ch21.txt

chapter: Accelerometers
==================
#define PI 3.14159

float find2dAngle(void){

    //LOCAL VARIABLES
    float alpha,
    double ax, ay;

    //POLL ACCELEROMETER FOR ACCELERATIONS, API SPECIFIC
    ax = getXacceleration();
    ay = getYacceleration();

    //FIND ANGLE
    alpha = atan2(ay,ax);

    if (alpha >= 0){
        alpha = alpha * (180/PI);
    else {
        alpha = alpha * (-180/PI) + 180;
    }

    return alpha;
}
    
    
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- (void)viewDidLoad
{
    UIAccelerometer *accelerometer = [UIAccelerometer sharedAccelerometer];
    accelerometer.delegate  = self;
    accelerometer.updateInterval = kPollingRate;
    [super viewDidLoad];
}
    
    
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- (void)accelerometer:(UIAccelerometer *)accelerometer 
didAccelerate:(UIAcceleration *)acceleration{
    [(SpriteView *)self.view setAcceleration:acceleration];
    [(SpriteView *)self.view draw];
}
    
    
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-(id)initWithCoder:(NSCoder *)coder {
    if((self = [super initWithCoder:coder])){
        self.sprite = [UIImage imageNamed:@"sprite.png"];
        self.currentPos = CGPointMake((self.bounds.size.width / 2.0f) +
(sprite.size.width / 2.0f), (self.bounds.size.height /2.0f)+(sprite.size.height /2.0f));
        xVelocity = 0.0f;
        yVelcoity = 0.0f;

        convertX = self.bounds.size.width / kWorldWidth;
        convertY = self.bounds.size.height / kWorldHeight;

    }
    return self;
}
    
    
====================================
- (void)setCurrentPos:(CGPoint)newPos {
    prevPos = currentPos;
    currentPos = newPos;

    if(currentPos.x <0){
        currentPos.x = 0;
        xVelocity = 0.0f;
    }
    if(currentPos.y <0){
        currentPos.y = 0;
        yVelcoity = 0.0f;
    }
    if(currentPos.x > self.bounds.size.width - sprite.size.width){
        currentPos.x = self.bounds.size.width - sprite.size.width;
        xVelocity = 0.0f;
    }
    if(currentPos.y > self.bounds.size.height - sprite.size.height){
        currentPos.y = self.bounds.size.height - sprite.size.height;
        yVelocity = 0.0f;
    }

    CGRect curSpriteRect = CGRectMake(currentPos.x, currentPos.y, 
currentPos.x+sprite.size.width, currentPos.y+sprite.size.height);
    CGRect prevSpriteRect = CGRectMake(prevPos.x, prevPos.y, 
prevPos.x+sprite.size.width, currentPos.y+sprite.size.height);
    [self setNeedsDisplayInRect:CGRectUnion(curSpriteRect, prevSpriteRect)];

}
    
    
====================================
- (void)draw {
    static NSDate *lastUpdateTime;

    if (lastUpdateTime != nil) {
        NSTimeInterval secondsSinceUpdate = -([lastUpdateTime
timeIntervalSinceNow]); //calculates interval in seconds from last update

        //Calculate displacement
        CGFloat deltaX = xVelocity * secondsSinceUpdate + 
((acceleration.x*g*secondsSinceUpdate*secondsSinceUpdate)/2); // METERS
        CGFloat deltaY = yVelocity * secondsSinceUpdate + 
((acceleration.y*g*secondsSinceUpdate*secondsSinceUpdate)/2); // METERS

        //Converts from meters to pixels based on defined World size
        deltaX = deltaX * convertX;
        deltaY = deltaY * convertY;

        //Calculate new velocity at new current position
        xVelocity = xVelocity + acceleration.x * g * secondsSinceUpdate; //assumes
acceleration was constant over last update interval
        yVelocity = yVelocity - (acceleration.y * g * secondsSinceUpdate); //assumes 
acceleration was constant over last update interval

        //Mutate currentPos which will update screen
        self.currentPos = CGPointMake(self.currentPos.x + deltaX, 
self.currentPos.y + deltaY);

    }

    [lastUpdateTime release];
    lastUpdateTime = [[NSDate alloc] init];

}
    
    
====================================
        CGFloat deltaX = xVelocity * secondsSinceUpdate +
((acceleration.x*g*secondsSinceUpdate*secondsSinceUpdate)/2); // METERS
    
    
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xVelocity = xVelocity + acceleration.x * g * secondsSinceUpdate;
    
    
==================