I am new to SpriteKit but not to iOS. I'm having a great deal of difficulty figuring out the conversions from UIKit coordinates to SKScene coordinates. In addition, their relations to the units used for the SpriteKit physics engine evades me.
Here's what I'm trying to do: I am launching a sprite with an initial velocity in both x and y directions. The sprite should start near the screen's bottom left corner (portrait mode) and leave near the bottom right corner. Another sprite should appear somewhere on the previous sprite's trajectory. This sprite is static.
The blue frame is the screen boundary, the black curve is the first sprite's trajectory and the red circle is the static sprite.
Now using the screen as 640 x 960. In my SKScene's didMoveToView: method I set the gravity as such:
self.physicsWorld.gravity = CGVectorMake(0.0f, -2.0f);
Then I make the necessary calculations for velocity and position:
"t" is time from left corner to right;
"y" is the maximum height of the trajectory;
"a" is the acceleration;
"vx" is velocity in the x direction;
"vy" is velocity in the y direction;
and
"Tstatic" is the time at which the dynamic sprite will be at the static sprite's position;
"Xstatic" is the static sprite's x-position;
"Ystatic" is the static sprite's y-position;
-(void)addSpritePair {
float vx, vy, t, Tstatic, a, Xstatic, Ystatic, y;
a = -2.0;
t = 5.0;
y = 800.0;
vx = 640.0/t;
vy = (y/t) - (1/8)*a*t;
Tstatic = 1.0;
Xstatic = vx*Tstatic;
Ystatic = vy*Tmark + 0.5*a*Tstatic*Tstatic;
[self spriteWithVel:CGVectorMake(vx, vy) andPoint:CGPointMake(xmark, ymark)];
}
-(void)spriteWithVel:(CGVector)velocity andPoint:(CGPoint)point{
SKSpriteNode *staticSprite = [SKSpriteNode spriteNodeWithImageNamed:#"ball1"];
staticSprite.anchorPoint = CGPointMake(.5, .5);
staticSprite.position = point;
staticSprite.name = #"markerNode";
staticSprite.zPosition = 1.0;
SKSpriteNode *dynamicSprite = [SKSpriteNode spriteNodeWithImageNamed:#"ball2"];
dynamicSprite.anchorPoint = CGPointMake(.5, .5);
dynamicSprite.position = CGPointMake(1 ,1);
dynamicSprite.zPosition = 2.0;
dynamicSprite.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:hoop.size.width/2];
dynamicSprite.physicsBody.allowsRotation = NO;
dynamicSprite.physicsBody.velocity = velocity;
dynamicSprite.physicsBody.affectedByGravity = YES;
dynamicSprite.physicsBody.dynamic = YES;
dynamicSprite.physicsBody.mass = 1.0f;
dynamicSprite.markerPoint = point;
dynamicSprite.physicsBody.restitution = 1.0f;
dynamicSprite.physicsBody.friction = 0.0f;
dynamicSprite.physicsBody.angularDamping = 0.0f;
dynamicSprite.physicsBody.linearDamping = 0.0f;
[self addChild:hoop];
[self addChild:marker];
}
When I execute the code, the following happens:
Can someone please help me out?
Related
I have to create a simulation in landscape which displays a sine function and a node which moves on the given path (the sine wave). So far I've created the sine wave with a simple sine wave with it's period (2*PI).
The question is how do I create the simulation of an infinite wave and the node moving up and down ?
My code so far is:
(CGMutablePathRef)sineWithAmplitude:(CGFloat)amp frequency:(CGFloat)freq
width:(CGFloat)width centered:(BOOL)centered
andNumPoints:(NSInteger)numPoints {
CGFloat offsetX = 0;
CGFloat offsetY = amp;
// Center the sinusoid within the shape node
if (centered) {
offsetX = -width/2.0;
offsetY = 0;
}
CGMutablePathRef path = CGPathCreateMutable();
// Move to the starting point
CGPathMoveToPoint(path, nil, offsetX, offsetY);
CGFloat xIncr = width / (numPoints-1);
// Construct the sinusoid
for (int i=1;i<numPoints;i++) {
CGFloat y = (amp * sin(2*M_PI*freq*i/(numPoints-1))*multiplier);
CGPathAddLineToPoint(path, nil, i*xIncr+offsetX, y+offsetY);
}
return path;
And the update method:
/* Called before each frame is rendered */
self.scaleMode = SKSceneScaleModeResizeFill;
// Create an SKShapeNode
SKShapeNode *node = [SKShapeNode node];
node.position = CGPointMake(x, y);
// Assign to the path attribute
node.path = [self sineWithAmplitude:20.0 frequency:frequency1 width:400.0 centered:YES andNumPoints:70];
//node.frame.size.height
node.strokeColor = [SKColor blackColor];
[self addChild:node];
x = x+400;
Until now I only display a wave, but the result should move right and look like the image.
