Comments on: Separating Axis Theorem (SAT) Explanation

By: How to resolve collisions of compound shapes using SAT? | Q&A System

How to resolve collisions of compound shapes using SAT? | Q&A System — Sun, 11 Dec 2011 09:30:27 +0000

[...] 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. [...]

By: Matt

Matt — Mon, 24 Oct 2011 01:25:06 +0000

In your article you mention that this technique does not provide the features of the two colliding objects. This is not true. This technique can be easily extended to provide the features of each object for further processing i.e. finding actual contact points.

By: Andy

Andy — Thu, 11 Aug 2011 21:55:25 +0000

Ah I got it!
var shape = new Polygon();
shape = Polygon.basicPolygon();

By: Andy

Andy — Thu, 11 Aug 2011 21:48:13 +0000

I can get circle and box working, but not polygon. How do I create a basicPolygon?

By: Andy

Andy — Wed, 10 Aug 2011 14:54:44 +0000

I agree with meming – Great tutorial, but a simple useage example is always nice!

By: Dave

Dave — Fri, 10 Jun 2011 15:07:23 +0000

Nice work!

Just thinking though – is all that shadow detection really necessary? What about:

1) I know the centroid (middle) of the two polygons
2) I know the angle and length of the line between the two centroids (hypot of a triangle)
3) I can work out the point that’s closest to the other shape on one object.
4) I can use that point and the hypot to create a plane (using a line equation) that sits against my first shape but perpendicular to the hypot.
5) And then I can test if any points in the other shape are beyond that line – maybe by checking against the lines normal value (dot or cross product – I always get them confused)?

I don’t know if that’s any faster – just musing. Seems like more math but less work and no loops?

By: dysseus88

dysseus88 — Sun, 29 May 2011 18:03:40 +0000

Thanks for this powerfull code. It will be very helpful to me and I see I am not the first. I was looking for solid explanations about SAT and thanks to you, I know this is exactly what I should use. Please, could you publish source code of the above demo ? I tkink it would be easier for everyone to use your library in the future by analyzing this example.

By: vladab

vladab — Thu, 31 Mar 2011 23:11:45 +0000

Thanks for the article it was really helpful in better learning of SAT.

By: dmc

dmc — Fri, 20 Aug 2010 03:47:23 +0000

Thanks a lot, this has been really helpful!

By: meming

meming — Tue, 06 Jul 2010 22:10:33 +0000

I totally understand whats going on, its just I dont know how to put this in code, I give this tut a 90% ( which is great ) but if you put a little code under each step, (especially when we create the “axis”) this would get an instant 110%. You wont have to reply to this, ill just spend an hour on google, but future viewers will want the same.