06 May 2003Stylable CGM XML Europe 2003, London Stylable CGM Dave Cruikshank The Boeing Company Lofton Henderson Henderson Consulting.

06 May 2003 Stylable CGMXML Europe 2003, London

Stylable CGM

Dave CruikshankThe Boeing Company

Lofton HendersonHenderson Consulting


CGM Version 4

• The CGM standard (ISO 8632:1999)– CGM V4 - Application Structuring

• Syntax to define application structures (APS) as graphical groups

• Syntax to associate attributes to APS• Definition of Semantics accomplished through

profiles


WebCGM Functionality

• WebCGM developed by CGM Open in collaboration with W3C graphics experts

• WebCGM profile approved by W3C – 1999

• WebCGM Release 2 published - 2001



• Requirements– Navigation

• Graphical object to graphical object within a CGM file• Graphical object to graphical object in another CGM file• Graphical object to a text objet

– Query• Search for a graphical object based on an attribute

– Data extraction• Retrieve non-graphical metadata from a graphical object


WebCGM Functionality• IG requirements

• Navigation

• Query

• Extraction

• Graphical Format Capabilities

• Structuring -- hierarchical object tagging

• Non-graphical properties

• Object id/naming

Begin APS <id> <type> <inh> ... APS Attribute <type> <val> ... Begin APS Body ...graphics to draw object... ...and/or, nested ApS...End Application Structure

CGM Capability



• Semantics4 APS types:

• grobject• layer• para• subpara

APS Attributes:

• Region• LinkURI• ViewContext• LayerName• LayerDescription• ScreenTip• Name• Content


WebCGM StructurePicture body

layer grobject

grobject para

grobject para

subpara

subpara

grobject para

subpara


Motivation for Stylability

• Interoperability among vendors demonstrated several times

• Proprietary DOM implementations being developed for external browser control


Approach

• CGM has inherent style, but…– WebCGM profile says:

• ‘While WebCGM is a binary file format and is not “stylable”, nevertheless WebCGM follows published W3C requirements for scalable graphics format where such are applicable’

– CSS2 says:• ‘CSS can be used with any structured

document format …’

– WebCGM is a structured document format


Approach

• Application of CSS2 to WebCGM much the way CSS1 was applied to legacy HTML

• Use of attribute selectors for specifying a style scheme to WebCGM


Requirements

• Scope– Granularity of application

• Picture• APS

– Control of individual graphical primitives out of scope


Requirements - color• Functions

– PictureScopeLineColor - RBG or relative scale– PictureScopeEdgeColor - RBG or relative scale– PictureScopeFillColor - RBG or relative scale– PictureScopeMarkerColor - RBG or relative scale– APSScopeLineColor - RBG or relative scale– APSScopeEdgeColor - RBG or relative scale– APSFillColor - RBG or relative scale– APSScopeMarkerColor - RBG or relative scale– PictureScopeRasterIntensity – relative scale– APSScopeRasterIntensity - relative scale


Requirements - color

INERTIAREALS

B

A

HEADRESTSHOULDER STRAPS

QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A


Requirements - color

INERTIAREALS

B

A


QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A


Requirements – line/edge weight

• Functions– PictureScopeLineWeight – absolute mm or

relative scale– PictureScopeEdgeWeight – absolute mm or

relative scale– APSScopeLineWeight – absolute mm or

relative scale– APSScopeEdgeWeight – absolute mm or

relative scale



INERTIAREALS

B

A


QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A



INERTIAREALS

B

A


QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A


Requirements – character height

• Functions– PictureScopeCharacterHeight – absolute mm or

relative scale– APSScopeCharacterHeight – absolute mm or

relative scale


Requirements – character height

INERTIAREALS

B

A


QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A


Requirements – character heightHEADRESTSHOULDER STRAPS

QUICK RELEASEBUCKLE

ARMREST

WAIST STRAPS

LUMBAR SUPPORT

CROTCH BELT

INBD/OUTBD LEVER

TOPMIDBOTTOM

ARMRESTADJUSTMENT

UP/DOWN LEVER

SAFETYVEST

PAD

FLIGHT CREWSEAT

(BELOW THE SEAT)

A

INERTIAREALS

B

A


Requirements

• Caveats– Applying style using CSS2 deviates from

the actual CGM attribute model• Character height scaling does not exist• Line weight scaling behaves differently

– “Undoing” style requires special handling• Remembering attributes of various primitives,

or• Re-interpreting a picture or APS


Issues/Resolution

• Binary/clear text– CGM is binary format– Style sheet should be ASCII text

• APSScopelinecolor grobject#xyz {color: red} – turn the lines in grobject with an apsid of xyz to red

– CGM Structured Data Record (SDR)• An issue for the WebCGM DOM when we deal

with multiple fields for attribute values of APS attributes


Issues/Resolution

• WebCGM tree model– Pictures contain:

• APS elements (nested) contain:– Graphical primitives (leaf nodes)

– Nodes at the APS level• <layer .. > | <grobject .. > | <para .. > |

<subpara>• Simplest with a tree with four kinds of element

nodes


Issues/Resolution

• Alignment with CSS– Possible to align element names with SVG

• CSS style sheet parsing might be reusable• But not much else

– Appropriate solution• Borrow principles from CSS, including matching

mechanisms• Customize solution for WebCGM DOM

requirements


Issues/Resolution

• CSS selectors– Minimal selector pattern matching set

* – matches any element (universal selector)grobject – matches any grobject APS (type selector)grobject#xyz – matches any grobject APS with an apsid of

xyz

– Attribute selectorsgrobject[name] – matches any grobject APS whose “name”

attribute is setgrobject[name=“bolt”] – matches any grobject APS whose

“name” attribute is set to “bolt”


Issues/Resolution

• WebCGM element names– For styling solution

• Elements selectors– picture layer

– grobject para

– subpara

• Attrubute selectors– Linkuri name

– screentip viewcontext

– region content

– layerdescription layername


Issues/Resolution

• Style rules declaration– Attribute types deviate

• LineColour is a CGM attribute applying to individual line primitives

• PictureScopeLineColor would apply to all lines in a picture

– Attribute values deviate• LineColour specified in WebCGM as an index into a

color table, or an RGB n-tuple, or an sRGB n-tuple• PictureScopeLinecolor would have an RGB n-tuple, or a

relative scale

– Align with CSS data types (RBG, scale, mm)


Issues/Resolution

• CSS inheritance model– Styling attributes should inherit

• Nested APS are affected by styling


Issues/Resolution

• Cascading precedence– Opposite of CSS

• User agent supplied style overrides author style

• Specificity– CSS rules apply

• In clashes, most specific rules


Issues/Resolution

• Processing model– Open questions

• How are styling rules communicated to the viewer?• Is there some sort of rule-by-rule interface?• Or, so you have to pass an entire style sheet at a time?• How do you turn off a style sheet after it has been

applied and return to author rules? (unapply rules)• How the the styling interface relate to the DOM? (DOM

will ‘get’ and ‘set’ all APSattr parameters)


Conclusions

• Preliminary design completed• ACSII text style sheet• Align with principles from CSS• Use a subset of CSS selectors• Use CGM clear text APS types and attributes• Apply CSS inheritance model• Override CSS cascading• Apply CSS specificity


Next Steps

• Define processing model

• WebCGM DOM– Adopt “appropriate” DOM Core elements

(level 1)– Adopt “appropriate” DOM Event elements

(levels 2 & 3)– Integrate CSS solution


?

06 May 2003Stylable CGM XML Europe 2003, London Stylable CGM Dave Cruikshank The Boeing Company Lofton Henderson Henderson Consulting.

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