i am developing a game, in this game i have Chain. chains One side is Static and another is dynamic. and chain is moving in ccTouchMove.as chain move,dynamic part get exten and looks like a curve. chain length is Fix. So how can i set fix Length and curve in it.
Refer me Which Joint i have to Use. i am trying RopeJoint but i get error in
b2RopeJointDef jd;
can some one send me sample code.
You can use rope joint and use code like this..
b2RopeJointDef rp;
rp.bodyA=dragonFlyAnchor; //define bodies
rp.bodyB=foodItemBody;
rp.localAnchorA = b2Vec2(0,0); //define anchors
rp.localAnchorB = b2Vec2(0,0);
rp.maxLength=((foodItemBody->GetPosition()) - dragonFlyAnchor->GetPosition() ).Length(); //define max length of joint = current distance between bodies
world->CreateJoint(&rp); //create joint
Related
I looked at a bunch of similar questions, and I cannot seem to find one that particularly answers my question. I am coding a simple 3d game, and I am trying to allow the player to pick up and move entities around my map. I essentially want to get a velocity vector that will "push" the physics object a distance from the player's eyes, wherever they are looking. Here's an example of this being done in another game (the player is holding a chair entity in front of his eyes).
To do this, I find out the player's eye angles, then get the forward vector from the angles, then calculate the velocity of the object. Here is my working code:
void Player::PickupOtherEntity( Entity& HoldingEntity )
{
QAngle eyeAngles = this->GetPlayerEyeAngles();
Vector3 vecPos = this->GetEyePosition();
Vector3 vecDir = eyeAngles.Forward();
Vector3 holdingEntPos = HoldingEntity.GetLocation();
// update object by holding it a distance away
vecPos.x += vecDir.x * DISTANCE_TO_HOLD;
vecPos.y += vecDir.y * DISTANCE_TO_HOLD;
vecPos.z += vecDir.z * DISTANCE_TO_HOLD;
Vector3 vecVel = vecPos - holdingEntPos;
vecVel = vecVel.Scale(OBJECT_SPEED_TO_MOVE);
// set the entity's velocity as to "push" it to be in front of the player's eyes
// at a distance of DISTANCE_TO_HOLD away
HoldingEntity.SetVelocity(vecVel);
}
All that is great, but I want to convert my math so that I can apply an impulse. Instead of setting a completely new velocity to the object, I want to "add" some velocity to its existing velocity. So supposing I have its current velocity, what kind of math do I need to "add" velocity? This is essentially a game physics question. Thank you!
A very simple implementation could be like this:
velocity(t+delta) = velocity(t) + delta * acceleration(t)
acceleration(t) = force(t) / mass of the object
velocity, acceleration and force are vectors. t, delta and mass scalars.
This only works reasonably well for small and equally spaced deltas. What you are essentially trying to achieve with this is a simulation of bodies using classical mechanics.
An Impulse is technically F∆t for a constant F. Here we might want to assume a∆t instead because mass is irrelevant. If you want to animate an impulse you have to decide what the change in velocity should be and how long it needs to take. It gets complicated real fast.
To be honest an impulse isn't the correct thing to do. Instead it would be preferable to set a constant pick_up_velocity (people don't tend to pick things up using an impulse), and refresh the position each time the object rises up velocity.y, until it reaches the correct level:
while(entPos.y < holdingEntPos.y)
{
entPos.y += pickupVel.y;
//some sort of short delay
}
And as for floating in front of the player's eyes, set an EyeMovementEvent of some sort that also sends the correct change in position to any entity the player is holding.
And if I missed something and that's what you are already doing, remember that when humans apply an impulse, it is generally really high acceleration for a really short time, much less than a frame. You wouldn't see it in-game anyways.
basic Newtonian/D'Alembert physics dictate:
derivate(position)=velocity
derivate(velocity)=acceleration
and also backwards:
integrate(acceleration)=velocity
integrate(velocity)=position
so for your engine you can use:
rectangle summation instead of integration (numerical solution of integral). Define time constant dt [seconds] which is the interval between updates (timer or 1/fps). So the update code (must be periodically called every dt:
vx+=ax*dt;
vy+=ay*dt;
vz+=az*dt;
x+=vx*dt;
y+=vy*dt;
z+=vz*dt;
where:
a{x,y,z} [m/s^2] is actual acceleration (in your case direction vector scaled to a=Force/mass)
v{x,y,z} [m/s] is actual velocity
x,y,z [m] is actual position
These values have to be initialized a,v to zero and x,y,z to init position
all objects/players... have their own variables
full stop is done by v=0; a=0;
driving of objects is done only by change of a
in case of collision mirror v vector by collision normal
and maybe multiply by some k<1.0 (0.95 for example) to account energy loss on impact
You can add gravity or any other force field by adding g vector:
vx+=ax*dt+gx*dt;
vy+=ay*dt+gy*dt;
vz+=az*dt+gz*dt;
also You can add friction and anything else you need
PS. the same goes for angles just use angle/omega/epsilon/I instead of x/a/v/m
to be clear by angles I mean rotation (pitch,yaw,roll) around mass center
I've had to completely revamp this question as I don't think I was explicit enough about my problem.
