iosobjective-cperformancecalayercabasicanimation

Changing the speed of CALayer in CABasicAnimation while rotating a wheel causes jerk effect

I develop an app which requires a wheel to be rotated around z axis with increasing or decreasing the speed of the wheel steadily over time. I use CABasicAnimation & my code is as follows. While i change the speed property of the layer at particular interval, it causes "Jerk" effect to the wheel.

/****/

CABasicAnimation* animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
animation.toValue = [NSNumber numberWithFloat:-2*M_PI];
animation.duration = 4.0f;
animation.repeatCount = INFINITY;
[animation setValue:@"left" forKey:@"side"];
[animation setDelegate:self];
animation.removedOnCompletion=NO;
animation.fillMode = kCAFillModeForwards;
animation.cumulative = YES;

imageLeft.layer.beginTime = CACurrentMediaTime();
/************/

In a timer I vary the speed of the CALayer of the imageview as follows where dPlayedPercentage is a variable.

imageLeft.layer.speed=1.0+dPlayedPercentage;

[imageLeft.layer addAnimation:animation forKey:@"SpinAnimation"];

I think it is due to the position resets while changing the speed property of CALayer. What should i do to rectify this. Or any other way to do this animation?

Solution

  • Adding the following code has rectified the jerk in the animation. 

    imageLeft.layer.timeOffset = [imageLeft.layer convertTime:CACurrentMediaTime() fromLayer:nil]; 
imageLeft.layer.beginTime = CACurrentMediaTime(); 
imageLeft.layer.speed=1.0+dPlayedPercentage;