[x3d-public] Edge cases of Extrusion
simon place
psiplace at netscape.net
Mon Aug 17 21:25:52 PDT 2015
> Extrusion is a really important and valuable node. I'm glad we are all
> looking at it again!
i played with them at lot, they seemed to me to have the potential for
simple progressive refinement, unlike IFS's where an editor is
required and changes tend to cause a knock on need for more editing.
> In addition to possible co-linearity/roundoff issues,
the changes needed to fix this are, i think, fundamental, and so
backward compatibility breaking.
did you read how the blaxxun player ignores the rotation and so has
something defined.(shame they didn't call it "Extrusion2" or
something.)
> I think we could
> define a consistent triangulation of side quads.
quad texturing is a bit separate because its the same problem with the
elevation node.
for me leaving it to the player maker, to make the best choice, is
fine, just what i felt was the best solution hasn't been chosen by any
player i know of; add a new point, and average of the existing 4 and
then have 4 triangles, like tessellation shaders, or the castle
engines over triangulation option.
On 16 August 2015 at 18:44, Don Brutzman <brutzman at nps.edu> wrote:
> Thanks for the helpful reference Simon. Really interesting details in that
> thread.
>
> Extrusion is a really important and valuable node. I'm glad we are all
> looking at it again!
>
> Extrusion support is mostly working, but it has always been difficult for
> different X3D players to implement Extrusion consistently. Perhaps there
> some edge cases overlooked by the specification which have something to do
> with that.
>
> Since there is so much discussion going on with Extrusion, we should start
> collecting all of the information about issues in one place... several of us
> are interested.
>
> As discussed previously, we probably should schedule a dedicated X3D meeting
> to explore in depth. This week is post-SIGGRAPH review, next week will be
> overshadowed by several of us attending the annual ISO Standards Committee
> meeting in London to review formal X3D progress and planned specifications.
> Early September perhaps?
>
> Wondering if a Web3D Consortium member is willing to maintain a public
> web3d.org page about this? I can do it if people like, but things might
> proceed faster with someone less overcommitted! 8)
>
>
> On 8/9/2015 7:27 PM, simon place wrote:
>>
>> FWIW
>>
>> see this discussion;
>> http://sourceforge.net/p/castle-engine/tickets/13/ ,where Extrusion,
>> as currently defined, is considered to be broken, having, as it does,
>> discontinuities exactly at co-linear spline point arrangements and
>> there being no way to consistently determine co-linearity due to
>> standard maths rounding issues.
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>
>
> In addition to possible co-linearity/roundoff issues, I think we could
> define a consistent triangulation of side quads. At least extrusions would
> render consistently among players then, and authors could reverse spine
> array order or crossSection array order if they preferred a particular
> tesselation.
>
> I was looking around for the primary list of Castle Game Engine recommended
> changes but had trouble finding it this time... got link?
>
> Xj3D mostly works, but still has a problem with handling of orientation
> array values:
> http://x3dgraphics.com/examples/X3dForAdvancedModeling/GeometricShapes/_viewpoints/ExtrusionExamplesTest.x3d._VP_Extrusion_examples.png
>
> Preliminary list of references for an Extrusion page:
>
> X3D Graphics Abstract Specification
> 13.3.5 Extrusion
>
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/geometry3D.html#Extrusion
>
> X3D for Web Authors, Chapter 6: Points Lines and Polygons, slides
> 54-72 and (with notes) slides 146-164
>
> http://x3dgraphics.com/slidesets/X3dForWebAuthors/Chapter06-GeometryPointsLinesPolygons.pdf
>
> X3D Example Archives: Conformance Nist, Geometry, Extrusion (18
> examples)
>
> http://www.web3d.org/x3d/content/examples/ConformanceNist/Geometry/Extrusion
>
> X3D Example Archives: VRML 2.0 Sourcebook, Chapter 15 - Extrusion
> (17 examples)
>
> http://www.web3d.org/x3d/content/examples/Vrml2.0Sourcebook/Chapter15-Extrusion
>
> X3D Example Archives: X3D for Web Authors, Chapter 06 - Geometry
> Points Lines Polygons
>
> http://x3dgraphics.com/examples/X3dForWebAuthors/Chapter06-GeometryPointsLinesPolygons
>
> X3D Example Archives: X3D for Advanced Modeling, Geometric Shapes,
> Extrusion Examples Test
>
> http://x3dgraphics.com/examples/X3dForAdvancedModeling/GeometricShapes/ExtrusionExamplesTest.x3d
>
> Helpful ExtrusionCrossSection prototype makes spine and crossSection
> geometries visible:
>
> http://www.web3d.org/x3d/content/examples/Basic/course/ExtrusionCrossSectionExampleTorus.x3d
>
> http://www.web3d.org/x3d/content/examples/Basic/course/ExtrusionCrossSectionExampleShip.x3d
>
> http://www.web3d.org/x3d/content/examples/Basic/course/ExtrusionCrossSectionPrototype.x3d
>
> X3D Tooltips: Extrusion
> http://www.web3d.org/x3d/content/X3dTooltips.html#Extrusion
>
> Castle Game Engine Geometry3D component
>
> http://castle-engine.sourceforge.net/x3d_implementation_geometry3d.php
>
> X3D Schematron: Extrusion diagnostic rules
> http://www.web3d.org/x3d/tools/schematron/X3dSchematron.html
>
> http://www.web3d.org/x3d/tools/schematron/X3dSchematronValidityChecks.sch
>
> <!-- ========= Extrusion ========== -->
> <rule context="Extrusion">
> <let name="crossSection"
