多个std :: vector可解决缓存问题？

Question

我有一个std::vector<DOUBLEPOINT>我正在使用std::vector<DOUBLEPOINT>曲线创建一个应用程序，并且结果实时显示。 我将贝塞尔曲线点转换为一串短线。 我将细线的坐标存储在上面的向量中。 这是我的问题： 当向量的大小超过高速缓存行时，事情就会变得非常缓慢。 我想知道是否最好有很多std::vector<DOUBLEPOINT> ，基本上每100点，它就会切换到另一个。 这样可以解决我的缓存问题吗？ 否则，我还能如何允许用户创建所需数量的点而又不会变得非常慢？ 我所有其他算法的运算速度都很快（例如多边形填充），所以这不是我的问题。 真正减慢速度的是std :: vector。

谢谢

    struct SHAPECONTOUR{

        std::vector<USERFPOINT> UserPoints;
        std::vector<DOUBLEPOINT> DrawingPoints;

        SHAPEOUTLINE Outline;

    };

I call UpdateShape() every time a point is added but I assure you my other algorithms are fast...


void OGLSHAPE::UpdateShape()
{
    if(Contour.size() == 0)
    {
        return;
    }
    for(int i = 0; i < Contour.size(); ++i)
    {
        Contour[i].DrawingPoints.clear();

     if(Contour[i].UserPoints.size() < 2)
     {
         break;
     }


    Contour[i].DrawingPoints.clear();
Contour[i].DrawingPoints.reserve(1000);
     for(unsigned int x = 0; x < Contour[i].UserPoints.size() - 1; ++x)
         SetCubicBezier(
             Contour[i].UserPoints[x],
             Contour[i].UserPoints[x + 1],
             i);




     //Remove Duplicates
     for(int j = 0; j < 2; ++j)
     {
         if(Contour[i].DrawingPoints.size() > 2)
             for(unsigned int x = 0; x < Contour[i].DrawingPoints.size() - 1; ++x)
             {
                 if(Contour[i].DrawingPoints[x].point[0] ==
                     Contour[i].DrawingPoints[x + 1].point[0] &&
                     Contour[i].DrawingPoints[x].point[1] ==
                     Contour[i].DrawingPoints[x + 1].point[1] 

                 )
                     Contour[i].DrawingPoints.erase(Contour[i].DrawingPoints.begin() + x);
             }
     }


     GenerateLinePoly(Contour[i].DrawingPoints,Contour[i].Outline.OutlineWidth);
     Contour[i].Outline.OutlineSize = OutlineVec.size()  / 2;
     glBindBufferARB(GL_ARRAY_BUFFER_ARB,Contour[i].Outline.OutlineVBO);
     glBufferDataARB(GL_ARRAY_BUFFER_ARB,sizeof(GLfloat) * OutlineVec.size(),&OutlineVec[0],GL_STATIC_COPY);


    }

    gluTessNormal(PolygonTesselator.tobj, 0, 0, 1);
    PolygonTesselator.Set_Winding_Rule(WindingRule); 

    //PolygonTesselator.SetDimensions(layer[currentlayer].Shapes[i].Dimensions,layer[currentlayer].Shapes[i].minima);

    PolygonTesselator.Begin_Polygon(); 
    for(unsigned int c = 0; c < Contour.size(); ++c)
    {
            PolygonTesselator.Begin_Contour();

            for(unsigned int j = 0; j < Contour[c].DrawingPoints.size(); ++j)
            {
                gluTessVertex(PolygonTesselator.tobj,&Contour[c].DrawingPoints[j].point[0],
                    &Contour[c].DrawingPoints[j].point[0]);
            }

            PolygonTesselator.End_Contour();

    }
    PolygonTesselator.End_Polygon();



    PolygonTesselator.TransferVerticies(
        ObjectVBOInt,
        TextureCoordsVBOInt,
        ObjectVBOCount,
        TextureCoordsVBOCount);
}

void OGLSHAPE::SetCubicBezier(USERFPOINT &a,USERFPOINT &b, int &currentcontour )
{





        double dx1 = a.RightHandle.x - a.UserPoint.x;
        double dy1 = a.RightHandle.y - a.UserPoint.y;
        double dx2 = b.LeftHandle.x - a.RightHandle.x;
        double dy2 = b.LeftHandle.y - a.RightHandle.y;
        double dx3 = b.UserPoint.x - b.LeftHandle.x;
        double dy3 = b.UserPoint.y - b.LeftHandle.y;

        float len = sqrt(dx1 * dx1 + dy1 * dy1) + 
            sqrt(dx2 * dx2 + dy2 * dy2) + 
            sqrt(dx3 * dx3 + dy3 * dy3);




        int NUM_STEPS =  int(len * 0.049);

