I'm making a platform and want to stop the character (a ball) from going through the ground.
Can I write an if statement similar to if (Ball.center.y == 463) Ball.center.y = 463;?
463 is the y position that the ground is in the game.
While that approach is certainly possible, typically you want to abstract away the details (such as the 463 y-position of the ground) so that your code is more robust. For example, if you changed the y-position of the ground, you would have to change the 463 value everywhere you use it!
But fundamentally, yes you would use an if statement somewhat like what you provided. One thing to note is that if the ground is at 463, your ball will be half-way through the ground (since you are looking at the y-position of the centre of the ball.
Moreso, you want a check that is not so absolute... what if the position of the ball somehow becomes lower than the ground? Say 462? What should the behavior be now?
Without getting into the physics and design of your program, you would at the very least want to change your statement to something like:
int ball_lower_bound = Ball.center.y - Ball.height/2;
int ground_bound = 463;
if (ball_lower_bound < ground_bound) {
ball_lower_bound = ground_bound;
}
Since you are using sprite kit you should use physics body to handle that.
This is in swift:
variables of your class:
let balCategory:UInt32 = 1 << 0
let groundCategory:UInt32 = 1 << 1
Then when you define your ball sprite:
ball.physicsBody.categoryBitMask = ballCategory
ball.physicsBody.collisionBitMask = groundCategory
ball.physicsBody.contactTestBitMask = groundCategory
Then when you define your ground sprite (hopefully you have a image for your ground, if not make a very thin transparent or have something just below the screens edge):
ground.physicsBody.categoryBitMask = groundCategory
ground.physicsBody.collisionBitMask = ballCategory
ground.physicsBody.contactTestBitMask = ballCategory
Hopefully you can translate it to objective C if you are using that.
Related
I am making a game with sprites that move and obstacles to learn SpriteKit. I want the sprites that move to collide with the obstacles and bounce off of them but I want the obstacles to stay fixed. How do I do this? I have tried the following with no success:
Setting obstacle.physicsBody?.isDynamic = true. This made the sprites go through the obstacle.
Fixing the movement and rotation of the object with SKConstraint. When I do this they just go through each other.
Setting the mass of the body to be really high as follows obstacle.physicsBody?.mass = CGPoint.maxFiniteMagnitude but this freezes the game. When I set it really high it doesn't seem to do anything.
Setting obstacle?.physicsBody.velocity = CGVector(dx: 0, dy: 0) when the objects collide. I know that the contact.bodyA and contact.bodyB are passed by value and not reference so I loop through an array with the obstacles and set the velocity this way. The obstacles are still pushed by the other sprites.
Update:
- Setting obstacle.physicsBody?.collisionBitMask = PhysicsCategory.none so the sprite collides with the obstacle but not the other way around.
The object is setup as follows, with fish being the other sprite:
obstacle.position = location
obstacle.physicsBody = SKPhysicsBody(rectangleOf: obstacle.size)
obstacle.physicsBody?.isDynamic = true
obstacle.physicsBody?.categoryBitMask = PhysicsCategory.obstacle
obstacle.physicsBody?.contactTestBitMask = PhysicsCategory.fish
obstacle.physicsBody?.collisionBitMask = PhysicsCategory.fish
obstacle.physicsBody?.usesPreciseCollisionDetection = true
self.obstacles.append(obstacle)
super.addChild(obstacle)
Please let me know if there is something I am doing wrong / misunderstanding. Thanks.
Found the answer here. One of the objects needs to have .physicsBody?.isDynamic = true. In this case I set the obstacle to false so it is stationary.
I've created a tiled map composed of multiple sprite nodes that are 367x367. I create this map like so:
for var i = 0; i < Int(multiplier); i++ {
for var j = 0; j < Int(multiplier); j++ {
// Positive
var map = SKSpriteNode(imageNamed: "tiledBackground.png")
var x = CGFloat(i) * map.size.height
var y = CGFloat(j) * map.size.height
map.position = CGPointMake(x, y)
self.addChild(map)
}
}
In the above example, the multiplier is 27 and the map size is 10,000x10,000.
This creates the map as expected, however I want this map to have boundaries that the player can't leave. I know how to create the boundaries, but I'm not sure what values to initialize the physics body with.
I've tried this: SKPhysicsBody(rectangleOfSize: map.mapSize) however that produced very erroneous results.
