SpriteKit Physics Collisions/APLShipSprite.m
/* |
File: APLShipSprite.m |
Abstract: |
This class adds game logic for a ship sprite. |
Version: 1.2 |
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*/ |
#import "APLShipSprite.h" |
#import "APLSpaceScene.h" |
/* Constants used to adjust ship behavior */ |
/* In an actual game, instead of hard coding these, you might want to load them from a property list */ |
static const NSInteger startingShipHealth = 10; |
static const NSInteger showDamageBelowHealth = 4; |
// Used to configure a ship explosion. |
static const CFTimeInterval shipExplosionDuration = 0.6; |
static const CGFloat shipChunkMinimumSpeed = 300; |
static const CGFloat shipChunkMaximumSpeed = 750; |
static const CGFloat shipChunkDispersion = 30; |
static const NSUInteger numberOfChunks = 30; |
static const CGFloat removeShipTime = 0.35; |
// Used to control the ship, usually by applying physics forces to the ship. |
static const CGFloat mainEngineThrust = 5; |
static const CGFloat reverseThrust = 1; |
static const CGFloat lateralThrust = 0.01; |
static const CGFloat firingInterval = 0.1; |
static const CGFloat missileLaunchDistance = 45; |
static const CGFloat engineIdleAlpha = 0.05; |
static const CGFloat missileLaunchImpulse = 0.5; |
// Useful random functions. |
static inline CGFloat myRandf() { |
return rand() / (CGFloat) RAND_MAX; |
} |
static inline CGFloat myRand(CGFloat low, CGFloat high) { |
return myRandf() * (high - low) + low; |
} |
// This enables debug code to show the bounding shape of the ship superimposed over the sprite. |
#define SHOW_SHIP_PHYSICS_OVERLAY 0 |
@interface APLShipSprite() |
// Child nodes used to add effects to the ship. |
@property SKEmitterNode* exhaustNode; |
@property SKEmitterNode* visibleDamageNode; |
@property CGFloat engineEngagedAlpha; |
@property CFTimeInterval timeLastFiredMissile; |
@end |
@implementation APLShipSprite |
+ (instancetype) shipSprite |
{ |
APLShipSprite* ship = [APLShipSprite spriteNodeWithImageNamed:@"spaceship.png"]; |
// This is a bounding shape that approximates the rocket. |
CGMutablePathRef boundingPath = CGPathCreateMutable(); |
CGPathMoveToPoint(boundingPath, NULL, -12, -38); |
CGPathAddLineToPoint(boundingPath, NULL, 12, -38); |
CGPathAddLineToPoint(boundingPath, NULL, 9, +18); |
CGPathAddLineToPoint(boundingPath, NULL, 2, +38); |
CGPathAddLineToPoint(boundingPath, NULL, -2, +38); |
CGPathAddLineToPoint(boundingPath, NULL, -9, +18); |
CGPathAddLineToPoint(boundingPath, NULL, -12, -38); |
#if SHOW_SHIP_PHYSICS_OVERLAY |
SKShapeNode *shipOverlayShape = [[SKShapeNode alloc] init]; |
shipOverlayShape.path = boundingPath; |
shipOverlayShape.strokeColor = [SKColor clearColor]; |
shipOverlayShape.fillColor = [SKColor colorWithRed:0.0 green:1.0 blue:0.0 alpha:0.5]; |
[ship addChild:shipOverlayShape]; |
#endif |
ship.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:boundingPath]; |
CGPathRelease(boundingPath); |
ship.physicsBody.categoryBitMask = shipCategory; |
ship.physicsBody.collisionBitMask = shipCategory | asteroidCategory | planetCategory | edgeCategory; |
ship.physicsBody.contactTestBitMask = shipCategory | asteroidCategory | planetCategory | edgeCategory; |
// The ship doesn't slow down when it moves forward, but it does slow its angular rotation. In practice, |
// this feels better for a game. |
ship.physicsBody.linearDamping = 0; |
ship.physicsBody.angularDamping = 0.5; |
return ship; |
} |
- (instancetype)initWithTexture:(SKTexture *)texture color:(SKColor *)color size:(CGSize)size |
{ |
if (self = [super initWithTexture:texture color: color size: size]) { |
_health = startingShipHealth; |
} |
return self; |
} |
- (void) showDamage |
{ |
// When the ship first shows damage, a damage node is created and added as a child. |
// If it takes more damage, then the number of particles is increased. |
if (!self.visibleDamageNode) |
{ |
self.visibleDamageNode = [NSKeyedUnarchiver unarchiveObjectWithFile:[[NSBundle mainBundle] pathForResource:@"damage" ofType:@"sks"]]; |
self.visibleDamageNode.name = @"damaged"; |
// Make the scene the target node because the ship is moving around in the scene. Smoke particles |
// should be spawned based on the ship, but should otherwise exist independently of the ship. |
self.visibleDamageNode.targetNode = self.scene; |
[self addChild:self.visibleDamageNode]; |
} |
else |
{ |
self.visibleDamageNode.particleBirthRate = self.visibleDamageNode.particleBirthRate * 2; |
} |
} |
- (void) makeExhaustNode |
{ |
SKEmitterNode *emitter = [NSKeyedUnarchiver unarchiveObjectWithFile:[[NSBundle mainBundle] pathForResource:@"exhaust" ofType:@"sks"]]; |
// Hard coded position at the back of the ship. |
emitter.position = CGPointMake(0,-40); |
emitter.name = @"exhaust"; |
// Make the scene the target node because the ship is moving around in the scene. Exhaust particles |
// should be spawned based on the ship, but should otherwise exist independently of the ship. |
emitter.targetNode = self.scene; |
