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## RE: [Algorithms] Skinning + Tangent vectors

 RE: [Algorithms] Skinning + Tangent vectors From: Sim Dietrich - 2002-02-28 17:34:41 ```You want the Z axis of your local space to always point 'out', like the vertex normal. If you want to handle flipped textures ( ie a texture mapped left to right in x from 1->0 in uv rather than 0->1 in uv, the easiest way is to use the Normal for your Z axis, as opposed to using SxT, or -SxT if it didn't match the normal's direction ( the approach I used to recommend ). As far as being faster, I mean that you already have to skin the normal, so using that for your texture space basis is cheaper than skinning the normal and the SxT vector. -----Original Message----- From: Adam Moravanszky [mailto:amoravanszky@...] Sent: Thursday, February 28, 2002 8:14 AM To: Sim Dietrich; 'John Harries '; 'Algorithms List ' Subject: Re: [Algorithms] Skinning + Tangent vectors Hmm. But if we assume c), then doesn't that imply that Normal == SxT * SIGNBIT , making your point a) be meaningless? I also don't understand what you mean by the Normal being 'cheaper' than SxT ... what are you talking about here? My app is fill limited at the moment so neither this, nor point b) matters for me. :-/ --Adam From: "Sim Dietrich" > In my experience with this, having helped implement it in several games, I > can tell you that : > > a) You should always use the Normal instead of SxT ( this is not only > cheaper, but helps with flipped textures ) > > b) You shouldn't bother renormalizing these vectors after transforming them, > assuming you don't have significant scales > > c) The assumption that S & T & Normal vectors are orthonormal is a good > assumption if your texels are mapped to be square. Because this is usually > true, or supposed to be true, it tends should work out if you make the > assumption that the tangent basis is orthonormal. > ```