const bool NotSimulation)
{
    const triangle_edge Edge = LastEdge(** Node, Order);

    for (const_link_iterator Link = Node->out_begin(); Link != Node->out_end(); ++Link) {

        // Get the reference to the possible next triangle
        const triangle & Tri = ** Link->terminal();

        // Check whether it's already been used
        if (NotSimulation || (Tri.StripID() != m_StripID)) {

            if (! Link->terminal()->marked()) {

                // Does the current candidate triangle match the required position for the strip?

                if ((Edge.B() == Tri.A()) && (Edge.A() == Tri.B())) {
                    Order = (ClockWise) ? ABC : BCA;
                    AddIndex(Tri.C(), NotSimulation);
                    return Link;
                }

                else if ((Edge.B() == Tri.B()) && (Edge.A() == Tri.C())) {
                    Order = (ClockWise) ? BCA : CAB;
                    AddIndex(Tri.A(), NotSimulation);
                    return Link;
                }

                else if ((Edge.B() == Tri.C()) && (Edge.A() == Tri.A())) {
                    Order = (ClockWise) ? CAB : ABC;
                    AddIndex(Tri.B(), NotSimulation);
                    return Link;
                }
            }
        }

    }

    return Node->out_end();
}



inline tri_stripper::const_link_iterator tri_stripper::BackLinkToNeighbour(const_tri_iterator Node, bool ClockWise, triangle_order & Order)
{
    const triangle_edge Edge = FirstEdge(** Node, Order);

    for (const_link_iterator Link = Node->out_begin(); Link != Node->out_end(); ++Link) {

        // Get the reference to the possible previous triangle
        const triangle & Tri = ** Link->terminal();

        // Check whether it's already been used
        if ((Tri.StripID() != m_StripID) && ! Link->terminal()->marked()) {

            // Does the current candidate triangle match the required position for the strip?

            if ((Edge.B() == Tri.A()) && (Edge.A() == Tri.B())) {
                Order = (ClockWise) ? CAB : BCA;
                BackAddIndex(Tri.C());
                return Link;
            }

            else if ((Edge.B() == Tri.B()) && (Edge.A() == Tri.C())) {
                Order = (ClockWise) ? ABC : CAB;
                BackAddIndex(Tri.A());
                return Link;
            }

            else if ((Edge.B() == Tri.C()) && (Edge.A() == Tri.A())) {
                Order = (ClockWise) ? BCA : ABC;
                BackAddIndex(Tri.B());
                return Link;
            }
        }

    }

    return Node->out_end();
}



void tri_stripper::MarkTriAsTaken(const size_t i)
{
    // typedef triangle_graph::node_iterator tri_node_iter;
    typedef triangle_graph::out_arc_iterator tri_link_iter;

    // Mark the triangle node
    m_Triangles[i].mark();

    // Remove triangle from priority queue if it isn't yet
    if (! m_TriHeap.removed(i))
        m_TriHeap.erase(i);

    // Adjust the degree of available neighbour triangles
    for (tri_link_iter Link = m_Triangles[i].out_begin(); Link != m_Triangles[i].out_end(); ++Link) {

        const size_t j = Link->terminal() - m_Triangles.begin();

        if ((! m_Triangles[j].marked()) && (! m_TriHeap.removed(j))) {
            size_t NewDegree = m_TriHeap.peek(j);
            NewDegree = NewDegree - 1;
            m_TriHeap.update(j, NewDegree);

            // Update the candidate list if cache is enabled
            if (Cache() && (NewDegree > 0))
                m_Candidates.push_back(j);
        }
    }
}



inline triangle_edge tri_stripper::FirstEdge(const triangle & Triangle, const triangle_order Order)
{
    switch (Order)
    {
    case ABC:
        return triangle_edge(Triangle.A(), Triangle.B());

    case BCA:
        return triangle_edge(Triangle.B(), Triangle.C());

    case CAB:
        return triangle_edge(Triangle.C(), Triangle.A());

    default:
        assert(false);
        return triangle_edge(0, 0);
    }
}



inline triangle_edge tri_stripper::LastEdge(const triangle & Triangle, const triangle_order Order)
{
    switch (Order)
    {
    case ABC:
        return triangle_edge(Triangle.B(), Triangle.C());

    case BCA:
        return triangle_edge(Triangle.C(), Triangle.A());

    case CAB:
        return triangle_edge(Triangle.A(), Triangle.B());

    default:
        assert(false);
        return triangle_edge(0, 0);
    }
}



inline void tri_stripper::AddIndex(const index i, const bool NotSimulation)
{
    if (Cache())
        m_Cache.push(i, ! NotSimulation);

    if (NotSimulation)
        m_PrimitivesVector.back().Indices.push_back(i);
}



inline void tri_stripper::BackAddIndex(const index i)
{
    if (Cache())
        m_BackCache.push(i, true);
}



inline void tri_stripper::AddTriangle(const triangle & Tri, const triangle_order Order, const bool NotSimulation)
{
    switch (Order)
    {
    case ABC:
        AddIndex(Tri.A(), NotSimulation);
        AddIndex(Tri.B(), NotSimulation);
        AddIndex(Tri.C(), NotSimulation);
        break;

    case BCA:
        AddIndex(Tri.B(), NotSimulation);
        AddIndex(Tri.C(), NotSimulation);
        AddIndex(Tri.A(), NotSimulation);
        break;

    case CAB:
        AddIndex(Tri.C(), NotSimulation);
        AddIndex(Tri.A(), NotSimulation);
        AddIndex(Tri.B(), NotSimulation);
        break;
    }
}



inline void tri_stripper::BackAddTriangle(const triangle & Tri, const triangle_order Order)
{
    switch (Order)
    {
    case ABC:
        BackAddIndex(Tri.C());
        BackAddIndex(Tri.B());
        BackAddIndex(Tri.A());
        break;

    case BCA:
        BackAddIndex(Tri.A());
        BackAddIndex(Tri.C());
        BackAddIndex(Tri.B());
        break;

    case CAB:
        BackAddIndex(Tri.B());
        BackAddIndex(Tri.A());
        BackAddIndex(Tri.C());
        break;
    }
}



void tri_stripper::AddLeftTriangles()
{
    // Create the last indices array and fill it with all the triangles that couldn't be stripped
    primitive_group Primitives;
    Primitives.Type = TRIANGLES;
    m_PrimitivesVector.push_back(Primitives);
    indices & Indices = m_PrimitivesVector.back().Indices;

    for (size_t i = 0; i < m_Triangles.size(); ++i)
        if (! m_Triangles[i].marked()) {
            Indices.push_back(m_Triangles[i]->A());
            Indices.push_back(m_Triangles[i]->B());
            Indices.push_back(m_Triangles[i]->C());
        }

    // Undo if useless
    if (Indices.size() == 0)
        m_PrimitivesVector.pop_back();
}



inline bool tri_stripper::Cache() const
{
    return (m_Cache.size() != 0);
}



inline size_t tri_stripper::CacheSize() const
{
    return m_Cache.size();
}




} // namespace triangle_stripper