So in my game I have Cocos2D + Box2D integrated. I know it is not recommended but I have my b2Bodys follow my CCSprites because I only need the collision part of Box2D. Anyway, using PhysicsEditor, I have created the most efficient body shapes I can and my game normally runs fine at 60FPS. My only issue is that, I want to prepare for the worst here. Lets say just under a really rare occurrence (like 1 in 10,000) the game lags for 5 seconds so that the FPS is around 10FPS. This would cause my main character to not collide with the platform under it. And in turn, it would make the character fall through the platform and the game would end unintentionally. So overall I just want to have a fallback plan when this happens.
So this is how I call the Box2D step:
world->Step(1/60.0f ,8, 8);
Then in my update method I do this to detect the collisions:
std::vector<b2Body *>toDestroy;
std::vector<MyContact>::iterator pos;
for(pos = _contactListener->_contacts.begin();
pos != _contactListener->_contacts.end(); ++pos) {
MyContact contact = *pos;
b2Body *bodyA = contact.fixtureA->GetBody();
b2Body *bodyB = contact.fixtureB->GetBody();
if (bodyA->GetUserData() != NULL && bodyB->GetUserData() != NULL) {
CCSprite *spriteA = (CCSprite *) bodyA->GetUserData();
CCSprite *spriteB = (CCSprite *) bodyB->GetUserData();
if (spriteA.tag == 1 && spriteB.tag == 2) {
toDestroy.push_back(bodyA);
} else if (spriteA.tag == 2 && spriteB.tag == 1) {
toDestroy.push_back(bodyB);
}
}
}
So how would I adjust what I am doing now to deal with the possible scenario I explained above? Thanks!
You will not be having this problem because your Box2D step interval is fixed. Your simulation will simply slow down when the framerate decreases.
It might occur if the timestep were multiplied by the frame's delta time. But even then you ought to first verify that you'll be having these problems by forcing the game to run at 10 fps before making any code changes.
Box2D have the option to define objects as bullets. This is to handle that fast moving objects don't pass through solid objects.
The syntax is something like this:
bodyDef.bullet = true;
This makes Box2D do a sweep from the old to the new position, and would catch those obstacle that you did not hit due to low frame rates.
Related
I'm using a SpriteKit game engine within XCode while developing a game that bounces a ball and platforms come from the sky and the objective is to bounce on the platforms to get higher. I need to add a velocity to the ball when it falls down + comes in contact with a platform. I'm having trouble trying to detect the balls Y position. I had something like this in the update method but nothing happens... I'm open to suggestions.
//The value of the _number instance variable is the Y position of the ball.
if (_number++) {
NSLog(#"UP");
}
if (_number--) {
NSLog(#"DOWN");
}
You can see a node's position by using code like this:
if(myNode.position.y > 0)
NSLog(#"y is greater than 0");
If you want to check a node's current speed (vector) you can do it like this:
if(myNode.physicsBody.velocity.dy > 0)
NSLog(#"Moving up");
if(myNode.physicsBody.velocity.dy < 0)
NSLog(#"Moving down");
Remember that position and speed (vector) are not the same thing.
You need to read the SKPhysicsBody docs to understand about CGVector and other important issues.
Alright, this:
if (_number++) {
NSLog(#"UP");
}
if (_number--) {
NSLog(#"DOWN");
}
doesn't work to do anything. It shouldn't even run. I don't why it doesn't give an error.
number++; is a simplified form of
number = number + 1;
You can't place it in an if statement.
First make the variable #property int ypos in your header.
Then every update compare the current y to the ypos.
After comparing, save the current y to ypos.
