iOS Animation 2D game - ios

Question

I'm making an application, for the iPhone, which is a 2D game.
I have done all the spritesheets, but now i need to animate some of them particulary :
My game is a game where your hero should avoid some obstacles. The borders should move to give the impression that the game is more difficult by increasing the speed (so the hero looks like going faster and faster). I have my image of the border, but really don't know how to animate it dynamically, and when the end of the image is coming, put the top of the image to come after it.
Note : I know how to make a translation, to animate an image but here i need to animate it faster and faster, so to change dynamically the speed of the animation.
Thanks for your help !
Code or a UIImageView :
nuages_bas2 = [[UIImageView alloc] initWithFrame:CGRectMake(-100, 0, 160, 1000)];
UIImage * ImageNuages = [UIImage imageNamed:#"Menu_nuage.png"];
nuages_bas2.image = ImageNuages;
nuages_bas2.alpha = 0.0f;
[menu_principale addSubview:nuages_bas2];
[nuages_bas2 release];
Code for one of the animations :
- (void)AnimationNuagesBas2
{
nuages_bas2.alpha = 1.0f;
CABasicAnimation * nuagesbas2 = [CABasicAnimation animationWithKeyPath:#"transform.translation.y"];
nuagesbas2.fromValue = [NSNumber numberWithFloat:480.0f];
nuagesbas2.toValue = [NSNumber numberWithFloat:-960.0f];
nuagesbas2.duration = 35.0f;
nuagesbas2.repeatCount = 10;
[nuages_bas2.layer addAnimation:nuagesbas2 forKey:#"nuagesbas2"];
}

Answer 1

First things first, if you're making a game, you probably should not be using UIKit unless it's something very simple. You should have a look at libraries like cocos2d
As for this question, you may want to look at CAKeyframeAnimation. I'll attempt to sketch out some code that will do something like this, but you'll probably want to modify it(Also, I don't have the means to test it).
Note, what follows below is a hack that consists of creating a keyframe animation where the object goes back and forth each time with a smaller duration.
- (void)AnimationNuagesBas2
{
nuages_bas2.alpha = 1.0f;
CAKeyframeAnimation * nuagesbas2 = [CAKeyframeAnimation animationWithKeyPath:#"transform.translation.y"];
float from = [NSNumber numberWithFloat:480];
float to = [NSNumber numberWithFloat:-960];
int repeatCount = 10;
float duration = 6;
float durationDecrease = 0.5;
float t = 0;
NSMutableArray * values = [NSMutableArray array];
NSMutableArray * times = [NSMutableArray array];
[values addObject:from];
[times addObject:[NSNumber numberWithFloat:0]];
for (int i = 0; i < repeatCount; i++){
t += duration/2;
[values addObject:to];
[times addObject:[NSNumber numberWithFloat:t]];
t += duration/2;
[values addObject:from];
[times addObject:[NSNumber numberWithFloat:t]];
duration -= durationDecrease;
}
[nuages_bas2.layer addAnimation:nuagesbas2 forKey:#"nuagesbas2"];
}
Another approach would be to set yourself as the delegate to the CABasicAnimation and set it with a repeatCount of 0. Then, every time it's done, you re-initiate it with a smaller duration.