Jumping a sprite while moving in a Bezier action

Question

I'm creating a game and I need the sprite to jump (move up and down basically) while it's moving on a bezier path so it moves vertically while it still follows the path. If I do this while it's moving along the bezier path:

[mySprite runAction:[CCJumpBy actionWithDuration:0.1 position:ccp(0,0) height:10 jumps:1]];

It jumps vertically but instantly it returns to the position on the path. What I want is to jump relative to the path.

Does anyone know anything about it?

It would looks something like this:

The curve is a sequence of CCBezierBy's by the way.

Thanks.

Answer 1

Your sprite follows the bezier curve over time. So the position of your sprite is defined as:

sprite.x = bezier(time).x;
sprite.y = bezier(time).y;

This function updates the position of your sprite every frame. This is why you only see your 'jump' for a very short time (something like 1/30th of a second). To add the curve of jumping you need to change the function to this:

sprite.x = bezier(time).x;
sprite.y = bezier(time).y + jump(force, time);

This way you add the position on the curve of the jump, as defined by the force of the jump and the time to the y position.

Alternatively if you don't want the jump height to stay relative to the bezier curve you can do this:

if(jumping)
    sprite.x = bezier(time).x;
    sprite.y = bezier(timeOfJumpStart).y + jump(force, time);
else
// old code

Now my answer is very general so I hope it makes sense, but without seeing your code this is the best I can do.

Answer 2

Aparently it is more simple than it looks. I had to sublclass CCJumpBy:

@implementation CCMyJumpBy

- (id)init
{
    self = [super init];
    if (self) {}
    return self;
}


-(void) update:(ccTime) t
{
    // parabolic jump (since v0.8.2)
    ccTime frac = fmodf( t * jumps_, 1.0f );
    ccTime y = height_ * 4 * frac * (1 - frac);
    y += delta_.y * t;
    ccTime x = delta_.x * t;
    [target_ setPosition: ccp( ((CCNode*)target_).position.x + x, ((CCNode*)target_).position.y + y )];//This is what has been changed
}
@end

Answer 3

The CCAction classes aren't very well suited to incorporate user-interaction. The primary use for them is animation, where you want your object to perform some fixed action/movement over time.

That being said, there are still ways to do what you want. The cleanest and most flexible approach would be to simply go ahead and implement the Bezier movement yourself, looking at the source of CCBezierBy might be a good starting point (you'll find the source in cocos2d/CCActionInterval.m), then factor in jump strength, much like Roy T. described in his answer.

If that's too much work or if you'd rather stick with CCBezierBy, then are also ways to do what you want. The simplest approach would be to have a CCNode which holds your sprite. Then you animate the CCNode using CCBezierBy and animate your sprite using CCJumpBy:

CCNode -> animated using CCBezierBy
   |
   +--- CCSprite -> is child of CCNode and is animated using CCJumpBy