> value="normalize-space(translate(@crossSection,',',' '))"/>
> <let name="spine"
> value="normalize-space(translate(@spine, ',',' '))"/>
> <let name="scale"
> value="normalize-space(translate(@scale, ',',' '))"/>
> <let name="orientation"
> value="normalize-space(translate(@orientation, ',',' '))"/>
> <let name="crossSectionCount"
> value="string-length($crossSection) -
> string-length(translate($crossSection,' ','')) + 1"/>
> <let name="spineCount" value="string-length($spine)
> - string-length(translate($spine, ' ','')) + 1"/>
> <let name="scaleCount" value="string-length($scale)
> - string-length(translate($scale, ' ','')) + 1"/>
> <let name="orientationCount"
> value="string-length($orientation) -
> string-length(translate($orientation, ' ','')) + 1"/>
> <let name="crossSectionResidue" value="translate($crossSection,
> '+-0123456789Ee., ','')"/>
> <let name="spineResidue" value="translate($spine,
> '+-0123456789Ee., ','')"/>
> <let name="scaleResidue" value="translate($scale,
> '+-0123456789Ee., ','')"/>
> <let name="orientationResidue" value="translate($orientation,
> '+-0123456789Ee., ','')"/>
> <extends rule="geometryNode"/>
> <extends rule="NoChildNode"/>
> <extends rule="creaseAngle"/>
> <report test="($crossSectionCount = 0)" role="warning">&NodeDEFname;
> missing crossSection </report>
> <report test="($spineCount = 0)" role="warning">&NodeDEFname;
> missing spine </report>
> <assert test="string-length($crossSectionResidue) = 0"
> role="error">&NodeDEFname; has illegal character <value-of
> select='$crossSectionResidue'/> in crossSection array
> (crossSection='<value-of select='@crossSection'/>') </assert>
> <assert test="string-length($scaleResidue) = 0"
> role="error">&NodeDEFname; has illegal character <value-of
> select='$scaleResidue'/> in scale array (scale='<value-of
> select='@scale'/>') </assert>
> <assert test="string-length($spineResidue) = 0"
> role="error">&NodeDEFname; has illegal character <value-of
> select='$spineResidue'/> in spine array (spine='<value-of
> select='@spine'/>') </assert>
> <assert test="string-length($orientationResidue) = 0"
> role="error">&NodeDEFname; has illegal character <value-of
> select='$orientationResidue'/> in orientation array (orientation='<value-of
> select='@orientation'/>') </assert>
> <!-- check for legal array tuples -->
> <assert test="(($crossSectionCount mod 2) = 0)"
> role="warning">&NodeDEFname; crossSection array size <value-of
> select='$crossSectionCount div 2'/> does not have legal number of MFVec2f
> values, must be evenly divisible by 2 (crossSection='<value-of
> select='@crossSection'/>') </assert>
> <assert test="(($scaleCount mod 2) = 0)"
> role="warning">&NodeDEFname; scale array size <value-of select='$scaleCount
> div 2'/> does not have legal number of MFVec2f values, must be evenly
> divisible by 2 (scale='<value-of select='@scale'/>') </assert>
> <assert test="(($spineCount mod 3) = 0)"
> role="warning">&NodeDEFname; spine array size <value-of select='$spineCount
> div 3'/> does not have legal number of MFVec3f values, must be evenly
> divisible by 3 (spine='<value-of select='@spine'/>') </assert>
> <assert test="(($orientationCount mod 4) = 0)"
> role="warning">&NodeDEFname; orientation array size <value-of
> select='$orientationCount div 4'/> does not have legal number of MFRotation
> values, must be evenly divisible by 4 (orientation='<value-of
> select='@orientation'/>') </assert>
> <!-- check for sufficient array size -->
> <assert test="(($spineCount = 0) or ($spineCount > 5))"
> role="error">&NodeDEFname; spine array size of <value-of
> select='$spineCount'/> is insufficient to define a line segment, must have 6
> or more values (spine='<value-of select='@spine'/>') </assert>
> <!-- check for matching array sizes -->
> <assert test="($scaleCount = 0) or ($scaleCount = 2) or
> (($scaleCount div 2) = ($spineCount div 3))"
> role="warning">&NodeDEFname; scale array size <value-of select='$scaleCount
> div 2'/> (scale='<value-of select='@scale'/>') must match spine array size
> <value-of select='$spineCount div 3'/> </assert>
> <assert test="($orientationCount = 0) or ($orientationCount = 4) or
> (($orientationCount div 4) = ($spineCount div 3))"
> role="warning">&NodeDEFname; orientation array size <value-of
> select='$orientationCount div 4'/> (orientation='<value-of
> select='@orientation'/>') must match spine array size <value-of
> select='$spineCount div 3'/> </assert>
> <report test="(@beginCap='TRUE' )" role="error">&NodeDEFname;
> beginCap='TRUE' capitalization is incorrect, define as beginCap='true'
> instead</report>
> <report test="(@beginCap='FALSE')" role="error">&NodeDEFname;
> beginCap='FALSE' capitalization is incorrect, define as beginCap='false'
> instead</report>
> <report test="(@endCap='TRUE')" role="error">&NodeDEFname;
> endCap='TRUE' capitalization is incorrect, define as endCap='true'
> instead</report>
> <report test="(@endCap='FALSE')" role="error">&NodeDEFname;
> endCap='FALSE' capitalization is incorrect, define as endCap='false'
> instead</report>
> <report test="not(/X3D[(@profile='Immersive') or (@profile='Full')] or
> /X3D/head/component[@name='Geometry3D'][number(@level) ge 4] or
> (count(preceding::*[local-name()=$NodeName]) > 0))"
> role="error">&NodeDEFname; requires at least <component name='Geometry3D'
> level='4'/> or <X3D profile='Immersive'/> </report>
> </rule>
> <!-- ========= ========= ========== -->
>
>
> 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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