Soft body chipmunk physics « cocos2d for iPhone

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Soft body chipmunk physics

(49 posts) (21 voices)

Started 11 months ago by Birkemose
Latest reply from barnaclau

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Birkemose
Moderator

As some of you might know, I released an IAP version of NightFlight.
Was a bit of a disappointment, since it only sold ONE IAP, and that was the one I bought myself for testing it. Will be a fun story for my grand children :)

I think my problem is, that my coding is good, but my game sucked. Not a single feature from Apple. Not even in farawayistan.
Anyways, there are other games to be made tomorrow.

As some of you also might know, I think Objective chipmunk is the one to use, so I made this demo featuring soft body dynamics and generic backstepping the physics.

Get the Flash Video

EDIT:
The framerate is locked to 30. It is not in any ways slow ;)

Posted 11 months ago #
hm50
Member

Wow!! Looks great Lars!!

(REALLY?!?! Only one IAP sale? WTH! I think the game is fun and well done!)

Posted 11 months ago #
riq
Key Master

soft body in chipmunk? great! You should send your patches to @slembcke

Posted 11 months ago #
Studder
Member

WOW! That looks amazing! Well done!

Posted 11 months ago #
Birkemose
Moderator

Here is an update with the final "blob" class. The texture can be rotated freely from the blobby shape, to keep the face in an upright position at all times, but to show the movement of the blobs, I locked the rotation.

Get the Flash Video

The soft body dynamics is made with a string of flat rectangular object tied together with joints, much like the driving belt of a tank.
I then hold the belt in position, using springs attached to a center point of gravity.
The problem with this approach, is, that unless you makes the springs stiffer than an Englishman's upper lip, they can not hold the shape in position under heavy load. To fix that, I simply added an extra shape ( in my case simply a round shape ) at the centre of gravity, to avoid the entire shape to collapse. By adjusting the size of the centre shape, I can control how much the blob can be compressed, while maintaining the "wobbly gelly" surface.

Another good thing is, that the blob actually only consists of 9 rectangular pieces in the belt. When the sprite is mapped upon the coordinates, it hides the jaggies of only 9 elements, but it still looks nice and squishy.
So an entire blob consists of 9 perimeter rectangular bodies, 1 centre round body, 9 springs and 9 joints. Easily runs 30+ on a 3G with 15 blobs.

Next step will be to splatter them on the wall ;)

EDIT:
Yeah, they are baby cocos ...

Posted 10 months ago #
skyhawk
Member

BWAHAHA! I love it!

Posted 10 months ago #
cocos2dbeginner
Member

Great! Awesome! What about Box2D? Did anyone port it to Box2D?

Posted 10 months ago #
symbly75
Member

@Birkemose That's pretty neat. I try to achieve the same thing as you're doing with Box2D. However, when I want to map my texture to my blob I don't even know where to begin. Could you please explain how you did it? It will be nice if you can also provide codes.

Thanks

Posted 10 months ago #

Birkemose
Moderator

The blob is made from m_centreBody, and m_perimeterBodies[ BLOG_SEGMENTS ]
The texture is rendered using a triangle fan.

The entire draw looks like this

-( void )draw {
	CGPoint segmentPos[ BLOB_SEGMENTS + 2 ];
	CGPoint texturePos[ BLOB_SEGMENTS + 2 ];
	CGPoint textureCenter;
	float angle, baseAngle;

	// calculate triangle fan segments

	segmentPos[ 0 ] = CGPointZero;
	for ( int count = 0; count < BLOB_SEGMENTS; count ++ ) {
		// get relative position and multiply for scale
		segmentPos[ count + 1 ] = ccpMult( ccpSub( m_perimeterBodies[ count ].pos, m_centerBody.pos ), BLOB_SKIN_SCALE );
	}
	segmentPos[ BLOB_SEGMENTS + 1 ] = segmentPos[ 1 ];

