Gradually increase speed of SpriteKit objects - ios

Question

I have a simple game with stones "raining" from top to bottom of the screen.
I am working with SpriteKit and I would like the stones to increase their speed by time like it would be level 1 level 2 level 3 and so on. Maximum speed should be easy to implement then.
I have a variable "speed" for the speed of the stones.
I think I could just use a timer and after 5s speed = 2, after 10s speed = 5, and so on, but I'm not sure how I can implement that.
EDIT:
I'm moving my stones with this:
-(void) moveStones{
SKAction *actionMove = [SKAction moveByX:0 y:-5 duration:0.25];
for(SKSpriteNode *stone in self.stones)
{
[stone runAction:actionMove];
}
}
And in my viewDidLoad I have the timer:
moveStones = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:#selector(moveStones) userInfo:nil repeats:YES];
If the timer does not respect the view, is there a way to move them without that timer?

Answer 1

If you are moving stones by physics, then after the stone is spawned you should apply an stronger impulse/force (based on current level) If you are moving them with actions, then change the speed of action, or lower the moveDuration. If you are moving stones by changing its position in update: method, then change the value which indicates how much points a sprite should move in every update call.
To implement time based actions like spawning stones or to decide when to change the speed of spawned nodes, you should use SKAction, or update: method and its passed parameter called currentTime. Using NSTimer for any of this in SpriteKit can lead to problems, because NSTimer don't respect view's , scene's or node's paused state, so its better to avoid using it.
Here is an example on how you can do what you want with SKAction. In this example you can see how to:
track the number of seconds passed
maintain the info about current level
spawn node with random delay
stop spawning nodes by using action key
and probably some more
GameScene.h
#import "GameScene.h"
#interface GameScene()
#property (nonatomic, assign) NSInteger counter;
#property (nonatomic, assign) NSInteger level;
#property (nonatomic, strong) SKLabelNode *debug;
#end
#implementation GameScene
// Here we set initial values of counter and level. Debug label is created here as well.
-(void)didMoveToView:(SKView *)view {
self.counter = 0;
self.level = 1;
self.backgroundColor = [SKColor grayColor];
self.debug = [SKLabelNode labelNodeWithFontNamed:#"ArialMT"];
self.debug.fontColor = [SKColor purpleColor];
self.debug.fontSize = 30.0f;
self.debug.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame));
self.debug.text = [NSString stringWithFormat:#"Counter : [ %ld ], Level [ %ld ]", (long)self.counter,(long)self.level];
[self addChild:self.debug];
}
//Method to start a timer. SKAction is used here to track a time passed and to maintain current level
-(void)startTimer{
__weak typeof (self) weakSelf = self; //make a weak reference to scene to avoid retain cycle
SKAction *block = [SKAction runBlock:^{
weakSelf.counter++;
//Maintaining level
if(weakSelf.counter < 5){
//level 1
weakSelf.level = 1;
}else if(weakSelf.counter >=5 && weakSelf.counter <10){
//level 2
weakSelf.level = 2;
}else{
//level 3
weakSelf.level = 3;
}
weakSelf.debug.text =
[NSString stringWithFormat:#"Counter : [ %ld ], Level [ %ld ]", (long)weakSelf.counter,(long)weakSelf.level];
}];
[self runAction:[SKAction repeatActionForever:[SKAction sequence:#[[SKAction waitForDuration:1], block]]] withKey:#"counting"];
}
//Method for stopping timer and reseting everything to default state.
-(void)stopTimer{
if([self actionForKey:#"counting"]){
[self removeActionForKey:#"counting"];
}
self.counter = 0.0f;
self.level = 1;
self.debug.text =
[NSString stringWithFormat:#"Counter : [ %ld ], Level [ %ld ]", (long)self.counter,(long)self.level];
}
//Get current speed based on time passed (based on counter variable)
-(CGFloat)getCurrentSpeed{
if(self.counter < 5){
//level 1
return 1.0f;
}else if(self.counter >=5 && self.counter <10){
//level 2
return 2.0f;
}else{
//level 3
return 3.0f;
}
}
//Method which stop generating stones, called in touchesBegan
-(void)stopGeneratingStones{
if([self actionForKey:#"spawning"]){
[self removeActionForKey:#"spawning"];
}
}
//You can use this useful method to generate random float between two numbers
- (CGFloat)randomFloatBetween:(CGFloat)smallNumber and:(CGFloat)bigNumber {
CGFloat diff = bigNumber - smallNumber;
return (((CGFloat) (arc4random() % ((unsigned)RAND_MAX + 1)) / RAND_MAX) * diff) + smallNumber;
}
//Method for generating stones, you run this method when you want to start spawning nodes (eg. didMoveToView or when some button is clicked)
-(void)generateStones{
SKAction *delay = [SKAction waitForDuration:2 withRange:0.5]; //randomizing delay time
__weak typeof (self) weakSelf = self; //make a weak reference to scene to avoid retain cycle
SKAction *block = [SKAction runBlock:^{
SKSpriteNode *stone = [weakSelf spawnStoneWithSpeed:[weakSelf getCurrentSpeed]];
stone.zPosition = 20;
[weakSelf addChild:stone];
}];
[self runAction:[SKAction repeatActionForever:[SKAction sequence:#[delay, block]]] withKey:#"spawning"];
}
//Returns stone with moving action added. Inside, you set standard things, like size, texture, physicsbody, name and position of a stone
-(SKSpriteNode*)spawnStoneWithSpeed:(CGFloat)stoneSpeed{
CGSize stoneSize = CGSizeMake(30,30); //you can randomize size here
CGPoint stonePosition = CGPointMake( [self randomFloatBetween:0.0f and:self.frame.size.width], CGRectGetMaxY(self.frame)); //you can randomize position here
SKSpriteNode *stone = [SKSpriteNode spriteNodeWithColor:[SKColor greenColor] size:stoneSize];
stone.name = #"stone"; //this helps if you want to enumerate all stones by name later on in your game
stone.position = stonePosition;
SKAction *move = [SKAction moveByX:0 y:-200 duration:3.25];
//one way to change speed
move.speed = stoneSpeed;
SKAction *moveAndRemove = [SKAction sequence:#[move, [SKAction removeFromParent]]];
[stone runAction:moveAndRemove withKey:#"moving"]; //access this key if you want to stop movement
return stone;
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
/* Called when a touch begins */
//just a simple way to start and stop a game
if(![self actionForKey:#"counting"]){
[self startTimer];
[self generateStones];
}else{
[self stopTimer];
[self stopGeneratingStones];
}
}
#end
And here is the result:
Now its up to you how you will set the speed. You can play with that.
If you want to skip some parts, or you don't know where to look, the heart of everything is in method called generateStones That is how you can spawn stones with a time delay by using SKActions. The another important method is spawnStoneWithSpeed: where you can see how to manipulate with speed of an action.
Another way to affect on node's moving speed, as I said, is to change duration parameter of method moveByX: duration:
Hope this helps!