CCMotionStreak working with CCMoveTo

I'm trying to use the CCMotionStreak to draw a path with a CCSprite.

Init:

CCMotionStreak* streak;
streak = [CCMotionStreak streakWithFade:100 minSeg:1 image:@"streak.png" width:5
    length:3 color:ccc4(0, 255, 255, 255)];streak.position = self.theHero.heroSprite.position;

When a touch ends:

-(void) ccTouchEnded:(UITouch*)touch withEvent:(UIEvent *)event
{
    [self unschedule:@selector(doStep:)];

    CGPoint touchLocation = [touch locationInView: [touch view]];
    CGPoint curPosition = [[CCDirector sharedDirector] convertToGL:touchLocation];

    [self.theHero.heroSprite stopAllActions];
        //cal the duration, speed is set to 85.0f
    float du = ccpDistance(self.theHero.heroSprite.position, curPosition) / 85.0f;
    [self.theHero.heroSprite runAction:[CCMoveTo actionWithDuration:du
                                                           position:curPosition]];

    [self schedule:@selector(doStep:)];
}

- (void)doStep:(ccTime)delta
{
        //update the position
    [streak setPosition:self.t开发者_Python百科heHero.heroSprite.position];
}

When I run the demo, the CCMotionStreak draws a line beautifully the first time I touched the screen, then when the sprite stops, I tried to touch somewhere else on the screen and the CCMotionStreak draws a second line successfully but I noticed that the CCMotionStreak lines "shakes" a little bit(offset a little bit) during the sprite moving and then "shakes back to normal position" when the sprite stops moving.

I hope someone can give me a hint, thanks :)

I suspect it's a timing bug. If the sequence is like the following, your CCMotionStreak will always be a little bit off:

1. [streak setPosition:self.theHero.heroSprite.position] -- Streak is at Hero's position
2. [CCMoveTo actionWithDuration:du ... -- Hero moves
3. Render, but hero and streak are at different positions

when you stop moving, they equalize.

I would suggest updating the motion streak within the Hero class, or use the scheduler to set priority so the [streak setPosition call happens after the CCMoveTo action updates to move the Hero.

Likely, the first move has the priorities correct and it works.