Extend sparrow with physics engine in core

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Extend sparrow with physics engine in core

(20 posts) (6 voices)

Started 1 year ago by seivan
Latest reply from Daniel

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seivan
Member

I was thinking of it would be good to add something like
http://code.google.com/p/chipmunk-spacemanager/wiki/Introduction
to Sparrow

Integrating a simpler physics engine wrapper into Sparrow.

For instance to be able to call

SPPhysicsManager *physManager = [[SPPhysicsManager alloc] init];
[physManager addWindowContainmentWithFriction:1.0 elasticity:1.0 inset:cpvzero];
SPPhysicsShape *ball = [physManager addCircleAt:cpv(240,160) mass:5.0 radius:15];
SPSprite *ballSprite = [SPSprite spriteWithShape:ball andImageWithContentsOfFile:@"ball.png"];

Would this be accepted into Sparrow?
If not, would this make it as an "addon" and would people here help to contribute. This is my second day in the world of physics engine.

Posted 1 year ago #
seivan
Member

Ouch, maybe move this into General Discussion and not troubleshoot >_> sorry about that.

Posted 1 year ago #
Oscar
Member

Would be lovely!

Posted 1 year ago #
seivan
Member

Yeah =) I could use some help though. But I am not sure wether or not to go with Chipmunk or Box2d. I have to read up on both before deciding.

Maybe a core-developer could give some insights on which physics engine would be best. And what class to extend. Maybe even go as far as picking the abstract display classes ?

Posted 1 year ago #
Daniel
Primary Feather

I must admit that I haven't yet found the time to evaluate the physics engines thoroughly enough. From what I read so far, I would prefer Chipmunk, as it has a simple C interface that should be easier to wrap than the C++ code Box2d (and easier to integrate into a Sparrow project).

A wrapper that makes one of those physics engines be easy to use from Sparrow would definitely make a lot of sense! I would opt for an add-on, a separate library or source code you can include in your app when the need for a physics engine arises. I want to keep the Sparrow core as lightweight as possible, only containing those parts that are needed by (almost) all games.

Posted 1 year ago #
seivan
Member

I am not arguing and I believe you are correct in what you are saying so I am agreeing, however I got a question;

Isn't physics and collisionDetection needed in most games anyway?
Everything from shooting a cannon and hitting bricks or see how far you get, to platform games to platform games with parallax, tiles games with buildings and enemies and etc.

Just curious..

Right now, as we speak, I am evaluating Chipmunk and Box2d
And I am preferring Box2d much more.
It isn't much more then just changing every implementation file to compile under .cpp.objc or something.

I need to look more into this.

Posted 1 year ago #
Daniel
Primary Feather

You're of course right, it is difficult to decide which parts have to come into the core of a game engine and which don't. Other developers will have other views on this, for sure.

However, there are a lot of games that don't require any physics: think of card or puzzle games (Tetris, SameGame, ...), quizzes, board games, etc.! Flash does not contain a physics engine either, and there are a lot of Flash games around that were built before someone created a decent physics engine for Flash.

If a physics engine was something simple that needs only one or two classes to work, I guess I would add it to the core nevertheless. But we're talking about a library that is quite complex and extensive. For that reason, I'd opt for making that part optional.

Posted 1 year ago #
freerunnering
Moderator

I would like to see a sparrow physics engine but i agree i think there is actually more files for box2d or chipmuck then for the rest of sparrow itself.
Also @seivan an easier way to make them compile objective c++ then making them compile under .cpp.objc is just to change the file name to .mm from .m

Posted 1 year ago #
seivan
Member

freerunning which way is the best? Neither has much difficulty for me.
I've been playing around with chipmunk lately. I seem to like it more and more
Mostly because it's easier to understand the concepts.

Also, not sure about box2d.
But in chipmunk you can take a shape and set a pointer to the sprite or whatever.

And in the updates do;
[(UIView *)shape->data setCenter:CGPointMake(shape->body->p.x, 480 - shape->body->p.y)];
(not sure how to make it with Sparrow yet, a bit embarrassed)

Posted 1 year ago #
ahnt
Moderator

interesting idea, I just wonder how to make it as lightweight and simple to use as the rest of sparrow.

