So in my Space Invaders game, all collisions were working perfectly until I added a physics body created from a edgeChainFromPath which is a single line to represent the ground (an SKShapeNode created from 2 points). Now my invader bombs (which move via SKAction) notify when they hit the ground but my invaders (moved in update() by manually updating their positions) do not. My ship missiles (also moved by SKAction) DO notify when contacting an invader.
Question : if a physicsBody is moved manually and comes into contact with another physicsBody, is didBeginContact not called? (All physics interactions - bitMasks, delegates etc - are set correctly). I'm thinking the answer is 'No it's not' because that's the only explanation and makes sense picturing how Sprite/Kit probably works. I.e. A contact occurs when the SK engine itself moves a node and realises that it's physicsBody is being drawn on top of another physicsBody.
Edit - just realised that I have other physicsBodies in my scene that are stationary and that the invaders DO collide with, so it's not an SKAction thing. The difference might be that the new node I've added is an edge-based body belonging to an SKShapeNode, rather than a volume-based body for a SKSPriteNode, but nothing in the documentation that I can find states that this shouldn't work.
New question : Do volume-based bodies being moved manually not collide with stationary edge-based bodies?
Ok - my bad. The invaders' physicsBodies had dynamic=false. Every other sprite was dynamic, so all other collisions were working. My new shape was an edge-based body which also are dynamic=false.
Made that one change and all is Ok. I need to update my checkPhysics() routine to test for this.
Edit: I really should have seen this earlier - checkPhysics() was not printing that invader notifies when contacting ground, which I just put down to a glitch that I'd fix later. Whereas checkPhysics() deliberately doesn't report on nodes with dynamic=false. I think that when I wrote the function, I assumed that you'd set dynamic=false deliberately to not be involved in collision/contact detection. I should change it to print a warning.
Related
I am currently working on a 2D endless runner, written in Swift3 and using Spritekit.
Short question:
Is there a way to only check for collisions on the right side of my character's rectangular physics body?
More info:
The platform on which the character runs is made of puzzle pieces and the user builds upon it as the game progresses. The character progresses left to right, in respect to the background (which goes right to left).
I want the character to automatically jump when he collides with a piece on his right side. However, any pieces that the player puts to the right of him (same Y value as the character) is of the same class as the pieces underneath him.
So the same code that checks for collision between the character and pieces to his right, and make him jump, will also make him jump as long as the game detects collision between the character and the pieces under him.
I have not been able to find another problem like mine, since usually others' characters are colliding with objects of different classes from their ground class.
Thanks!
P.S. I have tried to make my character a SKSpriteNode with two physics bodies, but I could not find any helpful documentation. If it helps any, my character also performs a looping running animation--though I can't imagine that would harm anything.
You could achieve that by detecting collisions with your rectangle and then deciding whether the collision was with the side of your interest or not. Here is a discussion about how to do that. Good luck!
Have you tried adding a non visible sub node (e.g. feetNode) to your character's sprite node and giving that sub node the physics body (class) for floor contact ?
Depending on the rest of your logic, it may allow you to use a different physics class for your character have more flexibility in collision detection.
In fact, you could probably use that approach with several sub nodes in your character's sprite node and have multiple collision behaviours for the character depending on what hits it.
Once you obtain the contact point of the 2 bodies that are colliding, determine which body is the one that is colliding by checking the categorymasks and then check its CGPoints x position. This x position can be compared to the other body's x position to know exactly which side it is colliding from.
if Body A's x position > Body B's x position, Body A is on the right and if not, its on the left.
As simple as that.
Hope this helps!
I am working on a game, and I am using an alpha mask to create an SKPhysicsBody for the basket + catcher. The SKView has showPhysics set to true.
I can't figure out what in the world the disc is hitting. There is no physics field there. When I recreate the reference node with SKSpriteNodes this works flawlessly. I would like to use a reference node though because it would make it easier to make lots of these quickly. Here is where I set up the reference node:
Here is where I create the scene itself:
I have zero idea at this point what is happening. Clearly there is an error with showing the physics as well, because there is no blue outline there.
I am seeming to have difficulty keeping my sprite nodes inside a map boundary that I have set up in the following way:
I have an SKNode *enemy that moves around an SKScene by goals and behaviors courtesy of GameplayKit from iOS 9. Currently the node wanders, and avoids obstacles that are defined GKPolygonObstacle objects. I have my bitmask set up so that any obstacle is deemd category wall, which the node is told to collide with (AKA disallow passing through).
In my didBeginContact:(SKPhysicsContact *)contact I am handling these collisions. All is working exactly as planned and there are no issues when manually moving this enemy.
However, the problem begins when I have the enemy wander around the scene through an SKGoal *wanderGoal set up as
// Low --> 0.5 Lowest --> 0.25
enemy.wanderGoal = [GKGoal goalToWander:low];
[enemy.agent.behavior setWeight:lowest forGoal:enemy.wanderGoal];
// Add obstacles to avoid for each of the inner map nodes
// that act as impassible areas for the enemy to pass through.
NSArray *obstacles = [SKNode obstaclesFromNodePhysicsBodies:innerMapArray];
/** This goal does not change --> enemies will ALWAYS
avoid the obstacles in the level map. This should always
be set to the highest priority of the enemy goals
*/
enemy.avoidGoal = [GKGoal goalToAvoidObstacles:obstacles maxPredictionTime:10];
// Highest --> 250
[enemy.agent.behavior setWeight:highest forGoal:enemy.avoidGoal];
The enemy moves randomly as expected, and seems to avoid the obstacles most of the time...yet on the occasion the enemy does in fact pass through the map barrier. Let me expand on this:
The map barrier is essentially a rectangle, and I have set up 2 nodes that act as a shell that represent the left half and the right half of this shape. These nodes have a thickness of 100 points so they are not simply CGPath refs but rather shapes. They act as these two brackets act: [] (my halves are flush touching at the middle).