	// move to absolute position
	for ( int count = 0; count < ( BLOB_SEGMENTS + 2 ); count ++ )
		segmentPos[ count ] = ccpAdd( m_centerBody.pos, segmentPos[ count ] );

	// remap skin
	// done to be able to control skin rotation independently from blob rotation

	baseAngle = [ UTIL angle:m_centerBody.pos b:m_perimeterBodies[ 0 ].pos ];

	texturePos[ 0 ] = CGPointZero;
	for ( int count = 0; count < BLOB_SEGMENTS; count ++ ) {
		// calculate new angle
		angle						= baseAngle + ( 2 * M_PI / BLOB_SEGMENTS * count );
		// calculate texture position
		texturePos[ count + 1 ].x	= sinf( angle );
		texturePos[ count + 1 ].y	= cosf( angle );
	}
	texturePos[ BLOB_SEGMENTS + 1 ] = texturePos[ 1 ];

	// recalculate to texture coordinates
	textureCenter = CGPointMake( 0.5f, 0.5f );
	for ( int count = 0; count < ( BLOB_SEGMENTS + 2 ); count ++ )
		texturePos[ count ] = ccpAdd( ccpMult( texturePos[ count ], 0.5f ), textureCenter );

	glColor4ub( m_color.r, m_color.g, m_color.b, 255 );

	glEnable( GL_TEXTURE_2D );
	glBindTexture( GL_TEXTURE_2D, [ m_skin name ] ); 

	// glDisableClientState( GL_TEXTURE_COORD_ARRAY );
	glDisableClientState( GL_COLOR_ARRAY );

	glTexCoordPointer( 2, GL_FLOAT, 0, texturePos );

	glVertexPointer( 2, GL_FLOAT, 0, segmentPos );

	glDrawArrays( GL_TRIANGLE_FAN, 0, BLOB_SEGMENTS + 2 );

}

EDIT:
baseAngle is the blobs rotation, in the video it is set to 0

Posted 10 months ago #

SunnyPianist
Member

Wow that is pretty awesome. Thanks for explaining how you achieved the effect. Though like symbly75 asked, would you mind sharing how you mapped the sprite to the body coordinates? I'm assuming you actually had to apply some skewing transformation in OpenGL?

EDIT: Nevermind, you posted 1 min before my post :) Thanks a ton!

Posted 10 months ago #
pfg2009
Member

Sweet! I love it - squishy cocos :)
Nicely done!

BTW: I like the time step reversal. Do you simply pass negative time values to cpSpace and it does all by itself? Cool!

Posted 10 months ago #
symbly75
Member

@Birkemose That's awesome. Thank you for showing me the code I truly appreciate it. I started to implement this into my game. Yet, there is one little tiny problem that I don't quite understand with this line of code:
glBindTexture( GL_TEXTURE_2D, [ m_skin name ] );
especially with this: [ m_skin name ]

Could you please kindly explain it to me what this is? and how can I obtain it?

Sorry for my noobness

Posted 10 months ago #
ehoffman
Member

@Birkemose I've found this post just now. Soft body dynamics, nice. :)

But what I really want to say: Yes you are a great programmer. And Nightflight is technically a really good game. The accelerometer - I've never seen something better on the iPhone. Really!

But. And now I ... ok ... now. There are a lot of discussions about "the market is full", "to much crap", ... I think, yes there are a lot of games. A lot of programmers. So what really counts is the customer. What do they want:

- Angry Birds
- Cut the Rope
- Spiel der Weisen (german quiz)
- Tiny Wings

Who is the main iPhone user?

- The iPhone was (is) very expensive. Available only with a contract from T-Mobile (Germany) or AT & T (US), right? Yes I know there are no contracts anymore, but it is changing slowly... At least it was and it is expensive.

So the main customer is a business (wo)men or someone who needs mail at every time of the day. So someone busy. What do they want? Yes, Entertainment. Nice graphics, something stupid. Something to make them laugh.

