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

[Brutzman, Donald (Don) (CIV)]

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