Re: AW: [cgmo-webcgm] scale transform

[Lofton Henderson <lofton@rockynet.com>]

Forrest, All -- 

A comment and a QUESTION:

I have no problem with adding the scale reference point (or center point,
or scale-origin point, or however you wish to call it).  For someone
who regularly needs to scale around a non-origin point, it is more
convenient than having to do translate-scale-translate every time. 
(Altho' script writers can easily provide a utility function to do
it.)

Before we make the change to the test, let's get everyone to agree about
it.  (Adding the scale-center point.)

*** HOWEVER ... ***

Rereading Forrest's message, I am confused about one thing.  We all
agree that the 'scale' function fixed point now is (0,0) in NVDC,
right?  (Editorial comment:  this should be stated explicitly
in the 'scale' method description -- everything else is explicit about
NVDC, and the center-point must be (0,0) since it is not settable
now.)

It seems like Forrest wants to scale about the *VDC* (not NVDC) origin,
but there is no way in DOM to find the VDC-NVDC offset (so he can't set
up trn-scl-trn).  Simply adding the NDVC center-point to scale()
doesn't solve that.

QUESTION:  Do you want:

1.) scale center-point (NVDC)?  (For convenience, since it is
achievable now by trn-scl-trn sequence.)
2.) or do you want the VDC-NVDC offset?  (E.g., a new attribute on
WebCGMPicture [1].)  (Adds new capability that is not presently
achievable.)
3.) or do you want both?


-Lofton.

[1]
http://www.w3.org/TR/2008/WD-webcgm21-20080917/WebCGM21-DOM.html#L5070


At 07:41 PM 1/25/2009 +0100, Ulrich Läsche wrote:
> Forrest,
>
> We agree with your
> request.  In our scale test we earlier used VDC.  Now, with
> rewriting the test, we should follow the route that you proposed. 
> The move-scale-move operation is odd in any case.
>
> Regards
> Ulrich
>  
> -----Ursprüngliche Nachricht-----
> Von: Forrest Carpenter
> [mailto:forrest@sdicgm.com]
> Gesendet: Saturday, January 24, 2009 12:26 AM
> An: 'WebCGM'
> Betreff: [cgmo-webcgm] scale transform
>  
> All,
>  
> If it not too late, I think we need to add a point in NVDCs to the scale
> function. In a use case, you might want to enlarge an APS around a
> point to show more detail while leaving other parts of the drawing
> unchanged. The simplest method to do this in VDCs is to do a translate
> such that the point is at (0,0), do the scale transform and then a
> translate that would move the point back to it s original
> position. Using NVDCs, you cannot do this unless you have a method of
> translating the (0,0) in VDCs to NVDCs. Currently there is no DOM
> function that would enable a user to compute the location in NVDCs of the
> (0,0) point in the CGM. To fix this we could add a point to the scale
> function or add functions that would return the location of (0,0) in
> NVDCs. 
>  
> Regards,
> Forrest