I'm just starting with cocos2d + box2d.
I would love to create a simple 2d ship game where you look from top(from the sky) down at the sea with the ships.
Could someone give me a very very basic example, how to apply wind to my world? Do I have to applyForce to each ship body?
And what about the gravity? Since it goes straight down, should I set it to 0? gravity.Set(0.0f, 0.0f)? It actually would pull down the ship..
Should I somehow deal with the water? e.g with density of it?
you would probably have to detect where the ships are and then apply force on them somehow.
and yes set gravity to 0.
and water wouldn't have to be an object at all. just like a background image.
If you are looking from the top and want to apply wind force to all your ships you can use gravity vector. In this case wind force will be applied to your objects automatically.
If there are other dynamic objects on the scene then it's a good idea to keep the list (std::list or NSMutableArray) of pointers to all your ships. Notice, that by default box2D is clearing all the forces each simulation step. You can disable this property or apply forces manually each simulation step
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I am building an IOS game in Cocos2d - Chipmunk - Spritebuilder. I need to make a characters orbit around around a point, and I was having quite some difficulty in implementing orbits with real physics.
So far, I have tried two methods, one is creating a distance joint from the player to the planet, and then applying a 90 degree force on the player where an angle is created between the end of the distance joint and an imaginary line drawn at a 90 angle to it. He moves around crazily and this method is not working for me.
I then tried calculating 180 points on the circumference at a radius from the planet (which is the bounds of detecting and implementing its effects on the player) - and then in a scheduled update method [character.physicsbody applyForce:nextCircumferencePoint]; This does not work, as he does not follow the path exactly and is quite far from it. I am thinking that I need to also apply a gravitational force towards the planet which would cause him to circle it. Though I don't know how to calculate that force, apply it, or if it would even help.
A third method which would never work, but was used for testing was to set his position to the next circumference point. He does orbit, but any collision won't work (such as if a piece of space junk goes in his way.) He will simply be positioned right over any other object. This world great if you don't need collisions, are writing your own physics engine. This is not a polished way of doing things, so will avoid it.
Please correct anything I have already done and tell me how it would work, or shed light on other options and how to implement them.
Check out my answer here. It's for box2d, but you can do it with Chipmunk. If bodyA position will change, orbit will be same. You just need to change speed of body movement for your needs, just increase smoothness and slow down your update method.
One of the powerups in my game is a vortex that attracts all coins. I know I have any cocos2d's moveto/bezierto methods available, but I don't know how to make them have tangential and radial speed.
The extra difficulty is that the vortex center can change in every step, so all movement has to be readjusted.
One way to achieve this without a physics engine is to use the rotation around point algorithm.
That covers the rotation around the vortex center. Once an object is rotation around the vortex, all you need to do is to reduce that object's distance from the center by a certain amount every frame. That way it will continue to move inwards.
The only tricky part then is to get the object from its initial position being "sucked into" the vortex. There's going to be a lot of tweaking needed. With a physics engine, that part would come natural from the physics itself and it would always look right.
This is not guaranteed for the manual solution and definitely not for actions, which aren't designed to track moving targets. For example, if you change a move action every frame by replacing the existing one with a new one, your object won't move at all. Every time you do that, there's a 1-frame delay before the new action does its work.
I am developing third-person shooting game using Bullet and Ogre. When the character model collides with an object in the world, such as a power-up, the collision applies a force to the character and causes them to spin. How can I prevent the collision applying a force to the character?
I have set a method for btDynamicsWorld::setInternalTickCallback and so I know which bodies are colliding and the btManifoldPoint.
Note that I applyTorque to the body in order to rotate them smoothly so I cannot simply prevent rotation.
Thanks for your help.
I am unfamiliar with the physics engines you mentioned, but I know a thing or two about real physics...
Basically if you draw a free body diagram and arrows that represent the forces, you can determine the net effect. Or if you know the desired net effect, you can figure out where you need to add forces or remove forces.
You could add an equal and opposite force/torque at the time of impact. This would make the net forces on your object zero.
Or you could take the elements that are causing the forces and make them massless. Force = mass * acceleration. If the mass is zero and your physics engine is based on real world physics, then it shouldn't cause any net forces on collision.
Hope that helps.
I have been experimenting with the box2D sample project within cocos2D for the iPhone and am wondering if box2D is the appropriate engine to use to make a moving object "stick" to a stationary object when the moving object is finished moving in a certain direction.
Here is a simplification of what I am trying to achieve: I have MovingObject, a dynamic rigid body, that moves vertically against gravity when enough force is applied to it. As MovingObject moves, it may overlap a static object, StationaryObject. When gravity diminishes MovingObject's velocity to zero such that it is no longer moving, I would like to have MovingObject remain where it is ONLY if it overlaps StationaryObject. If the object's do not overlap, MovingObject should start to move back down towards the ground per the force of gravity. During that descent, if MovingObject at any time overlaps StationaryObject, it should stop its descent and remain in that location as if it is stuck on StationaryObject.
I am able to get MovingObject to move per the forces I am applying to it, but not really sure how to make it stop and stay there once it reaches the top of its ascent, assuming it is overlapping StationaryObject.
Currently, I am experimenting with simple square/box objects but eventually both MovingObject StationaryObject will be defined as very different complex polygon shapes.
Thanks in advance for any insights and/or suggestions for achieving this.
Sounds like you'll want to change the type of fixture used for "MovingObject" while it "ascending" and then change it when it is "descending" so that it reacts differently (to overlaps).
by "overlap" it sounds like you want to achieve something similar to "one sided platforms" in a platform game (ie; Mario Bros.) - I would recommend looking into the solutions for one-sided platforms for starters.
For school I have to make a game for my iPod touch, I chose to do an asteroids game. I have just started with cocos2d but have read the wenderlich blog. I wanted to use chipmunk in my game, i want realisitc motion of the ship. Is there a tutorial on creating the asteroids motion?
Thanks.
Simple Way
Learn a bit about vectors. http://chortle.ccsu.edu/VectorLessons/vectorIndex.html
Movement is usually calculated by adding a vector scaled by a time delta to the current position. (Math talk makes simple things so complicated).
Basically: new_Pos = old_Pos + mov_Vec * time_delta
So by changing the mov_Vec you can increase/decrease speed.
You can also do it on x,y new_x = old_x + mov_x * time_delta
Using Physics Library
If you are using a physics library, you can apply force to an object to move it. You can also set the angular velocity if you want it to rotate.
If you were using Box2d you would do something like this:
body->ApplyImpulse( b2Vec2(1,1), body->GetWorldCenter() );
There's a difference between applying force and an impulse in box2d
Some sites to check out
http://gpwiki.org/
http://www.gamedev.net/
http://www.devmaster.net/
http://box2d.org/
Airship motion in space is pretty easy to simulate... I don't think you need a library for that.
The ship has a velocity vector: depending on your input method, you shall only add a vector to change the speed (or reduce modulo when braking, if braking is allowed).
Just limit the max modulo of the ship, and you're done.
Sorry if this isn't really a reply to your answer.
HIH