I also tried this: SKPhysicsBody(edgeLoopFromRect: CGRectMake(0, 0, map.mapSize.width, map.mapSize.height)) which built a physics body like it should (I have showPhysics = TRUE), however the physics body seemed to move with the player (I have the player moving and am centering the map on the player). You can see what I mean here: http://gyazo.com/675477d5dd86984b393b10024341188a (It's a bit hard to see, but that green line is the boundary for the physics body. When the tiled map ends (And where it turns grey), the physics body should stop as that's where the player shouldn't be allowed to move any more).
Just leave a comment if you need any more code (I believe I included anything that is relevant).
After messing around with a bit of my code I found a fix was to just add the physicsBody to my map instead of the scene. A rather easy fix, so I'm surprised I didn't think of it sooner.
With this in mind, I've answered my own question and no longer need help.
I am using SpriteKit's built in Physics Engine to build a game for iOS. Basically it involves a bouncing ball which moves via me manually setting it's initial velocity and bounces via resetting the velocity within the contact event with the floor.
The issue is, the actual maths for this environment do not add up. Using 'SUVAT' equations it's easy to determine how far the ball's x-displacement should be when it reaches the floor after being thrown with a certain velocity, however (with gravity set to -9.81), it barely moves a couple of pixels.
I simplified the problem to just trying to shoot a ball a certain distance upwards (in the y-direction) and the same thing happened, it moves a couple of points up and then just falls to the floor, at least a 20th of how far it should move.
This is how I have set the physics environment up:
self.physicsWorld.contactDelegate = self;
self.physicsWorld.gravity = CGVectorMake(0.0, -9.81);
And then this is my function for generating this ball (shooting upwards) example. Mathematically it should reach the height of the tower:
-(void)generateTestBall {
self.ball = [SKSpriteNode spriteNodeWithImageNamed:#"ball"];
SKSpriteNode * tower = [SKSpriteNode spriteNodeWithImageNamed:#"player"];
self.ball.position = CGPointMake(self.scene.size.width/2,self.scene.size.height/2);
self.ball.size = CGSizeMake(20,20);
self.ball.color = [SKColor redColor];
self.ball.colorBlendFactor = 1;
tower.position = CGPointMake(self.scene.size.width/2 + 20,self.scene.size.height/2+100);
tower.size = CGSizeMake(20,200);
tower.color = [SKColor blueColor];
tower.colorBlendFactor = 1;
[self addChild:tower];
[self addChild:self.ball];
self.ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:10];
self.ball.physicsBody.affectedByGravity = YES;
self.ball.physicsBody.linearDamping = NO;
self.ball.physicsBody.dynamic = YES;
CGFloat ballVel = sqrt(2*9.81*tower.size.height);
NSLog(#"%f",ballVel);
self.ball.physicsBody.velocity = CGVectorMake(0.0f, ballVel);
}
Please can someone explain what I am doing wrong? I've double checked my maths (I'm a maths student so fingers crossed that's not the issue)!
Thanks!
Steve
So I FINALLY managed to figure it out. Just incase anyone else is experiencing the same issue I'll post the answer here:
The issue was that, although gravity is (apparently) in ms^-2 and velocity m2^-1 (to replicate earth), any distances in Objective C are measured in POINTS rather than the required form of METRES. Therefore any calculation done with x,y position / size values taken from SKSpriteNodes etc will be a certain factor out.
After running a few tests I found the factor to roughly be 157. This means that you must multiply any sizes / distances in POINTS by 157 to get the relative 'METRE' value which will work with SUVAT.
The actual numbers themselves seem a bit ridiculous as they're all very big (velocity, distance etc) but that doesn't actually pose a problem anyway as they all now work relative to each other!
Hope this helps anyone!
Steve
I am building a game with Xcode's spritekit. Its a platform game and right now it functions well with flat ground pieces. I was wondering if it was possible to ignore transparency in the png for collisions. That is to say, If i have a ground piece with a curved floor and transparency filling the troughs, can i make the player walk the curves instead of a square bounding box covering the whole thing? The only example i can find is in the Gamemaker GML language, you can do "precise" collisions such that blank space in the images do not count as part of the sprite. I can supply code if necessary but this seems like more of a conceptual question. Thanks in advance
Hey there's a easy solution for this provided in the Apple Documentation.
SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:#"Spaceship"];
sprite.physicsBody = [SKPhysicsBody bodyWithTexture:sprite.texture size:sprite.texture.size];
This creates a physics body around the physical paths of the texture.
