Cocos2D-使精灵平滑跟随并旋转以触摸

Question

I'm trying to make a sprite to smoothly follow & rotate according to touch on the screen. The player is not forced to touch on the sprite itself to make it move, as he can only control one sprite at a time. So wherever the touch is on the screen, the player must follow the movement. Here's what I have so far :

In GameScene.m :

- (BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event
{
    CGPoint location = [touch locationInView:[touch view]];
    location = [[CCDirector sharedDirector] convertToGL:location];

    lastTouchLocation = location;

    return YES;
}

- (void) ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event
{
    CGPoint location = [touch locationInView:[touch view]];
    location = [[CCDirector sharedDirector] convertToGL:location];

    //moveBy determine the translate vector
    CGPoint moveBy = ccpSub(lastTouchLocation, location);
    [player moveBy:moveBy];

    lastTouchLocation = location;
}

And here's Player.m :

- (float) calculateAngleForNextPoint:(CGPoint) point
{
    CGPoint nextPoint = point;
    CGPoint pos = self.position;

    float offX = nextPoint.x - pos.x;
    float offY = nextPoint.y - pos.y;

    float angle = atan2f(offY, offX);
    angle = CC_RADIANS_TO_DEGREES(angle);
    angle = -angle + 90;

    return angle;
}

- (void) moveBy:(CGPoint)_pos
{
    CGPoint newPos = ccpSub(self.position, _pos);
    float angle = [self calculateAngleForNextPoint:newPos];

    self.position = newPos;
    self.rotation = angle;   

}

This code works well, but the rotation is not smooth at all, mainly when the player moves his finger slowly on the screen, the sprite goes crazy! I tried many things, like setting up actions, but the touchMoved method is called too rapidly to use Actions.

What should I do to solve this? Thanks a lot!

Answer 1

One option is to use a Physics Engine (chipmunk, box2d, ...) and have a damped spring between your finger position and your sprite.

If you can't afford a physics engine in your game, and you want a smooth real-life like movement, you should keep the sprite position, velocity and acceleration (idem for angle, angular velocity, angular acceleration). Your finger movement will then update the accelerations (like a spring would do), and you then start a scheduler to update the velocity and position 60 times/second.

That's how I'd do it