From: Andreas Neumann <a.neumann@carto.net>

Date: Mon, 01 Sep 2008 23:15:17 +0200

Message-ID: <48BC5B65.5080003@carto.net>

To: Manuel Strehl <svg@manuel-strehl.de>

CC: www-svg@w3.org

Date: Mon, 01 Sep 2008 23:15:17 +0200

Message-ID: <48BC5B65.5080003@carto.net>

To: Manuel Strehl <svg@manuel-strehl.de>

CC: 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. 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 Monday, 1 September 2008 21:16:01 GMT

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