如何在Cocos2D游戏中实现A*寻路算法(五)

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跟随着黄色砖块前进

现在我们已经找到了我们的路径,我们只需要让猫咪跟随它.

我们接下来要做的是记住整个路径,并且使得猫咪根据路径一步一步的移动.

在CatSprite.h中建立一个存储路径的数组,在CatSprite的@interface的私有段内添加:

NSMutableArray *shortestPath;

然后完成CatSprite.m中的如下修改:

// Add inside the CatSprite private properties and methods section
@property (nonatomic, retain) NSMutableArray *shortestPath;

// After the CatSprite @implementation
@synthesize shortestPath;

// Inside initWithLayer
self.shortestPath = nil;

// Inside dealloc   
[shortestPath release]; shortestPath = nil;

现在我们将创建一个存储整个路径并且管理开始动画的方法,在CatSprite.m中完成如下修改:

// Add inside the CatSprite private properties and methods section
- (void)constructPathAndStartAnimationFromStep:(ShortestPathStep *)step;

// Inside moveToward, comment out the pathFound BOOL
//BOOL pathFound = NO;

// Inside moveToward, replace pathFound = YES with this:
[self constructPathAndStartAnimationFromStep:currentStep];

// Also comment all of the debugging statements below that.

// Inside moveToward, replace if (!pathFound) with this:
if (self.shortestPath == nil) { // No path found

// Add this new method:

// Go backward from a step (the final one) to reconstruct the shortest computed path
- (void)constructPathAndStartAnimationFromStep:(ShortestPathStep *)step
{
    self.shortestPath = [NSMutableArray array];

    do {
        if (step.parent != nil) { // Don‘t add the last step which is the start position (remember we go backward, so the last one is the origin position ;-)
            [self.shortestPath insertObject:step atIndex:0]; // Always insert at index 0 to reverse the path
        }
        step = step.parent; // Go backward
    } while (step != nil); // Until there is no more parents

    for (ShortestPathStep *s in self.shortestPath) {
        NSLog(@"%@", s);
    }
}

注意在moveToward方法中,我们调用了一个新的方法替换了原来的在控制台中打印结果的代码,并且我们删除了pathFound变量.像往常一样,constructPathAndStartAnimationFromStep方法中的注释详细解释了实际发生了什么.

现在编译运行,如果你触摸和我们之前说过的相同的瓦块,你应该看到如下日志:

<ShortestPathStep: 0x6b37160>  pos=[24;1]  g=1  h=4  f=5
<ShortestPathStep: 0x6b37340>  pos=[23;1]  g=2  h=3  f=5
<ShortestPathStep: 0x6b37590>  pos=[22;1]  g=3  h=2  f=5
<ShortestPathStep: 0x6b395c0>  pos=[21;1]  g=4  h=3  f=7
<ShortestPathStep: 0x6b37ae0>  pos=[20;1]  g=5  h=4  f=9
<ShortestPathStep: 0x6b38c60>  pos=[20;2]  g=6  h=3  f=9
<ShortestPathStep: 0x6b36510>  pos=[20;3]  g=7  h=2  f=9
<ShortestPathStep: 0x6b3b850>  pos=[21;3]  g=8  h=1  f=9
<ShortestPathStep: 0x6b3cf30>  pos=[22;3]  g=9  h=0  f=9

注意它和以前是相似的,除了现在它是从开始到结束(反转以前的结果)并且存放在数组中的数据更便于我们去使用.

最后要做的事情是通过遍历shortestPath数组并且动画显示猫咪跟随的路径.为了实现这个目的,我们将创建一个方法从数组中弹出每一步的数据,使得猫咪可以移动到该位置,并且添加一个回调方法去重复调用这个方法直到路径完成.

在CatSprite.m中完成以下修改:

// Add inside the CatSprite private properties and methods section
- (void)popStepAndAnimate;

// Add to bottom of constructPathAndStartAnimationFromStep
[self popStepAndAnimate];

// Add new method
- (void)popStepAndAnimate
{   
    // Check if there remains path steps to go through
    if ([self.shortestPath count] == 0) {
        self.shortestPath = nil;
        return;
    }

    // Get the next step to move to
    ShortestPathStep *s = [self.shortestPath objectAtIndex:0];

    // Prepare the action and the callback
    id moveAction = [CCMoveTo actionWithDuration:0.4 position:[_layer positionForTileCoord:s.position]];
    id moveCallback = [CCCallFunc actionWithTarget:self selector:@selector(popStepAndAnimate)]; // set the method itself as the callback

    // Remove the step
    [self.shortestPath removeObjectAtIndex:0];

    // Play actions
    [self runAction:[CCSequence actions:moveAction, moveCallback, nil]];
}

编译然后运行…

我们的猫咪自动移动到你点击的位置上了 :-)