# 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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### How to find 2D grid cells swept by a moving circle?

I'm making a game based on a 2D grid, with some cells passable and some not. Dynamic objects can move continuously, independent of the grid, but need to collide with impassable cells. I wrote an ...
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### How do I determine if one polygon completely contains another?

I have 2 polygons. I know the vertex coordinates of both polygons. What's the best way to check if one is completely inside the other? For example, the algorithm should only recognize the black ...
7k views

### 2D object-aligned bounding-box intersection test

I have two object-aligned bounding boxes (i.e. not axis aligned, they rotate with the object). I'd like to know if two object-aligned boxes overlap. (Edit: note - I'm using an axis-aligned bounding ...
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### Moving objects colliding when using unalligned collision avoidance (steering)

I'm having trouble with unaligned collision avoidance for what I think is a rare case. I have set two objects to move towards each other but with a slight offset, so one of the objects is moving ...
9k views

### How do I calculate collision response between a sphere and a plane?

I'm trying to create a simple 3D game and need to constrain the player within the limits of the game world. When the player hits the sides of the world I want the player's ship to bounce off slightly. ...
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### Simulating an object floating on water

I'm working on a top down fishing game. I want to implement some physics and collision detection regarding the boat moving around the lake. I would like for be able to implement thrust from either the ...
613 views

### How to detect collisions between sprite and a user generated shape of some sort?

How to detect a collision between a sprite and a user-generated shape of some sort. For example. There are some objects on the screen. The user takes their finger and draws a circle shape around an ...
901 views

### Separating axis theorem with multiple polygons?

I am attempting to implement the separating axis theorem in C#. I have a function that can calculate the minimum translation vector between two polygons. However, I can't seem to create a function ...
466 views

### Platform jumping problems with AABB collisions

See the diagram first: When my AABB physics engine resolves an intersection, it does so by finding the axis where the penetration is smaller, then "push out" the entity on that axis. Considering ...
366 views

### Connecting physics simulations with different coordinate-systems

I want objects to move between two physics simulations through a "window" and collide with those from both simulations in case they intersect the window plane. The coordinate systems of the ...
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### How do I induce collision events in LibGDX 3D?

In the code below I've put an example of something I want to do. I have the camera and I want it to stop moving whenever it hits one of the boxes, how do I do this? ...
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### Ball vs 45-degree slope collision detection

I have a simple game in which the player moves a ball around. The ball bounces off of walls. Right now I have square walls(■) implemented: I use simple bounding-box collisions to check if the player ...
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### 2D Platformer Collision Handling

I am trying to create a 2D platformer (Mario-type) game and I am some having some issues with handling collisions properly. I am writing this game in C++, using SDL for input, image loading, font ...
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### How to handle pixel-perfect collision detection with rotation?

Does anyone have any ideas how to go about achieving rotational pixel-perfect collision detection with Bitmaps in Android? Or in general for that matter? I have pixel arrays currently but I don't know ...
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### Reconciling Flocking and A* (Theory)

For my RTS game I have got A* pathfinding working, and that's fine. Basic collision detection exists too. When a unit is moving it checks if the position it will occupy next move is a node occupied ...
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### Reusable top-down collision class

I've recently picked up monogame and am working on a simple top down game to get me started and learn the basics. I've got the movement and the rotation to follow the mouse sorted out but I'm stuck ...
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### Collision Detection Game Design and Architecture

I've reading some articles about collision detection. My question here is about ideas on the design for it. Baically I have a C++ game that has a main loop with entities with an update method. Based ...
839 views

### Collision detection: a bunch of special cases?

I'm writing a simple physics engine in 2D. My first goal is to get collision detection working. I know that my objects will eventually be made up of primitive shapes, but I was wondering - would a ...
6k views

### Given a plane and a point, how can I determine which side of the plane the point is on?

Given the point Vector pos = new Vector(0.0, 0.20156815648078918, -78.30000305175781, 1.0); and the plane (triangle) ...
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### 2D AABB vs AABB Sweep : How to calculate hit normal?

I've implemented a 2D AABBvsAABB sweep cast into my game, however, I'm having difficulty calculating the hit normal of the sweep cast. I have the sweep direction, both a and b AABB positions and xy ...
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### 2D AABBs and resolving multiple collisions

Okay, so this is a problem I've been trying to figure out for quite some time. Mine is a 2D platformer game with a world made up of (usually) immobile tiles and mobile sprites, both of which use AABBs ...
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### Collision detection problems using AABB's

I implemented a simple collision detection routine using AABB's between my main game sprite and various platforms (Please see code below). It works great, but I'm now introducing gravity to make my ...
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### How to perform collision detection in 3D space?