I'm attempting to learn the ropes of Box2D Web. I started having problems when I wanted to learn how to put multiple shapes in one rigid body (to form responsive concave bodies). One of the assumptions I made was that this kind of feature would only really be useful if I could change the positions of the shapes (so that I can be in control of what the overall rigid body looked like). An example would be creating an 'L' body with two rectangle shapes, one of which was positioned below and to-the-right of the first shape.
I've gotten that far in so-far-as I've found the SetAsOrientedBox method where you can pass the box its position in the 3rd argument (center).
All well and good. But when I tried to create two circle shapes in one rigid body, I found undesirable behaviour. My instinct was to use the SetLocalPosition method (found in the b2CircleShape class). This seems to work to an extent. In the debug draw, the body responds physically as it should do, but visually (within the debug) it doesn't seem to be drawing the shapes in their position. It simply draws the circle shapes at the centre position. I'm aware that this is probably a problem with Box2D's debug draw logic - but it seems strange to me that there is no online-patter regarding this issue. One would think that creating two circle shapes at different positions in the body's coordinate space would be a popular and well-documented phenomina. Clearly not.
Below is the code I'm using to create the bodies. Assume that the world has been passed to this scope effectively:
// first circle shape and def
var fix_def1 = new b2FixtureDef;
fix_def1.density = 1.0;
fix_def1.friction = 0.5;
fix_def1.restitution = .65;
fix_def1.bullet = false;
var shape1 = new b2CircleShape();
fix_def1.shape = shape1;
fix_def1.shape.SetLocalPosition(new b2Vec2(-.5, -.5));
fix_def1.shape.SetRadius(.3);
// second circle def and shape
var fix_def2 = new b2FixtureDef;
fix_def2.density = 1.0;
fix_def2.friction = 0.5;
fix_def2.restitution = .65;
fix_def2.bullet = false;
var shape2 = new b2CircleShape();
fix_def2.shape = shape2;
fix_def2.shape.SetLocalPosition(new b2Vec2(.5, .5));
fix_def2.shape.SetRadius(.3);
// creating the body
var body_def = new b2BodyDef();
body_def.type = b2Body.b2_dynamicBody;
body_def.position.Set(5, 1);
var b = world.CreateBody( body_def );
b.CreateFixture(fix_def1);
b.CreateFixture(fix_def2);
Please note that I'm using Box2D Web ( http://code.google.com/p/box2dweb/ ) with the HTML5 canvas.
It looks like you are not actually using the standard debug draw at all, but a function that you have written yourself - which explains the lack of online-patter about it (pastebin for posterity).
Take a look in the box2dweb source and look at these functions for a working reference:
b2World.prototype.DrawDebugData
b2World.prototype.DrawShape
b2DebugDraw.prototype.DrawSolidCircle
You can use the canvas context 'arc' function to avoid the need for calculating points with sin/cos and then drawing individual lines to make a circle. It also lets the browser use the most efficient way it knows of to render the curve, eg. hardware support on some browsers.
Since it seems like you want to do custom rendering, another pitfall to watch out for is the different call signatures for DrawCircle and DrawSolidCircle. The second of these takes a parameter for the axis direction, so if you mistakenly use the three parameter version Javascript will silently use the color parameter for the axis, leaving you with an undefined color parameter. Hours of fun!
DrawCircle(center, radius, color)
DrawSolidCircle(center, radius, axis, color)
I'm trying to make a system of "chunks" in Box2D - i.e. shapes that are attached together in a big lump, so that you can break chunks off into their own body.
Currently, my system is very basic (just starting really) and modelled after the "Breakable" test in the Box2D testbed. It's a body with quite a few basic box fixtures (which will later become polygons). When you click a body, it deletes the fixture and creates a new body with the same fixture, rotation, etc in the same place as the old "chunk".
However, I can only get it to create the new body at the big body's origin
(->GetWorldCenter). What I want to do is find the global location of the fixture to be deleted and replaced, so I can make the new chunk there.
I've read some stuff about b2PolygonShape having a "centroid", but I'm not sure how to access and use that...
To put it simply, I want to find the global location (as x+y or a b2Vec2) of a FIXTURE, NOT a body (that's easy). The fixture will move with the body it's attached to, but I only currently need the position for one frame (having it update would be useful too though).
For Box2D position of the body not so important. Body position is only shift for fixture coordinates. It do not impact to simulation process. So, I don't understand, why you so care about this.
I made something like this, and can say, that using big body's origin works fine. You can see into Box2D testbed to Breakable test. There also used big body's origin. Only reason to calculate new coordinates that I see is strange behavior of SetAngle method.
