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Questions tagged [collision-detection]

Collision detection is the determination of whether or not two or more entities make contact with each other during gameplay.

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78
votes
6answers
37k views

How does a collision engine work?

How exactly does a collision engine work? This is an extremely broad question. What code keeps things bouncing against each other, what code makes the player walk into a wall instead of walk through ...
63
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10answers
95k views

What is the fastest way to work out 2D bounding box intersection?

Assume that each Box object has the properties x, y, width, height and have their origin at their center, and that neither the objects nor the bounding boxes rotate.
60
votes
9answers
7k views

How to avoid circular dependencies between Player and World?

I'm working on a 2D game where you can move up, down, left and right. I have essentially two game logic objects: Player: Has a position relative to the world World: Draws the map and the player So ...
53
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10answers
70k views

most efficient AABB vs Ray collision algorithms

Is there a known 'most efficient' algorithm for AABB vs Ray collision detection? I recently stumbled accross Arvo's AABB vs Sphere collision algorithm, and I am wondering if there is a similarly ...
51
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7answers
9k views

2D Platformer AABB collision problems

I have a problem with AABB collision resolution. I resolve AABB intersection by resolving the X axis first, then the Y axis. This is done to prevent this bug: http://i.stack.imgur.com/NLg4j.png The ...
46
votes
4answers
7k views

A ball hits the corner, where will it deflect?

I need to brush up my trigonometry and hope you can help here with a simple mathematical model. Here is my model so far in the image attached. I am aware that the frame animation has other problems ...
39
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6answers
6k views

Hexagon collision detection for fast moving objects?

A object has a position and a speed vector. Usually only the position is used to check if two objects collide, this is problematic for very fast moving objects as it can happen that the object moves ...
29
votes
3answers
19k views

How many and which axes to use for 3D OBB collision with SAT

I've been implementing the SAT based on: Dynamic Collision Detection using Oriented Bounding Boxes [PDF] On page 7, in the table, it refers the 15 axis to test so we can find a collision, but with ...
29
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6answers
18k views

How do I calculate distance between a point and an axis-aligned rectangle?

I have a 2D rectangle with x, y position, height and width, and a randomly positioned point nearby. Is there a way to check if this point might collide with the rectangle if it is closer than a ...
28
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6answers
6k views

How to decide which GameObject should handle the collision?

In any collision, there are two GameObjects involved right? What I want to know is, How do I decide which object should contain my OnCollision*? As an example, let'...
27
votes
2answers
16k views

Quad tree vs Grid based collision detection

I'm making a 4 player co-op r-type game, and I'm about to implement the collision detection code. I've read a lot of articles and stuff about how to handle collision detection, but I'm having a hard ...
27
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7answers
9k views

What is a good algorithm to detect collision between moving spheres?

If (for the purpose of collision detection) 3D objects are represented in a game by spheres, what is a good algorithm to detect a collision between spheres? If each object has a position as of the ...
24
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4answers
12k views

Should collision detection be done server-side or cooperatively between client/server?

I am working on an online game that will have very heavy collision detection processing. Player models will collide with other players, mobs, structures, terrain, and solid objects that only exist ...
24
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9answers
3k views

Is there a simple way to stop enemies standing in the same spot?

So: top-down game, my enemies chase the player, when they get within a certain distance they stand still and fire. If they're all coming from the same direction they all end up standing in the same ...
23
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6answers
5k views

How to optimize the distance function?

While developing a reasonably simple RTS-like game, I noticed my distance calculations were causing an impact in performance. At all times, there are distance checks to know if a unit is in range to ...
23
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5answers
17k views

Collision Resolution

I know quite well how to check for collisions, but I don't know how to handle the collision in a good way. Simplified, if two objects collide I use some calculations to change the velocity direction. ...
22
votes
4answers
4k views

Momentum and order of update problems in my physics engine

This question is a "follow-up" question from my previous one, regarding collision detection and resolution, which you can find here. If you don't want to read the previous question, here's a brief ...
22
votes
4answers
8k views

How to deal with corner collisions in 2D?