// The exhaust node is always emitting particles, but the alpha of the particles is adjusted depending on whether |
// the engines are engaged or not. This adds a subtle effect when the ship is idling. |
self.engineEngagedAlpha = emitter.particleAlpha; |
emitter.particleAlpha = engineIdleAlpha; |
[self addChild:emitter]; |
self.exhaustNode = emitter; |
} |
- (void)makeExhaustNodeIfNeeded |
{ |
if (!self.exhaustNode) |
{ |
[self makeExhaustNode]; |
} |
} |
- (void) applyDamage: (NSInteger) amount |
{ |
// If the ship takes too much damage, blow it up. Otherwise, decrement the health (and show damage if necessary). |
if (amount >= _health) |
{ |
if (_health > 0) |
{ |
_health = 0; |
[self explode]; |
} |
} |
else |
{ |
_health -= amount; |
if (_health < showDamageBelowHealth) |
{ |
[self showDamage]; |
} |
} |
} |
- (void)explode |
{ |
// Create a bunch of explosion emitters and send them flying in all directions. Then remove the ship from the scene. |
APLSpaceScene *scene = (APLSpaceScene*) self.scene; |
for (NSUInteger i = 0; i < numberOfChunks; i++) |
{ |
SKEmitterNode *explosion = [scene newExplosionNode: shipExplosionDuration]; |
CGFloat angle = myRand(0,M_PI*2); |
CGFloat speed = myRand(shipChunkMinimumSpeed,shipChunkMaximumSpeed); |
explosion.position = CGPointMake(myRand(self.position.x-shipChunkDispersion, self.position.x+shipChunkDispersion), |
myRand(self.position.y-shipChunkDispersion, self.position.y+shipChunkDispersion)); |
// Use the physics system to animate the movement of the explosion chunks. As implemented, these chunks do not |
// collide or hit anything. |
explosion.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:0.25]; |
explosion.physicsBody.collisionBitMask = 0; |
explosion.physicsBody.contactTestBitMask = 0; |
explosion.physicsBody.categoryBitMask = 0; |
explosion.physicsBody.velocity = CGVectorMake(cos(angle)*speed,sin(angle)*speed); |
[scene addChild:explosion]; |
} |
// Once the ship is covered with particles it is removed. |
[self runAction:[SKAction sequence:@[[SKAction waitForDuration:removeShipTime],[SKAction removeFromParent]]]]; |
} |
- (CGFloat)shipOrientation |
{ |
// The ship art is oriented so that it faces the top of the scene, but Sprite Kit's rotation default is to the right. |
// This method calculates the ship orientation for use in other calculations. |
return self.zRotation + M_PI_2; |
} |
- (CGFloat)shipExhaustAngle |
{ |
// The ship art is oriented so that it faces the top of the scene, but Sprite Kit's rotation default is to the right. |
// This method calculates the direction for the ship's rear. |
return self.zRotation - M_PI_2; |
} |
- (void)activateMainEngine |
{ |
/* |
Add flames out the back and apply thrust to the ship. |
*/ |
CGFloat shipDirection = [self shipOrientation]; |
[self.physicsBody applyForce:CGVectorMake(mainEngineThrust*cosf(shipDirection), mainEngineThrust*sinf(shipDirection))]; |
[self makeExhaustNodeIfNeeded]; |
self.exhaustNode.particleAlpha = self.engineEngagedAlpha; |
self.exhaustNode.emissionAngle = [self shipExhaustAngle]; |
} |
- (void)deactivateMainEngine |
{ |
/* |
Cut the engine exhaust. |
*/ |
[self makeExhaustNodeIfNeeded]; |
self.exhaustNode.particleAlpha = engineIdleAlpha; |
self.exhaustNode.emissionAngle = [self shipExhaustAngle]; |
} |
- (void)reverseThrust |
{ |
/* |
Apply a small amount of thrust to reduce the ship's speed. (No visible special effect). |
*/ |
CGFloat reverseDirection = [self shipOrientation] + M_PI; |
// calculate an impulse to thrust the ship forward. |
[self.physicsBody applyForce:CGVectorMake(reverseThrust*cosf(reverseDirection), reverseThrust*sinf(reverseDirection))]; |
} |
- (void)rotateShipLeft |
{ |
/* |
Apply a small amount of thrust to turn the ship to the left. (No visible special effect). |
*/ |
[self.physicsBody applyTorque:lateralThrust]; |
} |
- (void)rotateShipRight |
{ |
/* |
Apply a small amount of thrust to turn the ship to the right. (No visible special effect). |
*/ |
[self.physicsBody applyTorque:-lateralThrust]; |
} |
- (void)attemptMissileLaunch:(NSTimeInterval)currentTime |
{ |
/* Fire a missile if there's one ready */ |
CFTimeInterval timeSinceLastFired = currentTime - self.timeLastFiredMissile; |
if (timeSinceLastFired > firingInterval) |
{ |
self.timeLastFiredMissile = currentTime; |
CGFloat shipDirection = [self shipOrientation]; |
APLSpaceScene *scene = (APLSpaceScene*) self.scene; |
SKNode *missile = [scene newMissileNode]; |
missile.position = CGPointMake(self.position.x + missileLaunchDistance*cosf(shipDirection), |
self.position.y + missileLaunchDistance*sinf(shipDirection)); |
[scene addChild:missile]; |
// Start with the ship's velocity, and then give it a little kick. |
missile.physicsBody.velocity = self.physicsBody.velocity; |
[missile.physicsBody applyImpulse: CGVectorMake(missileLaunchImpulse*cosf(shipDirection), |
missileLaunchImpulse*sinf(shipDirection))]; |
} |
} |
@end |
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