My question is such:
How can I prevent the enemy from passing through these obstacles with using either physics with the bitmask categories, or by the goal behavior? (Or both together)
I understand that while a GKGoal is a suggested behavior it does not guarantee this goal to be reached (but it can be ~95% sure it wont happen as Apple's AgentsCatalog shows). But, what I don't understand is why the enemy does not simply "slide" along the edge of the boundary as the goal tells it to (try to) "pass" through such boundary.
This "sliding" behavior does happen when I manually move the enemy around the scene, and as I attempt to move it passed a boundary deemed an obstacle, it slides towards the direction that I am having it move (just as any video game does that has map boundaries).
SO
If someone can help me prevent this from happening / explain how to approach preventing the enemy from ever passing through these (supposedly) "impassible" areas, I would be most appreciative.
FYI: If you are unclear with what I am describing / how I have created any objects, please ask and I will provide more info to help.
I'm working on a game in which the user should be able to trigger 'rods' that come out from the edge of the screen to displace elements on screen (balls). These projectiles roughly resemble pool-cues. Or perhaps pinball plungers, except that they start from the 'loaded' position (mostly offscreen), and when triggered, they eject out, then quickly retreat.
I'm unclear how I should build these with Sprite Kit.
The game uses the PhysicsEngine, and the onscreen balls should be effected both by gravity AND they should be displaced when they collide with the rods. However the rods should neither be effected by gravity, not displaced when they collide with the balls -- they should simply retreat regardless of whether they've made contact with the balls.
I realize I can set the affectedByGravity property for the rods. However because they will still displace slightly when they collide with the balls. How can I 'fix' or 'peg' them in place? Do I need to use an SKPhysicsSlidingJoint? If so, has anyone encountered any examples online? Is there a simpler way to do this?
A related physics engine, Box2D distinguishes static, kinematic, and dynamic bodies.
Kinematic bodies can move and will collide with other objects, but they are themselves not affected by dynamic bodies or forces like gravity. Thus, consider setting rod.dynamic = NO; but animate it with actions. See also here in the reference for SKPhysicsBody.
I'm pretty new to Box2D and cocos2d. I'm trying to do something which I thought would be pretty simple, but it is turning out to be more difficult than I had expected and I cannot find a working answer anywhere.
Basically, I want to move a b2body and rotate it to a certain point with animation.
I can get it to the correct position and rotation with:
targetBody->SetTransform(b2Vec2(10.0f,1.0f),10);
But I have no idea how to animate it there over time. I tried using cocos2d animation on the sprite used for the body, but that doesn't do anything. Any ideas?
There are a couple of ways you could do this.
You could use SetTransform every time step to update the position of the body gradually over time, in effect performing the animation yourself. The drawback with this method is that the body is 'teleporting' to the new position rather than moving, so it has no momentum, which means you can get odd results if it hits anything along the way. Still, if you know it will not hit anything or does not need to react to a collision this would be ok.
The other way is to SetLinearVelocity and SetAngularVelocity to give the body proper movement. This will keep the results of a collision realistic, and you don't need to keep updating anything every timestep. On the other hand, you will need to detect when the body has arrived at the desired position and then set the velocities back to zero, otherwise it will just keep moving. For dynamic bodies you will also need to counter gravity somehow, either by setting the gravity scale of the body to zero, or by applying an upwards force to balance gravity, or by changing the body type to kinematic during the move.
In general, you use Box2D to simulate the physical behavior of objects in relation to each other. The rules of mechanics implemented by Box2D dictate how your cocos2d CCSprites move if you continuously update the translation and rotation of your sprites according to their corresponding Box2d b2Body. You will have some kind of repeatedly invoked tick: method in which you step your Box2d world along in time, and in which you update your sprite positions according to simulation results of Box2d.
This pattern corresponds to b2Bodys of type b2_dynamicBody. Physical laws dictate the motion of the body in this case, and your sprites will follow these simulation results. This is why setting a conflicting position of a sprite by means of a CCAction or even directly will be undone almost instantaneously with the next tick:.
Solution 1: kinematic body type
However, there do exist other modes for a b2Body, and one of these is b2_kinematicBody in which the translation is no longer governed by the world but by the velocities or angular speeds you dictate through setters. So it would be one solution to work with body type b2_kinematicBody as in:
b2BodyDef bdef;
bdef.type = b2_kinematicBody;
With this you would manipulate the velocity and angular speed of a b2Body explicitly. In this case, Box2d is still responsible for moving bodies around, but according the velocities you dictate, and without any force effects of collision or gravity applied to this particular body. Also with this strategy, your CCSprites will follow b2Bodys. Setting conflicting positions for your sprites directly or by applying a CCAction would not make sense for the same reason as described above.
Solution 2: decouple sprites from Box2d
An alternative way to animating sprites would be to fully decouple those sprites from Box2d. In this case, you would simply not have any b2Body that governs the position of the sprite you are going to animate. Now, in this case, only you will dictate the position and rotation of your CCSprite, i.e. directly either through its position property or by applying a CCAction.