Simulating Physics - SpriteKit Programming Guide
It's all in how you instantiate the physicsBody of the node in question.
node.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:node.size];
is probably the easiest and most common way of making a physicsBody, but will also create the issue you've identified above, because, for all collision purposes, the node is a rectangle.
take a look at the documentation for SKPhysicsBody to see the other options available to you. PolygonFromPath and BodyWithBodies are probably the best suited for what you're doing.
SKPhysicsBody is the right move, just wanted to note that it does make sense to have a separate (simplified) mask-image for SKPhysicsBody to improve your performance, simplified from color and geometry standpoint, and here's the code:
let birdMask: UInt32 = 0x1 << 0
let pipeMask: UInt32 = 0x1 << 1
//...
pipeImage = SKSpriteNode(imageNamed: "realImage")
//... size and position
let maskTexture = SKSpriteNode(imageNamed: mask)
maskTexture.size = pipeImage!.size // size of texture w/ real imageNamed
pipeImage!.physicsBody?.usesPreciseCollisionDetection = true
pipeImage!.physicsBody = SKPhysicsBody(texture: maskTexture.texture!, size: size)
pipeImage!.physicsBody?.affectedByGravity = false // disable falling down...
pipeImage!.physicsBody?.allowsRotation = false
pipeImage!.physicsBody?.isDynamic = true
pipeImage!.physicsBody?.friction = 0
pipeImage!.physicsBody?.categoryBitMask = pipeMask
pipeImage!.physicsBody?.collisionBitMask = birdMask | pipeMask
pipeImage!.physicsBody?.contactTestBitMask = birdMask | pipeMask
and more detailed example/guide.
I'm currently trying to make a basic platformer with XNA and I'm wondering how to create a "jumping effect." I currently have basic keyboard input which allows for sideways movement, but I would like my sprite to slowly progress into a jump rather than instantly teleporting there (right now I have something like Rectangle.Y += 40 every time I jump, making the sprite instantly appear there). Does anyone have any insight?
I'm not totally across how to implement this in XNA/C#, but in Flash games I've made I just added a vertical velocity property. I'll try write everything as C# as I can..
Example; create the velocity property:
float verticalVelocity = 0;
Vertical velocity should be constantly reduced (by gravity). Set up a gravity property somewhere accessible from your player:
float Gravity = 2.5;
And in your update() method for the player, increment the verticalVelocity by Gravity. Also increment the Y position of your player by the verticalVelocity. This will simulate falling:
verticalVelocity += Gravity;
Position.Y += verticalVelocity; // this may be -= in XNA, not sure where the y axis beings
When you hit a surface, the velocity should be reset to 0.
And finally, to jump, simply subtract a given value from verticalVelocity:
public void Jump(float height)
{
// Only jump if standing on a surface.
if(verticalVelocity == 0)
verticalVelocity -= height;
}
You'll eventually want to add gravity and possibly other forces to your game, so I highly recommend you save yourself a lot of pain and implement some kind of basic force system. This can be done using Vector2s, as you can just add them to the speed of your character. Then just apply an instantaneous force to your character to push it up.
If you really don't want to use a physics engine, you can make a Vector2 with the high point of the jump for the Y and the characters X, and then use the Vector2.Lerp method to interpolate between the characters position and the end point of the jump.
This is generally a very bad system to use, and I highly recommend you either use an existing physics engine, or make your own simple one.
use a sinusoidcode should look something like this:
float ground = 0.0f;
float angle = 330.0f;
jump(){
if(ground == 0.0f)ground = Rectangle.Y;
if(Rectangle.Y <= ground)
{
Rectangle.Y+=Math.Sin(angle/(Math.Pi*180));
angle++;
}
}
You can accurately create a gravity effect if you modify the ySpeed dynamically, as opposed to just adding 40.
You want to declare a ySpeed
ySpeed = 0;
Then you want to use an acceleration variable
acceleration = 0.25;
Okay, now that we've done that, let's add gravity, provided that our player isn't touching the floor.
if(playerLocationY + playerHeight > floorLocationY)
{
gravity = false;
}
else
{
gravity = true;
}
if(gravity)
{
ySpeed += acceleration;
}
Now that we've got that down, we want to include something that allows us to jump.
if(KeyPressed == UP)
{
ySpeed -= acceleration;
}
This will move our player in the upward direction
We now want to make sure we actually move, so let's add one last line and we're done.
playerLocationY += ySpeed;
Congratulations, you made it.