I try to begin new game development that has rotating circle that has one or many holes as in the attached image , the problem is I need to use circle collides for the big circle., in addition I need to use small collides for the smaller holes to prevent and particles(smaller circles ) input the circle and to count no of collisions occurred
enter image description here
The circle collider itself does not have this functionality since it can only check collisions between perfect circles. (Behind the scenes all circle colliders just check the distance between points and these distances do not work with holes) The best solution I can think of would be to use a polygon collider and make a rough circle that you can then remove parts of (would require some advanced geometry but not impossible). I have tried simillar things in 3D and with the mesh collider, removing parts of it using a method known as CSG (Wikipedia) and something simillar should be possible in 2D however it is really, really hard and even experienced programmers struggle to come up with a system that can handle every scenario.
All hope is not lost though, depending on what you need the collision for, there might be other ways. If you just need to check if two objects intersect and don't want rigibodys and stuff to interact with the collider just checking the distance between the big circle and the object (too figure out if it's close enough) and then checking the distance between the object and the holes (too see if it's inside a hole on thus not colliding) is the best way to solve the issue.
I'm sure someone who have done more in this field than I have will be able to help you out but without more information of what you need it's impossible to say. It all depends on the circumstances!
Related
Like the image attached, I want to get a polygon collider of the area of the biggest collider subtract the areas of these two smaller colliders inside the big one?
I just want to have a collider that covers only the gray area in the image below.
At runtime please, it's ok to get a composite / polygon or what other types of collider.
Thanks very much.
Fastest way would indeed be to have 3 separate Colliders, and when collision happens with the big one, you also check that it does NOT happen with the two smaller colliders.
Check the Clipper library for polygon operations (also worth checking the eppz! Geometry library, which itself uses Clipper).
You can then use the resulting polygon "paths" (as it's called in the Clipper library) to create several EdgeCollider2Ds (you can [set its points][4] to create the shape of each polygon.
There is a problem with this approach though, which is that in the end you will not have a "solid" collider with an inside and an outside, and instead you will just have lines to collide with. Hopefully this will not be an issue for most of the cases.
I am not sure but you could use separate box colliders to get the same affect. Just need multiple references in the script.
I'm working on a 2D physics game that involves collisions between objects which at the moment use complex polygon colliders.
When the objects collide, I get the normal of the contact point using otherObject.contacts[0].normal, and knock the objects apart in equal-but-opposite directions using Rigidbody2D.AddForceAtPosition, with the force being the normal multiplied by a constant.
Most of the time this works flawlessly, but I've found that when the collision occurs with a concave section (aka: an inward "dip") in the polygon collider, the normal will be flipped, and the objects will instead get pushed towards each other.
Alternatively, are there any other ways I could go about solving this?
The blue circled area is an example of a problematic concave section
Alternatively, are there any other ways I could go about solving this?
Yes, the standard thing in vid games is that most stuff has many small simple colliders, rather than one large complex collider.
This is a basic of game engineering.
(It can be very surprising to hobbyists and folks new to the field.)
So, imagine a car in any ordinary 3D game. You'd have a collider for the rear bumper, one for the front, maybe one for "left doors" and so on. Very typically, each has to react in a different way, and you need to know which area was touched.
In your case if the 2D poly has say 12 edges, just make 12 "small" as it were colliders for each of the edges.
We know nothing about your setup since no screenshot, but that could possibly work.
Note however that Unity's 2D poly collider in fact already does know to slice the object in to smaller triangle-like shapes if it is concave - I'm surprused it dinnae work for you.
Further: now that we can see your image.
In any video game on Earth, the way you'd do that helmet is with a square collider as in orange:
If (for some reason .. why? for what purpose? how? where? what possible reason could there be?) you were making the most precise video game, ever created by humans, on an entirely new plane of engineering, for some imaginary new hardware with quantum warpspace cores, ... in that case ... you'd maybe add the two extra colliders to cover the horns. But nobody would ever notice the difference.
I appreciate you may be doing something exceptionally unusual, like a "close up game" ("you're an atom in medieval Scandinavia, bouncing off helmets" or whatever), in which case there'd be some other solution.
The very short answer is you've stumbled on one of the most surprising things about game technology ... we use crappy, simple, colliders, you've been tricked all your life in every title you play!
I'm new to using xna and I want to make my player collide with with multipe walls from the same class. So I looked around and I understood that the best way for doing that is to create a list of variables containing the walls id's and make a loop that circles them all and then returns the variable of the objects that collide.
My question is if there is a faster more efficient way for doing that? I mean if I have like 10000 objects that loop can cause a lot of memory use.
Thx in advance
Option 1) If these 10000 object are walls of a level, then you should probably use some sort of grid (like this very old example: https://en.wikipedia.org/wiki/The_Legend_of_Zelda#mediaviewer/File:Legend_of_Zelda_NES.PNG)
With a grid you only have to check collision with adjacent objects, or only with objects that are nearby.
Option 2) If these 10000 objects are enemies or bullets that move more freely, then you could also calculate the distance first and only check for collision if the objects are nearby.
But may I ask why you are using XNA? I used to work with XNA 4.x but in my understanding it is pretty much dead (http://www.computerandvideogames.com/389018/microsoft-email-confirms-plan-to-cease-xna-support). If you're new to XNA, I would advice to use other software to make games (like Unity3D). In Unity3D the hard part of collision detection is done for you (is has standard functions for collision detection) and Unity3D also works with C# (like XNA)
You always want to do the least amount of processing to get the job done. For a tiled 2D game you usually have a 2 dimensional grid. When the player want to walk on a certain tile you can check that tile if it is allowed to walk there. In this case you just have to check a single tile. If you have a lot of NPC's you could divide your map into sections and keep track of in what sections the NPC's are. Now you just have to do collision detection on the enemies within your section.
