iPad：如何通过滑动并继续按照滑动速度来移动精灵

Question

我有一个精灵（球的图像）我可以使用触摸和移动移动它。我还确定了该精灵的位置（x轴，y轴）的变化率，这取决于滑动周期。

现在我需要继续根据其速度和方向进行那个精灵。这是我的代码 -

Touch Event

- (BOOL)ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {

  CGPoint location = [touch locationInView: [touch view]];
  CGPoint convertedLocation = [[CCDirector sharedDirector] convertToGL:location];

  self.touchStartTime = [event timestamp];
  self.touchStartPosition = location;

  if (YES == [self isItTouched:self.striker touchedAt:convertedLocation]) {
    self.striker.isInTouch = YES;
  }

  return YES;
}

- (void)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {

  CGPoint location = [touch locationInView: [touch view]];
  CGPoint convertedLocation = [[CCDirector sharedDirector] convertToGL:location];

  self.touchLastMovedTime = [event timestamp];
  self.touchMovedPosition = convertedLocation;


  if(self.striker.isInTouch == YES){
    self.striker.position = self.touchMovedPosition;
  }

}
- (void)ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event {

  CGPoint location = [touch locationInView: [touch view]];
  CGPoint convertedLocation = [[CCDirector sharedDirector] convertToGL:location];

  self.touchEndTime = [event timestamp];
  self.touchEndPosition = location;

  if( self.striker.isInTouch == YES 
    && ( self.touchEndTime - self.touchLastMovedTime ) <= MAX_TOUCH_HOLD_DURATION )
  {
    float c = sqrt( pow( self.touchStartPosition.x - self.touchEndPosition.x, 2 ) 
        + pow( self.touchStartPosition.y - self.touchEndPosition.y, 2 ) );

    self.striker.speedx =  ( c - ( self.touchStartPosition.y - self.touchEndPosition.y ) ) 
                         / ( ( self.touchEndTime - self.touchStartTime ) * 1000 );

    self.striker.speedy =  ( c - ( self.touchStartPosition.x - self.touchEndPosition.x ) ) 
             / ( ( self.touchEndTime -   self.touchStartTime ) * 1000 );

    self.striker.speedx *= 4;
    self.striker.speedy *= 4;

    self.striker.isInTouch = NO;
    [self schedule:@selector( nextFrame ) interval:0.001];

  }

}

Scheduled Method to move Sprite

- (void) nextFrame {

  [self setPieceNextPosition:self.striker];
  [self adjustPieceSpeed:self.striker];

  if( abs( self.striker.speedx ) <= 1 && abs( self.striker.speedy ) <= 1 ){
    [self unschedule:@selector( nextFrame )];
  }
}

SET next Position

- (void) setPieceNextPosition:(Piece *) piece{

  CGPoint nextPosition;
  float tempMod;
  tempMod = ( piece.position.x + piece.speedx ) / SCREEN_WIDTH;
  tempMod = (tempMod - (int)tempMod)*SCREEN_WIDTH;
  nextPosition.x = tempMod;

  tempMod = ( piece.position.y + piece.speedy ) / SCREEN_HEIGHT;
  tempMod = (tempMod - (int)tempMod)*SCREEN_HEIGHT;
  nextPosition.y = tempMod;

  piece.position = nextPosition;
}

Set new Speed

- (void) adjustPieceSpeed:(Piece *) piece{

  piece.speedx =(piece.speedx>0)? piece.speedx-0.05:piece.speedx+0.05;
  piece.speedy =(piece.speedy>0)? piece.speedy-0.05:piece.speedy+0.05;
}

. 虽然，目前我正在使用静态速度调整技术，但我希望根据初始速度（我欣赏任何想法），使其动态（我欣赏任何想法）

Answer 1

谢谢@all。 我的解决方案如下 -

//in adjustSpeed method
  piece.speedx -= piece.speedx * DEACCLERATION_FACTOR;
  piece.speedy -= piece.speedy * DEACCLERATION_FACTOR;

//and simply, free the sprite to move from ccTouchMoved method not ccTouchEnd
  if(self.striker.isInTouch == YES && distance_passed_from_touch_start>=a_threashold){
    //calculate speed and position here as it was in ccTouchEnd method
    self.striker.isInTouch = NO;
    [self schedule:@selector( nextFrame ) interval:0.001];

  }

.

Answer 2

看起来你很接近。您正在调度触摸端上的选择器，计算速度，并根据该速度移动精灵，直到它抑制出来，所以所有机械件都在那里。

如果是什么样子是物理学。例如，你正在做一些奇怪的事情，速度慢慢地慢一点，它根本不会看起来不太真实。

要做的是在提升手指时找到精灵的“速度向量”。虽然您可以尝试对此进行瞬间速度，但我发现它更好地对其进行了更好地样品，并将其平均到它们以获得最终速度。

然后，一旦你有那个向量（它看起来像x和y速度，就像你现在一样），你想通过这样做的事情来抑制速度（未提前未经测试的伪码）：

 float speed = sqrt( speedx * speedx + speedy * speedy );
 if (speed == 0) {
     // kill motion here, unschedule or do whatever you need to
 }
 // Dampen the speed.
 float newSpeed = speed * .9;
 if (newSpeed < SOME_THRESHOLD) newSpeed = 0;
 speedx = speedx * newSpeed / speed;
 speedy = speedy * newSpeed / speed;
 //  Move sprite according to the new speed

.

这将保持球与释放时的相同方向，逐渐放慢速度，直到它停止。有关更多信息，特别是如果您想做一些弹跳或任何东西，谷歌介绍了向量代数。