While I was messing with spritekit, I noticed that even the restitution is set to 1.0 (with linearDamping and friction both 0), if the node's velocity is small, it will not bounce. E.g. in the code below, I create an edge on the left, and have a ball hit the edge. I noticed that in the x direction, whenever the velocity is larger than 150, the ball will bounce; otherwise it'll just stick to the wall and stop moving.
So I am wondering, is there a way to change this threshold so that the ball can bounce even with a low speed? Thanks!
self.physicsWorld.gravity = CGVectorMake(0, 0);
SKNode *leftEdge = [[SKNode alloc] init];
leftEdge.physicsBody = [SKPhysicsBody bodyWithEdgeFromPoint:CGPointZero toPoint:CGPointMake(0.0, self.size.height)];
leftEdge.position = CGPointZero;
[self addChild:leftEdge];
SKShapeNode *ball = [SKShapeNode shapeNodeWithCircleOfRadius:30];
ball.position = CGPointMake(self.size.width * 0.3, self.size.height * 0.5);
ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:30];
ball.physicsBody.velocity = CGVectorMake(-150, 0.0);//not bounce
ball.physicsBody.restitution = 1.0;
ball.physicsBody.friction = 0.0;
ball.physicsBody.linearDamping = 0.0;
[self addChild:ball];
When two bodies collide both of their restitution and friction (as well as many other) properties are taken into account. So give the wall a restitution of 1 and a friction of 0 for an elastic collision.
Related
I have rectangle shape paddle node, my question is - is it possible to "cut" node in half so when, for example ball, hit right side of node ball will go back with bigger angle, that it came, and same thing on other side. Im bad with words so, here are image of what I want to do :
For paddle node i use this code:
paddle = [[SKSpriteNode alloc] initWithImageNamed: #"board.png"];
paddle.name = paddleCategoryName;
paddle.position = CGPointMake(self.frame.origin.x + 50, CGRectGetMidY(self.frame));
[self addChild:paddle];
paddle.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:paddle.frame.size];
paddle.physicsBody.restitution = 0.1f;
paddle.physicsBody.friction = 0.4f;
paddle.physicsBody.dynamic = NO;
and for ball :
ball = [SKSpriteNode spriteNodeWithImageNamed: #"ball.png"];
[self addChild:ball];
ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:ball.size.width];
ball.physicsBody.friction = 0.0f;
ball.physicsBody.restitution = 1.0f;
ball.physicsBody.linearDamping = 0.0f;
ball.physicsBody.allowsRotation = NO;
Im trying to make a node move using SKAction but whenever I add the node and move it, it begins to jitter up and down along the y axis like crazy!
Any ideas?
I've tried using MoveToY, MoveTo, etc.. and no luck not sure what is causing the jitter..
Thanks..
-(void)addEnemy{
enemy = [SKSpriteNode spriteNodeWithImageNamed:#"enemy"];
enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(40, 40)];
enemy.physicsBody.dynamic = YES;
enemy.physicsBody.usesPreciseCollisionDetection = YES;
enemy.physicsBody.categoryBitMask = enemyHitCatagory;
enemy.physicsBody.contactTestBitMask = bulletHitCatagory;
enemy.physicsBody.collisionBitMask = bulletHitCatagory;
enemy.position = CGPointMake(random() % 300, CGRectGetMaxY(self.frame));
enemy.size = CGSizeMake(40, 40);
enemy.zPosition = 5;
SKAction *attack = [SKAction moveTo:(CGPointMake(20, 300)) duration:(3)];
[enemy runAction:[SKAction repeatAction:attack count:1]];
[self addChild:enemy];
}
This is happening because the physics bodies are colliding. By default, an SKPhysicsBody has a restitution of 0.2, making it a little bouncy. Setting enemy.physicsBody.restitution = 0 and doing the same for the physics body your enemy is colliding with should resolve the jitter you're seeing.
I'm kind of new with SpriteKit and I'm having some troubles with the physics, I've tried many things to make a SKSpriteNode move with a force or an impulse but it never moves, only gravity affects it when i set it.
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
self.anchorPoint = CGPointMake(0.5, 0.5);
myWorld = [SKNode node];
[self addChild:myWorld];
SKSpriteNode* map = [SKSpriteNode spriteNodeWithImageNamed:#"grass"];
[myWorld addChild:map];
self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:map.frame];
self.physicsBody.friction = 0.0f;
self.physicsBody.categoryBitMask = 2;
self.physicsWorld.gravity = CGVectorMake(0.0, 0.0);
self.physicsWorld.contactDelegate = self;
pointOfView = [SKSpriteNode spriteNodeWithColor:[UIColor colorWithWhite:1 alpha:0.2] size:CGSizeMake(300, 548)];
[myWorld addChild:pointOfView];
pointOfView.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:pointOfView.frame.size];
pointOfView.physicsBody.friction = 0.0f;
pointOfView.physicsBody.restitution = 1.0f;
pointOfView.physicsBody.linearDamping = 0.0f;
pointOfView.physicsBody.allowsRotation = NO;
pointOfView.physicsBody.collisionBitMask = 2;
pointOfView.physicsBody.categoryBitMask = 3;
[pointOfView.physicsBody applyImpulse:CGVectorMake(10.0f, -10.0f)];
}
return self;
}
Here is most of my code in my main scene, there's nothing else except some empty methods like update or touchesBegan.. Am I missing something ? I've tried so many things, i'm starting to lose it haha
Thanks very much for any help !
