UIAccelerometer 加速計(轉)

UIAccelerometer加速計是用來檢測iphone手機在x.y.z軸三個軸上的加速度。要得到此類調用:

UIAccelerometer *accelerometer = [UIAccelerometer sharedAccelerometer];

同時，你須要設置它的delegate。

UIAccelerometer *accelerometer = [UIAccelerometer sharedAccelerometer];

accelerometer.delegate = self;

accelerometer.updateInterval = 1.0/60.0;

委託方法：- (void) accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration中的UIAcceleration是表示加速度類。包含了來自加速計UIAccelerometer的真是數據。它有3個屬性的值x、y、z。iphone的加速計支持最高以每秒100次的頻率進行輪詢。此時是60次。

1) 應用程序能夠經過加速計來檢測搖動，如：用戶能夠經過搖動iphone擦除繪圖。

也能夠用戶連續搖動幾回iphone，執行一些特殊的代碼：

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

{

static NSInteger shakeCount = 0;

static NSDate *shakeStart;

NSDate *now = [[NSDate alloc] init];

NSDate *checkDate = [[NSDate alloc] initWithTimeInterval:1.5f sinceDate:shakeStart];

if ([now compare:checkDate] == NSOrderedDescending || shakeStart == nil)

{

shakeCount = 0;

[shakeStart release];

shakeStart = [[NSDate alloc] init];

}

[now release];

[checkDate release];

if (fabsf(acceleration.x) > 2.0 || fabsf(acceleration.y) > 2.0 || fabsf(acceleration.z) > 2.0)

{

shakeCount++;

if (shakeCount > 4)

{

// -- DO Something

shakeCount = 0;

[shakeStart release];

shakeStart = [[NSDate alloc] init];

}

}

}

2） 加速計最多見的是用做遊戲控制器。在遊戲中使用加速計控制對象的移動！ 在簡單狀況下，可能只需獲取一個軸的值，乘上某個數（靈敏度），而後添加到所控制對象的座標系中。在複雜的遊戲中，由於所創建的物理模型更加真實，因此必須 根據加速計返回的值調整所控制對象的速度。

在cocos2d中接收加速計輸入input.使其平滑運動，通常不會去直接改變對象的position.經過：

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

{

// -- controls how quickly velocity decelerates(lower = quicker to change direction)

float deceleration = 0.4; 

// -- determins how sensitive the accelerometer reacts(higher = more sensitive)

float sensitivity = 6.0;

// -- how fast the velocity can be at most

float maxVelocity = 100;

// adjust velocity based on current accelerometer acceleration

playerVelocity.x = playerVelocity.x * deceleration + acceleration.x * sensitivity;

// -- we must limit the maximum velocity of the player sprite, in both directions

if (playerVelocity.x > maxVelocity)

{

playerVelocity.x = maxVelocity;

}

else if (playerVelocity.x < - maxVelocity)

{

playerVelocity.x = - maxVelocity;

}

}

上面deceleration是減速的比率，sensitivity是靈敏度。maxVelocity是最大速度，若是不限制則一直加大就很難停下來。

playerVelocity.x = playerVelocity.x * deceleration + acceleration.x * sensitivity;

中 playervelocity是一個速度向量。是累積的。

- (void) update: (ccTime)delta

{

// -- keep adding up the playerVelocity to the player's position

CGPoint pos = player.position;

pos.x += playerVelocity.x;

// -- The player should also be stopped from going outside the screen

CGSize screenSize = [[CCDirector sharedDirector] winSize];

float imageWidthHalved = [player texture].contentSize.width * 0.5f;

float leftBorderLimit = imageWidthHalved;

float rightBorderLimit = screenSize.width - imageWidthHalved;

// -- preventing the player sprite from moving outside the screen

if (pos.x < leftBorderLimit)

{

pos.x = leftBorderLimit;

playerVelocity = CGPointZero;

}

else if (pos.x > rightBorderLimit)

{

pos.x = rightBorderLimit;

playerVelocity = CGPointZero;

}

// assigning the modified position back

player.position = pos;

}