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.
Related
To summarize the problem(s):
I have two bodies in my world so far, one being the ground, the other one being a falling box called "fallingStar".
1) I do not understand why my bullet world is not aligned with my drawn world unless I set an offset of btVector3(2,2,2) to the (btDefault)MotionState.
There is no fancy magic going on anywhere in the code that would explain the offset. Or at least I could not find any reason, not in the shaders, not anywhere.
2) I expected to be able to use multiple instances of btDefaultMotionState, to be precise, I wanted to use one instance for the falling entity and place it somewhere above the ground and then create another instance for the ground that should simply be aligned with my graphics-ground, ever unmoving.
What I am experiencing in regards to 2) is that for whatever reason the btDefaultMotionState instance for the falling entity is always also influencing the one for the ground, without any reference.
Now to the code:
Creation of the fallingBox:
btCollisionShape *fallingBoxShape = new btBoxShape(btVector3(1,1,1));
btScalar fallingBoxMass = 1;
btVector3 fallingBoxInertia(0,0,0);
fallingBoxShape->calculateLocalInertia(fallingBoxMass, fallingBoxInertia);
// TODO this state somehow defines where exactly _ALL_ of the physicsWorld is...
btDefaultMotionState *fallMotionState = new btDefaultMotionState(btTransform(btQuaternion(0,0,0,1), btVector3(2,2,2)));
//btDefaultMotionState *fallMotionState = new btDefaultMotionState();
btRigidBody::btRigidBodyConstructionInfo fallingBoxBodyCI(fallingBoxMass, fallMotionState, fallingBoxShape, fallingBoxInertia);
/*btTransform initialTransform;
initialTransform.setOrigin(btVector3(0,5,0));*/
this->fallingBoxBody = new btRigidBody(fallingBoxBodyCI);
/*fallMotionState->setWorldTransform(initialTransform);
this->fallingBoxBody->setWorldTransform(initialTransform);*/
this->physicsWorld->addBody(*fallingBoxBody);
Now the interesting parts to me are the necessary offset of btVector3(2,2,2) to align it with my drawn world and this:
btTransform initialTransform;
initialTransform.setOrigin(btVector3(0,5,0));
this->fallingStarBody = new btRigidBody(fallingStarBodyCI);
fallMotionState->setWorldTransform(initialTransform);
If I reenable this part of the code ALL the bodies again show an offset, but NOT just 5 up, which I could somehow comprehend if for whatever reason the worldTransform would effect every entity, but about 2,2,2 off... which I cannot grasp at all.
I guess that this line is useless:
fallMotionState->setWorldTransform(initialTransform); as it does not change anything whether it's there or not.
Now to the code of the ground creation:
btCompoundShape *shape = new btCompoundShape();
... just some logic, nothing to do with bullet
btTransform transform;
transform.setIdentity();
transform.setOrigin(btVector3(x + (this->x * Ground::width),
y + (this->y * Ground::height),
z + (this->z * Ground::depth)));
btBoxShape *boxShape = new btBoxShape(btVector3(1,0,1)); // flat surface, no box
shape->addChildShape(transform, boxShape);
(this portion just creates a compoundshape for each surface tile :)
btRigidBody::btRigidBodyConstructionInfo info(0, nullptr, shape);
return new btRigidBody(info);
Here I purposely set the motionstate to nullptr, but this doesn't change anything.
Now I really am curious... I thought maybe the implementation of btDefaultMotionState is a singleton, but it doesn't look so, so... why the hell is setting the motionState of one body affecting the whole world?
Bullet is a good library but only few dedicate time to write good documentation.
To set position of a btRigidBody, try this :-
btTransform transform = body -> getCenterOfMassTransform();
transform.setOrigin(aNewPosition); //<- set orientation / position that you like
body -> setCenterOfMassTransform(transform);
If your code is wrong only at the set transformation part (that is what I guess from skimming your code), it should be solved.
Note that this snippet works only for dynamic body, not static body.
About CompoundBody:-
If it is a compound body, e.g. shape B contains shape C.
Setting transformation of B would work (set body of B), but not work for C.