Place this in your Update method.
if (ball.position.y > _ypos)
{
//going up
}
else if (ball.position.y < _ypos)
{
//going down
}
_ypos = ball.position.y;
P.S. I haven't had access to a computer so the formatting might suck from my phone
I am using cocos2dx and setup two Sprites with same Physics Body definitions see below
PhysicsBody *physicsBody=PhysicsBody::createBox(size,PhysicsMaterial(1.0f,0.0,0.5f),Vec2(0, size.height*0.5));
physicsBody->setGravityEnable(true);
physicsBody->setCategoryBitmask(1);
physicsBody->setCollisionBitmask(1);
physicsBody->setContactTestBitmask(true);
physicsBody->setDynamic(true);
physicsBody->setContactTestBitmask(0xFFFFFFFF);
physicsBody->setMass(5.0f);
node->setPhysicsBody(physicsBody);
I am defining a collision detection between both the physics bodies
auto contactListener=EventListenerPhysicsContactWithBodies::create(player1->getPhysicsBody(), player2->getPhysicsBody());
contactListener->onContactBegin = CC_CALLBACK_1(Game::onPlayerContact, this);
_eventDispatcher->addEventListenerWithSceneGraphPriority(contactListener, this);
I don't want these two bodies to collide with each other or, any effect of physics if they collide. I am doing
bool Game::onPlayerContact(cocos2d::PhysicsContact &contact){
auto nodeA = contact.getShapeA()->getBody()->getNode();
auto nodeB = contact.getShapeB()->getBody()->getNode();
if(nodeA != NULL && nodeB != NULL){
printf("\nPlayers collided");
}
return false;
}
I am not able to bypass the contact between two bodies, what else should be done to avoid collision?
Please Help.
Thanks.
Collision filtering allows you to prevent collision between shapes. Cocos2d-x supports collision filtering using category and groups bitmasks.
Cocos2d-x supports 32 collision categories. For each shape you can specify which category it belongs to. You also specify what other categories this shape can collide with. This is done with masking bits. For example:
auto sprite1 = addSpriteAtPosition(Vec2(s_centre.x - 150,s_centre.y));
sprite1->getPhysicsBody()->setCategoryBitmask(0x02); // 0010
sprite1->getPhysicsBody()->setCollisionBitmask(0x01); // 0001
auto sprite3 = addSpriteAtPosition(Vec2(s_centre.x + 150,s_centre.y + 100),2);
sprite3->getPhysicsBody()->setCategoryBitmask(0x03); // 0011
sprite3->getPhysicsBody()->setCollisionBitmask(0x03); // 0011
then in your collision callback. Do this.
if ((shapeA->getCategoryBitmask() & shapeB->getCollisionBitmask()) == 0
|| (shapeB->getCategoryBitmask() & shapeA->getCollisionBitmask()) == 0)
{
// shapes can't collide
ret = false;
}
source : http://www.cocos2d-x.org/wiki/Physics
You may want to check the Queries Under the Physics
http://www.cocos2d-x.org/wiki/Physics
Perhaps the Point Query..
Basically the Box2d has sensors which are used to detect contact and not any collision...
i recommend using Box2d over Cocos2d Physics...It is much Better..
The only way I can think to do it is to check velocities for all physics bodies during every collisions.
- (BOOL)ccPhysicsCollisionBegin:(CCPhysicsCollisionPair *)pair piece:(CCNode *)pieceA piece:(CCNode *)pieceB{
float x = 0;
float y = 0;
for (int i = 0; i < [[_physicsWorld children] count]; i++) {
x = x + [[[_physicsWorld children][i] physicsBody] velocity].x;
y = y + [[[_physicsWorld children][i] physicsBody] velocity].y;
}
if ( x == 0 && y == 0 ) {
NSLog(#"stopped");
}
return YES;
}
This logs “stopped” multiple times when the scene first loads, then doesn’t log “stopped” again, even after physics bodies have clearly started moving and colliding and then come to a stop.
Ideally I'd like a delegate method that would notify me when all physics bodies have stopped moving, but I can't seem to find one.
