Search found 43 matches

by RandyGaul
Mon Sep 18, 2017 8:50 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Correct Contact Manifold
Replies: 3
Views: 49905

Re: Correct Contact Manifold

Hello everyone! How do people finde correct hit points based on analysis of Minkowski difference? 2 algorithms I know of: expanding polytope algorithm (basically quick hull), or minkowski portal refinement. Both algorithms have unattractive qualities. I prefer getting contact points like Dirk prese...
by RandyGaul
Sat Sep 09, 2017 9:49 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Algorithm help / Connecting Centroids
Replies: 11
Views: 125604

Re: Algorithm help / Connecting Centroids

You can find your planes by performing plane slicing. Start with a simple convex shape, like an AABB, and slice it with many planes. Something like this: AABB bounds = WrapAllPoints(points, extra_radius); std::vector<ConvexHull> hulls; for (int i = 0; i < points.size(); ++i) { Point a = points[i]; C...
by RandyGaul
Thu Sep 07, 2017 10:46 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Algorithm help / Connecting Centroids
Replies: 11
Views: 125604

Re: Algorithm help / Connecting Centroids

I would point out the interior of the bubbles form a 3D Voronoi diagram.
by RandyGaul
Thu May 04, 2017 2:04 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Non-linear Gauss-Seidel solver
Replies: 11
Views: 113844

Re: Non-linear Gauss-Seidel solver

Wasn't post projection (NGS) sort of hacky? As in J was stolen from the velocity derivation and plugged in to form a psuedo position formula? Description of this by Cline in his nice paper: https://pdfs.semanticscholar.org/476d/fce4be549655938c499663af246702cbc781.pdf. In there it seems J is taken f...
by RandyGaul
Fri Apr 14, 2017 5:14 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Continuous GJK
Replies: 7
Views: 26642

Re: Continuous GJK

Yes, the problem is the axis flips. It can flip when the axis goes from penetrating to non-penetrating, and can also flip as the two vectors rotate relative to one another: https://en.wikipedia.org/wiki/Cross_pro ... roduct.gif
by RandyGaul
Fri Apr 07, 2017 8:01 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Continuous GJK
Replies: 7
Views: 26642

Re: Continuous GJK

We use this technique in Source 2 and it works great. It is not trivial to extend to 3d due to the non-convexity of the edge-edge case though. Would it be possible to elaborate on what the "non-convexity" of edge-edge is? After studying Box2D, it seems like an approach could be to form a ...
by RandyGaul
Wed Aug 17, 2016 4:18 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: How to compute BoxBox contact point ?
Replies: 6
Views: 15095

Re: How to compute BoxBox contact point ?

They wrote dBoxBox like that because it made sense to them at the time to write it like that. They probably derive a lot of the math on paper and then translated it into code. If you want to know what c1 - k1 - k3 is then you need to go through the math and draw pictures of what everything is. You c...
by RandyGaul
Thu May 12, 2016 8:19 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Steiner's Theorem for Composite Bodies
Replies: 12
Views: 34059

Re: Steiner's Theorem for Composite Bodies

Oh I see what you meant. I thought the old post was shifting to COM with a subtraction (I didn't read carefully).

I = I_cm + md^2, d^2 -> always positive, aka the distance from origin matters, and any vector (positive or negative) fixed on the origin will be the same result.
by RandyGaul
Mon May 02, 2016 12:20 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Steiner's Theorem for Composite Bodies
Replies: 12
Views: 34059

Re: Steiner's Theorem for Composite Bodies

Usually inertia tensors are calculated in model space (or local space) of the rigid body. Let's call the rigid body's reference frame A. Say we have a convex hull fixed in A. When A rotates the hull will rotate about A's origin, remaining fixed. When the inertia tensor of the hull is computed the te...
by RandyGaul
Tue Feb 16, 2016 10:24 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Lightweight engine for simulating dice?
Replies: 4
Views: 13354

Re: Lightweight engine for simulating dice?

Here's a minimalistic 3D library with only 3D AABB collision detection, that does pretty much exactly what you're asking for and not much else: https://github.com/RandyGaul/qu3e I'm the author of the library, so if you'd still like to implement your own solution I'd be happy to discuss in more detai...
by RandyGaul
Thu Aug 06, 2015 3:18 am
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Persistent Manifold & Contact breaking threshold
Replies: 4
Views: 12445

Re: Persistent Manifold & Contact breaking threshold

I myself haven't implemented EPA, but if it's possible to identify the features that produce a point of contact then the caching of data from one point to another can happen through some book-keeping, like a check for matching contact point IDs. This would avoid any annoying threshold tweaking. As f...
by RandyGaul
Sat May 30, 2015 5:29 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Bilateral advancement 3D GJK feature extraction problems
Replies: 12
Views: 31063

Re: Bilateral advancement 3D GJK feature extraction problems

IIRC point most penetrating, since that is what we'll want to drive towards 0 penetration with the root solver.
by RandyGaul
Fri May 29, 2015 7:28 pm
Forum: Research and development discussion about Collision Detection and Physics Simulation
Topic: Bilateral advancement 3D GJK feature extraction problems
Replies: 12
Views: 31063

Re: Bilateral advancement 3D GJK feature extraction problems

I just enumerated the possibilities with some if-statements and a switch. Perhaps this might add some value to the discussion: http://pastebin.com/WAHSnRqw Also Dirk, I'm curious if you know if anyone has ever placed feature extraction into GJK itself. It seemed to me to be a little silly to do this...