Comments for sevenson.com.au

Comment on Separating Axis Theorem (SAT) Explanation by dmc

dmc — Fri, 20 Aug 2010 03:47:23 +0000

Thanks a lot, this has been really helpful!

Comment on Separating Axis Theorem (SAT) Explanation 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.

Comment on Separating Axis Theorem (SAT) Explanation by Adam Baker

Adam Baker — Thu, 20 May 2010 06:55:17 +0000

In fact, now I have some feedback: it would be worth emphasizing more that it’s necessary to use normals from *both* polygons as axes.

Comment on Separating Axis Theorem (SAT) Explanation by Adam Baker

Adam Baker — Wed, 19 May 2010 06:49:03 +0000

This is a great explanation, thanks!

Comment on Reflection in ActionScript 3 by Joel Grøndrup

Joel Grøndrup — Mon, 19 Apr 2010 22:05:48 +0000

Hi Andrew

Wow, thanks for a brilliant class. Usually I use a reflection class from pixelfumes.com, but I don’t think it’s working well with dynamic textfields. However, your class does and it’s pretty easy to use.

A little usage information would be nice though, but I figured it out. For anyone else, this class creates a sprite that you have to add to the display list and place with X and Y coordinates. Have a look in the classfile for setting alpha and other options…

Joel Grøndrup

Comment on Separating Axis Theorem (SAT) Explanation by Andrew Sevenson

Andrew Sevenson — Sat, 27 Mar 2010 11:05:24 +0000

Hmm – good question. Its been a while since I wrote it so I had to have a look at the code again.
At a quick glance it looks like the vOffset is the vector between two shapes, and the sOffset seems to be a scalar used to calc the projected points of the second shape. I can’t remember exactly why it is there – my instinct is that it would be to keep the objects in the same coordinate space – but if yours works without it, maybe it isn’t needed :p

Comment on Separating Axis Theorem (SAT) Explanation by wwwebber

wwwebber — Wed, 24 Mar 2010 09:43:30 +0000

Great post…question, I used your code as a basis for my own SAT test..question though–what is the purpose of sOffset and vOffset? Intersection tests in my version, work perfectly, without using either of these.

Comment on Separating Axis Theorem (SAT) Explanation by Andrew Sevenson

Andrew Sevenson — Sun, 31 Jan 2010 11:51:01 +0000

Ah yes – you are absolutely correct. I’ve fixed that now – thanks for that

Comment on Separating Axis Theorem (SAT) Explanation by Vanderful

Vanderful — Sun, 31 Jan 2010 11:38:36 +0000

Great tuto !

Just some details:
In your first sentence you talk about concave polygons instead of convex ones.
The axis to be kept is the one which has the minimal overlap (not the greatest).

Anyway, really nice work !

Comment on Separating Axis Theorem (SAT) Explanation by Andrew Sevenson

Andrew Sevenson — Sun, 31 Jan 2010 01:51:12 +0000

Hi Will,

I had a quick look at the implementation you posted. It appears to be checking for a collision only, and not actually figuring out how to separate them. If you were to use the ‘axis’ property directly after that method you would always get the last axis that was tested, which is not necessarily the the shortest path of separation.

To get the right axis, you would have to keep track of which axis had the shortest amount of overlap. This should be as simple as having another vector variable declared and checking it each time an axis is tested. If you get to the end and there is a collision, simply use the vector you have stored for the separation.

At least, that is how my code works.

Hope that helps