Scrolling platform game - Box2D and camera

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Scrolling platform game - Box2D and camera

(10 posts) (3 voices)

Started 1 year ago by steg90
Latest reply from steg90

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steg90
Member

Hi all,

I've got a scrolling platform game which I use the CCTMXTiledMap class to do the rendering. I use to update the screen (scroll it) by doing the following:

[node setPosition: newPos2];

Where newPos2 was calculated dependent on which way the player was moving (left or right). Ok this works well, but when wanting to implement Box2D collision, it won't work as the Box2D won't move with the scrolling map. So, am I better to use the Camera object to do the scrolling instead?

[self.camera setCenterX:_currentXPos centerY:0 centerZ:0];
[self.camera setEyeX:_currentXPos eyeY:0 eyeZ:20];

That way, my Box2D body's should work fine.

Any help and advice is much appreciated.

Regards,
Steve

Posted 1 year ago #
Questor
Member

Steve,

Sounds like you're on the right path. You could either use/move the camera or move the game layer (as opposed to the Tilemap).

Regards,
Q

Posted 1 year ago #
steg90
Member

Hi Questor,

The problem I'm getting when moving the camera or indeed the layer instead of the map is the player moves relative with the layer, how would I make the player stay in the center of the screen?

I did go back to moving the tilemap and moved the Box2D bodies relative to the tile they where fixed too (b2Body->SetTransform), but I'm sure moving the Box2D bodies isn't a good idea?

Any advice is much appreciated.

Regars,
Steve

Posted 1 year ago #
Questor
Member

Steve,

Yeah, using b2Body->SetTransform for all the bodies is gonna end up being problematic in the long run. Not sure why your box2d world is not staying in sync with your tilemap... make sure that if you are using a parallaxNode, that your main tilemap has it's parallaxRatio param set to ccp(1.0f,1.0f) in the addChild method of the parallax layer like this:
[parallaxNode addChild:<TILEMAP VARIABLE> z:1 parallaxRatio:ccp(1.0f,1.0f) positionOffset:CGPointZero];

Also, there are several posts discussing the general game scroll issue... You may want to take a look at these threads:

http://www.cocos2d-iphone.org/forum/topic/1029
http://www.cocos2d-iphone.org/forum/topic/309#post-1746

They should get you pointed in the right direction.

Regards,
Q

Posted 1 year ago #
steg90
Member

Thanks Questor,

It is getting messy with the SetTransform, giving me lots of issues and seems to be a lot of work. The bodies will stay in synch with the tiles if I do use moving layer approach. But if I do use that approach, how do I keep my main character/player in the center of the screen?

What do I need to do in the case kPlayerTag to do this?

for(b2Body *b = world->GetBodyList(); b; b=b->GetNext())
{
if(b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite*)b->GetUserData();
switch(sprite.tag)
{
case kPlayerTag: // player sprite
{
sprite.position = ccp(_currentXPos + b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
}
}
// etc
}

Another issue I'm having is, how do you allow a player to jump up through platforms and then land on them instead of colliding with a platform that is above them I'd like them to pass through the platform and then land on it when coming down - I'm really stuck with this.

Regards,
Steve

Posted 1 year ago #
steg90
Member

Hi,
I've now modified the code to scroll the layer, a lot simpler than having to keep updating the Box2D bodies, although, I still have to update the player sprite body:

for(b2Body *b = world->GetBodyList(); b; b=b->GetNext())
{
if(b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite*)b->GetUserData();
switch(sprite.tag)
{
case kPlayerTag: // player sprite - may put rotation back in at later date
{
CGPoint screenPos = [self position];
CGPoint temp;
temp = ccp(240 - screenPos.x,b->GetPosition().y * PTM_RATIO);
b2Vec2 b2Position = b2Vec2(temp.x/PTM_RATIO,temp.y/PTM_RATIO);
b->SetTransform(b2Position,0);

sprite.position = ccp(240 - screenPos.x,b->GetPosition().y * PTM_RATIO);
}
}
break;
}

Is there any way of getting the box2d body to follow the player sprite without having to use SetTransform?

Many thanks,
Steve

Posted 1 year ago #
Night Elf
Member

Put the player on a different layer? That's if you're controlling the player outside of the physics simulation. After that, just move the body to the correct place to match the player's position.

If you want the player to move reallisticaly and properly interact with the physics world, you must apply velocities or forces to move it and have the camera follow the player.

Also, in any case, it'd be better to just save the player's body instead of traversing the whole list of bodies and doing a switch on each one to find it. Just remember the body's pointer when you create it.

Posted 1 year ago #
steg90
Member

Thanks,

I could put the player on another layer, but would still have the problem of the box2D body still needing to be updated. I've got the player and body in the correct position now. Using SetTransform on the body is working, although for some reason walking into a platform now doesn't cause a collision, but jumping and landing on top of it does?!?!

The player is moved using a velocity when jumping, when moving left or right, just the layer moves.

_playerBody->SetLinearVelocity(velocityVec);

I guess as I have got the players body in my class, I wouldn't need the for loop and switch as shown in previous code?

Regards,
Steve

Posted 1 year ago #
Questor
Member

Steve,

"although for some reason walking into a platform now doesn't cause a collision, but jumping and landing on top of it does?!?!"

Are you using the (box2d testbed) logic for one-sided platforms? If so then that would explain why you can walk into the platform from the side, since collisions with one-sided platforms *only* occur if the player is coming from above the platform.

Regards,
Q

Posted 1 year ago #
steg90
Member

Hey Q,

Cheers for that, not had much time to develop today, will look at this 'one-sided platform' you mention.

Cheers,
Steve

Posted 1 year ago #

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