The circle is the node that goes up and down while the wave simulates too. Any help will be greatly appreciated.
I'm working on a universal app.
I want to applyTorque to a Paddle
But the problem is the paddle sizes are bigger on a ipad than the one one iphone.
How can I calculate the torque to apply the same affect to the Paddle's physicalBody?
SKSpriteNode *bar = [SKSpriteNode spriteNodeWithImageNamed:nameImage];
bar.name = #"bar";
bar.size = CGSizeMake(PaddleWidth, PaddleHeight);
bar.physicsBody =[SKPhysicsBody bodyWithTexture:bar.texture size:bar.size];
bar.physicsBody.restitution = 0.2;
bar.physicsBody.angularDamping = 0;
bar.physicsBody.friction = 0.02;
bar.physicsBody.mass=.2;
[paddle addChild:bar];
SKSpriteNode *anchor = [SKSpriteNode spriteNodeWithColor:[SKColor clearColor] size:CGSizeMake(PaddleWidth, PaddleHeight)];
anchor.name = #"anchor";
anchor.size = CGSizeMake(PaddleHeight, PaddleHeight);
anchor.position = CGPointMake(bar.position.x + bar.size.width/2, 0);
[paddle addChild:anchor];
CGFloat anchorRadius = anchor.size.width/20;
anchor.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:anchorRadius];
anchor.physicsBody.dynamic = NO;
CGPoint positionInScene = [self convertPoint:anchor.position toNode:self.scene];
pin = [SKPhysicsJointPin jointWithBodyA:bar.physicsBody
bodyB:anchor.physicsBody
anchor:positionInScene];
pin.shouldEnableLimits = YES;
pin.lowerAngleLimit = -0.5;
pin.upperAngleLimit = 0.5;
[self.scene.physicsWorld addJoint:pin];
-(void)flip{
SKNode *bar=[self childNodeWithName:#"bar"];
CGFloat torque;
torque=10;
[bar.physicsBody applyTorque:torque];
}
You can use the size of the paddle as a factor in the torque value:
CGSize paddleSize = <Initialize with paddle size>
CGFloat torque=paddleSize.width * factor; // factor will be the value you need to multiply in order to reach your desired value
So if for example paddle width is 100 use a constant factor of 0.05
On the iPad the different paddle width will make the torque value to be calculated accordingly using the same factor value as above.
You can set a constant mass of the physicsBody so that the torque applied affects the paddle the same way regardless of the node's size.
//While instantiating the physicsBody for the "bar" node
bar.physicsBody.mass = 0.2; //This will need to be adjusted according to your needs.
From the documentation:
The mass of the body affects its momentum as well as how forces are
applied to the object.
Problem
Scaling up a 2D image, scales up from the image centre point, however. I need it to scale up from a specific co-ordinate?
[backgroundImage setScale:rifleZoom];
My current technique to scaling up the image.
I need to scale up from centre screen as opposed to centre image
Now my way to place a rifle shot on the screen # centre is this way:
CGPoint positionNow = CGPointMake(backgroundImage.position.x, backgroundImage.position.y);
CGPoint positionPrev = CGPointMake(0.5, 0.5);
float xdiff = positionNow.x - positionPrev.x;
float ydiff = positionNow.y - positionPrev.y;
CGPoint newPositionOne = CGPointMake(0.5- xdiff, 0.5 - ydiff);
newPositionOne = CGPointMake(newPositionOne.x/rifleZoom, newPositionOne.y/rifleZoom);
Now this works perfectly no matter how much the image is scaled, however. I cannot seem to implement it into scaling the image up from the centre of the screen opposed to centre of the image.
What I've Tried
I've tried to change the position of the image before scaling it up. To the same same point make as newPositionOne However, this does not work or not being done right.
EDIT
This scales and brings centre to screen centrepoint, or messes up completely. It's a little too off the cuff to make a decision exactly what it's doing.
