Cocos2D旋转炮塔到指定角度(三)

到目前为止都很美好!

但是却有一点奇怪,因为炮塔一下子跳转到指定位置去射击,并不是平滑的跟随触摸去转动到指定位置.你可以修复这个问题,但是这需要略微一点的重构(refactoring).

首先打开HelloWorldLayer.h,在你的类中添加下面一个实例变量:

CCSprite *_nextProjectile;

然后回到HelloWorldLayer.m中按如下代码修改ccTouchesEnded方法:

- (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    if (_nextProjectile != nil) return;

    // Choose one of the touches to work with
    UITouch *touch = [touches anyObject];
    CGPoint location = [self convertTouchToNodeSpace:touch];

    // Set up initial location of projectile
    CGSize winSize = [[CCDirector sharedDirector] winSize];
    _nextProjectile = [[CCSprite spriteWithFile:@"projectile2.png"] retain];
    _nextProjectile.position = ccp(20,winSize.height/2);

    // Determine offset of location to projectile
    CGPoint offset = ccpSub(location,_nextProjectile.position);

    // Bail out if you are shooting down or backwards
    if (offset.x <= 0) return;

    // Determine where you wish to shoot the projectile to
    int realX = winSize.width + (_nextProjectile.contentSize.width/2);
    float ratio = (float) offset.y / (float) offset.x;
    int realY = (realX * ratio) + _nextProjectile.position.y;
    CGPoint realDest = ccp(realX,realY);

    // Determine the length of how far you're shooting
    int offRealX = realX - _nextProjectile.position.x;
    int offRealY = realY - _nextProjectile.position.y;
    float length = sqrtf((offRealX*offRealX)+(offRealY*offRealY));
    float velocity = 480/1; // 480pixels/1sec
    float realMoveDuration = length/velocity;

    // Determine angle to face
    float angleRadians = atanf((float)offRealY / (float)offRealX);
    float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);
    float cocosAngle = -1 * angleDegrees;
    float rotateDegreesPerSecond = 180 / 0.5; // Would take 0.5 seconds to rotate 180 degrees,or half a circle
    float degreesDiff = _player.rotation - cocosAngle;
    float rotateDuration = fabs(degreesDiff / rotateDegreesPerSecond);
    [_player runAction:
     [CCSequence actions:
      [CCRotateTo actionWithDuration:rotateDuration angle:cocosAngle],[CCCallBlock actionWithBlock:^{
         // OK to add now - rotation is finished!
         [self addChild:_nextProjectile];
         [_projectiles addObject:_nextProjectile];

         // Release
         [_nextProjectile release];
         _nextProjectile = nil;
     }],nil]];

    // Move projectile to actual endpoint
    [_nextProjectile runAction:
     [CCSequence actions:
      [CCMoveTo actionWithDuration:realMoveDuration position:realDest],[CCCallBlockN actionWithBlock:^(CCNode *node) {
         [_projectiles removeObject:node];
         [node removeFromParentAndCleanup:YES];
    }],nil]];

    _nextProjectile.tag = 2;

    [[SimpleAudioEngine sharedEngine] playEffect:@"pew-pew-lei.caf"];
}

看起来代码不少,但是实际你并没有修改太多,大多数都仅仅是很小的重构,以下是代码做出的改变:

• 在方法开始处如果_nextProjectile不为nil则直接退出,意思是你正在处理射击操作
• 之前你使用的是一个名为projectile的局部变量,然后立即把它添加到场景中.在新的版本中你创建了一个实例变量_nextProjectile,但是没有立即添加到场景中.
• 你定义了炮塔旋转的速度为180 / 0.5,意味着半秒钟旋转180度.
• 去计算旋转特定的角度需要多长时间
• 然后开始一个顺序action去旋转炮塔到正确的角度,然后调用一个block去将导弹添加到场景中.

偶鸟,试一试吧!编译运行项目,然后现在炮塔应该旋转的平滑多了 ;)

原文地址:Rotating Turrets: How To Make A Simple iPhone Game with Cocos2D 2.X Part 2