Cocos2d iPhone: Rotate Sprite using Accelerometer

Question

Hi,

I'm trying to rotate a sprite using the accelerometer. when I tilt right, I want him to rotate slightly to the right, and when I tilt left, I want him to rotate slightly to the left...

Thanks in advance, Reed

Answer 1

Shouldn't be too difficult. Just have somewhere in your code that handles the UIAccelerometerDelegate class and apply changes to your sprites based on the values you receive through parameters to the – accelerometer:didAccelerate: callback.

Apple docs for the delegate class are available at...

https://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIAccelerometerDelegate_Protocol/UIAccelerometerDelegate/UIAccelerometerDelegate.html

Answer 2

Hey,

Firs off - in your h file you need to make the following variables:

UIAccelerationValue accelerationX;
UIAccelerationValue accelerationY;
float currentRawReading;
float calibrationOffset;

Also ensure that your h file has:

@interface myViewName : UIViewController <UIAccelerometerDelegate>

Then in your .m file just below your imports at the top put:

#define kFilteringFactor 0.05
CGFloat DegreesToRadians(CGFloat degrees) {return degrees * M_PI / 180;};
CGFloat RadiansToDegrees(CGFloat radians) {return radians * 180/M_PI;};

Then in your .m file on your viewDidLoad Function put:

UIAccelerometer *accel = [UIAccelerometer sharedAccelerometer];
accel.delegate = self;
accel.updateInterval = 1.0f/60.0f;  

also add the following function to your .m file:

-(void) accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration{

accelerationX = acceleration.x * kFilteringFactor + accelerationX * (1.0 - kFilteringFactor);
accelerationY = acceleration.y * kFilteringFactor + accelerationY * (1.0 - kFilteringFactor);

// keep the raw reading, to use during calibrations
currentRawReading = atan2(accelerationY, accelerationX);

float rotation = -RadiansToDegrees(currentRawReading);

targetView.transform = CGAffineTransformMakeRotation(-(DegreesToRadians(rotation)));
//targetView.transform = CGAffineTransformRotate(targetView.transform, -(rotation * 3)); //if you want easing
}

you will have to tweak it slightly based on what view or object you are targeting -- but thats pretty much it.

Hope this helps,

Michael