And thats it. I can explain that in detail, but now I need to sleep. Just saw this post and needed to answer ;)

regards, Eike

Posted 10 months ago #
Birkemose
Moderator
@pfg2009
I made descendants of ChipmunkBody and ChipmunkSpace.
Each myChipmunkBody is capable of storing a record of packed information ( basically pos and rotation, and some of my own stuff ). I use fixed time interval of 33mS for all physics, and as a minimum package is 6 bytes, each body takes only 180 bytes/second to store.
In myChipmunkSpace, I have added a stepBackwards method, that simply places bodies according to the stored information.
By interpolating the stored data, you can rewind at any speed, even slow motion.
As I try to minimize dynamic allocation in pr. frame loops, the buffers I implemented is FIFO buffers, capable of storing 10 seconds.

@symbly75
m_skin is a CCtexture2D. Only other lines including m_skin is during initialization / dealloc of the blob
```
// load skin
m_skin = [ [ [ CCTextureCache sharedTextureCache ] addImage:BLOB_FILENAME ] retain ];
// clean up
[ m_skin dealloc ];
```
( Ohh ... the power of cocos2D )
Posted 10 months ago #
Birkemose
Moderator

@ehoffman
Thx for the kind words. When the only copy you sold of your game, is to yourself, encouragement is sometimes required ;)

I was aware from the start, that NightFlight wasn't going to win me any prices. You of cause always hope that someone at the american Apple store used to be a huge X-Wings fan, and gave it a major feature, but the chances of winning in Lotto would have been greater.
So apart from a few bruises to my professional pride, I regard it as a learning process, and a step on the way towards making a great game some day.

What really surprised me in the process, is like you say, the ultra short attention span of the "gamer". I don't mean that in any bad way, but the target audience is completely different to that on more traditional gaming platforms. People want a quick fix and a laugh, and I wouldn't be surprised if the average time a game is played, is under a minute.

Anyways. Apart from that I need a really really good artist, it is for sure something I will honor in my next attempt.

Posted 10 months ago #
EvilRabbit
Member

@Birkemose

Softbody stuff looks excellent. Well done.

Posted 10 months ago #
ehoffman
Member

@Birkemose

the ultra short attention span of the "gamer"

This is the point. They are not gamer. If you buy a dedicated gaming thing (PSP, Nintendo, ...) you buy it for playing. The reasons to buy an iPhone:

1. It is indeed a phone. You can call someone ;)
1.5 SMS
2. E-Mail, Web
3. Appointsments, Contacts
4. Music? (iPod)

So I think gaming is not the primary reason to buy such a device. It is a "nice to have" feature. They play on the way to work, in boring meetings, at the German Bundestag (really I know that ;), ...

As the customer is like this, they like:

- puzzle games
- puzzle games
- puzzle games
- and some good made "Geschicklichkeitsspiel" (game of skill???)

Artwork is very important. Most time I spend creating artwork -> I'm not an designer. So if you can hire, do it.

How much sales did you have in Germany? One - then it was me :)

I have some nice ideas for games which could be successful. But as in September we have elections ... If you are interested in some ideas PM me.

regards, Eike

Posted 10 months ago #
x0661t
Member

could you post your project source code here? i'm trying to do the same thing on box2d, got no any results :(

Posted 10 months ago #
pfg2009
Member

@Birkemose: cool, thanks for going into so much detail!

Posted 10 months ago #
ehoffman
Member

@Birkemose http://www.appannie.com/nightflight/features/

You have a mini-feature ...

Featured in iTunes in 3 places
Games > Action > What's Hot
Games > Action > What's Hot > See All
Games > Arcade > What's Hot > See All

Posted 10 months ago #
Birkemose
Moderator

@x0661t
Sorry, I cant post the entire project, and the blob class is obj chipmunk, so it would be of little use in box2d.
If you have specific questions, feel free to ask.

