在spriteKit中让粒子发射极轨迹跟踪手指路径

Question

我在Xcode中创建了一个粒子发射器，它有相当长的跟踪时间。当我把它移到粒子发生器里面时，它会在我的鼠标路径下留下一条小径。

一些关于我的目标的背景信息：，在我的spriteKit游戏中，用户在屏幕上拉着手指拍摄移动的物体。我试图创建一个“子弹时间”效果，其中对象减速和高亮时，当当前手指位置接触他们。当手指停止移动或耗尽弹药时，touchesEnded方法就会被触发，射击所有突出显示的对象。目前，我有一个路径，他们旅行显示为一条线绘制到屏幕上使用SKShapeNode & CGPath，但我想要用发射轨迹高亮显示这条线索。

在开始触摸的方法中，我创建了一个圆圈SpriteNode，它在手指移动到的任何地方移动(物理碰撞是附在圆圈上的，而不是路径)。我把粒子轨迹发射器附加到这个圆圈上，当我在屏幕上移动它时，它和一起移动，但是没有留下轨迹。

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

    UITouch *touch = [touches anyObject];
    CGPoint touchLocation = [touch locationInNode:self];

    pathToDraw = CGPathCreateMutable();
    startPoint = touchLocation;
    CGPathMoveToPoint(pathToDraw, NULL, touchLocation.x, touchLocation.y);

    lineNode = [SKShapeNode node];
    lineNode.path = pathToDraw;
    lineNode.lineWidth = 2;
    lineNode.zPosition = 110;
    lineNode.strokeColor = [SKColor whiteColor];
    [self addChild:lineNode];

    circle = [SKSpriteNode spriteNodeWithTexture:[animationsAtlas textureNamed:@"anim_countdown_9"]];
    circle.name = @"circle";
    circle.scale = 0.3;
    circle.alpha = 0.5;
    circle.zPosition = 110;
    circle.position = touchLocation;

    circle.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:20];
    circle.physicsBody.categoryBitMask = weaponCategory;
    circle.physicsBody.dynamic = NO;
    circle.physicsBody.contactTestBitMask = billyCategory;
    circle.physicsBody.collisionBitMask = 0;

    [self addChild:circle];

    pathEmitter = [SKEmitterNode skt_emitterNamed:@"FollowPath"];
    //pathEmitter.position = circle.position;
    //pathEmitter.targetNode = self;
    //pathEmitter.scale = 0.2;
    //pathEmitter.zPosition = 60;
    [circle addChild:pathEmitter];
}

在touchesMoved方法中，我将圆圈相应地移动到新位置

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

UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInNode:self];

circle.position = currentPoint;

SKAction *wtf = [SKAction followPath:pathToDraw asOffset:NO orientToPath:YES duration:0.1];
//pathEmitter.position = currentPoint;
//[pathEmitter runAction:wtf];
//pathEmitter.particleAction = wtf;
pathEmitter.particleAction = [SKAction moveTo:currentPoint duration:1.0];

CGPathAddLineToPoint(pathToDraw, NULL, currentPoint.x, currentPoint.y);

lineNode.path = pathToDraw;

我尝试过设置pathEmitter.targetNode =self；像这个帖子那样的，Making a particle follow a path in spriteKit建议，但是发射器根本就没有出现。

如果我将particleAction设置为followPath，它也不会留下任何痕迹。

在我的代码中，您可以看到我已经注释掉了一些行，基本上我已经尝试了我能想到的targetNode和particleAction的每一个组合。

关于如何让发射器在我的手指路径上留下痕迹，有什么建议吗？

谢谢

Answer 1

我认为这个代码就是你所需要的；

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

    UITouch *touch = [touches anyObject];
    CGPoint touchLocation = [touch locationInNode:self];


    circle = [SKSpriteNode spriteNodeWithTexture:[animationsAtlas textureNamed:@"anim_countdown_9"]];
    circle.name = @"circle";
    circle.scale = 0.3;
    circle.alpha = 0.5;
    circle.zPosition = 110;
    circle.position = touchLocation;

    circle.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:20];
    circle.physicsBody.categoryBitMask = weaponCategory;
    circle.physicsBody.dynamic = NO;
    circle.physicsBody.contactTestBitMask = billyCategory;
    circle.physicsBody.collisionBitMask = 0;

    [self addChild:circle];

    pathEmitter = [NSKeyedUnarchiver unarchiveObjectWithFile: [[NSBundle mainBundle] pathForResource:@"FollowPath"ofType:@"sks"]];
    pathEmitter.position = CGPointMake(0, -60);
    [circle addChild:pathEmitter];

}


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

    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInNode:self];

    circle.position = currentPoint;

}

- (void)update:(CFTimeInterval)delta
{
    if (!pathEmitter.targetNode) {
        pathEmitter.targetNode = self;
    }
}

Answer 2

实际上，pathEmitter.targetNode = self；是会让你有一个粒子在物体移动时留下轨迹的方法，我没有看到为什么它对你不起作用，因为我很久以前就使用过这个方法了，检查一下你的位置，特别是touchesMoved方法