When you need expensive collision, pixel perfect or polygon collision you should first check if an object is even close with a simple radius float or BoundingSphere only then you go on with more expensive collision detection.
Same goes for pretty much anything, if you have a 100x100 tilemap but only need to draw 20x10 for the screen then you should just render that portion by calculations. In unreal, mappers create invisible boxes, when inside these boxes it only draws a certain part of the map and only checks collision within these boxes. GameDev is all about tricks to make things work smoothly.
xcode 5 iOS7 sprite kit.
My wish is to make a sprite that has its own gravity.
Like a planet. If another sprite comes within a certain range of it, it will slowly pull the other sprite closer.
I have two sprites. One moving and one stationary. When the moving sprite gets in a given distance of the stationary sprite the stationary sprite gravity should slowly pull the other sprite towards it. This way the moving sprite would change its path in a soft curve.
My idea would be to calculate the distance from the stationary object to any other object and if close enough start pulling and if the moving object gets out of range ageing, then stop pulling.
Would probably need to research some vector calculation.
Thats my immediate thoughts.
Is this possible and how? Does it already exist?
A friend of mine did this for his physics dissertation. multibody gravity simulation. So yeah you can but you need to be willing to learn some maths. Apparently there is a clever optimisation to make it run decently nlog(n) rather than n^2). you probably want to ask this on the physics version of stack overflow to get a good answer. I have the code at home ... will post it later but you will want an explanation - i used it in an xna app. Its badass once you get it working - although if you want naturally orbiting objects then you will want to code them using parametric equations for easy and cool orbits. Simply because its hard to solve and with time even using double will result in some errors (the good implementations also work out the error and adjust - again will post later). But the real problem is solving for stable orbits. You then use the algorithm for free moving bodies such and player objects / npcs. Although solving accurate movement for npc in a changing field is v hard.
you want to look at this question: Jon Purdys answer is the one you want
multi body physics - gravity
and this one (which is linked from above) ...
https://gamedev.stackexchange.com/a/19404
There is not a dead-simple way of doing that in any platform as far as I know maybe except for some game engines/platforms that export for different platforms (cocos2d, construct 2 etc).
What you need is a physics engine whether you write one (which is a complicated but fun thing to do) or use an available one.
Luckily I've found a link describing the usage of the famous 2D physics engine "Box2D" on iOS.
This one explains how you can include Box2D in an openGL application (but you can apply this to other environments (sprite kit) I think altough I'm not an iOS guy);
http://www.iforce2d.net/b2dtut/setup-ios
Anyways, you now know what to look for...
For iOS 8.0+ : you have SKFieldNode : radialGravityField()
For iOS 8.0- : one solution could be : 3 to 9
add your sprite ( planet ) with its physics
add an invisible SKNode ( the gravity zone ) with its own physics, as a child of your sprite, but with a radius much more than your sprite's one
you have a little explanation about invisible node here : https://developer.apple.com/documentation/spritekit/skphysicsworld
both, your sprite and the invisible node are centered in a zero gravity world
we look for contact and not collision ( set correctly your bit masks )
when any object get in contact with the invisible node ( gravity zone ), first you remove any moving action or impulse from it and then we add to this object an SKAction to move it toward the center of your sprite ( planet )
at second contact between this object and your sprite ( planet ), you remove all actions again from the object with a velocity = zero
Hi Guys I am doing some work on iOS and the work requires use of OpenGL es. So now I have a bunch of squares, cubes and triangles on the screen. Some of these geometries might overlap. Any ideas/ approaches for touch detection?
Regards
To follow up on the answer already given, squares, cubes and triangles are convex shapes so you can perform ray-object intersection quite easily, even directly from the geometry rather than from the mathematical description of the perfect object.
You're going to need to be able to calculate the distance of a point from the plane and the intersection of a ray with the plane. As a simple test you can implement yourself very quickly, for each polygon on the convex shape work out the intersection between the ray and the plane. Then check whether that point is behind all the planes defined by polygons that share an edge with the one you just tested. If so then the hit is on the surface of the object — though you should be careful about coplanar adjoining polygons and rounding errors.
Once you've found a collision you can easily get the length of the ray to the point of collision. The object with the shortest distance is the one that's in front.
If that's fast enough then great, otherwise you'll probably want to look into partitioning the world or breaking objects down to their silhouettes. Convex objects are really simple — consider all the edges that run between one polygon and the next. If only exactly one of those polygons is front facing then the edge is part of the silhouette. All the silhouettes edges together can be projected to a convex 2d shape on the view plane. You can then test touches by performing a 2d point-in-polygon from that.
A further common alternative that eliminates most of the maths is picking. You'd render the scene to an invisible buffer with each object appearing as a solid blob in a suitably unique colour. To test for touch, you'd just do a glReadPixels and inspect the colour.
For the purposes of glu on the iPhone, you can grab SGI's implementation (as used by MESA). I've used its tessellator in a shipping, production project before.
I had that problem in the past. What I have used is an implementation of glu unproject that you can find on google (it uses the inverse of the model view projection matrix and the viewport size). This allows you to map the 2D screen coordinates to a 3D vector into the world. Then, you can use this vector to intersect with your objects and see which one intersects (or comes really close to doing so).
I do hope there are better ways of doing this, so I look forward to other answers as well!
Once you get the inverse-modelview and cast your ray (vector), you still need to know if the ray intersects your geometry. One approach would be to grab the depth (z in view coordinate system) of the object's center and extend (stretch) your vector just that far. Then see if the vector's "head" ends within the volume of your object or not (you need the objects center and e.g. Its radius, if it's a sphere)