@ehoffman
The original game sold a few ( thank you for the german contribution ;), and has ( very ironically ), been in the danish "whats hot" sub game section since release. The "lite" IAP version, never got any features, and so far only sold the one IAP I bought for testing.
That IS a fun story ... in ten years ;)

But it is food for thought, and I look at it this way.
If you know the game mastermind, the best opening is 4 different colors, with no hits. That is pretty much what I accomplished with NightFlight.

Posted 10 months ago #
x0661t
Member

@Birkemose

i create some round bodies in box2d in circle and connect them with a joint. How did you make your texture to skew when it's collide with something? :)

Thanks!

Posted 10 months ago #
ehoffman
Member

@x0661t Have a look at the draw method in this thread. As I understood this is how they are drawn.

Posted 10 months ago #
x0661t
Member

i did, but i can't understand it, could you show me part of the code that is responsible for skew of the texture plz?

Thanks!

Posted 10 months ago #
Birkemose
Moderator

@x0661t
There is NO skew part, OpenGL does it all for you.

Think of it this way.

You have a square texture with a white circle.
You then create a square OpenGL object, and maps the corners of the object to the corners of the texture.

When you render the OpenGL object, you would see a white circle.

Now. If you reduce the height of the OpenGL object to 50%, making a rectangle, but DO NOT change the texture mapping, you will NOT see the upper or lower half of a white circle, but you will see a flat white ellipse.
Same thing if you only moved one corner of the OpenGL object around, the entire texture would still be rendered.
OpenGL does all the skewing and stretching and compressing for you.

Maybe it is misleading that I texture map on every draw. In the demo video you can remove that part. I only do it to keep my sprite facing upwards at all times.

Posted 10 months ago #

ehoffman
Member

As Birkemose described, there is a center body and around it small rectangles, like a chain. Now he calculated a triangle fan and remaps the vertices on the border of the fan to the coordinates of the small rectangles (center.pos + rectangle.pos). Then it's again mapped to u/v texture coordinates (0-1).

This code:

// calculate triangle fan segments

	segmentPos[ 0 ] = CGPointZero;
	for ( int count = 0; count < BLOB_SEGMENTS; count ++ ) {
		// get relative position and multiply for scale
		segmentPos[ count + 1 ] = ccpMult( ccpSub( m_perimeterBodies[ count ].pos, m_centerBody.pos ), BLOB_SKIN_SCALE );
	}
	segmentPos[ BLOB_SEGMENTS + 1 ] = segmentPos[ 1 ];

	// move to absolute position
	for ( int count = 0; count < ( BLOB_SEGMENTS + 2 ); count ++ )
		segmentPos[ count ] = ccpAdd( m_centerBody.pos, segmentPos[ count ] );

And this:

// recalculate to texture coordinates
	textureCenter = CGPointMake( 0.5f, 0.5f );
	for ( int count = 0; count < ( BLOB_SEGMENTS + 2 ); count ++ )
		texturePos[ count ] = ccpAdd( ccpMult( texturePos[ count ], 0.5f ), textureCenter );

The code in between is important only, if you want to rotate the skin independent of the base body. It just rotates the texture coordinates.

The code at the end is just GL drawing...

Posted 10 months ago #

symbly75
Member

@Birkemose I managed to get it working right after I posted my recent question. Thank you very much. You're my life savior.

Posted 10 months ago #
slembcke
Administrator

Hey, I forgot about this thread. That looks surprisingly good when texture mapped for only 9 control points.

That reminds me that I should add something like this to my list of tutorials. I've separately explained to like a half dozen people how to make a Gish-like game in Chipmunk. heh.

Posted 10 months ago #
x0661t
Member

Has anyone implemented it in Box2D? What joints do you use? I'm using b2RevoluteJoint and it looks like a bit fail.

Posted 10 months ago #
hm50
Member

Again, GREAT JOB @Birkemose !

Posted 10 months ago #

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