i'm new to XNA 4.0 and i want to create a space ship shooter game. When i kill the enemy i want to draw a explode texture where it death and the explode texture will disappear for 2 seconds. I managed to draw a explode texture when enemy died by using boolean if enemy is die or not in Draw method but i don't know how to remove it after 2 seconds. Thank you for your help.
if (alive)
sp.Draw(enemyTexture, enemyPos, Color.White);
else
sp.Draw(explode, enemyPos, Color.White);
Do a similar check for two second interval between the start of the explosion and its end. You could just save the time of explosion and check if it is 2 seconds or more older than the current time, like so:
TimeSpan explosionTime;
if (itsTimeToExplode)
explosionTime = gameTime.TotalGameTime;
Then you make a check to see if it is time to remove the explosion animation:
if (gameTime.TotalGameTime.TotalMilliseconds - explosionTime.TotalMilliseconds >= 2000) // 2000 milliseconds is 2 seconds
RemoveExplosionAnimation();
You can put the explosionTime inside your enemy class and only delete the enemy after it's dead and the explosion animation has been played.
You need to count the time inside Update method using gameTime variable.
When your counter reaches 2s, just make alive = false;
But better idea is to make class for your explosion sprite with update and draw methods
and handle the counting and rendering from there.
Related
I've finished my game which uses the method + (SKAction *)moveToY:(CGFloat)y duration:(NSTimeInterval)sec to move sprites and when they collide with another sprite they disappear but when one of them collides with another object and disappears the other sprites that are falling down make some lag and I don't know if I could use another method to move sprites without lag.
PS: The sprites move a little bit fast(from y:0to y:568 in 0.5 seconds), is that maybe the problem?
In an iOS game that uses Sprite Kit along with the contact detection in Sprite Kit's build-in physics engine, I decrease the Hero's number lives by one each time he gets in contact with an enemy. This is done from the didBeginContact method.
However, it seems like that method is not just called once, when the contact begins, but called continuously as long as the Hero and the enemy overlaps: when I set a breakpoint in that method, I can see, that it is the exact same physics body instances that exist as contact.bodyA and contact.bodyB. The result is, that the Hero will lose multiple lives, even though he only passes one single enemy.
If the Hero meets the same enemy again later, he should get one more live subtracted, and therefore I cannot just maintain a seenEnemies hash set to deal with the problem above.
The question is now: how would you make sure that only one live is subtracted for each Hero/enemy contact?
The reason why the didBeginContact is being fired multiple times is because you have multiple contact points happening on concave shapes.
If you look at the picture below, you will see I have 2 sprites, a black star and a red rectangle. When the black star hits the red rectangle, it hits it on multiple points, circled in blue. Sprite Kit will then do a call for each line intersection, so that the developer can use the contactPoint variable for each of these contacts.
I had the same problem (score increasing multiple times for a single enemy destroyed and multiple life points being lost for a single instance of damage.) A user on the Apple forums thinks that it's a bug in [SKPhysicsBody bodyWithTexture:size:] but I don't believe that's the case, because it was happening with other constructors too.
First off, the categoryBitMask and contactTestBitMask are very important, obviously. Take a look at Apple's SpriteKit Physics Collisions sample code:
// Contacts are often a double dispatch problem; the effect you want is based on the type of both bodies in the contact. This sample this in a brute force way, by checking the types of each. A more complicated example might use methods on objects to perform the type checking.
// The contacts can appear in either order, and so normally you'd need to check
each against the other. In this example, the category types are well ordered, so
the code swaps the two bodies if they are out of order. This allows the code
to only test collisions once.
What I did to solve it was setting a flag after handling each condition. In my case, I was testing whether bodyA.node.parent was nil in didBeginContact, because I called removeFromParent() on the missile/enemy nodes to destroy them.
I think you should expect the event to fire multiple times and your code in there has to make sure it's processed only once.
I figured out easy solution:
Just change either body's categoryBitMask value to 0 or non-used value right after it detected contact.
For example:
if (firstBody.categoryBitMask == padCategory && secondBody.categoryBitMask == colorBallCategory) {
secondBody.categoryBitMask = 0;
// DO OTHER THING HERE
}
I came across the same issue. In my case the didBeginContact() was called many times (I counted up to 5 times) for one contact of a bullet with the enemy. As the bullet is a simple circle format, I agree with #SFX that it cannot be a bug just in Texture-Bodies. The tests have shown that there was no call to update() between the didBeginContact() calls. So the solution is simple (Swift):
var updatesCalled = 0
...
internal update() {
updatesCalled ++
}
...
internal func didBeginContact(contact: SKPhysicsContact) {
NSLog("didBeginContact: (\(contact.contactPoint.x), \(contact.contactPoint.y)), \(updatesCalled)")
if(updatesCalled == 0) {return} // No real change since last call
updatesCalled = 0
... your code here ...