FYI: I'm using the standard Chipmunk physics engine that's baked into Cocos2d V3.0
Chipmunk has a internal mechanism, which can, if activated, automatically deactivate physics bodies. My approach (I am using cocos2dx 3.11.1 and not -obj version with chipmunk 7.0.1) is:
activate the chipmunk idle mechanism (0.5 second - meaning, if an object is not moving for longer than 0.5 second it will be deactivated):
cpSpaceSetSleepTimeThreshold(space, 0.5f);
You do not need to use
cpSpaceSetIdleSpeedThreshold(space, <speed>);
because chipmunk calculates the threshold speed for you (according the gravitation used).
use this code for determination if all objects are not moving (static and kinetic bodies never sleep):
bool isAnyPhysicsBodyMoving(){
int i = 0; bool isMoving = false;
const Vector<PhysicsBody*>& bodies = getPhysicsWorld()->getAllBodies();
while( i < bodies.size() && !isMoving){
PhysicsBody *body = bodies.at(i);
isMoving = cpBodyGetType(body->getCPBody()) == CP_BODY_TYPE_DYNAMIC
&& !body->isResting();
i++;
}
return isMoving;
}
use static (and not kinetic) body for walls, in order to let objects sleep:
// wall
Size visibleSize = Director::getInstance()->getWinSize();
Vec2 origin = Director::getInstance()->getVisibleOrigin();
float border = 10.0f;
Size wallBodySize = Size(visibleSize.width+2*border, visibleSize.height+2*border);
PhysicsBody *wallBody = PhysicsBody::createEdgeBox(wallBodySize, PhysicsMaterial(1.0f, 1.0f, 0.5f), border);
Node* wall = Node::create();
wall->addComponent(wallBody);
wall->setAnchorPoint(Vec2(0.5f, 0.5f));
wall->setPosition(Point(visibleSize.width/2+origin.x, visibleSize.height/2+origin.y));
cpVect tt;
tt.x = wall->getPosition().x; tt.y = wall->getPosition().y;
//set position manually and BEFORE adding the object into the space
cpBodySetPosition(wallBody->getCPBody(), tt);
cpBodySetType(wallBody->getCPBody(), CP_BODY_TYPE_STATIC);
addChild(wall);
Any dynamic body connected to a kinetic body (for example laying on) will never sleep.
test it with DEBUG activated
getPhysicsWorld()->setDebugDrawMask(PhysicsWorld::DEBUGDRAW_ALL);
the boxes (their content) must become grey (=sleeping) and not red (=active):
In order to let it work, I have:
added an access method (to get cpSpace) in CCPhysicsWorld.h:
inline cpSpace* getSpace() const { return _cpSpace; }
Fix call of
cpBodySetTorque(body, 0.0f);`
in CCPhysicsBody.cpp to
if (body->t != 0.0f){
cpBodySetTorque(body, 0.0f);
}
Fix call of
cpBodySetPosition(_cpBody, tt);`
in CCPhysicsBody.cpp to
if (!cpveql(tt, cpBodyGetPosition(_cpBody))){
cpBodySetPosition(_cpBody, tt);
}
Steps 2. and 3. are necessary to avoid setting of the same physics body properties, which wake up a sleeping body.
The advantage of this approach is, that the chipmunk does not make any calculations for such physical bodies - saving CPU and battery.
I found something that works.
tl;dr
The basic idea is to keep track of the positions of the sprites myself, and then periodically check them to see if any of them have moved since they were last checked.
Longer version
I created a subclass of CCNode with the class name Piece.
These are my objects that are added to the physics world.