I'm writing a top down 2d XNA game. Since its my first I'm trying to write the physics and collision stuff myself to learn it. Whenever my player sprite character attempts to move into a position ...
21
votes
6answers
7k views

Collision 100% avoidance implementation

I'm an absolute beginner with game development and all I know about collision avoidance/resolution, I learnt it on or through this site in the past week... so don't hesitate to correct me if what I'm ...
20
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3answers
35k views

OBB vs OBB Collision Detection

Say you have two Bounding Box Objects each of them storing the current vertices of the box in a vector with all the vertices of the object rotated and translated relative to a common axis. Here is an ...
19
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7answers
7k views

How can I detect the player being crushed in a 2D platformer?

I'm checking collision for a platformer character as shown in #1. The red dots are the pixels that are checked and the grey lines indicate the axes they pertain to. I like the results I get from ...
19
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7answers
6k views

How do I make A* agents avoid other agents?

I'm implementing a multi agent A* algorithm on a tile map. Agents move only in the X and Y axes. I avoid collisions between them by checking where the others are when calculating paths. It works fine ...
19
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3answers
8k views

How do I test if a circle and concave polygon intersect?

I have a polygon (sometimes convex, but often concave), and a bunch of circles with different radii. How can I find out if a circle is intersecting/overlapping with the polygon? I could split my ...
19
votes
2answers
5k views

Where should collision detection logic be placed?

I am developing a small 2D game engine. The characters have a paint method which currently does the following: Calculate the new position of the character as per its speed, etc. Update the collision ...
17
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1answer
18k views

Fast, accurate 2d collision

I'm working on a 2d topdown shooter, and now need to go beyond my basic rectangle bounding box collision system. I have large levels with many different sprites, all of which are different shapes and ...
16
votes
1answer
22k views

a simple 2D rectangle collision algorithm that also determines which sides that the rectangles collide?

I initially tried out implementing rectangular intersection, which works well. However, when I have to apply the physics system, such as velocity, acceleration, and directional vectors, I would have ...
16
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2answers
5k views

Best/Efficient way to implement a 3d Collision

I've already programmed a 2d based collision system for a previous game. It was my first collision system and it was ugly. I was looking for collision between objects by checking all objects with all ...
16
votes
3answers
814 views

Building a Plattformer - How to determine if a player is allowed to jump?

I'm building a simple Plattformer Jump n' Run Style game. I do not use tiles - instead i've geometrical shapes for my level entities (and the player is one too). I finished my collision detection code ...
16
votes
1answer
2k views

How to resolve collisions of compound shapes using SAT?

SAT is a decent way to determine collisions between arbitrary convex polygons. You'll even get the vector that is needed to resolve a collision. To resolve collisions between complex (non-convex) ...
15
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4answers
4k views

Is it a bad idea to “map” the mouse position on the screen so that collision detection works regardless of resolution?

Consider a game who's default resolution is 800x600. Objects with collision masks are placed in a game world of size 800x600. The collision masks can detect when the mouse collides with them. Now ...
15
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3answers
12k views

Collision resolution in case of collision with multiple objects

I have static objects and movable objects. The collisions are detected using the separating-axis-theorem. For example, in this situation I have two static objects (in red): and a movable object ...
14
votes
3answers
10k views

Resolving a collision with forces

In my 2D physics engine, I can detect AABB vs AABB collisions, and resolve them by finding the shortest penetration vector and adding it to the AABB's position. Doing this "pushes" the first AABB ...
14
votes
3answers
7k views

Are collision detection always O(n^2)?

Are physics engine able to decrease that complexity, for example by grouping objects who are near each other and check for collisions inside this group instead of against all objects ? (for example, ...
14
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5answers
3k views

How can I optimize a collision engine where order is significant and collision is conditional based on object group?

