i am working on rope physics. i have implemented one rope using Revolute joints ..
I'm making rope connecting dynamic bodies (via b2RevoluteJoints).i successfully created it.Now i also attach one dynamic body at the end of rope . & i m releasing my this rope with this body downwards , now somehow my joints between my dynamic rope bodies are stretched & then breaks , I want my rope looks smoother.
my joints are like this
b2RevoluteJointDef revoluteJointDef;
revoluteJointDef.bodyA = referenceBody;//provided by testbed
revoluteJointDef.bodyB = lastLink;
revoluteJointDef.localAnchorA = startPos;//world coords, because m_groundBody is at (0,0)
revoluteJointDef.localAnchorB.Set(0,0);//center of circle
world->CreateJoint( &revoluteJointDef );
revoluteJointDef.bodyA = lastLink;//the last added link of the chain
revoluteJointDef.bodyB = chainBase;
revoluteJointDef.localAnchorA.Set(0,linkWidth);//the regular position for chain link joints
revoluteJointDef.localAnchorB.Set(0,linkWidth);//a little in from the edge of the circle
world->CreateJoint( &revoluteJointDef );
Is there any way to make strong joints ??
can we achieve this by working on Density of bodies & gravity of world ??
please help .....
I had a similar problem (but with the centrifugal force of swinging a larger object at the end of the rope). To solve the problem of the breaking chain/rope you need to make the larger object less dense, but this then introduces a knock on problem - now your "larger" dynamic object gets held correctly by the rope but does not interact with the rest of the world as it should.
To solve this problem I did something a bit hacky and implemented my own collision handler which would apply a collision impulse to the thing that my larger object collided with as if it were heavier. So...
make your object at the end of the rope very low density so that the rope holds
implement some supplemental collision handlers for your object to make it seem like your object is more dense to other objects (sensor = true may help with this as well).
It is not strictly in the spirit of the physics simulator, as we should be able to set our parameters and let the rules take care of everything - basically it would be nice if the revolute joints were unbreakable.
Related
I have a rope with pin joints between chain rings. It had worked perfectly.
I now want to simulate real chain, so I added limits for pin joints as such:
pinJoint.upperAngleLimit = CGFloat(M_PI / 6)
pinJoint.lowerAngleLimit = CGFloat(-M_PI / 6)
pinJoint.shouldEnableLimits = true
However, when I use a ball-like start of the chain, I get pictures 3-4 (shown below)
I tried to use constraints, but they weren't really helpful
Have you tried to use Matti's rope module? This worked pretty well for me. The simulation became very unstable based on the mass of the ball. Try reducing the mass of the rope links and the ball. Also, if the rope spins too fast the physics will also become unstable.
I think next time I will try using Verlet integration like this example. This also has the advantage of being able to attach on both ends.
xcode 5 iOS7 sprite kit.
My wish is to make a sprite that has its own gravity.
Like a planet. If another sprite comes within a certain range of it, it will slowly pull the other sprite closer.
I have two sprites. One moving and one stationary. When the moving sprite gets in a given distance of the stationary sprite the stationary sprite gravity should slowly pull the other sprite towards it. This way the moving sprite would change its path in a soft curve.
My idea would be to calculate the distance from the stationary object to any other object and if close enough start pulling and if the moving object gets out of range ageing, then stop pulling.
Would probably need to research some vector calculation.
Thats my immediate thoughts.
Is this possible and how? Does it already exist?
A friend of mine did this for his physics dissertation. multibody gravity simulation. So yeah you can but you need to be willing to learn some maths. Apparently there is a clever optimisation to make it run decently nlog(n) rather than n^2). you probably want to ask this on the physics version of stack overflow to get a good answer. I have the code at home ... will post it later but you will want an explanation - i used it in an xna app. Its badass once you get it working - although if you want naturally orbiting objects then you will want to code them using parametric equations for easy and cool orbits. Simply because its hard to solve and with time even using double will result in some errors (the good implementations also work out the error and adjust - again will post later). But the real problem is solving for stable orbits. You then use the algorithm for free moving bodies such and player objects / npcs. Although solving accurate movement for npc in a changing field is v hard.
you want to look at this question: Jon Purdys answer is the one you want
multi body physics - gravity
and this one (which is linked from above) ...
https://gamedev.stackexchange.com/a/19404
There is not a dead-simple way of doing that in any platform as far as I know maybe except for some game engines/platforms that export for different platforms (cocos2d, construct 2 etc).
What you need is a physics engine whether you write one (which is a complicated but fun thing to do) or use an available one.
Luckily I've found a link describing the usage of the famous 2D physics engine "Box2D" on iOS.
This one explains how you can include Box2D in an openGL application (but you can apply this to other environments (sprite kit) I think altough I'm not an iOS guy);
http://www.iforce2d.net/b2dtut/setup-ios
Anyways, you now know what to look for...