It's a bit late, but the answer is here: Not able to apply impulse to SKSpriteNode physics body
The problem is that you've created a physics body with bodyWithEdgeLoopFromRect; this creates a static physics body which won't respond to applyImpulse. You need to add the physics body using bodyWithRectangleOfSize: instead.
pointOfView.physicsBody.dynamic = YES;
The dynamic property decides if a sprite should be affected by physics forces.
you have written wrong code your pointOfView not affected by gravity you are just applying a small impusle on it.
change this line self.physicsWorld.gravity = CGVectorMake(0.0, 0.0) to self.physicsWorld.gravity = CGVectorMake(0.0, -9.8); if u looking for negative gravity towards up direction and CGVectorMake(0.0, 9.8) if you looking for positive gravity towards downwards. and try to apply impulse after a interval [pointOfView.physicsBody applyImpulse:CGVectorMake(10.0f, -10.0f)];
I'm making a simple space shooter in Sprite Kit. I have asteroid rock sprites that are randomly added to my scene. I give them a random velocity within a certain range. However, once added to the scene their velocity decreases every second and eventually they stop. as they get closer to the bottom of the screen their velocity decreases at a slower rate. I have gravity of my physics world set to (0,0).
below is the method that adds the rocks to the scene
- (void)addRock {
SPRockNode *rock = [SPRockNode rock];
float dy = [SPUtil randomWithMin:SPRockMinSpeed max:SPRockMaxSpeed];
rock.physicsBody.velocity = CGVectorMake(0, -dy);
float y = self.frame.size.height + rock.size.height;
float x = [SPUtil randomWithMin:10 + rock.size.width max:self.frame.size.width - 10 - rock.size.width];
rock.position = CGPointMake(x, y);
[self addChild:rock];
}
I set up the physics world in my scenes initWIthSize method
self.physicsWorld.contactDelegate = self;
self.physicsWorld.gravity = CGVectorMake(0, 0);
below is the code for my rock node class
+ (instancetype)rock {
SPRockNode *rock = [self spriteNodeWithImageNamed:#"rock"];
rock.name = #"Rock";
float scale = [SPUtil randomWithMin:50 max:100] / 100.0f;
rock.xScale = scale;
rock.yScale = scale;
NSInteger randomInt = [SPUtil randomWithMin:1 max:3];
if (randomInt == 1) {
SKAction *oneRevolution = [SKAction rotateByAngle:-M_PI*2 duration: 1.0];
SKAction *repeat = [SKAction repeatActionForever:oneRevolution];
[rock runAction:repeat];
} else {
SKAction *oneRevolution = [SKAction rotateByAngle:M_PI*2 duration: 1.0];
SKAction *repeat = [SKAction repeatActionForever:oneRevolution];
[rock runAction:repeat];
}
[rock setupPhysicsBody];
return rock;
}
- (void)setupPhysicsBody {
self.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.frame.size];
self.physicsBody.affectedByGravity = NO;
self.physicsBody.categoryBitMask = SPCollisionCategoryRock;
self.physicsBody.collisionBitMask = 0;
self.physicsBody.contactTestBitMask = SPCollisionCategoryProjectile | SPCollisionCategoryShip;
}
any ideas on what causing them to slow down? I dont modify their velocity anywhere else but the addRock method. is there air resistance or something like that on by default? I just dont understand why their velocity is decreasing.
It sounds like you are having an issue with linear damping.
From SKPhysicsBody reference :
This property is used to simulate fluid or air friction forces on the body. The property must be a value between 0.0 and 1.0. The default value is 0.1. If the value is 0.0, no linear damping is applied to the object.
Try adding this :
rock.physicsBody.linearDamping = 0.0f;
It's worthwhile to give the SKPhysicsBody class reference a reading at least once. It only takes a short while, but can save you a ton of time if you have become acquainted with it's properties and methods.
If I apply an impulse of 1 in the y direction, the ball bounces back and forth without losing any energy. However, if the initial impulse is 0.5 or below, the ball loses all energy instantly when it hits the wall. Why is this happening? I have a pretty good understanding of the properties of the SKPhysicsBody class. Try this code to see if you get the same behavior on your computer.
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
/* Setup your scene here */
self.physicsWorld.gravity = CGVectorMake(0.0f, 0.0f);
SKPhysicsBody* borderBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
self.physicsBody = borderBody;
self.physicsBody.friction = 0.0f;
self.backgroundColor = [SKColor colorWithRed:0.7 green:0.7 blue:0.7 alpha:1.0];
SKShapeNode *ball = [SKShapeNode node];
CGMutablePathRef pathToDraw = CGPathCreateMutable();
[ball setStrokeColor:[UIColor blackColor]];
CGPathMoveToPoint(pathToDraw, NULL, 0, 0);
CGPathAddEllipseInRect(pathToDraw, NULL, CGRectMake(-16, -16, 32, 32));
ball.path = pathToDraw;
ball.position = CGPointMake(size.width / 2, size.height / 2);
ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:ball.frame.size.width/2];
ball.physicsBody.friction = 0.0f;
ball.physicsBody.restitution = 1.0f;
ball.physicsBody.linearDamping = 0.0f;
ball.physicsBody.allowsRotation = NO;
[self addChild:ball];
[ball.physicsBody applyImpulse:CGVectorMake(0, 0.5)];
}
return self;
}
When the collision velocity is small enough (such as your CGVector of (0, 0.5)), Box2d underlying the Sprite Kit physics engine will compute the collision as inelastic (i.e. as if the restitution was 0, removing any bounciness), and the node will not bounce.
This is, per the Box2d documentation, to prevent jitter.
In the Box2d source code, you even have this line:
/// A velocity threshold for elastic collisions. Any collision with a relative linear
/// velocity below this threshold will be treated as inelastic.
#define b2_velocityThreshold
Your impulse should be above this threshold for the restitution to be respected.