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From "Bishop, Michael W. CONTR J9C880" <Michael.Bis...@je.jfcom.mil>
Subject RE: Scaling around a center point...
Date Mon, 19 Dec 2005 15:33:57 GMT
OK, I know I'm replying to myself, but the mail server here was down
from Friday to Monday.  I see Archie's response in the mailing list
archives.  I'm still not sure I understand why the rotation doesn't
occur as I expect, but I see what you're talking about in the example.

So even though I don't entirely understand the problem, is there a
solution?  How can I rotate a non-uniformly scaled element around its
center?

Michael Bishop

-----Original Message-----
From: Bishop, Michael W. CONTR J9C880
[mailto:Michael.Bishop@je.jfcom.mil] 
Sent: Friday, December 16, 2005 4:18 PM
To: batik-users@xmlgraphics.apache.org
Subject: RE: Scaling around a center point...

Well, when you rotate(t, x, y) you are rotating around the center point.
What it does under the hood (if I understand correctly) is:

Translate the coordinate system to x, y (the center point)
Rotate (which should rotate around the above-mentioned center point)
Translate back to the original coordinate system.

I guess I don't see how axes come into play.  I imagine a turntable.  If
the spindle is always the center point, it doesn't matter the shape of
the object you're sticking on there, it should rotate around the center.

I'm not even sure how I'd put something in the center of the ellipse;
that'd be an entirely different element in my understanding.

Michael Bishop

-----Original Message-----
From: Archie Cobbs [mailto:archie@dellroad.org] 
Sent: Friday, December 16, 2005 3:37 PM
To: batik-users@xmlgraphics.apache.org
Subject: Re: Scaling around a center point...

Bishop, Michael W. CONTR J9C880 wrote:
> I don't understand why that would make a difference.  Regardless of
the
> axis, the center point doesn't change, does it?
> 
> -----Original Message-----
> From: Archie Cobbs [mailto:archie@dellroad.org] 
> Sent: Friday, December 16, 2005 3:10 PM
> To: batik-users@xmlgraphics.apache.org
> Subject: Re: Scaling around a center point...
> 
> If you take a non-circular ellipse, then stretch it, you change its
> apparent "axis". You are assuming that the ellipse's axis doesn't
change
> (an inferring rotation angle from it), but that's not true when you
> stretch non-uniformly.

Correct, the center point doesn't change... but what does that have
to do with it? I don't understand your question.

Try putting a big "R" in the middle of the ellipse or something so you
can tell how much it *really* rotated and you'll see what I'm talking
about.

-Archie

________________________________________________________________________
__
Archie Cobbs      *        CTO, Awarix        *
http://www.awarix.com

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