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Re: Pseudo3D by distorting the bounding box

From: Manuel Strehl <svg@manuel-strehl.de>
Date: Tue, 2 Sep 2008 08:44:11 +0200 (CEST)
Message-ID: <00e0cba0149992d345cfbd01ee54a619.squirrel@ml11.de>
To: www-svg@w3.org


> fyi - there was just a paper and presentation at the SVG Open on the
> topic of achieving 3D effects in SVG at the SVG Open 2008 in
> Nuremberg.

thanks, I know. Actually I talked to Anthony and told him, that I'll send
my proposal via this list. However, I'd like to ask everyone else
interested in pseudo-3D to sync efforts with Jun and Anthony.

For my formula from yesterday: I'll promise for future formulas to sleep
one night before posting them.

* It will only be valid for objects that are star-shaped with respect to
P(x,y) (I mentioned something like that)
* error: Of course, the displacements have to be weighted with the
distance from the original bounding box to give useful results, e.g., for

P(x,y) -> P(x',y'), with

x' = x + (deviation_left*(1 - x_rel/width) - deviation_right*(x_rel/width)),
y' = y + (deviation_top*(1 - y_rel/height) -

y_rel = 0 for a point lying on the top line of the original bounding box,
y_rel = height for a point on the bottom line of the bb.

Something like that...


> https://www.svgopen.org/2008/papers/86-Achieving_3D_Effects_with_SVG/
> The authors, Jun Fujisawa and Anthony Grasso, intend to write a spec
> proposal for a separate module for perspective transformations in SVG.
> You could participate in this effort as part of the SVG interest group
> if you want.
> Andreas
> Manuel Strehl wrote:
>> Hi,
>> formulas: Sorry, I don't do this usually, so it will not be quite
>> usable. In fact it's just a thought. I don't know, if it would display
>> correctly and in the sense intended.
>> * expand/contract the referenced path to meet width and height of the
>> element's bounding box
>> * P(x,y) an undistorted point of the element
>> * A displayed point P'(x', y') will depend on the deviations of the
>> bounding box from the border of the referenced path
>> * If the two deviations, say, at the top and at the bottom are equal, y'
>> = y, same for left/right and the x axis
>> * otherwise x' = x + (deviation_left - deviation_right), y' = y +
>> (deviation_top - deviation_bottom)
>> It is quite probable, that one has to take the x deviation for y into
>> account, since there can be dependencies for complex paths (leading to
>> some kind of convergence calculation). That's not respected by the above
>> instructions. Also for twisted paths, spirals and so on, I guess you'll
>> have a hard time to define the deviation clearly.
>> On implementor's side in the linear case (see below) it should be
>> possible to look at how, e.g., GIMP is doing it for pixels or,
>> for a simple example in SVG (only trapezoids), Inkscape's plugin
>> "perspective.py", usually living at /usr/share/inkscape/extensions or
>> %ProgramFiles%\Inkscape\share\extensions. It does it with a simple
>> python based geometry library (~250 lines code).
>> The path structure would not neccessarily be conserved (the "non-linear
>> case"). Consider some "waving path" like a "rectangular" with sinusoid
>> curves as borders as the source for the distortion. Then a distorted
>> "normal" rectangular would take on this shape, hence the linear borders
>> get "waved". This, however, is not implemented in any of the above
>> examples. But I think, it would be a very powerful feature.
>> For sake of implementing, the feature could be restricted to a path with
>> four straight lines, but I think, it would hugely diminish the power of
>> the idea.
>> Best,
>> Manuel
>> Dr. Olaf Hoffmann schrieb:
>>> Having some experience already with 3D transformations
>>> and different projections from 3D to 2D, I'd like to ask some
>>> questions or to give some suggestions about this, just to
>>> get a personal impression:
>>> Maybe it would already help to have some formulas to see,
>>> how such transformation can be implemented?
>>> If you have it for some examples or even some simulations,
>>> how this works this could help. For example PHP-scripts doing
>>> the  transformation and presenting the result in current SVG,
>>> this could be already used to explore the behaviour
>>> and possible difficulties and applications ...
>>> Especially do this conversions conserve the structure
>>> of the path (straight lines are still straight lines or points,
>>> cubic beziers are converted just in other cubic beziers
>>> just by conversion of points and control points etc) or
>>> does it create completely new paths, a viewer has to
>>> calculate for each device pixel?
>>> I think, with such a simple approach the viewer has
>>> not to care in a specific way about the rendering order
>>> as this happens for non trivial 3D-2D projections?
> --
> --
> Andreas Neumann
> Böschacherstrasse 6
> CH-8624 Grüt (Gossau ZH)
> Switzerland
> Phone: ++41-44-2736668
> Email: a.neumann@carto.net
> Web: http://www.carto.net/neumann/
> SVG Examples: http://www.carto.net/papers/svg/samples/
> SVG.Open: http://www.svgopen.org/
Received on Tuesday, 2 September 2008 06:45:34 UTC

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