If you still want centroid, look at ComputeCentroid, located at b2PolygonShape.cpp. Pay attention, method don't declared at b2PolygonShape.h. You can copy code from cpp and use it like this:
b2Fixture* chunk = ...;
b2Vec2 chunkCentroidLocal = ComputeCentorid(chunk->m_vertices,
chunk->m_vertexCount);
b2Vec2 chunkCentroidWorld = bigBody->GetWorldPoint(chunkCentroidLocal);
p.s. Don't forget to transform polygon points, when you will create new body. Simply find difference between big body and new body, and subtract it from every point of polygon.
b2Vec2 shift = chunkCentroidWorld - bigBody->GetWorldCenter();
b2Vec2 newVertices = new b2Vec2[chunk->m_vertexCount];
for(int i = 0; i< chunk->m_vertexCount; i++)
{
newVertices[i] = chunk->m_vertices[i] - shift;
}
I have a maze game that using cocos2d
I have one main sprite that can save "friend" sprite
Once "friend" sprite collide with main sprite, the "friend" sprite will follow main sprite everywhere.
Now I dont know how to make "friend" sprite follow main sprite with static distance and smooth movement.
I mean if main sprite going up, "friend" will be at behind the main sprite.
If main sprite going left, "friend" sprite will be at right of main sprite.
Please help me and share me some code...
You can implement the following behaviour by using the position of your main sprite as the target for the friend sprite. This would involve implementing separation (maintaining a min distance), cohesion (maintaining max distance) and easing (to make the movement smooth).
The exact algorithms (and some more) are detailed in a wonderful behavior animation paper by Craig Reynolds. There are also videos of the individual features and example source code (in C++).
The algorithm you need (it is a combination of multiple simpler ones) is Leader following
EDIT : I have found two straightforward implementations of the algorithms mentioned in the paper with viewable source code here and here. You will need to slightly recombine them from flocking (which is mostly following a centroid) to following a single leader. The language is Processing, resembling java-like pseudcode, so I hope the comprehension should be no problem. The C++ sourcecode I mentioned earlier is also downloadable but does not explicitly feature leader following.
I am not aware of any cocos2d implementations out there.
I have a simple solution kind of working fine. Follow the cocos2d document getting started lesson 2, Your first game. After implement the touch event. Use the following code to set seeker1 to follow cocosGuy:
- (void) nextFrame:(ccTime)dt {
float dx = cocosGuy.position.x - seeker1.position.x;
float dy = cocosGuy.position.y - seeker1.position.y;
float d = sqrt(dx*dx + dy*dy);
float v = 100;
if (d > 1) {
seeker1.position = ccp( seeker1.position.x + dx/d * v *dt,
seeker1.position.y + dy/d * v *dt);
} else {
seeker1.position = ccp(cocosGuy.position.x, cocosGuy.position.y);
}
}
The idea is at every step, the follower just need to move towards the leader at a certain speed. The direction towards the leader can be calculated by shown in the code.
I have a tire in my screen and I would like to have a rope connected to the top of the tire and to the top of the screen. I have incorporated physics into my game with chipmunk+spaceManager so I need to some how have this rope react to the physics also. I just need it to move back and forth with the tire when it gets hit. I have used a cpConstraintNode to get a line drawn to use it as a rope up to this point but everything I have seen and looked into, there is no way to attach a CCSprite to a constraint. So my question is How would I go about creating this rope and have it react the same as the tire when it is moving? Here is my code that I have done with the constraint: I am using cocos2d and chipmunk + spaceManger
//The "rope"
cpVect a1 = cpv(0,30); //Local coordinates of tire
cpVect a2 = cpv(70,320); //World coordinates (staticBody is at (0,0))
//calculate the length of the rope
float max = cpvdist(cpBodyLocal2World(upper->body, a1), a2);
cpConstraint *rope = [game.spaceManager addSlideToBody:upper->body fromBody:game.spaceManager.staticBody toBodyAnchor:a1 fromBodyAnchor:a2 minLength:1 maxLength:max];
cpConstraintNode *ropeNode = [cpConstraintNode nodeWithConstraint:rope];
ropeNode.color = ccBLUE;
This post presents a great way to draw ropes in Cocos2D using Verlet Integration.
The only drawback is that the example uses Box2D. But the code can be ported to chipmunk.
If you're wanting to use the VRope project on github to integrate VRope and chipmunk, I've created a new branch that does just that. You'll find it at:
VRope Chipmunk Branch
An example of using it is:
Creation
pinPointJoint =
cpSlideJointNew(body,
body2,
body.anchorPoint,
body2.anchorPoint,
minimumLength,
maximumLength);
cpSpaceAddConstraint(space, pinPointJoint);
rope = [[VRope alloc] init:pinPointJoint batchNode:ropeBatchNode];
Updating
[rope update:delta];