Using SKPhysicsBody to create a vehicle - macos

Question

I am trying to make a vehicle (in this case a train) move based on player input. If I move the train via an SKAction, the wheels do not rotate. I could use the applyForce method on its physics body, but it I need more control. I need to make it move a certain distance over a certain amount of time. How can this be accomplished?
-(void)didMoveToView:(SKView *)view {
SKTexture *trainBodyTexture = [SKTexture textureWithImageNamed:#"levelselect_trainbody"];
SKSpriteNode *trainBody = [[SKSpriteNode alloc] initWithTexture:trainBodyTexture];
trainBody.zPosition = 0;
trainBody.position = CGPointMake(300, 500);
trainBody.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:trainBody.size];
[self addChild:trainBody];
SKTexture *trainWheelTexture = [SKTexture textureWithImageNamed:#"levelselect_trainwheel"];
SKSpriteNode *trainWheel1 = [[SKSpriteNode alloc] initWithTexture:trainWheelTexture];
trainWheel1.zPosition = 1;
trainWheel1.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:trainWheel1.size.width/2];
trainWheel1.physicsBody.allowsRotation = YES;
trainWheel1.position = CGPointMake(220, 400);
[self addChild:trainWheel1];
SKSpriteNode *trainWheel2 = [[SKSpriteNode alloc] initWithTexture:trainWheelTexture];
trainWheel2.zPosition = 1;
trainWheel2.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:trainWheel2.size.width/2];
trainWheel2.physicsBody.allowsRotation = YES;
trainWheel2.position = CGPointMake(380, 400);
[self addChild:trainWheel2];
SKShapeNode *dot = [SKShapeNode shapeNodeWithCircleOfRadius:10];
dot.zPosition = 2;
dot.fillColor = [NSColor redColor];
dot.position = CGPointMake(0, -20);
[trainWheel1 addChild:dot];
SKPhysicsJointPin *pin = [SKPhysicsJointPin jointWithBodyA:trainBody.physicsBody bodyB:trainWheel1.physicsBody anchor:trainWheel1.position];
SKPhysicsJointPin *pin2 = [SKPhysicsJointPin jointWithBodyA:trainBody.physicsBody bodyB:trainWheel2.physicsBody anchor:trainWheel2.position];
[self.scene.physicsWorld addJoint:pin];
[self.scene.physicsWorld addJoint:pin2];
//[trainWheel1 runAction:[SKAction moveByX:300 y:0 duration:3]];
[trainBody.physicsBody applyForce:CGVectorMake(3000, 0)];
}
UPDATE: Implemented With A Train Class (suggested by Jaffer Sheriff)
Train.h
#import <SpriteKit/SpriteKit.h>
#interface Train : SKSpriteNode
-(void) createPhysics;
-(void) moveLeft;
-(void) moveRight;
#end
Train.m
#import "Train.h"
#interface Train()
#property SKSpriteNode *trainBody, *trainWheelFront, *trainWheelRear;
#property SKPhysicsWorld *physicsWorld;
#end
#implementation Train
-(instancetype) init {
if (self = [super init]) {
[self initTrainBody];
[self initWheels];
}
return self;
}
-(void) initTrainBody {
SKTexture *trainBodyTexture = [SKTexture textureWithImageNamed:#"levelselect_trainbody"];
_trainBody = [[SKSpriteNode alloc] initWithTexture:trainBodyTexture];
_trainBody.zPosition = 0;
_trainBody.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:_trainBody.size];
[self addChild:_trainBody];
}
-(void) initWheels {
SKTexture *_trainWheelTexture = [SKTexture textureWithImageNamed:#"levelselect_trainwheel"];
_trainWheelFront = [[SKSpriteNode alloc] initWithTexture:_trainWheelTexture];
_trainWheelFront.zPosition = 1;
_trainWheelFront.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:_trainWheelFront.size.width/2];
_trainWheelFront.physicsBody.allowsRotation = YES;
_trainWheelFront.position = CGPointMake(-80, -82);
[self addChild:_trainWheelFront];
_trainWheelRear = [[SKSpriteNode alloc] initWithTexture:_trainWheelTexture];
_trainWheelRear.zPosition = 1;
_trainWheelRear.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:_trainWheelRear.size.width/2];
_trainWheelRear.physicsBody.allowsRotation = YES;
_trainWheelRear.position = CGPointMake(80, -82);
[self addChild:_trainWheelRear];
//dot used to see if wheels are rotating, no other point
SKShapeNode *dot = [SKShapeNode shapeNodeWithCircleOfRadius:10];
dot.zPosition = 2;
dot.fillColor = [NSColor redColor];
dot.position = CGPointMake(0, -20);
[_trainWheelFront addChild:dot];
}
//this method is called after the train node is added to the scene in GameScene otherwise will get error adding joints before node is in scene
-(void) createPhysics {
SKPhysicsJointPin *pin = [SKPhysicsJointPin jointWithBodyA:_trainBody.physicsBody bodyB:_trainWheelFront.physicsBody anchor:_trainWheelFront.position];
SKPhysicsJointPin *pin2 = [SKPhysicsJointPin jointWithBodyA:_trainBody.physicsBody bodyB:_trainWheelRear.physicsBody anchor:_trainWheelRear.position];
[self.scene.physicsWorld addJoint:pin];
[self.scene.physicsWorld addJoint:pin2];
}
-(void) moveLeft {
SKAction *rotateLeft = [SKAction rotateByAngle:6*M_PI duration:0.2];
[_trainWheelFront runAction:rotateLeft];
[_trainWheelRear runAction:rotateLeft];
}
-(void) moveRight {
SKAction *rotateRight = [SKAction rotateByAngle:-6*M_PI duration:0.2];
[_trainWheelFront runAction:rotateRight];
[_trainWheelRear runAction:rotateRight];
}
#end
GameScene.m
#import "GameScene.h"
#import "Train.h"
#interface GameScene()
#property Train *train;
#end
#implementation GameScene
-(void)didMoveToView:(SKView *)view {
[self initTrain];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyPressed:) name:#"KeyPressedNotificationKey" object:nil]; //using notifications and custom view class to handle key presses
}
-(void) initTrain {
_train = [[Train alloc] init];
_train.position = CGPointMake(500, 300);
[self addChild:_train];
[_train createPhysics];
}
-(void)update:(CFTimeInterval)currentTime {
/* Called before each frame is rendered */
}
-(void) keyPressed:(NSNotification*)notification {
NSNumber *keyCodeObject = notification.userInfo[#"keyCode"];
NSInteger keyCode = keyCodeObject.integerValue;
NSLog(#"keycode = %lu", keyCode);
switch (keyCode) {
case 123:
[self leftArrowPressed];
break;
case 124:
[self rightArrowPressed];
break;
}
}
-(void) leftArrowPressed {
SKAction *moveLeft = [SKAction moveByX:-200 y:0 duration:0.2];
[_train runAction:moveLeft];
[_train moveLeft];
}
-(void) rightArrowPressed {
SKAction *moveRight = [SKAction moveByX:200 y:0 duration:0.2];
[_train runAction:moveRight];
[_train moveRight];
}
#end
Note: This solution causes the entire train to flip and freak out when the left/right keys are pressed. It seems like my pin joints are incorrect, but they seem correct to me :/