(because C is just a shape, transformation support only body.)
If I want to change relative transformation of C to B, I would create a whole new compound shape and a new rigid body. Don't forget to remove old body & shape.
That is a library limitation.
P.S.
I can't answer some of your doubt/questions, these information are what I gathered after stalking in Bullet forum for a while, and tested by myself.
(I am also coding game + game library from scratch, using Bullet and other open sources.)
Edit: (about the new problem)
it just slowly falls down (along with the ground itself, which should
not move as I gave it a mass of 0)
I would try to solve it in this order.
Idea A
Set to the compound mass = 0 instead, because setting a child shape's mass has no meaning.
Idea B
First check -> getCenterOfMassTransform() every time-step , is it really falling?
If it is actually falling, to be sure, try dynamicsWorld->setGravity(btVector3(0,0,0));.
If still not work, try with very simple world (1 simple object, no compound) and see.
Idea C (now I start to be desperate)
Ensure your camera position is constant.
If the problem is still alive, I think you now can create a simple test-case and post it in Bullet forum without too much effort.
Lower amounts of lines of code = better feedback
What you are describing is not normal bullet behavior. Your understanding of the library is correct.
What you are most likely dealing with is either a buffer overrun or a dangling pointer. The code you have posted does not have an obvious one of either, so it would be coming from somewhere else in your codebase. You might be able to track that down using a well-placed memory breakpoint.
You "might" be dealing with a header/binary version inconsistency issue, but that's less likely as you would probably be seeing other major issues.
Just had the exact same type of behavior with the DebugDrawer suspended on top of the world. Solved it by passing to Bullet Physics the projectionview matrix alone, without the model matrix that he has and multiplies with already:
glUseProgram(shaderID);
m_MVP = m_camera->getProjectionViewMatrix();
glUniformMatrix4fv(shaderIDMVP, 1, GL_FALSE, &m_MVP[0][0]);
if (m_dynamicWorld) m_dynamicWorld->debugDrawWorld();
So I'm working on a project for a class and I'm still trying to figure out how to go about doing something.
I am making a game where there is a board of squares or hexagons, they are either black or white, each being a state of being "Flipped", and when you click one square/hexagon, it flips all the adjacent shapes too.
Here is an image of what I am aiming to create.
Assignment images
I have gotten it running with squares, but now I need to do it with Hexagons. With the squares I registered a mouseclick as being within a square parameters of the x and y location of the click, and the state changes are assigned to a list of values assigned similarly to how the shapes were assigned within a list.
I will include a quick recording of the square program running in a folder I'm going to link.
Now, I believe I can't apply this kind of system to hexagons since they don't really line up like the squares did.
So how would I go about making a click register within a single hexagon on a grid? I have already drawn out the grid, but I am stuck on what to do to register a click to allow a hexagon to change it's state from un-flipped to flipped. I'm pretty sure I know what to do for the state change itself, but I don't know how to go about this, would it involve something with making a separate Class or something? I would appreciate any help with this.
I'll put a dropbox link here for the progress I made so far, and a pdf manual for graphics.py.
Dropbox: Python files
You can view the python code in your web-browser with dropbox too, I don't really want to fill this page pull of an entire thing of code..
Any help and feedback would be wonderful, thank you c:
so, TL;DR: How do you register a click within a polygon shape in python that allows it to change a value (within a list?) and change its visual appearance.
Just for the general side of your question, you can use a test to check if a point (x, y) is inside a polygon (formed by a list of x, y pairs).
Here's one such solution: http://www.ariel.com.au/a/python-point-int-poly.html
# determine if a point is inside a given polygon or not
# Polygon is a list of (x,y) pairs.
def point_inside_polygon(x,y,poly):
n = len(poly)
inside =False
p1x,p1y = poly[0]
for i in range(n+1):
p2x,p2y = poly[i % n]
if y > min(p1y,p2y):
if y <= max(p1y,p2y):
if x <= max(p1x,p2x):
if p1y != p2y:
xinters = (y-p1y)*(p2x-p1x)/(p2y-p1y)+p1x
if p1x == p2x or x <= xinters:
inside = not inside
p1x,p1y = p2x,p2y
return inside
This can be used in a way that is quite symmetrical to your drawing code, as you also form polygons in the same way for drawing as you would to test to see if the cursor is inside a hex.