        if(NUM_STEPS > 55)
        {
            NUM_STEPS = 55;
        }
        double subdiv_step  = 1.0 / (NUM_STEPS + 1);
        double subdiv_step2 = subdiv_step*subdiv_step;
        double subdiv_step3 = subdiv_step*subdiv_step*subdiv_step;

        double pre1 = 3.0 * subdiv_step;
        double pre2 = 3.0 * subdiv_step2;
        double pre4 = 6.0 * subdiv_step2;
        double pre5 = 6.0 * subdiv_step3;



        double tmp1x = a.UserPoint.x - a.RightHandle.x * 2.0 + b.LeftHandle.x;
        double tmp1y = a.UserPoint.y - a.RightHandle.y  * 2.0 + b.LeftHandle.y;

        double tmp2x = (a.RightHandle.x - b.LeftHandle.x)*3.0 - a.UserPoint.x + b.UserPoint.x;
        double tmp2y = (a.RightHandle.y - b.LeftHandle.y)*3.0 - a.UserPoint.y + b.UserPoint.y;

        temp.point[0] = a.UserPoint.x;
        temp.point[1] = a.UserPoint.y;

        //a user
        //a right
        //b left
        //b user

        double dfx = (a.RightHandle.x - a.UserPoint.x)*pre1 + tmp1x*pre2 + tmp2x*subdiv_step3;
        double dfy = (a.RightHandle.y - a.UserPoint.y)*pre1 + tmp1y*pre2 + tmp2y*subdiv_step3;

        double ddfx = tmp1x*pre4 + tmp2x*pre5;
        double ddfy = tmp1y*pre4 + tmp2y*pre5;

        double dddfx = tmp2x*pre5;
        double dddfy = tmp2y*pre5;

        int step = NUM_STEPS;

        // Suppose, we have some abstract object Polygon which
        // has method AddVertex(x, y), similar to LineTo in
        // many graphical APIs.
        // Note, that the loop has only operation add!

        while(step--)
        {


            temp.point[0]  += dfx;
            temp.point[1]  += dfy;
            dfx  += ddfx;
            dfy  += ddfy;
            ddfx += dddfx;
            ddfy += dddfy;

            Contour[currentcontour].DrawingPoints.push_back(temp);
        }


        temp.point[0] = (GLdouble)b.UserPoint.x;
        temp.point[1] = (GLdouble)b.UserPoint.y;
        Contour[currentcontour].DrawingPoints.push_back(temp);


}

void OGLSHAPE::GenerateLinePoly(const std::vector<DOUBLEPOINT> &input, int width)
{
    OutlineVec.clear();
    if(input.size() < 2)
    {
        return;
    }



    float w = width / 2.0f;

    //glBegin(GL_TRIANGLES);
    for( size_t i = 0; i < input.size()-1; ++i )
    {
        POINTFLOAT cur;
        cur.x = input[i].point[0];
        cur.y = input[i].point[1];


        POINTFLOAT nxt;
        nxt.x = input[i+1].point[0];
        nxt.y = input[i+1].point[1];

        POINTFLOAT b;
        b.x = nxt.x - cur.x;
        b.y = nxt.y - cur.y;

        b = normalize(b);



        POINTFLOAT b_perp;
        b_perp.x = -b.y;
        b_perp.y = b.x;


        POINTFLOAT p0;
        POINTFLOAT p1;
        POINTFLOAT p2;
        POINTFLOAT p3;

        p0.x = cur.x + b_perp.x * w;
        p0.y = cur.y + b_perp.y * w;

        p1.x = cur.x - b_perp.x * w;
        p1.y = cur.y - b_perp.y * w;

        p2.x = nxt.x + b_perp.x * w;
        p2.y = nxt.y + b_perp.y * w;

        p3.x = nxt.x - b_perp.x * w;
        p3.y = nxt.y - b_perp.y * w;

        OutlineVec.push_back(p0.x);
        OutlineVec.push_back(p0.y);
        OutlineVec.push_back(p1.x);
        OutlineVec.push_back(p1.y);
        OutlineVec.push_back(p2.x);
        OutlineVec.push_back(p2.y);

        OutlineVec.push_back(p2.x);
        OutlineVec.push_back(p2.y);
        OutlineVec.push_back(p1.x);
        OutlineVec.push_back(p1.y);
        OutlineVec.push_back(p3.x);
        OutlineVec.push_back(p3.y);



        // only do joins when we have a prv
        if( i == 0 ) continue;

        POINTFLOAT prv;
        prv.x = input[i-1].point[0];
        prv.y = input[i-1].point[1];

        POINTFLOAT a;
        a.x = prv.x - cur.x;
        a.y = prv.y - cur.y;

        a = normalize(a);

