[x3d-public] PTM paper from Michalis Kamburelis; proposed PTM component by Kwan Hee Yoo

Wed Jan 23 17:51:58 PST 2019

btw InstantPlayer
 just put attributes on Lights
http://doc.instantreality.org/tutorial/dynamic-shadows/

On Thu, Jan 24, 2019 at 10:32 AM Nicholas Polys <npolys at vt.edu> wrote:

> See also:
>
> https://doc.x3dom.org/tutorials/lighting/shadows/index.html
> https://doc.x3dom.org/tutorials/lighting/shadows/example.html
>
> br,
> _n
>
>
> On Thu, Jan 24, 2019 at 10:29 AM Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
>> Many thanks for your in-depth analysis.  Kwan Hee, Dick and I similarly
>> went on a big journey over the years about whether this is inside Shape
>> node or not.  It is interesting and tricky.
>>
>> Treating PTM capabilities as somewhat similar to a direction projector
>> light source within the scene, similar to other lights, seemed to resolve
>> several logical conflicts.  Yet aspects of texture mapping remain. Hence
>> the current approach treats it as a separate component, defined as a
>> collection of functionality at a similar level in the specification
>> organization.
>>
>> In the interests of further convergence, if you want to suggest diffs to
>> the current draft that better integrates alternatives you have explored,
>> please feel free to do so.
>>
>> As promised I will work with Kwan Hee Yoo to get examples online (along
>> with X3D 4.0 XML schema/DTD plus X3DUOM) to facilitate further testing and
>> implementation.  As it turns out, I am sitting next to him here in Seoul
>> and we have agreed to work on further progress during lunch today!
>>
>> Having fun with X3D Projective Texture Mapping   8)
>>
>> On 1/23/2019 10:51 PM, Michalis Kamburelis wrote:
>> >   Brutzman, Donald (Don) (CIV) <brutzman at nps.edu> wrote:
>> >> Michalis, if you have done any further work beyond the reference
>> below, could you please ensure that we have the latest greatest from you
>> related to this topic.
>> >
>> > My work on projective texturing is part of my "shadow maps"
>> > extensions, documented on
>> > https://castle-engine.io/x3d_extensions_shadow_maps.php .
>> >
>> > Of course it can be used without shadow maps too, just to cast
>> > textures. The goal was to easily define a way to project texture from
>> > a light source or a viewpoint, using "ProjectedTextureCoordinate" node
>> > that can be used in a similar way to the standard
>> > "TextureCoordinateGenerator". In particular, casting a texture from a
>> > light source is essential to perform shadow mapping, that's why I
>> > developed my projective texturing extension "by the way" of developing
>> > shadow maps extensions.
>> >
>> > A simple example how does it look like is on:
>> >
>> https://github.com/castle-engine/demo-models/blob/master/shadow_maps/projective_texturing_simple.x3dv
>> > . You can open it with view3dscene (
>> > http://michalis.ii.uni.wroc.pl/view3dscene-snapshots/ ). I also attach
>> > a screenshot.
>> >
>> > Notable differences from my approach and Kwan's:
>> >
>> > (I'm not trying to say here which one is better! I like Kwan's
>> > approach. But I explain how, and why, my approach was different.)
>> >
>> > 1. Kwan adds projector nodes that are defined outside of "Shape".
>> > Projector node affects many shapes, using the "global" or "scoped"
>> > mechanism.
>> >
>> >      In contrast, my "ProjectedTextureCoordinate" is placed within a
>> > "texCoord" field of a geometry. So you need to explicitly add it to
>> > the relevant geometry nodes. My "ProjectedTextureCoordinate" was
>> > modeled after standard "TextureCoordinateGenerator", so it cooperates
>> > with multi-texturing in the same way. You can have 1st texture layer
>> > coordinates determined by "ProjectedTextureCoordinate", and 2nd
>> > texture layer coordinates determined by something else (like
>> > "TextureCoordinateGenerator" or explicit "TextureCoordinate").
>> >
>> > 2. Kwan projector nodes define their own projection parameters. The
>> > node type ("TextureProjectorPerspective" or
>> > "TextureProjectorParallel") determines if the projection is
>> > perspective or orthogonal.
>> >
>> >      In contrast, my "ProjectedTextureCoordinate" refers to a light
>> > source / viewpoint node. You can use DEF / USE mechanism to refer to
>> > an existing light source / viewpoint this way, or you can define new
>> > light source / viewpoint inside. The projection parameters and type
>> > are determined looking at the node type (e.g. "OrthoViewpoint" or
>> > "DirectionalLight" result in orthogonal projection, "Viewpoint" or
>> > "SpotLight" result in perspective projection). In some cases I needed
>> > to add addtional fields to lights, see
>> >
>> https://castle-engine.io/x3d_extensions_shadow_maps.php#section_light_parameters
>> > . E.g. all light sources have a new "projectionNear", "projectionFar"
>> > fields.
>> >
>> >      This was a necessity in my case. We *need* to have projection
>> > parameters specified at a light source, to make shadows maps possible
>> > from this light source. Then we can guarantee using the same
>> > projection parameters when (A) generating the shadow maps, and when
>> > (B) displaying the shadow maps. If projection parameters used for (A)
>> > and (B) would be different, shadow maps would not work OK.
>> >
>> > 3. In summary, my specification modifies more stuff in X3D. It relies
>> > on existing "texCoord" field, light sources and viewpoints nodes, and
>> > uses them. I also had to extend existing light sources with new
>> > fields.
>> >
>> > Regards,
>> > Michalis
>>
>> all the best, Don
>> --
>> Don Brutzman  Naval Postgraduate School, Code USW/Br
>> brutzman at nps.edu
>> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
>>  +1.831.656.2149
>> X3D graphics, virtual worlds, navy robotics
>> http://faculty.nps.edu/brutzman
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>>
>
>
> --
> Nicholas F. Polys, Ph.D.
>
> Director of Visual Computing
> Virginia Tech Research Computing
>
> Affiliate Professor
> Virginia Tech Department of Computer Science
>

-- 
Nicholas F. Polys, Ph.D.

Director of Visual Computing
Virginia Tech Research Computing

Affiliate Professor
Virginia Tech Department of Computer Science
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