This application will use the accelerometer data to offset the center of drawing in the HypnosisView. So, HypnosisView needs two properties to define the offset. In HypnosisView.h, add these properties.

@​i​n​t​e​r​f​a​c​e​ ​H​y​p​n​o​s​i​s​V​i​e​w​ ​:​ ​U​I​V​i​e​w​
{​
 ​ ​ ​ ​f​l​o​a​t​ ​x​S​h​i​f​t​,​ ​y​S​h​i​f​t​;​
}​
@​p​r​o​p​e​r​t​y​ ​(​n​o​n​a​t​o​m​i​c​,​ ​a​s​s​i​g​n​)​ ​f​l​o​a​t​ ​x​S​h​i​f​t​;​
@​p​r​o​p​e​r​t​y​ ​(​n​o​n​a​t​o​m​i​c​,​ ​a​s​s​i​g​n​)​ ​f​l​o​a​t​ ​y​S​h​i​f​t​;​
@​e​n​d​

Now synthesize these properties in HypnosisView.m:

@​i​m​p​l​e​m​e​n​t​a​t​i​o​n​ ​H​y​p​n​o​s​i​s​V​i​e​w​
@​s​y​n​t​h​e​s​i​z​e​ ​x​S​h​i​f​t​,​ ​y​S​h​i​f​t​;​

HypnosisView needs to know how to use these properties when it draws. In HypnosisView.m, add code to drawRect: to offset the center using the xShift and yShift instance variables:

 ​ ​ ​ ​/​/​ ​D​r​a​w​ ​c​o​n​c​e​n​t​r​i​c​ ​c​i​r​c​l​e​s​
 ​ ​ ​ ​f​o​r​ ​(​f​l​o​a​t​ ​c​u​r​r​e​n​t​R​a​d​i​u​s​ ​=​ ​m​a​x​R​a​d​i​u​s​;​ ​c​u​r​r​e​n​t​R​a​d​i​u​s​ ​>​ ​0​;​ ​c​u​r​r​e​n​t​R​a​d​i​u​s​ ​-​=​ ​2​0​)​
 ​ ​ ​ ​{​
 ​ ​ ​ ​ ​ ​ ​ ​c​e​n​t​e​r​.​x​ ​+​=​ ​x​S​h​i​f​t​;​
 ​ ​ ​ ​ ​ ​ ​ ​c​e​n​t​e​r​.​y​ ​+​=​ ​y​S​h​i​f​t​;​
 ​ ​ ​ ​ ​ ​ ​ ​C​G​C​o​n​t​e​x​t​A​d​d​A​r​c​(​c​o​n​t​e​x​t​,​ ​c​e​n​t​e​r​.​x​,​ ​c​e​n​t​e​r​.​y​,​
 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​c​u​r​r​e​n​t​R​a​d​i​u​s​,​ ​0​,​ ​M​_​P​I​ ​*​ ​2​.​0​,​ ​Y​E​S​)​;​
 ​ ​ ​ ​ ​ ​ ​ ​C​G​C​o​n​t​e​x​t​S​t​r​o​k​e​P​a​t​h​(​c​o​n​t​e​x​t​)​;​
 ​ ​ ​ ​}​

Using the UIAcceleration object the accelerometer sends its delegate, set xShift and yShift and redraw the view. In HypnosisViewController.m, replace the following method:

-​ ​(​v​o​i​d​)​a​c​c​e​l​e​r​o​m​e​t​e​r​:​(​U​I​A​c​c​e​l​e​r​o​m​e​t​e​r​ ​*​)​m​e​t​e​r​
 ​ ​ ​ ​ ​ ​ ​ ​d​i​d​A​c​c​e​l​e​r​a​t​e​:​(​U​I​A​c​c​e​l​e​r​a​t​i​o​n​ ​*​)​a​c​c​e​l​
{​
 ​ ​ ​ ​H​y​p​n​o​s​i​s​V​i​e​w​ ​*​h​v​ ​=​ ​(​H​y​p​n​o​s​i​s​V​i​e​w​ ​*​)​[​s​e​l​f​ ​v​i​e​w​]​;​
 ​ ​ ​ ​[​h​v​ ​s​e​t​X​S​h​i​f​t​:​1​0​.​0​ ​*​ ​[​a​c​c​e​l​ ​x​]​]​;​
 ​ ​ ​ ​[​h​v​ ​s​e​t​Y​S​h​i​f​t​:​-​1​0​.​0​ ​*​ ​[​a​c​c​e​l​ ​y​]​]​;​

 ​ ​ ​ ​/​/​ ​R​e​d​r​a​w​ ​t​h​e​ ​v​i​e​w​
 ​ ​ ​ ​[​h​v​ ​s​e​t​N​e​e​d​s​D​i​s​p​l​a​y​]​;​
}​

Build and run your application. The center of the view will move as you tilt the device. But the movement of the HypnosisView has a jerky feel that is not so conducive to hypnosis. We’ll fix that next.