ipad：如何通过滑动来移动精灵并根据滑动速度继续前进

Question

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

现在我需要继续那个精灵根据它的速度和方向移动。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使其动态（我很欣赏任何想法）

Answer 1

看起来你已经很接近了。您在触摸端安排一个选择器，计算速度，并根据该速度移动精灵，直到它减弱，因此所有机械部件都在那里。

看起来可疑的是物理原理。例如，你正在做一些奇怪的事情，以减慢球的速度，这看起来根本不现实。

您想要做的是找到手指抬起时精灵的“速度矢量”。虽然您可以尝试为此执行瞬时速度，但我发现最好对几个周期进行采样并对其进行平均以获得最终速度。

然后，一旦你得到了这个向量（它看起来像 x 和 y 速度，就像你现在一样），你想通过做这样的事情来抑制速度（前面未经测试的伪代码）：

 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

这将使球继续前进与释放时的方向相同，逐渐减速直至停止。有关更多信息，特别是如果您想做一些弹跳或其他任何操作，请搜索向量代数简介。

Answer 2

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];

  }