For iOS 8.0+ : you have SKFieldNode : radialGravityField()
For iOS 8.0- : one solution could be : 3 to 9
add your sprite ( planet ) with its physics
add an invisible SKNode ( the gravity zone ) with its own physics, as a child of your sprite, but with a radius much more than your sprite's one
you have a little explanation about invisible node here : https://developer.apple.com/documentation/spritekit/skphysicsworld
both, your sprite and the invisible node are centered in a zero gravity world
we look for contact and not collision ( set correctly your bit masks )
when any object get in contact with the invisible node ( gravity zone ), first you remove any moving action or impulse from it and then we add to this object an SKAction to move it toward the center of your sprite ( planet )
at second contact between this object and your sprite ( planet ), you remove all actions again from the object with a velocity = zero
I have been working on a Unity ping pong game using the Leap Motion. I use rigidbody.MovePosition() to move the paddle. However, when I hit the ball (which uses gravity), the paddle launches it too far. Even when I change the masses of both, it doesn't do anything.
What variable should I change to reduce this energy going into the ball?
From the following link.
"MovePosition will put your object at the target location, no matter what. It may push aside other objects in a realistic way, or may blast them out of the way, or may just pass right through them. But it will gladly move you through a solid wall or a mountain.
If you're using MovePosition on a rigidbody to add from where you currently are, it looks like AddForce. With AddForce, the physics step does all the work: applies your velocity, sees the collision and handles the bounce. With MovePosition, the physics step sees you're mysteriously overlapping a solid object. If it isn't too much, it will bounce you apart."
You won't need to use MovePosition. Instead, you can figure out the direction of the shot (based on the position of the ball relative to the paddle). Then you can add an impulse force in that direction to the ball.
Pseudo-code (from the following link):
Vector3 shootDir = ballPosition - paddlePosition; // Calculate direction of the shot
shootDir.Normalize(); // Normalize the shot vector
ball.AddForce(shootDir * speed, ForceMode.Impulse); //Add impulse force in correct direction.
Credit due to Owen Reynolds and Tim Michels.
I use Unity3D and I have a player with a rigidbody. I add force tto the body for moving the player. My player walks over a terrain but is able to walk up mountains that are to steep to climb. I want to limit the player so it cannot walk up a slope that is to steep.
I know there is a CharacterController component that has this functionality, but I have to use the rigidbody, so I want the same but on my rigidbody.
I can get the normal of the triangle I am standing on, and calculate its angle, but I cannot seem to make the player stop moving up the slope. Only make the player stop moving (which makes the player unmovable once it hits a angled slope)
Any ideas how to solve this problem?
It's difficult to answer without more details on how you're using the physics engine. How/Are you using friction? What angle are you applying the force? Is it always horizontal or at the angle of the floor? Does the player have a mass?
Anyway I can think of a few ways to solve this
Go the pure physics route. Using player mass, friction, force angle, gravity, etc. Get the physics to handle these situation for you. This may take a fair amount of time and programming.
Keep the rigid body but fake the forces. Scale the force you are applying to the body of the player with the angle of the triangle the player is on. You can either use trigonometry to work out what you should apply or your own mapping. By your own mapping I mean set an angle where 0 force is applied (say 45 degree) and do a linear(or non linear) scale on the force applied so on flat ground force is 1 and at 45 force is 0.
Don't use rigid bodies. There is a reason most games don't use rigid bodies to control characters. It's hard and complicated and most of the time not worth the time it would take. Of course I don't know the details of your project so if this isn't an option, fine.
Hope that gives you some things to think about.
I am writing Cocos2D box2d game for iPhone.
I've 2 dynamic bodies, and I hope they are applied force from outside, but they don't apply force each other and detect their collision.
How can I achieve this?
And also I hope they move together at the same position after collision.
How can I do this?
they don't apply force each other and detect their collision
Sounds like you might want to look at collision filtering. This answer has a bit of code that changes the collision filtering index of a body dynamically https://stackoverflow.com/a/11283206/735204
they move together at the same position after collision
Probably some kind of joint (eg weldjoint?)
From the manual: http://www.box2d.org/manual.html
Joints are used to constrain bodies to the world or to each other. Typical examples in games include ragdolls, teeters, and pulleys. Joints can be combined in many different ways to create interesting motions.
Some joints provide limits so you can control the range of motion. Some joint provide motors which can be used to drive the joint at a prescribed speed until a prescribed force/torque is exceeded.
Joint motors can be used in many ways. You can use motors to control position by specifying a joint velocity that is proportional to the difference between the actual and desired position. You can also use motors to simulate joint friction: set the joint velocity to zero and provide a small, but significant maximum motor force/torque. Then the motor will attempt to keep the joint from moving until the load becomes too strong.
Sorry about last answer, just checking that I can write it.
What about this?
bodyDef.isSensor = true;
and use ContactListener to detect collision. Box2d for collision detection
Also you can use box2d filters. For example:
REMEMBER: if groupIndex < 0, same bodies never collide with each other. That is what you need.
b2Filter bodyFilter;
bodyFilter.groupIndex = -1;
bodyFilter.categoryBits = 0x0002;
fixtureDef.filter = bodyFilter;