You can modify the above implementation also to work with this Point type you are using to draw the polygons.
The rest you should be able to figure out, especially considering that you managed the input handling and drawing for the square grid.
Im using SFML 2.1 for graphics and my game structure follows SFML book quite closely (SceneGraph implementation etc)
My world consists mostly of characters (around 1-400, moving around) and tiles (3600, stationary) and I'll check for collisions everytime something moves
In worst case scenario with ~400 characters moving around and ~3600 tiles, I have 4000 possible entities with collision and 800 collision check calls (separate X and Y movement) each frame -> 3.2M collision checks in total.
Almost all my entities have size of 16x16 pixels and I've been looking into implementing either quadtree or simpler grid for collision detection, which should bring number of collision checks down quite a bit. By grid I mean http://conkerjo.wordpress.com/2009/06/13/spatial-hashing-implementation-for-fast-2d-collisions/
But I have no idea how I should implement simple grid for example. All help is welcome. There's propably even a lot better ways to bruteforce this.
Entity update step.
I do X/Y-axis movement separately. Because I want to slide against entities when colliding diagonally.
Move entity horizontally
Check and handle collisions
Move entity vertically
Check and handle collisions
Repeat 1-4 for all entities
.
void Entity::updateCurrent(sf::Time dt, CommandQueue& commands)
{
setPreviousPosition(getPosition());
move(sf::Vector2f(mVelocity.x, 0) * dt.asSeconds());
handleCollision();
setPreviousPosition(getPosition());
move(sf::Vector2f(0, mVelocity.y) * dt.asSeconds());
handleCollision();
}
I've had the following problem before when I tried to handle both X and Y movement at the same time:
I had no idea if I should reset X or Y position after collision.
Collision handling.
I'll handle collisions only when entities are moving (currently only character entities, later projectiles and some special tiles)
if entity is tile -> do nothing
if entity is character -> check collisions with characters and tiles and reset movement if collision happened
.
void Entity::handleCollision()
{
if (getCategory() & Category::Tile)
return;
if (getCategory() & Category::Character)
{
std::set<SceneNode::Pair> collisionPairs;
checkCollision(*mSceneGraph, collisionPairs);
for (SceneNode::Pair pair : collisionPairs)
{
if (matchesCategories(pair, Category::Character, Category::NonPassableCharacterOrTile))
{
resetPreviousPosition();
break;
}
}
}
}
I'll check collision simply by using SFML's intersects-function. This is propably good enough for this?
bool collision(const SceneNode& l, const SceneNode& r)
{
return l.getBoundingRect().intersects(r.getBoundingRect());
}
If I were to implement grid or quadtree for collision detection, when should I populate it, when update? Should I update it every time I move one entity, or should I try to come up with a way to move all entities at once, then build grid/quadtree and only after that try to handle all collisions.
So my questions are: (1) In this scenario how and when should I do collision handling? My current implementation works, but I think I do it too often and all examples I looked into grids/quadtrees assumed that I do first all movement and do collision detection and handling after.
and (2) When do I clear/populate/update my grid/quadtree. For example if I have 3600 tiles and 3 moving characters. Should I seek for entity each time one moves in the grid and try to move it to different grid cell / tree branch?
Edit:
What I'll propably try next unless anyone gives better advice
Updated update step.
Is this smart or in anyway reasonable way to do this?
Remove entity from grid/quadtree
Move entity horizontally
Add entity to grid/quadtree
Check and handle collisions
Remove entity from grid/quadtree
Move entity vertically
Add entity to grid/quadtree
Check and handle collisions
Repeat 1-8 for all entities
.