#implementation Piece {
float _previousX;
float _previousY;
}
-(void)updatePreviousScreenXandY{
_previousX = self.position.x;
_previousY = self.position.y;
}
-(BOOL)hasntMoved{
float currentX = self.position.x;
float currentY = self.position.y;
if ( currentX == _previousX && currentY == _previousY ) {
return TRUE;
}else{
return FALSE;
}
}
This is in my CCNode that acts as the game scene
-(void)doStuffAfterPiecesStopMoving:(NSTimer*)timer{
BOOL noPiecesHaveMoved = TRUE;
for (int i = 0; i < [[_physicsWorld children] count]; i++) {
if ( [[_physicsWorld children][i] hasntMoved] == FALSE ) {
noPiecesHaveMoved = FALSE;
break;
}
}
if ( noPiecesHaveMoved ) {
[timer invalidate];
NSLog(“Pieces have stopped moving”);
}else{
NSLog(“Pieces are still moving”);
[self updateAllPreviousPiecePositions];
}
}
-(void)updateAllPreviousPiecePositions{
for (int i=0; i < [[_physicsWorld children] count]; i++) {
Piece *piece = (Piece*)[_physicsWorld children][i];
[piece updatePreviousScreenXandY];
}
}
All I have to do is
[NSTimer scheduledTimerWithTimeInterval:TIME_BETWEEN_CHECKS
target:_gamePlay
selector:#selector(doStuffAfterPiecesStopMoving:)
userInfo:nil
repeats:YES];
and it’ll run whatever code I want after all Piece nodes have stopped moving.
The key to getting it to work well is to get the values for the Chipmunk space’s sleepTimeThreshold and the timer above’s time as low as possible.
My experimenting suggests the following settings work okay, but anything lower will cause problems (i.e. collisions not taking place properly):
sleepTimeThreshold = 0.15
my timer = 0.05
If anyone has a different/better solution or improvements to the above code, please post.
I'm writing a 2D ball game with sprite kit on iOS 7 and currently struggling on one physic simulation.
To explain the expected behavior: if a ball is dropped into a tea cup, it will circle around, loosing speed and finally stand still in the center of the cup.
I've tried to archive this with gravity, but gravity in sprite kit only applies to vertical X and Y axis, not Z-axis. I also tried to use level gravity by switching gravity values with small physic bodies on beginContact depending on the current ball position in the tea cup. But some contacts are dropped and the result is far away to look realistic.
I think I need to solve this in the update: method, but I have no idea which way to go.
Any advice greatly welcome and I need to mention that I'm not an expert on math, please explain your path to go. :-)
Since there's no built-in support for this kind of behavior in SpriteKit, rather than trying to hack existing functions to get what you want, you're probably better off integrating some published 2D physics formulas in your x,y 2D world. I would think that something like simulating magnetic or a homing behavior might be right for this.
A simple example would be something like (in the scene's -update: method):
CGFloat strength = 0.5; //(some scaling value)
CGPoint ballLocation = ball.position;
CGPoint cupLocation = cup.position;
[ball.physicsBody applyForce:CGVectorMake((cupLocation.x - ballLocation.x) * strength,
(cupLocation.y - ballLocation.y) * strength)];
following Joshd great idea, I have created an NSArray with like explained in my comment above. Hope this snippets does help some others...
The result could be found on youtube: http://youtu.be/Uephg94UH30
Sorry for the bad Airplay frame rate, it runs perfectly smooth on my iPad
The -update: functions does the work but only triggered if _meditationIsActive. This bool is set in -didBeginContact: when any ball gets in contact with a hole.