I've got to write, what can be summed up as, a complete 3D game from scratch this semester. Up until now I have only programmed 2D games in my spare time, the transition doesn't seem tough, the game's ...
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### Finding the point of collision

I'm writing a 2D rigid body simulator. The objects being simulated are convex polygons. My question involves how to decide on the "point" of collision, so that when I apply a response force, I can ...
346 views

### Determining whether two fast moving objects should be submitted for a collision check

I have a basic 2D physics engine running. It's pretty much a particle engine, just uses basic shapes like AABBs and circles, so no rotation is possible. I have CCD implemented that can give accurate ...
2k views

### How do I create a draggable object which snaps to obstacles in the way?

I bring yet-another-drag-with-mouse question (I am using Unity with C#), but with a less common particular detail: the existence of obstacles in the middle of the way trough which dragging occurs (3D ...
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### How can I prevent rigid bodies from moving through each other using Unity's built-in physics?

I'm trying to create a game where objects can be dragged, but I'm having trouble with the physics. With rigid bodies that have similar masses, they sometimes push through each other when dragged and ...
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### In Box2D, how can I get the compression force on a specific body?

I'm using Box2D. As you can see, there are three dynamic bodies connected to each other (think of it as a table from front view). LEG1 and LEG2 are connected to the static body (it's the ground body). ...
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### Collisions between players in multiplayer racing game

I'm creating a simple racing game (spaceships, no gravity) using p2.js, phaser and node.js. What I have done: Client receives world state from server: extrapolate other players based on latest ...
578 views

### 3D collision avoidance: finding the updated velocity vector (outside the “collision-velocities” cones)

I am trying to understand and implement the mechanism of a fully 3D collision avoidance (steering behavior) system for flight movement (six degrees of freedom), currently focusing on circumventing ...
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### Tile-based 2D collision detection problems

I'm trying to follow this tutorial http://www.tonypa.pri.ee/tbw/tut05.html to implement real-time collisions in a tile-based world. I find the center coordinates of my entities thanks to these ...
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### Using PhysX, how can I predict where I will need to generate procedural terrain collision shapes?

In this situation, I have terrain height values I generate procedurally. For rendering, I use the camera's position to generate an appropriate sized height map. For collision, however, I need to have ...
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### How to determine collision direction between two rectangles?

I am trying to figure out how to determine the direction a collision occurs between two rectangles. One rectangle does not move. The other rectangle has a velocity in any direction. When a collision ...
7k views

### A more sophisticated ball-paddle collision algorithm for Breakout?

I have a simple breakout game I'm working on. The collision code is solid; things bounce as they should and don't pass through things or do other funkiness, but the reflection is a bit simplistic. As ...
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### MMO Collision detection

I am building a MMO game server for a 2D game and am currently implementing the collision detection, and I am would like to know what I should do. Lets say I have 1000 players playing and 10,000 ...
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### Stuck in Wall after rectangle bounding box collision

Using XNA's built in Intersects() on two Rectangles, I can detect a collision and set my velocity to zero. However, the object is stuck there and can't get out! How can I resolve this collision ...
865 views

### Your recommendation for path construction from a single background image?

So I currently have my background as a single PNG and some obstacles (like blocks as part of that PNG). In order to create a path, I currently store pixels above a unique green color (my hill) and use ...
23k views

### How do I make a game tick method?

I've seen in some other simple 2D games that a "tick" method is used to sync game logic and graphics rendering. My main reason for using this is due to my collision detection malfunctioning, since ...
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### Sidescroller variable terrain heightmap for walking/collision

I've been fooling around with moving on sloped tiles in XNA and it is semi-working but not completely satisfactory. I also have been thinking that having sets of predetermined slopes might not give me ...
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### Why do Physics Engines use collision margins?

When using a physics engine in a game (such as Bullet), you usually need to define a collision margin for each object. I'm a beginner to game development, and I don't understand the purpose of a ...
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### Tiled based map collision detection problem

I'm working on a tile-based Mario clone. This works all fine when walking and falling. But when the player jumps near a wall and walks to the right in the air, then the player get stuck on the wall. ...
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### 3D collision-detection middleware [closed]

(I've split this question into two. For 2D, see: 2D collision-detection middleware) Are there any recommendable middleware available for 3D collision detection? I believe I've heard Bullet has a ...
935 views

### Polygon editor to draw collision data over image [closed]

I need an editor to plot a polygon over the texture for of a ship in my game. It would look like this.. Where the red is the collision outline and the image is the texture. I want to store the ...
8k views

### How do I find the intersection of two lines

I have a bounding box on my character, its position in the previous frame an the current frame. The bounding box is axis aligned. My character is running around inside a cave, I have a list of ...
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### Collision Systems Implementation

Just curious what might be a good way to implement a decent collision system. As a class inherited by a base Entity class? Currently I'm stuck and could just use a couple better ideas than my own. ...
623 views

### How to represent a game character in code?

In a previous game I wrote I had a game character class. This class tracked the location, velocity, and a set of states. Except the states were tied very close to the animation. Each state would have ...
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### Identifying quad patterns in a two-dimensional array

In the tech demo I'm trying to make, tetrominoe-style blocks will be placed by the player, at which point the game checks to see if they've made a quad with any existing shapes on the board (a 2D ...
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### Implementing Separating Axis Theorem (SAT) and Minimum Translation Vector (MTV)

I was following codezealot's tutorial on SAT and MTV and trying to implement it myself but I've come a cropper when it comes to getting the correct MTV. Here is my example: (Cue pretty pictures...) I'...