Entity::move()
{
grid.getCell(getPosition()).remove(this);
... move x
grid.getCell(getPosition()).add(this);
... if collision, reset x
grid.getCell(getPosition()).remove(this);
... move y
grid.getCell(getPosition()).add(this);
... if collision, reset y
}
Entity::checkCollision()
{
list<Entity*> possibleColliders;
possibleColliders = grid.getEntitiesInRectangle(x - s, y - s, x + s, y + s);
... now only check collision against possibleColliders
}
I think a quadtree would work quite well and since it will be standalone there's really no issue in adding it into your current system.
The important question you've ask is probably, when to populate and update the quadtree. I think this largely depends on your use case. Since you have around 400 characters that can change position for each frame, it probably wouldn't make a lot of difference if you try to move the nodes in the quadtree or if you fully rebuild the quadtree. Which is really more performant depends on your algorithm and datastructure, which would need some performance testing.
In this tutorial, they also suggest to rebuild the quadtree every frame iteration.
For the "how to fix collision handling" you'll need to provide more information/a separate SO question, since it's not that clear what the issue is.
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 have recently been getting into OpenGL/SDL and playing around with objects in 2D/3D Space and as i'm sure most newbies to this area do, have a few queries, about the 'best' way to do something. I quote best, because i'm assuming there isn't a best way, it's personal preference.
So, I have an entity, a simple GL_QUAD, which I want to move around. I have keyboard events setup, i can get the keypress/release events, not a problem.
I have an entity class, which is my GL_QUAD, pseudo implementation....
class Entity
{
void SetVelocity(float x, float y);
}
I then have this event handler code...
if theEvent.Key = UPARROW AND theEvent.State = PRESSED
Entity.SetVelocity(0.0f, -1.0f);
else if theEvent.Key = UPARROW AND theEvent.State = RELEASED
Entity.SetVelocity(0.0f, 0.0f);
My question is, is this the best way to move my entity? This has led me to thinking that we could make it a little more complex, by having a method for adjusting the X/Y Velocity, seperately. As SetVelocity would forget me X velocity if i started moving left? So i could never travel diagonally.
For Example...
class Entity
{
void SetXVelocity(float x);
void SetYVelocity(float y);
}
if theEvent.Key = UPARROW AND theEvent.State = PRESSED
Entity.SetYVelocity(-1.0f);
else if theEvent.Key = UPARROW AND theEvent.State = RELEASED
Entity.SetYVelocity(0.0f);
if theEvent.Key = LEFTARROW AND theEvent.State = PRESSED
Entity.SetXVelocity(-1.0f);
else if theEvent.Key = LEFTARROW AND theEvent.State = RELEASED
Entity.SetXVelocity(0.0f);
This way, if I have an XVelocity and I then press the UPARROW, I will still have my XVelocity, as well as a new YVelocity, thus moving diagonally.
Is there a better way? Am I missing something very simple here?
I am using SDL 1.2, OpenGL, C++. Not sure if there is something in SDL/OpenGL which would help?
Thanks in advance for your answers.
The question is really general since it depends on how you want to model the movement of your objects in your world.
Usually every object has its velocity which is calculated basing on an acceleration and capped to a maximum. This means that a key press alters the acceleration of the object for the specified frame which is then calculated and applied to the current velocity of the object.
This is done through an update phase which goes through all the objects and calculates the velocity change according to the object acceleration. In this way you don't bother to modify the velocity itself but you let your engine to do its calculations depending on the state of every object..
acceleration is applied over a period of time, so in the example by #jack, you would apply an acceleration 10m/s^2 over a time period of one second.
you should also modify your application to make it time based, not frame based.
have a look at this basic game physics introduction, and I would also really have a look at the GameDev.net Physics Tutorials
I assume the way you want movement to work is that you want the player to move only when a key is held.
In short: your solution is fine.
Some potential gotchas to take consideration of: What happens if both left and right is pressed?
Well, what you describe here is a simple finite state machine. You have the different directions in which you can move (plus no movement at all) as the states, and the key-events as transitions. This can usually be implemented quite well using the state pattern, but this is often quite painful in C++ (lots of boilerplate code), and might be over the top for your scenario.
There are of course other ways to represent speed and direction of your entity, e.g. as a 2D-vector (where the length gives the speed). This would enable you to easily represent arbitrary directions and velocities.