        POINTFLOAT a_perp;
        a_perp.x = a.y;
        a_perp.y = -a.x;

        float det = a.x * b.y  - b.x * a.y;
        if( det > 0 )
        {
            a_perp.x = -a_perp.x;
            a_perp.y = -a_perp.y;

            b_perp.x = -b_perp.x;
            b_perp.y = -b_perp.y;
        }

        // TODO: do inner miter calculation

        // flip around normals and calculate round join points
        a_perp.x = -a_perp.x;
        a_perp.y = -a_perp.y;

        b_perp.x = -b_perp.x;
        b_perp.y = -b_perp.y;

        size_t num_pts = 4;

        std::vector< POINTFLOAT> round( 1 + num_pts + 1 );
        POINTFLOAT nc;
        nc.x = cur.x + (a_perp.x * w);
        nc.y = cur.y + (a_perp.y * w);

        round.front() = nc;

        nc.x = cur.x + (b_perp.x * w);
        nc.y = cur.y + (b_perp.y * w);

        round.back() = nc;

        for( size_t j = 1; j < num_pts+1; ++j )
        {
            float t = (float)j/(float)(num_pts+1);
            if( det > 0 )
         {
             POINTFLOAT nin;
             nin = slerp2d( b_perp, a_perp, 1.0f-t );
             nin.x *= w;
             nin.y *= w;

             nin.x += cur.x;
             nin.y += cur.y;

             round[j] = nin;
         }
            else
         {
             POINTFLOAT nin;
             nin = slerp2d( a_perp, b_perp, t );
             nin.x *= w;
             nin.y *= w;

             nin.x += cur.x;
             nin.y += cur.y;

             round[j] = nin;
         }
        }

        for( size_t j = 0; j < round.size()-1; ++j )
        {

            OutlineVec.push_back(cur.x);
            OutlineVec.push_back(cur.y);


            if( det > 0 )
         {
             OutlineVec.push_back(round[j + 1].x);
             OutlineVec.push_back(round[j + 1].y);
             OutlineVec.push_back(round[j].x);
             OutlineVec.push_back(round[j].y);
         }
            else
         {

             OutlineVec.push_back(round[j].x);
             OutlineVec.push_back(round[j].y);

             OutlineVec.push_back(round[j + 1].x);
             OutlineVec.push_back(round[j + 1].y);
         }
        }
    }

}

Answer 1

我对缓存一无所知，但是它可能有助于手动扩展向量，而不是让它在添加向量时一次扩展一个值。

根据此参考 ，可以调用reserve来增加向量的最大大小。 我建议您以长度为100的向量开始，并在第100个插槽填满后再请求100个插槽。

这个答案可能没有解决这个问题，因为我不知道缓存与std::vector的关系如何，但是您可能会遇到我描述的问题。

Answer 2

这可能不是问题的根源。 但是您可能想尝试使用迭代器，而不是在所有地方建立索引。 它可以帮助编译器做出更好的优化决策。 std::for_each看起来像是一个可能的候选者，您可以遵从另一个函数，例如：

void OGLSHAPE::real_update_shap(SHAPECONTOUR &contour) {
    if(contour.UserPoints.size() < 2) {
        return;
    }
    // do your thing!
}

void OGLSHAPE::UpdateShape() {
    // no need to explicitly test if empty, for_each won't do anything if the vector
    // has no elements
    std::for_each(Contour.begin(), Contour.end(), std::bind1st(std::mem_fun(real_update_shape), this));
}

或者至少使用一些引用来帮助编译器。 例如，将其转换为：

 //Remove Duplicates
 for(int j = 0; j < 2; ++j)
 {
     if(Contour[i].DrawingPoints.size() > 2)
         for(unsigned int x = 0; x < Contour[i].DrawingPoints.size() - 1; ++x)
         {
             if(Contour[i].DrawingPoints[x].point[0] ==
                 Contour[i].DrawingPoints[x + 1].point[0] &&
                 Contour[i].DrawingPoints[x].point[1] ==
                 Contour[i].DrawingPoints[x + 1].point[1] 

             )
                 Contour[i].DrawingPoints.erase(Contour[i].DrawingPoints.begin() + x);
         }
 }

对于这样的事情：

 //Remove Duplicates
 for(int j = 0; j < 2; ++j)
 {
     // reference to the one we care about, this may be allowed to be const
     // but I am not sure since it depends on your specific use cases, if it can be
     // it is better to shoot for const correctness as much as possible.
     // PS: types in all caps is very ugly, people will think it's a macro!
     SHAPECONTOUR &current_contour = Contour[i];
     if(current_contour.DrawingPoints.size() > 2)
         for(unsigned int x = 0; x < current_contour.DrawingPoints.size() - 1; ++x)
         {
             if( current_contour.DrawingPoints[x    ].point[0] ==
                 current_contour.DrawingPoints[x + 1].point[0] &&
                 current_contour.DrawingPoints[x    ].point[1] ==
                 current_contour.DrawingPoints[x + 1].point[1])

             current_contour.DrawingPoints.erase(current_contour.DrawingPoints.begin() + x);
         }
 }

这是可以提供帮助的事情之一，绝对不会造成伤害。 因此，值得一试。