vec flowField[][];
float flowSpacing=50;
float buffer=0;
float flowX;
float flowY;
float flowTransfer=.022;
float flowDecay=.852;
float flowMultuiplier=.8;
float flowCap=6;
boolean useFF=true;
void manageFlowField()
{//to be called by draw()
  if(useFF)
  {
    updateFlowField();
    if(displayUI)
      drawFlowField();
    if(mousePressed)
    {
      vec vf=findFlowVec(nv(mouseX,mouseY));
      vec pm=new vec(pmouseX,pmouseY);
      vec mp=new vec(mouseX,mouseY);
      vec mv=new vec(pm,mp);
//      flowField[int(vf.x)][int(vf.y)].add(mv);  
    }    
  }
}
void updateFlowField()
{
  for(int fy=0;fy<flowY;fy++)
  {
    for(int fx=0;fx<flowX;fx++)
    {
      vec v=new vec();
      if(fy>0)
      {
        v=new vec(flowField[fx][fy-1].x*flowTransfer,flowField[fx][fy-1].y*flowTransfer);
        flowField[fx][fy].add(v);
//        flowField[fx][fy-1].sub(v);
      }
      if(fx>0)
      {
        v=new vec(flowField[fx-1][fy].x*flowTransfer,flowField[fx-1][fy].y*flowTransfer);
        flowField[fx][fy].add(v);
//        flowField[fx-1][fy].sub(v);
      }
      if(fy<flowY-1)
      {
        v=new vec(flowField[fx][fy+1].x*flowTransfer,flowField[fx][fy+1].y*flowTransfer);
        flowField[fx][fy].add(v);
//        flowField[fx][fy+1].sub(v);
      }
      if(fx<flowX-1)
      {
        v=new vec(flowField[fx+1][fy].x*flowTransfer,flowField[fx+1][fy].y*flowTransfer);
        flowField[fx][fy].add(v);
//        flowField[fx+1][fy].sub(v);
      }

      if(fy>1)
      {
        v=new vec(flowField[fx][fy-2].x*flowTransfer,flowField[fx][fy-2].y*flowTransfer*.7);
        flowField[fx][fy].add(v);
      }
      if(fx>1)
      {
        v=new vec(flowField[fx-2][fy].x*flowTransfer,flowField[fx-2][fy].y*flowTransfer*.7);
        flowField[fx][fy].add(v);
      }
      if(fy<flowY-2)
      {
        v=new vec(flowField[fx][fy+2].x*flowTransfer,flowField[fx][fy+2].y*flowTransfer*.7);
        flowField[fx][fy].add(v);
      }
      if(fx<flowX-2)
      {
        v=new vec(flowField[fx+2][fy].x*flowTransfer,flowField[fx+2][fy].y*flowTransfer*.7);
        flowField[fx][fy].add(v);
      }
      flowField[fx][fy].mul(flowDecay);
      flowField[fx][fy].x=constrain(flowField[fx][fy].x,-flowCap,flowCap);
      flowField[fx][fy].y=constrain(flowField[fx][fy].y,-flowCap,flowCap);
    }
  }
//  println(flowField[0][0].x);
}
void createFlowField()
{
  if(flowSpacing<=0)
    flowSpacing=1;
  flowX=1+(width+buffer*2)/flowSpacing;
  flowY=1+(height+buffer*2)/flowSpacing;
  flowField=new vec[int(flowX)][int(flowY)];
//  int xLength=flowField.length;
//  int yLength=flowField[0].length;
  for(int fy=0;fy<flowY;fy++)
  {
    for(int fx=0;fx<flowX;fx++)
    {
      flowField[fx][fy]=new vec();
    }
  }
}
vec findFlowVec(vec v)
{
  vec p=new vec();
  p.x=round((v.x/width)*flowX);
  p.y=round((v.y/height)*flowY);
  p.x=constrain(p.x,0,flowX-1);
  p.y=constrain(p.y,0,flowY-1);
  return p;
}
void drawFlowField()
{
  if(!drawFF||!useFF)
    return;
  for(int fy=0;fy<flowY;fy++)
  {
    for(int fx=0;fx<flowX;fx++)
    {
      vec v=flowField[fx][fy];
      vec p=new vec(fx,fy);
      p.mul(flowSpacing);
      noFill();
      stroke(255);
//      point(p.x,p.y);
      line(p.x,p.y,p.x+v.x,p.y+v.y);
    }
  }
}