Cocos2d-x 寻路算法之二 离目的地的距离优先

转自--->Waiting For You：http://www.waitingfy.com/archives/831

1.介绍：

figure 1

接上一篇《Cocos2d-x 寻路算法之一 距离优先》，看这个图，我们发现这个寻路算法有点傻，明明终点在右侧却每个方向都找。难道没有其他办法了吗？从现实生活中我们知道东西如果在东边，当然是往东边搜索才是最好的办法。

2.开始动手

figure 2

计算机中如何表示离目标近呢？ 用图来解释就是这样的，目标在右上角，我们往右走，从X轴的角度来说离目标又近了一步，同理往上走是在Y轴上里目标近一步。最好的一步应该是图中-2的点，X轴和Y轴同时离目标近了一步。简单地转换成代码就是下面的这样：

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bool comparebyWhichNearerGoalSimpleWay(Cell *c1,Cell *c2){ int distanceOfC1AndGoal = abs (g_goalX - c1->getX()) + (g_goalY - c1->getY()); distanceOfC2AndGoal = (g_goalX - c2->getX()) + (g_goalY - c2->getY()); if (distanceOfC1AndGoal <= distanceOfC2AndGoal){ return false ; } else { true ; } }

扔到heap的比较条件中我们轻易地就实现了按照离目标距离优先的寻路算法，startPathFinding整个方法都不要改，只需要传进去上面提到的比较方法就行了。

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typedef bool (*compareTwoCells)(Cell *c1,Cell *c2);

void HelloWorld::startPathFinding(compareTwoCells compareMethod, startX,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important; background:none!important"> startY,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important; background:none!important"> goalX,monospace!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; min-height:inherit!important; background:none!important"> goalY){

Cell *startCell = _m_Map.Get(startX,startY);

vector<Cell*> vecCells;

vecCells.push_back(startCell);

make_heap(vecCells.begin(),vecCells.end(),compareMethod);

startCell->setMarked( true );

Cell *NowProcessCell;

while (vecCells.size() != 0){

pop_heap(vecCells.begin(),compareMethod);

NowProcessCell = vecCells.back();

vecCells.pop_back();

(NowProcessCell->getX() == _goalX && NowProcessCell->getY() == _goalY){ //the goal is reach

return ;

}

for ( i = 0; i < 8; ++i){ //check eight direction

indexX = NowProcessCell->getX() + DIRECTION[i][0];

indexY = NowProcessCell->getY() + DIRECTION[i][1];

(indexX >= 0 && indexX < xLineCount && indexY >= 0 && indexY < yLineCount

&& _m_Map.Get(indexX,indexY)->getpassable() == ){ //check is a OK cell or not

Cell *cell = _m_Map.Get(indexX,indexY);

float beforedistance = disTANCE[i] * cell->getWeight() + _m_Map.Get(NowProcessCell->getX(),

NowProcessCell->getY())->getdistance(); //calculate the distance

(cell->getMarked() == false ){

cell->setMarked( );

cell->setLastX(NowProcessCell->getX());

cell->setLastY(NowProcessCell->getY());

cell->setdistance(beforedistance);

vecCells.push_back(cell); //only push the unmarked cell into the vector

push_heap(vecCells.begin(),compareMethod);

{ // if find a lower distance,update it

(beforedistance < cell->getdistance()){

cell->setdistance(beforedistance);

cell->setLastX(NowProcessCell->getX());

cell->setLastY(NowProcessCell->getY());

//distance change,so make heap again

}

}

}

}

}

}

startPathFinding(comparebyWhichNearerGoalSimpleWay,_playerX,_playerY,_goalX,_goalY); //demo