}
I tried didEndContact() but that was not called at all. I didn't investigate further into this.
BTW: I just switched from Android, and I'm impressed by the easiness and stability of this System :-)
Here is an option that makes the player invulnerable after being hit for a set time:
A. Create a variable that makes the player invulnerable to losing a life after being hit for a few seconds.
Create a global Boolean variable called isInvuln (set to FALSE) and an NSTimeInterval called invulnTime.
In the method that handles the player and enemy making contact, check to see if isInvuln is False before taking a life. (if isInvuln is true ... do nothing)
If isInvuln is false, take a life then set isInvuln to true.
if(self.isInvuln == FALSE){
self.player.lives-=1;
self.isInvuln = True;}
Add to your updateWithCurrentTime:
if(self.isInvuln==True){
self.invulnTime += timeSinceLast;}
if (self.invulnTime > 3) {
self.isInvuln = FALSE:}
self.invulnTime= 0;
This will make it so that when an enemy and player collide, the player loses a life and becomes invulnerable 3 seconds. After that 3 seconds, the player can take damage again. If the enemy contacts the player within the 3 invulnerable seconds, the contact method does nothing. Hope this helps spark ideas to tackle your problem.
In my experience, didEndContact & didBeginContact are both called multiple times while the objects overlap. This is also happening in SceneKit using iOS 9, so I have to assume it's an intended behavior.
I have my first game application in development. In this game, the only character that the user controls will get to jump from one block to another. It's like Mario (in Mario Brothers) jumping from one moving lift to another. If he fails, he'll die. So how could you tell a free fall from a short fall as a result of a successful jump? One thing I thought I could do is measuring character's vertical velocity. So I have the following lines of code. It's used with didSimulatePhysics
SKNode *player = [self childNodeWithName:#"//player"]; // It's the node characterizing the game character
CGVector v = player.physicsBody.velocity;
if (v.dy < -2000) {
[self endTheScene:kEndReasonLose]; // The character has died from free fall => game is over
}
When the game character jumps, the game application can record a vertical velocity of -2022.466797. So this measure won't work. What else can I do? Set an invisible bar and see if the game character has touched it with intersectsNode? That can also fail. I have never developed a game before. So I don't know how they do it, which kind of makes me realize how impressive Nintendo game developers are. Some 30 years later, I still can't do it.
Thank you for your advice.
Update
The following can tell whether or not the character has died from free fall, I think.
- (void)didSimulatePhysics {
if (self.isMoving) {
// isMoving is an instance variable (BOOL): YES if the game has started
CGVector v = player.physicsBody.velocity;
BOOL hasFallen = self.lastFallenDate ? [self.lastFallenDate timeIntervalSinceNow] < -2.0 : YES; // lastFallenDate is an instance variable recording the time when the character fell last time
if (hasFallen) {
if (v.dy < -1500) {
[self endTheScene:kEndReasonLose];
}
}
}
}
Yet, I think Apple has a bug to fix as far as SKAction is concerned. No matter I do, audio will kick in exactly about 5 seconds after the game started although the character is not falling.
- (void)endTheScene:(EndReason)endReason {
if (endReason == kEndReasonLose) {
SKAction *lossAudio = [SKAction playSoundFileNamed:#"failureAudio.caf" waitForCompletion:NO];
[self runAction:lossAudio];
}
}
Super Mario Bros was a tile-based game: the screen was divided up into a number of square regions each of which being represented by a value. Each tile would have a separate sprite blitted to that region of the screen depending on the tile id, and based on that tile's properties Shigeru et al could determine if mario could stand on it, if it would hurt him or if he was free to fly. There's no magic to this, you just have to check where he is!
If you aren't concerned with the damage your Mario will take (i.e can he land a jump from any height as long as it is onto solid ground) this is easy: If his y position is ever lower than the lowest solid platform in your world, he has died:
Ignore velocity; check y position.
If you don't want him to survive a jump from the top of a building, you need to look at his velocity: Is he travelling fast enough that the force of impact would end his life?:
Ignore y position; check velocity
How do you know he is on a platform? A physic node?
Honestly, you can put a 'floor' plane stretching your world and anchor it at the bottom of your scene to catch dying plumbers and it won't impact performance - infact it will be more efficient than running these checks in your Update method.
Edit to add
Don't bother with intersections, -(void)didBeginContact:(SKPhysicsContact*)contact will alert you to any collision that occurred as long as you are a delegate. Skip the update loop completely: this will trigger for any collisions and won't be missed
Background
I'm making an iOS app for kids where you can use your finger to drag balls around on a screen.
I'm using Chipmunk 7.0.0 for the physics simulation.