if (_lastCheck > 0.005)
{
if (_meditationIsActive)
{
CGFloat strength = 0.1; //(some scaling value)
CGPoint ballLocation;
CGPoint holeLocation;
for (MeditationHole * holeObj in _meditationHoles)
{
if (holeObj.connectedMeditationBall != nil)
{
ballLocation = holeObj.connectedMeditationBall.position;
holeLocation = holeObj.position;
[holeObj.connectedMeditationBall.physicsBody applyForce:CGVectorMake(
(holeLocation.x - ballLocation.x) * strength, (holeLocation.y - ballLocation.y) * strength)];
}
}
_meditationIsActive = [self doesMeditationApplies];
}
_lastCheck = 0;
}
At the end I'm checking if there is a valid ball out of the array in contact with a hole to avoid checking during every update. This is done with the following function where position check +/- 48 detects a ball close to a hole and +/-1 ball stands still
- (bool)doesMeditationApplies
{
bool isInArea = NO;
int perfectMatchCount = 0;
for (MeditationHole * holeObj in _meditationHoles)
{
if (holeObj)
{
if (holeObj.connectedMeditationBall != nil)
{
MeditationBall * ballObj = holeObj.connectedMeditationBall;
if ((ballObj.position.x >= holeObj.position.x - 48) &&
(ballObj.position.x <= holeObj.position.x + 48) &&
(ballObj.position.y >= holeObj.position.y - 48) &&
(ballObj.position.y <= holeObj.position.y + 48))
{
isInArea = YES;
}
else
{
holeObj.connectedMeditationBall = nil;
}
if ((ballObj.position.x >= holeObj.position.x - 1) &&
(ballObj.position.x <= holeObj.position.x + 1) &&
(ballObj.position.y >= holeObj.position.y - 1) &&
(ballObj.position.y <= holeObj.position.y + 1))
{
perfectMatchCount++;
isInArea = YES;
}
}
}
}
if (perfectMatchCount == _oxydStonesMax)
{
if (_sound)
{
self.pauseMusicPlaybackBlock(YES);
NSLog(#"PlaySound Meditation");
[OxydScene PlaySystemSound:#"Win2"];
}
isInArea = NO;
[self showPauseScreenWithWin:YES andPauseOnly:NO];
}
return isInArea;
}
I'm currently trying to make a basic platformer with XNA and I'm wondering how to create a "jumping effect." I currently have basic keyboard input which allows for sideways movement, but I would like my sprite to slowly progress into a jump rather than instantly teleporting there (right now I have something like Rectangle.Y += 40 every time I jump, making the sprite instantly appear there). Does anyone have any insight?
I'm not totally across how to implement this in XNA/C#, but in Flash games I've made I just added a vertical velocity property. I'll try write everything as C# as I can..
Example; create the velocity property:
float verticalVelocity = 0;
Vertical velocity should be constantly reduced (by gravity). Set up a gravity property somewhere accessible from your player:
float Gravity = 2.5;
And in your update() method for the player, increment the verticalVelocity by Gravity. Also increment the Y position of your player by the verticalVelocity. This will simulate falling:
verticalVelocity += Gravity;
Position.Y += verticalVelocity; // this may be -= in XNA, not sure where the y axis beings
When you hit a surface, the velocity should be reset to 0.
And finally, to jump, simply subtract a given value from verticalVelocity:
public void Jump(float height)
{
// Only jump if standing on a surface.
if(verticalVelocity == 0)
verticalVelocity -= height;
}
You'll eventually want to add gravity and possibly other forces to your game, so I highly recommend you save yourself a lot of pain and implement some kind of basic force system. This can be done using Vector2s, as you can just add them to the speed of your character. Then just apply an instantaneous force to your character to push it up.
If you really don't want to use a physics engine, you can make a Vector2 with the high point of the jump for the Y and the characters X, and then use the Vector2.Lerp method to interpolate between the characters position and the end point of the jump.
This is generally a very bad system to use, and I highly recommend you either use an existing physics engine, or make your own simple one.
use a sinusoidcode should look something like this:
float ground = 0.0f;
float angle = 330.0f;
jump(){
if(ground == 0.0f)ground = Rectangle.Y;
if(Rectangle.Y <= ground)
{
Rectangle.Y+=Math.Sin(angle/(Math.Pi*180));
angle++;
}
}
You can accurately create a gravity effect if you modify the ySpeed dynamically, as opposed to just adding 40.
You want to declare a ySpeed
ySpeed = 0;
Then you want to use an acceleration variable
acceleration = 0.25;
Okay, now that we've done that, let's add gravity, provided that our player isn't touching the floor.
if(playerLocationY + playerHeight > floorLocationY)
{
gravity = false;
}
else
{
gravity = true;
}
if(gravity)
{
ySpeed += acceleration;
}
Now that we've got that down, we want to include something that allows us to jump.
if(KeyPressed == UP)
{
ySpeed -= acceleration;
}
This will move our player in the upward direction
We now want to make sure we actually move, so let's add one last line and we're done.
playerLocationY += ySpeed;
Congratulations, you made it.