CGPoint positionNow = CGPointMake(backgroundImage.position.x, backgroundImage.position.y);
CGPoint positionPrev = CGPointMake(0.5, 0.5);
float xdiff = positionNow.x - positionPrev.x;
float ydiff = positionNow.y - positionPrev.y;
CGPoint newPositionOne = CGPointMake(0.5- xdiff, 0.5 - ydiff);
newPositionOne = CGPointMake(newPositionOne.x/rifleZoom, newPositionOne.y/rifleZoom);
double xPosition = newPositionOne.x / backgroundImage.size.width;
double yPosition = newPositionOne.y / backgroundImage.size.height;
CGPoint prevAnchorPoint = backgroundImage.anchorPoint;
backgroundImage.anchorPoint = CGPointMake(xPosition,yPosition);
double positionX = backgroundImage.position.x + (backgroundImage.anchorPoint.x - prevAnchorPoint.x) * backgroundImage.size.width;
double positionY = backgroundImage.position.y + (backgroundImage.anchorPoint.y - prevAnchorPoint.y) * backgroundImage.size.height;
backgroundImage.position = CGPointMake(positionX,positionY);
[backgroundImage runAction:[SKAction repeatAction:[SKAction scaleTo:rifleZoom duration:1.0] count:1]];
You can use the anchor point property of the background node to change the point from which image scales. By default the anchorPoint is at (0.5,0.5). This indicates the center of the node. If you make the anchorPoint (0,0), then its moved to the bottom left corner.
anchorPoint : Defines the point in the sprite that corresponds to the
node’s position. You specify the value for this property in the unit
coordinate space. The default value is (0.5,0.5), which means that the
sprite is centered on its position.
When you shift the anchorPoint, you have to adjust the background position again to counteract the movement due to changing the anchorPoint.
So you can use,
CGPoint xPosition = convertedPoint.x / background.size.width
CGPoint yPosition = convertedPoint.y / background.size.height
CGPoint prevAnchorPoint = background.anchorPoint
background.anchorPoint = CGPointMake(xPosition,yPosition)
CGFloat positionX = background.position.x + (background.anchorPoint.x - prevAnchorPoint.x) * background.size.width
CGFloat positionY = background.position.y + (background.anchorPoint.y - prevAnchorPoint.y) * background.size.height
background.position = CGPointMake(positionX,positionY)
I'm building a game using spriteKit.
I created a spriteNode called 'planet' and set a velocity. It drops down from the top of the screen with constant speed to the bottom of the screen. However, it slows down towards the middle of the screen and stops moving entirely. I added the method 'moveTowardPosition' as an attempt to fix this issue by forcing the objects to move offscreen. Does anyone have an idea of what the issue might be?
Thanks!
Here is the setup of the object:
-(void)physicsBodySetup
{
//initializes the physicsBody
self.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:40];
self.physicsBody.affectedByGravity = NO;
//sets its category mask
self.physicsBody.categoryBitMask = TKCollisionCategoryPlanet;
//planet doesn't collide with anything
self.physicsBody.collisionBitMask = 0;
//the planet can get into contact with an astranaut
self.physicsBody.contactTestBitMask = TKCollisionCategoryAstronaut |
}
//adds 'planet' to the screen at random position
//#param frame: the frame of the main view
-(void)addPosition:(CGRect)frame
{
//specifies a random position to add the planet on the screen
float randomPositionY = frame.size.height + self.size.height;
float randomPositionX = [TKUtil randomWithMin:10+self.size.width max:frame.size.width-10 - self.frame.size.width];
self.position = CGPointMake(randomPositionX, randomPositionY);
[self velocitySetup];
}
-(void)velocitySetup
{
//initializes the speed to be a constant
self.planetSpeed = TKPlanetSpeed;
self.physicsBody.velocity = CGVectorMake(0, self.planetSpeed);
}
//#param position: the point of planet on the screen
-(void)moveTowardsPosition:(CGPoint)position
{
float offScreenX = position.x;
float offScreenY = position.y - 2000;
CGPoint pointOffScreen = CGPointMake(offScreenX, offScreenY);
float Distance = pointOffScreen.y - position.y;
float time = Distance / self.planetSpeed;
SKAction *movePlanet = [SKAction moveTo:pointOffScreen duration:time];
NSArray *sequence = #[movePlanet, [SKAction removeFromParent]];
[self runAction:[SKAction sequence:sequence]];
}
The default value of friction is 0.2. So you can try:
self.physicsBody.friction = 0.0
now it won't be affected by surface anymore.
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.