Answer 1

Default Initializer of SkSpriteNode is - (instancetype)initWithTexture:(SKTexture *)texture color:(SKColor *)color size:(CGSize)size; Try this,
#interface Train : SKSpriteNode
- (instancetype)initTrainWithColor:(UIColor *) color andSize:(CGSize) size;
-(void) animateWheelsWithTime:(float) time;
#end
#interface Train ()
{
SKSpriteNode *wheel1;
SKSpriteNode *wheel2;
NSMutableArray *wheelsArray;
}
#end
#implementation Train
- (instancetype)initTrainWithColor:(UIColor *) color andSize:(CGSize) size
{
self = [super initWithTexture:nil color:color size:size];
if (self)
{
[self addWheels];
}
return self;
}
-(void)addWheels
{
wheelsArray = [[NSMutableArray alloc]init];
wheel1 = [SKSpriteNode spriteNodeWithImageNamed:#"wheel"];
[wheel1 setPosition:CGPointMake(-(self.frame.size.width/2.0f-wheel1.frame.size.width/2.0f), - (self.frame.size.height/2.0f - wheel1.frame.size.height/2.0f))];
[self addChild:wheel1];
wheel2 = [SKSpriteNode spriteNodeWithImageNamed:#"wheel"];
[wheel2 setPosition:CGPointMake((self.frame.size.width/2.0f-wheel2.frame.size.width/2.0f), - (self.frame.size.height/2.0f - wheel2.frame.size.height/2.0f))];
[self addChild:wheel2];
[wheelsArray addObject:wheel1];
[wheelsArray addObject:wheel2];
}
-(void) animateWheelsWithTime:(float) time
{
for (SKSpriteNode *wheel in wheelsArray)
{
SKAction *act = [SKAction rotateByAngle:3*M_PI duration:time];
[wheel runAction:act];
}
}
#end
In GameScene.m add train like this,
-(void) addTrain
{
Train *train1 = [[Train alloc]initTrainWithColor:[UIColor yellowColor] andSize:CGSizeMake(150, 100)];
[train1 setPosition:CGPointMake(self.size.width/2.0f, self.size.height/2.0f)];
[self addChild:train1];
SKAction *act = [SKAction moveTo:CGPointMake(self.size.width/2.0f, self.size.height - 50) duration:2];
[train1 runAction:act];
[train1 animateWheelsWithTime:2];
}
I tried and it works.