I've adapted the Chipmunk demo code to implement the dragging functionality.
I'm using 2 ms fixed time step. (It's not like my app has anything better to do...)
Issue
I've recently added code to play a sound whenever the balls collide with each other or with a wall, which I'm doing inside a postSolve callback:
static void postSolve(cpArbiter *arb, cpSpace *space, cpDataPointer userData)
{
GameLayer *layer = (__bridge GameLayer *)userData;
[layer collisionHandler:arb];
}
-(void) collisionHandler:(cpArbiter*)arb
{
if(cpArbiterIsFirstContact(arb)) {
[[SimpleAudioEngine sharedEngine] playEffect:kCollisionEffectFilename];
}
}
Here's the problem... When I drag a ball into a wall, it generates a very large number of collisions, even when filtering on cpArbiterIsFirstContact, and it sounds terrible. It appears that the ball is bouncing off the wall, being driven back into wall by the constraint, rinse, and repeat. I'd like to play the collision sound only once or twice in this scenario.
Things I've tried that don't seem to work...
Filtering using cpArbiterTotalKE, cpArbiterTotalImpulse, or relative velocity: Impulse, kinetic energy, and relative velocity are all in the range of typical collisions.
Using a separate callback: The ball really is bouncing off the wall multiple times.
Reducing the step size: The physics engine actually takes longer to converge.
Rate limiting the sound effects: Better, but the ball still makes noise even after it looks like it's stationary.
Question
Is there a way to filter collisions for trapped bodies?
A simple and effective solution is to avoid playing the sound in quick succession.
When the ball contacts with the wall, check if the ball's "last contact" timer is lower than the current time. If so, play the sound and set the ball's "last contact" time to the current time plus x, where x is the timeout duration the sound shouldn't play again (ie 0.5 seconds).
In cocos2d-iphone you can add up an update method's deltaTime to keep track of time. There are also a number of ways to get system time, for example [NSDate date].timeIntervalSince1970 gives you the current number of seconds since 1970. I know, seems ridiculous, but if you get that number again sometime later, and subtract the previous number of seconds you get the difference in seconds, that's all that counts.
So you are using a constraint to drag the ball around, and the ball is elastic correct? Have you tried tweaking the constraint parameters at all? If the constraint has a lower maxForce, the chance for oscillations would drop significantly.
Another thing that can help is to increase the space's collision slop (how much shapes are allowed to overlap). The default value is 0.1 (in whatever scale you are using), but increasing it to a pixel or so can help this sort of thing significantly without being very visible.
I discovered a lot of new info since I posted this question so I have completely rewritten it:
I have run into some problems while implementing gravity and jumping in my tile-based game.
Sometimes when my character lands between tiles after a jump, the characters falls through them.
The problem certainly is not that my speed is too high since my max speed is the same as my tile-size. Also, the problem does not occur after every time the character jumps. I can often make a jump, get to max velocity, and still land well. But sometimes the character just falls through.
My level exists of layers of tiles. Each layer has it's own collision-type. So every tile in the same layer, follows the same rules for collision.
In my current set-up all layers use per-pixel collision.
This is how I update the player coordinates
http://pastebin.com/qVc6gv6T
This is the class where I calculate my collissions.
http://pastebin.com/7GqrFih6
In the update I just do:
controls.Update(player);
physicsEngine.HandleCollissions(levelManager, player);
I imagine that the problem could be because the player gets moved to another tile after collission. Collides with the other tile. But that doesn't count since the other tile already has been checked for collision?
Or could it be because I use foreach instead of for-loops?
You say the error occurs after jumping. So, your character falls toward a tile (has some positive velocity.Y) and hits it. The collision code executes the // the player comes FROM ABOVE and collides with the tile block. You run a loop that sets player velocity to zero and moves the player out of collision. This loops calls a function using a term tile as an argument. I assume you loop through a set of tiles in order to collide with more than a single square. Am I right?
If I am, then the problem occurs after that first collision and correction. Now your player has a velocity.Y of 0, but they are colliding with a new tile. So in spite of your comment about the meaning of your else block, you may have more position changes happening:
if (player.Velocity.Y > 0)
else // if (moveVector.Y < 0) // what you commented
else // if (moveVector.Y <= 0) // what your else really means
Now sometimes (only when you have slightly mis-alligned per-pixel collisions) you have course corrections happening the the wrong direction. That would produce a fall-through effect. You could try setting a break point in the // the player comes FROM UNDER and collides with the tile block, and then running the program in a scenario that shouldn't cause player.WorldPositionY += 1; to happen. If it happens when it wasn't supposed to, then you have your culprit.
I am doing a lot of speculation here. I think you should post more code so that we can know for sure. But perhaps a paste bin would be appropriate place for it.