Precise Movement « cocos2d for iPhone

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Precise Movement

(9 posts) (2 voices)

Started 2 years ago by akaii
Latest reply from bradparks

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akaii
Member

I have a scheduled method that gets called every interval of X.X seconds. When I call that method, it also runs a MoveTo action on a particular node over the same interval of time that the scheduler is on. When the action ends, the next iteration of the method will get called and and the Node will move again.

My objective is smooth repetition of movement, but I notice that movement actually looks jerky, with Node noticably stopping right before the next MoveTo kicks in to get it moving again. This means that either Node is arriving early/the Action is finishing early instead of on time OR the next Action is starting late, for some reason.

Is there anyway I could increase the precision of the scheduler, and the starting/running time of the action?

Posted 2 years ago #
bradparks
Member

Maybe using an ease action would make the starts/stops softer?

http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:actions_ease?s=ease

Posted 2 years ago #
akaii
Member

I'm trying for movement with a constant velocity in a straight line. Using easing would actually make the problem worse, since the stops would be accentuated by the object slowing down/speeding up right before/after the stop.

Using a RepeatForever action does smoothen the movement, but then, it outpaces the scheduled task, and I need the two to be synchronized. The scheduled task plays sounds at certain points during the interval, and the timing is sensitive and needs to match the motion of the object.

I expected the two to match, since I'm handing them the same value, and I thought all the scheduled tasks and actions were synched to a global clock. Aren't they?

Posted 2 years ago #
bradparks
Member
I think 100% syncing of time across events can't be guaranteed, as it may take too long for one event to complete, and by the time it completes, the target time has already passed... That's why sometimes time based stuff skips frames, to catch up to where it should be, in "time"...

Could you maybe use a Repeat Forever action with a sequence of MoveTo,CallFunc actions, where the MoveTo does your move, and the CallFunc plays your sound? If you need it to change constantly, then you could make them both CallFunc's and have it so each method uses a member variable to know where to go to next / which sound to play next...
```
id moveCallFunc = [CallFunc actionWithTarget:self selector:@selector(doMove)];
id soundCallFunc = [CallFunc actionWithTarget:self selector:@selector(doSound)];
id ra = [RepeatForever actionWithAction:[Sequence actions: moveCallFunc, soundCallFunc, nil]];

[mySprite runAction:ra];

- (void) doMove
{
  id actionTo = [MoveTo actionWithDuration: 2 position:[self nextPos]];
  [self runAction:actionTo];
}

- (void) doSound
{
  // Code to play a sound or whatever.
}
```
CallFunc Action:
http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:actions_special?s=callfunc
Posted 2 years ago #
akaii
Member

I'm already using a similar scheme with schedules for the sound instead of the action. Is the timing of a scheduled function significantly different from the timing of a running action?

Posted 2 years ago #
akaii
Member

Also, I can't use a sequence, since I will be playing multiple sounds during the course of the object's movement. I need two timers running in parallel, and tightly synched, and not just one.

Posted 2 years ago #
bradparks
Member

Maybe you want frame based animation instead of time based animation? The following thread talks about it a bit:

http://www.cocos2d-iphone.org/forum/topic/2468#post-15431

and this thread talks about integrating the Zwoptex code into Cocos, which sounds like it's in the works for 0.9 (?), I think:

http://www.cocos2d-iphone.org/forum/topic/1713#post-10816

and maybe, though I haven't tried it, the "Speed" action will do this, as this post seems to suggest, but I haven't tried it ;-)

http://www.cocos2d-iphone.org/forum/topic/679#post-4077

Posted 2 years ago #
akaii
Member

No animation, unfortunately, just movement.

The Speed action, is similar to something I've already tried (and the results are more or less the same). Prior, I've tried to get it to move more smoothly by modifying the time taken by the action with a multiplier (which I think, is the same thing the Speed action does).

The problem is, this is an estimate, so if I change the speed of the movement and sound, the estimate no longer applies and I either undercompensate (which means that the sudden stop is still there) or I overcompensate (the object will teleport forward when I re-synchronize the movement to an absolute position). I get the same effect with the Speed action. What rate could I use for the Speed action that would correct the speed of the object regardless of what time and target I pass to MoveTo?

Posted 2 years ago #
bradparks
Member

hey there... by frame based animation, all I meant was "frame based".... I guess I shouldn't have put animation ;-)

take a look at this specific post:

http://www.cocos2d-iphone.org/forum/topic/1713#post-10827

it talks about why @Zwopple created a frame based system.... and the discussion that follows in the post means that this is going to be part of cocos in the future... but probably not for awhile (0.9, I think)

@slipster216 had some good points on how you could use a frame based approach to sync multiple parts... where of course your multiple parts aren't part of a composite animation, they're syncing a movement with a sound...

http://www.cocos2d-iphone.org/forum/topic/1713#post-10855

It may or may not work for you... hope it helps!

Posted 2 years ago #

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