is it possible to spawn objects in the same location, but make their bodies not join together?
Basically i have a bunch of b2bodies that i spawn at a given time, and i need them to bounce off each other rather than stick to each other..
So this would create a sort of explosion of the created bodies because they repel against each
other.
Anyone have any ideas?
Is this possible with box2d?
Based from my experience, dynamic bodies with single fixtures would immediately repel each other the moment their physics simulation steps begin. Bodies with multiple fixtures would have problems if their fixtures crisscross each other because they would stick together.
I'm not sure if you can get explosion this way, because the repulsion force is usually weak. What you can do is to set up a contact listener that would detect contacts and apply opposing forces to bodies that are touching during spawning. Or maybe you can do AABB query before spawning a body to check if there is already a body at the spawn location, and apply the forces to the bodies.
Related
Is there any quick way to get all contacting bodies with specific b2bBody?
for example i have 200 cricles(dynamic bodies) and want to know how many circle contacting with each circle
The most efficient way is to use the BeginContact and EndContact callbacks of the contact listener to update a list for each body, of what it is currently touching.
This page might help: http://www.iforce2d.net/b2dtut/collision-callbacks
That example only tracks the number of touching bodies by using a simple integer counter, but you could also use a std::set or similar structure to keep track of which bodies they are.
I just started using Cocos2D this week. While playing around with Box2d i was wondering if it was possible to move CCSprites with the help of CCActions and use box2ds collisiion detection feature to detect collision between those sprites..
I'm pretty sure this must be possible?
If you don't need real physics behavior, I'd highly recommend to "manually" deal with your collision logic. That said, for your scenario I would start with this approach.-
Create one body per sprite, and assign each sprite to the user data.
Your 'static' scenario would map to static bodies (i.e floor, platforms, etc...)
Your 'dynamic' sprites would map to dynamic bodies, which only fixture would be marked as sensor
You'd register a b2ContactListener to listen for the collisions.
As for the tricky part, you'd need to set in each iteration of the main loop, the position of each body to the position of each sprite (of course, translating pixels to meters), in order to avoid that they just behave as physics bodies. You could try just to not calling world->step, but not sure if contactListener would work then.
Hope it helps!
I'm new to the Qt3D module and am currently writing a game in Qt5/C++ using Qt3D. This question is about "Am I on the correct path?" or "Can you give me some advice on...".
The scene of the game has a static part (the "world") and some objects (buildings and movable units). Some of the buildings might be animated in the future, but most of them are very static (but of course destructible).
I divide the quesion into two parts: How to handle copies of the same model placed at different positions in the scene and how to manage the scene as a whole in the viewer class.
Redundant objects in the scene:
Of course the objects share the same library of buildings / movable units, so it would be dumb to upload the models for these objects to the graphics card for every instance of such a unit. I read through the documentation of QGLSceneNode, from which I guess that it is designed to share the same QGeometryData among multiple scene nodes, but apply different transformations in order to place the objects at different positions in my scene. Sharing the same QGLSceneNode for all instances of a building would be the wrong way, I guess.
I currently have a unit "library class" telling me the properties of each type of building / movable unit, among other things the geometry including textures. Now, I'd provide a QGeometryData for each building in this library class, which is uploaded on the loading procedure of the game (if I decide to do this for all buildings at startup...).
When creating a new instance of a unit, I'd now create a new QGLSceneNode, request the QGeometryData (which is explicitly shared) from the library and set it on the node. Then I set the transformation for this new node and put it in my scene. This leads us to the second part of my question:
Manage the scene as a whole:
My "scene" currently is neither a QGLSceneNode nor a QGLAbstractScene, but a struct of some QGLSceneNodes, one for each object (or collection of objects) in the scene. I see three approaches:
My current approach, but I guess it's "the wrong way".
The composition: Putting everything as child nodes in one root QGLSceneNode. This seemed the correct way for me, until I realized that it is very difficult to access specific nodes in such a composition. But when would I even need to access such "specific" nodes? Most operations require to take all nodes into account (rendering them, updating positions for animations), or even operate on a signal-slot-basis so I even don't need to find the nodes manually at all. For example, animations can be done using QPropertyAnimations. Acting on events can also be done by connecting a QObject in the game engine core (all buildings are QObjects in the engine's core part) with the corresponding QGLSceneNode.
But this approach has another downside: During rendering, I might need to change some properties of the QGLPainter. I'm not sure which properties I need to change, this is because I don't know Qt3D enough and can't guess what can be done without changing the properties (for example: using a specific shader to render a specific scene node).
Then I found QGLAbstractScene, but I can't see the advantages when comparing with the two solutions above, since I can't define the rendering process in the scene. But maybe it's not the correct location where to define it?
Which is the best approach to manage such a scene in Qt3D?
With "best" I mean: What am I going to do wrong? What can I do better? What other things should I take into account? Have I overlooked anything important in the Qt3D library?
I am working on a simple 2D openGL project. It contains a main actor you can control with the keyboard arrows. I got that to work okay. What I am wanting is something that can help explain how to make another actor object follow the main actor. Maybe a tutorial on openGL. The three main things I need to learn are the actor following, collision detection, and some kind of way to create gravity. Any good books or tutorials to help get me in the right direction would be great.
You could use a physics library like Chipmunk Physics, which lets you attach springs and things between the two objects and detect when they hit each other and other things.
A pre-rolled library would be good, but the concepts you describe are ones you need to know if you are going to do any sort of game programming anyways:
A simple way to make one actor follow behind another is to have the lead actor store its position every time it moves. Feed these positions to a trailing actor with a delay of a few values - the longer the delay, the further behind they travel. Simple, but doesn't handle dynamic collision (other actors moving the block collision.)
Collision detection in 2D can simply be axis aligned (AA) bounding boxes. Search for this and you'll see the 4 ifs or so that are needed.
Gravity is just adding a fixed velocity (usually down) to every object every game loop. This is constant acceleration which is exactly how gravity works.
I'm making slow but steady progress with a Cocos2d game, but I'm stuck creating moving platforms.
The main character needs physics and collision detection, and is therefore a chipmunk shape/body. I wrote a class to iterate over the TMXTiledMap in order to cut back on the amount of bodies in the chipmunk space. So with a map like this
----------
--------x-
-xxx----x-
----------
instead of having 5 individual bodies (rects), there are two bodies, One is three tiles wide, the other is two tiles tall.
I've managed to get the code working to identify which tiles are part of a moving platform and to move the tiles as needed.
However, the bodies need to move with the tiles in order for this to work properly. And this is where I'm stuck. The bodies are of a static mass so...
platformShape->body->p = cpv(x,y);
Doesn't do anything (I'm guessing that this is the expected behavior).
But if I set their mass to anything other than static, all the physics comes into play and the bodies do not behave as expected, or they behave perfectly depending on you how you look at it. They move erratically and the rotate when they hit another body (eg: the main character). What I'm after is the typical type of moving platform you would expect to find in a typical platform game that moves smoothly in any given direction.
My question is; Has anyone implemented something like this before and what was your technique? Or, if you were to implement something like this, how would you do it?
The relevant code is here. I put it in a pastebin since I figure it's more of a conceptual misunderstanding than anything else.
It turns out you need to call
cpRehashStaticShapes
Obvious really, but easy to miss in my opinion.