ipad：如何通过滑动移动精灵，并根据滑动速度继续前进

Question

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

现在我需要继续按照它的速度和方向继续这个精灵。这里是我的代码 -

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，目前我使用静态速度调整技术，但我希望让它动视初始速度（我明白任何想法）

Answer 1

谢谢@all。 我有我的解决方案，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

看起来你有它八九不离十。您正在调度触摸板上的选择器，计算速度，并根据该速度移动精灵，直到它消失，所以所有机械碎片都在那里。

看起来iffy是物理学。例如，你用速度来做一些奇怪的事情来减慢球的速度，这些球看起来并不现实。

你想要做的是找到手指抬起时精灵的“速度矢量”。虽然你可以尝试为此做一个瞬间速度，但我发现它可以更好地回溯到几个周期，并对它们进行平均以获得最终速度。

然后，一旦你已经得到了矢量（它看起来像一个x和y的速度，像你现在），你想要做这样的事情（提前未经考验的伪代码），以抑制速度：

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 

这样可以使球沿着与释放时相同的方向运动，逐渐减速直至停止。欲了解更多信息，特别是如果你想做一些反弹或任何事情，谷歌的矢量代数的介绍。