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From: Lewis_Evans@Playstation.sony.com
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: Pivots
Date: 13 Nov 1997 15:04:39 -0000
Organization: Sony Computer Entertainment Europe - 119.SS5
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From: Lewis_Evans@Playstation.sony.com
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To:       Lewis Evans
cc:
From:     news @ playstation.co.uk
Subject:  Re: Pivots:scee.yaroze.programming.3d_graphics




From: "Provenzano Stefano" <dragon@azzurra.it>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: Pivots
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Lewis_Evans@Playstation.sony.com ha scritto nel messaggio
<64btcs$qkv1@emeka.playstation.co.uk>...
>
>
>Hi all,
>I have a question about the rotations in 3D.
>Can the psx handle the pivots for the 3D model's rotations?
>
>-- By pivots, do you mean rotation around internal axes of a model, those
>axes being defined
>by pairs of vertices? Or the points where models are attached to each
>other?
I mean the rotation center of the model. The point where I apply the
rotation on the model. Is this a fix point or I can place it on the model
where I would?

Basically, the inherent rotation is always around the centre of the object.
However, there's a simple method to achieve rotation about any point in
object space;
suppose the vector from the object centre to the point of rotation is v1 in
object coordinate space:
firstly translate a matrix by this vector, then perform the rotation (which
is now occurring around your new point),
then translate back by the vector v1.
     Lewis