# Tagged Questions

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 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 ...
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### How did LoZ: A Link to the Past handle sub-tile collisions?

The Legend of Zelda: A Link To The Past is rendered with 16×16 tiles. How did they implement collision with tiles where only a quarter or half is occupied? You can see such tiles in the cliff corners ...
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### 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 ...
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### Platformer collision problems

I am working on a platformer 2D, and i am currently focusing on collision. I have the actual rectangle(class: Rect) and i can detect if the player-model is intersepting it. However, when it comes from ...
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### 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.
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### Microsoft XNA Platformer Example, is the Collsion Detection implemented accurately?

The example provided by Microsoft seems as if the collision detection (from what I can see) will have a small error. When the user collides with an Unpassable tile, the depth of the intersection is ...
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### 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 ...
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### 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 ...
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### How do I detect the direction of 2D rectangular object collisions?

After this question, I need some more help. How can I find out which side of a rectangle a collision came from and react accordingly? The blue arrows are the paths that some circular objects ...
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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 ...
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### 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....
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### How to implement uniform grids

Up until now, I implemented all-against-all collision detection in my games. It worked fine. But I reached a point where implementing this kind of collision detection, makes the game run poorly, ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### How do I prevent my platformer's character from clipping on wall tiles?

Currently, I have a platformer with tiles for terrain (graphics borrowed from Cave Story). The game is written from scratch using XNA, so I'm not using an existing engine or physics engine. The tile ...
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### How can I implement fast, accurate 2D collision detection?

I'm well aware of how to detect if two or more 2D objects collide but I'm interested in how to decide whether to check for a collision. In previous projects, I just had every object check against ...
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### How can I use Rectangle.Intersect() to resolve collisions in XNA?

I have a 2D game written in XNA, and I've been trying to fine-tune my collision resolution. All of my game objects are squares, which means detecting a collision is easy - use the position and the ...
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### Small, High-Speed Object Collisions: Avoiding Tunneling

EDIT/UPDATE: My biggest question right now is whether step 3's "t=..." equation is a good idea or there a better way to do it. Most other issues have been partially or fully addressed, but no ...
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### How do I calculate the angle of the slope at a point on a 2D bitmap terrain?

I have an arbitrary destructible bitmap terrain like the one in "Worms". It's easy to work out if a character or missile intersects the terrain, but how do I work out the angle of the slope at the ...
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### Finding the contact point with SAT

The Separating Axis Theorem (SAT) makes it simple to determine the Minimum Translation Vector, i.e., the shortest vector that can separate two colliding objects. However, what I need is the vector ...
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### per pixel based collision detection

I was wondering if anyone had any ideas on how to get per pixel collision detection for the android. I saw that the andEngine has great collision detection on rotation as well but couldn't see where ...
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### 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 ...
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### 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 ...
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### How many and which axes to use for 3D OBB collision with SAT

I've been implementing the SAT based on: http://www.geometrictools.com/Documentation/DynamicCollisionDetection.pdf for 3D collisions On page 7, in the table, it refers the 15 axis to test so we can ...
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### How do I make a curved surface out of rectangular blocks?

For a Peggle-like game, I want to make blocks that follow a curve, like this: The blocks would then disappear as the ball hits them. I managed to draw some horizontally, but I'm having trouble ...
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### 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 ...
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### Which Side Was Hit?

I am working on an Android game and I have two objects A and B (both rectangles) and when they collide I simply want to know which side of B was hit. I have detected the collision fine, but I am ...
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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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### 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 ...
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### 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 ...
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### How to separate colliding objects without creating more collisions

Suppose I use a simple discrete collision detection system where I move all objects then check for collisions. I want any colliding objects to be separated (of course) and assigned appropriate ...
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### Breakout Collision: Detecting the side of collision

I am writing a breakout clone (my first game) and am totally stuck as to how I figure out which side of the brick was hit. I have a collision detection method that looks like this: DetectCollision(...
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### How can I implement rectangle collision response?

I am working on a game in JavaScript and my current implementation of collision uses the shortest distance to push the intersecting object away, which isn't always correct. I've made this diagram of ...
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### How do I resolve a collision of a rectangle with two rectangular tiles at once?

I am having some problems with collision detection between a player and the environment in a tile-based game. I have a player objects, Tiles and what I call MapObjects. The tiles are all 16×16. The ...
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### Making an efficient collision detection system

I'm very new to game development (just started 3 months ago) and I'm learning through creating a game engine. It's located here. In terms of collision, I know only brute-force detection, in which case,...
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### How do I find the point of impact with 2D per-pixel collision detection?

I'm creating a platformer and have implemented per-pixel collision detection. However, this has caused 2 obstacles that I've yet to figure out. The first obstacle, which this question is about, is ...
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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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### Collision detection - Smooth wall sliding, no bounce effect

I'm working on a basic collision detection system that provides point - OBB collision detection. I have around 200 cubes in my environment and I check (for now) each of them in turn and see if it ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### What's the most efficient way to find the intersection point of a missile and a bitmap terrain?

Following up on my earlier question about finding the slope of a 2D bitmap terrain I now need to know the best way of finding the point on the 2D terrain that the missile hit. Obviously, I can see if ...
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### How can I improve my collision detection's performance?

I'm new to programming and want to speed up the collision detection in my C++ 2D platformer game engine. Currently, only the player's collision detection works: Every frame, the player's update ...
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### 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 ...
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### 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 ...