If this is your first time on this question, I suggest reading the pre-update part below first, then this part. Here's a synthesis of the problem, though: Basically, I have a collision detection ...
14
votes
2answers
8k views

How do I handle collision detection so fast objects are not allowed to pass through walls?

I'm creating a 2d sidescrolling shooter, and I'm having a little trouble with collision detection for the bullets. Everything including the bullets are objects with their own polygons / update methods....
14
votes
5answers
30k views

Ignore collisions with some objects in certain contexts

I'm making a racing game with cars in Unity. The car has a boost/nitro powerup. While boosting, I wouldn't want to be deviated when colliding with zombies, but I do want to be deviated when colliding ...
13
votes
2answers
2k views

How does one perform collision detection on objects made of many small triangles?

I understand that any shape can be created (or approximated) by smaller triangles. Any rectangle can be created by 2 smaller triangles. Any circle can be created by many thin "pizza slice" triangles. ...
13
votes
6answers
7k views

How do I handle Isometric collision detection?

I would like to make an isometric run-jump style platformer. The player should be able to jump on top of platforms above the floor, hit the side of objects etc. I'll be using a 2D game engine so I ...
13
votes
1answer
6k views

How can I define a complex collision area on top of a tile map?

As many people recommended, I am using Tiled map editor to create a map for my game and it's great particularly because libgdx framework also provides with API for maps from Tiled. I understand I can ...
13
votes
3answers
9k views

2D game collision response: SAT & minimum displacement along a given axis?

I'm trying to implement a collision system in a 2D game I'm making. The separating axis theorem (as described by metanet's collision tutorial) seems like an efficient and robust way of handling ...
13
votes
4answers
7k views

Faster 2D Collision detection

Recently I've been working on a fast-paced 2d shooter and I came across a mighty problem. Collision detection. Sure, it is working, but it is very slow. My goal is: Have lots of enemies on screen and ...
13
votes
3answers
5k views

What is the best way to handle simultaneous collisions in a physics engine?

I'm writing a 2d physics engine in javascript so that I can learn more about physics in video games. I have it working correctly for rigid body collisions, except for if any body collides with two or ...
13
votes
5answers
5k views

2D Rope Collision Detection

I'm wanting to create a rope that can collide with objects like in the following youtube video: 2D Game Physics Rope I'm thinking that you implement the verlet integration which uses points and ...
13
votes
1answer
3k views

Quad trees/grid based collision - putting logic into action

First of all, I've only been writing my own game logic for a short while, so I apologize if this might seem straight forward. I've been reading a lot about quad trees and grid based collision ...
12
votes
4answers
8k views

How to solve the ground check problem?

I noticed a problem in Unity's third person controller's ground check. The ground check should detect whether or not the player is standing on the ground. It does so by sending out a ray beneath the ...
12
votes
3answers
26k views

Is there a good way to get pixel-perfect collision detection in XNA?

Is there a well-known way (or perhaps reusable bit of code) for pixel-perfect collision detection in XNA? I assume this would also use polygons (boxes/triangles/circles) for a first-pass, quick-test ...
12
votes
5answers
4k views

2D Level design/editing/saving questions [closed]

I thought about making a simple 2D Sidescroller game like SuperMario. Then i wondered about how to save, load or create the levels for the game. The first thing i thought of was drawing a simple ...
12
votes
6answers
5k views

What's the fastest way checking if two moving AABBs intersect?

I have two AABBs that are moving, what's the fastest way to check if they will intersect under a frame? By moving I mean not just to check with the usual rectangle intersection method, I mean some ...
12
votes
5answers
24k views

Unity: how to detect collision occuring on child object, from a parent script?

I've an enemy, with this structure Enemy Body Head Arm Left Arm right And so on. I also have a collider for each part of the body. In my "Enemy" object I've attached a script and in that script ...
12
votes
2answers
3k views

Storing coordinates of every object in server side in MMOs

In an MMORPG: Is it typical or feasible to store the coordinates of every tree, bush rock.. etc in the server side for collision detection? If so, what would be a feasible way to store such a huge ...