I would like to have something like a SPDisplayObjectContainer only that it is a SPPhysicsObjectContainer. The thing to add would be a list of points defining the outline, and the outline is what the object interacts with. And I can add any graphic on top of it. I would also like to define the outline to be a circle.

The next thing I would like to have is a SPPhysicsStage which I use to addObjects to, and these Objects are the SPPhysics objects defined above. In the physics stage I can define the gravity vector, viscosity, friction etc.

The physics stage automatically updates the colision, rotation and whatever. If the user has to apply forces either a vector is added to the object or a rotation, or a vector to a point within the object is applied.

And like touches, I would like to get an event that contains an array of pointer pairs, and the pairs point back the the objects that just collided.

I am dreaming here, but that is the weight I would like this thing to be. But I also know that a physics engine is not something you could just write of the batch.

Cheers Arend

Posted 1 year ago #
seivan
Member
Actually what I had in mind was extending current SPDisplayObjectContainers with bodies.

Since normally (correct me if I am wrong) when dealing with physics bodies and visual sprites you deal with two parts of the same "thing".

The visual representation and the physical body in space. And when it comes down to it, you apparently never handle the visual representation explicitly. For instance let me show you an example;
```
int num = 4;
    cpVect verts[] = {
        cpv(-15,-25),
        cpv(-15, 15),
        cpv( 15, 15),
        cpv( 15,-25),
    };
    cpBody *body = cpBodyNew(50.0f, cpMomentForPoly(50.0f, 4, verts, cpvzero));
    body->p = cpv(135.0f, 335.0f);

    //      body->w = 10.0f;
    cpSpaceAddBody(space, body);

    cpShape *whiteSquare;
    whiteSquare = cpPolyShapeNew(body, 4, verts, cpvzero);
    whiteSquare->e = 0.3f; whiteSquare->u = 0.3f;
    whiteSquare->data = ball; //IMPORTANT, ball is a ImageView
```
Now, here is the good part. If you take a look at the whiteSquare pointer, it has a ->data variable.
That data points to the sprite or imageview.
So everytime whiteSquare moves it sends it's new locations to the ->data variable (which in this case is a ImageView)
That method looks like
[(UIView *)shape->data setCenter:CGPointMake(shape->body->p.x, 480 - shape->body->p.y)];

Now if we somehow could add tweens with vectors, and have the advanceTime move the bodies instead of the sprites.
We'd be good to go!
Posted 1 year ago #
ahnt
Moderator

I guess I was thinking too much.
But not every object is a box, but sometimes a polygon, and on top of that collisions in 2D also cause rotations and angular momentum, especially when polygons rotate and collide. Also collisions are a big part of the physics engine.

Anyway creating a tween for updating a body sounds good, I just think that it will cause more work then necesary, normally each object has its motion and rotation vector, from that and all collisions you compute the new vectors and update the positions and rotations, and next frame again and again. Creating tweens at this moment would move the bodies, but a tween would exactly be valid for one update, so why bother creating them when they are "meaningless" in the next update?

But you are right the image is different from the object. So we could add body as a property to image, but that is I guess more of a style question.

Cheers Arend

Posted 1 year ago #
seivan
Member

These are just theories, I have zero experience, so I don't expect them to be right and I was hoping to be proven wrong =)

Posted 1 year ago #
ahnt
Moderator

sorry, I didn't want to cut you off or anything, I just wanted to explain what the difference between a tween and a physics engine update is.

Cheers Arend

Posted 1 year ago #
seivan
Member

No I love the explanation, no need for an apology!

Posted 1 year ago #
Daniel
Primary Feather

Thanks a lot for your suggestions on that topic! Both of your descriptions contain a lot of brilliant ideas.

Now I'd just need enough time to implemented all those ideas
Believe me, I'd love to do it without any delay, if I just had more time ...!!

Posted 1 year ago #
enbr
Moderator

I would also love to see Chipmunk implemented although I understand that you don't have a lot of time. If there's anything I can do to help this move along please let me know.

Posted 1 year ago #
Daniel
Primary Feather

Thanks a lot for the offer! I may come back to it =)

Posted 1 year ago #
enbr
Moderator

And I will donate also.

Posted 1 year ago #
Daniel
Primary Feather

Thanks a lot for you support, enbr! =)
It really means a lot to me.

Posted 1 year ago #

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