How do you move an IOS SKSprite at a consistent speed

问题

Playing around with SKSprites in the IOS SpriteKit, and I basically want to have a sprite randomly move a certain direction for a certain distance, then pick a new random direction and distance.. Simple enough, create a method that generates the random numbers then creates the animation and in the completion block of the animation have it callback the same routine.

THis does work, but it also keeps the animation from moving at the same velocity since the animations are all based on duration.. If the object has to move 100 it moves at 1/2 the speed it moves if the next random tells it to move 200... So how the heck do I have it move with a consistent speed?

回答1:

@Noah Witherspoon is correct above - use Pythagorus to get a smooth speed:

//the node you want to move
SKNode *node = [self childNodeWithName:@"spaceShipNode"];

//get the distance between the destination position and the node's position
double distance = sqrt(pow((destination.x - node.position.x), 2.0) + pow((destination.y - node.position.y), 2.0));

//calculate your new duration based on the distance
float moveDuration = 0.001*distance;

//move the node
SKAction *move = [SKAction moveTo:CGPointMake(destination.x,destination.y) duration: moveDuration];
[node runAction: move];

回答2:

Using Swift 2.x I've solved with this little method:

func getDuration(pointA:CGPoint,pointB:CGPoint,speed:CGFloat)->NSTimeInterval {
    let xDist = (pointB.x - pointA.x)
    let yDist = (pointB.y - pointA.y)
    let distance = sqrt((xDist * xDist) + (yDist * yDist));
    let duration : NSTimeInterval = NSTimeInterval(distance/speed)
    return duration
}

With this method i can use an ivar myShipSpeed and directly call my actions for example :

let move = SKAction.moveTo(dest, duration: getDuration(self.myShip.position,pointB: dest,speed: myShipSpeed))
self.myShip.runAction(move,completion: {
  // move action is ended
})

回答3:

As an extension to @AndyOS's answer, if you're going to move only along one axis (X for example) you can simplify the math by doing this instead:

CGFloat distance = fabs(destination.x - node.position.x);

来源：https://stackoverflow.com/questions/19105631/how-do-you-move-an-ios-sksprite-at-a-consistent-speed

标签

ios

sprite-kit

skspritenode

skaction