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• Support-function in the GJK-algorithm.

  - by Marcus Johansson

  I am trying to implement the GJK-algorithm but I got stuck instantly. The problem is to implement the Support-function that isn't O(n^2). As it is now I'm computing the complete Minkowski difference, and then there is really no point in doing the GJK-algorithm. (or is it?) What I mean by Support-function is the function that returns the point in the Minkowski difference that is furthest away in a specified direction. I assume this shouldn't be O(n^2) as it is in my current implementation.

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• Can GJK be used with the same "direction finding method" every time?

  - by the_Seppi

  In my deliberations on GJK (after watching http://mollyrocket.com/849) I came up with the idea that it ins not neccessary to use different methods for getting the new direction in the doSimplex function. E.g. if the point A is closest to the origin, the video author uses the negative position vector AO as the direction in which the next point is searched. If an edge (with A as an endpoint) is closest, he creates a normal vector to this edge, lying in the plane the edge and AO form. If a face is the feature closest to the origin, he uses even another method (which I can't recite from memory right now) However, while thinking about the implementation of GJK in my current came, I noticed that the negative direction vector of the newest simplex point would always make a good direction vector. Of course, the next vertex found by the support function could form a simplex that less likely encases the origin, but I assume it would still work. Since I'm currently experiencing problems with my (yet unfinished) implementation, I wanted to ask whether this method of forming the direction vector is usable or not.

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• Collision Detection algorithms with early Collision exit

  - by Grieverheart

  I'm using collision detection in Monte Carlo simulations and at the moment I'm using GJK which is quite fast. I can't help to think it could be done even faster though. In the simulations, about 70% of the time GJK is run, it detects a collision. Thus collisions are more than non-collisions in my case. Most collision detection algorithms I know have an early non-collision exit test. Are there any collision detection algorithms that have an early collision detect instead of non-collision and could be potentially faster than GJK in case of collision?

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• Javascript Graph Layout Engine

  - by GJK

  I'm looking for a Javascript library/engine that can do graph layouts. (And when I say layouts, I mean logically position vertices nicely.) The graphs I'm working with are all m-ary trees. M is usually no more than 5 or 6, but it can be greater in some cases. I do have something that I use now, Graphviz's node program, and it works perfectly. The problem is, when running a web app, I have to send a request to the server every time I want a layout. Preferably, I would like something written in Javascript that can be quickly run on the client side. All it needs to do is provide layout information (relative positioning and whatnot). I don't need it to draw to a canvas or use SVG or anything, all I'm interested in is the layout. Library use like jQuery or RaphaelJS is fine by me. I'll work with it. I'm just looking for something to speed things along a little. Also, I'd consider writing my own if I could find a nice description of an algorithm to do the layouts. But I really don't want to spend too much time. I have something that works now, so getting it on the client side is just a bonus, not a necessity.

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• (conditional) Multiple Event Handlers C#

  - by gjk

  A portion of my program requires a "flag" retrieval, that is I am fetching a value that is either True or False, and based on this return value two things could follow. 1) The flag is true, aka "go ahead", and I retrieve data from a database. 2) The flag is false, and I want to prevent the data from being retrieved. Now, this check has to be performed before any function that would call upon the database in question. I decided to implement this check in the form of an event handler attached to GUI objects that would trigger this data inquiry. This check event handler is called first upon necessary events, and my question is: How do I stop subsequent event handlers from firing if the FIRST event handler (my flag checker) comes up FALSE? Thanks

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• Convex Hull for Concave Objects

  - by Lighthink

  I want to implement GJK and I want it to handle concave shapes too (almost all my shapes are concave). I've thought of decomposing the concave shape into convex shapes and then building a hierarchical tree out of convex shapes, but I do not know how to do it. Nothing I could find on the Internet about it wasn't satisfying my needs, so maybe someone can point me in the right direction or give a full explanation.

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