This clause addresses conformance of VRML files, VRML generators and
VRML browsers.
The primary objectives of the specifications in this clause are:
to promote interoperability by eliminating arbitrary subsets of, or
extensions to, ISO/IEC 14772;
to promote uniformity in the development of conformance tests;
to promote consistent results across VRML browsers;
to facilitate automated test generation.
7.1.3 Scope
Conformance is defined for VRML files and for VRML browsers. For VRML
generators, conformance guidelines are presented for enhancing the likelihood
of successful interoperability.
A concept of base profile conformance is defined to ensure interoperability
of VRML generators and VRML browsers. Base profile conformance is based
on a set of limits and minimal requirements. Base profile conformance is
intended to provide a functional level of reasonable utility for VRML generators
while limiting the complexity and resource requirements of VRML browsers.
Base profile conformance may not be adequate for all uses of VRML.
This clause addresses the VRML data stream and implementation requirements.
Implementation requirements include the latitude allowed for VRML generators
and VRML browsers. This clause does not directly address the environmental,
performance, or resource requirements of the generator or browser.
This clause does not define the application requirements or dictate application
functional content within a VRML file.
The scope of this clause is limited to rules for the open interchange
of VRML content.
7.2 Conformance
7.2.1 Conformance of VRML
files
A VRML file is syntactically correct according to ISO/IEC
14772 if the following conditions are met:
The VRML file contains as its first element a VRML header comment
(see 4.2.2, Header).
All entities contained therein match the functional specification of
the corresponding entities of ISO/IEC 14772-1. The VRML file shall
obey the relationships defined in the formal grammar and all other syntactic
requirements.
The sequence of entities in the VRML file obeys the relationships specified
in ISO/IEC 14772-1 producing the structure specified in ISO/IEC 14772-1.
All field values in the VRML file obey the relationships specified
in ISO/IEC 14772-1 producing the structure specified in ISO/IEC 14772-1.
No nodes appear in the VRML file other than those specified in
ISO/IEC 14772-1 unless required for the encoding technique or those defined
by the PROTO or EXTERNPROTO entities.
The VRML file is encoded according to the rules of ISO/IEC 14772.
It does not contain behaviour described as undefined elsewhere in this
specification.
A VRML generator is conforming to this part of ISO/IEC 14772 if all VRML
files that are generated are syntactically correct.
A VRML generator conforms to the base profile if it can be configured
such that all VRML files generated conform to the base profile.
7.2.3 Conformance of VRML browsers
A VRML browser conforms to the base profile if:
It is able to read any VRML file that conforms to the base profile.
It presents the graphical and audio characteristics of the VRML nodes
in any VRML file that conforms to the base profile, within the latitude
defined in this clause.
It correctly handles user interaction and generation of events as specified
in ISO/IEC 14772, within the latitude defined in this clause.
There is no minimum complexity which is required of (or appropriate for)
VRML generators. Any compliant set of nodes of arbitrary complexity may
be generated, as appropriate to represent application content.
7.3.2 Minimum support requirements for browsers
This subclause defines the minimum complexity which shall be supported
by a VRML browser. Browser implementations may choose to support greater
limits but may not reduce the limits described in Table
7.1. When the VRML file contains nodes which exceed the limits implemented
by the browser, the results are undefined. Where latitude is specified in
Table 7.1 for a particular node, full support is
required for other aspects of that node.
7.3.3 VRML requirements for conforming to the base
profile
In the following table, the first column defines the item for which conformance
is being defined. In some cases, general limits are defined but are later
overridden in specific cases by more restrictive limits. The second column
defines the requirements for a VRML file conforming to the base profile;
if a VRML file contains any items that exceed these limits, it may not be
possible for a VRML browser conforming to the base profile to successfully
parse that VRML file. The third column defines the minimum complexity for
a VRML scene that a VRML browser conforming to the base profile shall be
able to present to the user. The word "ignore" in the minimum
browser support column refers only to the display of the item; in particular,
set_ events to ignored exposedFields must still generate corresponding
_changed events.
Table 7.1 -- Specifications for VRML browsers
conforming to the base profile
Item
VRML File Limit
Minimum Browser Support
All groups
500 children.
500 children. Ignore bboxCenter and bboxSize.
All interpolators
1000 key-value pairs.
1000 key-value pairs.
All lights
8 simultaneous lights.
8 simultaneous lights.
Names for DEF/PROTO/field
50 utf8 octets.
50 utf8 octets.
All url fields
10 URLs.
10 URLs. URN's ignored.
Support `http', `file', and `ftp' protocols.
Support relative URLs where relevant.
URL references VRML files conforming to the base profile
PROTO definition nesting depth
5 levels.
5 levels.
SFBool
No restrictions.
Full support.
SFColor
No restrictions.
Full support.
SFFloat
No restrictions.
Full support.
SFImage
256 width. 256 height.
256 width. 256 height.
SFInt32
No restrictions.
Full support.
SFNode
No restrictions.
Full support.
SFRotation
No restrictions.
Full support.
SFString
30,000 utf8 octets.
30,000 utf8 octets.
SFTime
No restrictions.
Full support.
SFVec2f
15,000 values.
15,000 values.
SFVec3f
15,000 values.
15,000 values.
MFColor
15,000 values.
15,000 values.
MFFloat
1,000 values.
1,000 values.
MFInt32
20,000 values.
20,000 values.
MFNode
500 values.
500 values.
MFRotation
1,000 values.
1,000 values.
MFString
30,000 utf8 octets per string, 10 strings.
30,000 utf8 octets per string, 10 strings.
MFTime
1,000 values.
1,000 values.
MFVec2f
15,000 values.
15,000 values.
MFVec3f
15,000 values.
15,000 values.
Anchor
No restrictions.
Ignore parameter. Ignore description.
Appearance
No restrictions.
Full support.
AudioClip
30 second uncompressed PCM WAV.
30 second uncompressed PCM WAV. Ignore description.
Background
No restrictions.
One skyColor, one groundColor, panorama images as per ImageTexture.
Billboard
Restrictions as for all groups.
Full support except as for all groups.
Box
No restrictions.
Full support.
Collision
Restrictions as for all groups.
Full support except as for all groups. Any navigation behaviour acceptable
when collision occurs.
Color
15,000 colours.
15,000 colours.
ColorInterpolator
Restrictions as for all interpolators.
Full support except as for all interpolators.
Cone
No restrictions.
Full support.
Coordinate
15,000 points.
15,000 points.
CoordinateInterpolator
15,000 coordinates per keyValue. Restrictions as for all interpolators.
15,000 coordinates per keyValue. Support as for all interpolators.
Cylinder
No restrictions.
Full support.
CylinderSensor
No restrictions.
Full support.
DirectionalLight
No restrictions.
Not scoped by parent Group or Transform.
ElevationGrid
16,000 heights.
16,000 heights.
Extrusion
(#crossSection points)*(#spine points) <= 2,500.
(#crossSection points)*(#spine points) <= 2,500.
Fog
No restrictions.
"EXPONENTIAL" treated as "LINEAR"
FontStyle
No restrictions.
If the values of the text aspects character set, family, style
cannot be simultaneously supported, the order of precedence shall be: 1)
character set 2) family 3) style. Browser must display all
characters in ISO 8859-1 character set 2.[I8859].
Group
Restrictions as for all groups.
Full support except as for all groups.
ImageTexture
JPEG and PNG format. Restrictions as for PixelTexture.
JPEG and PNG format. Support as for PixelTexture.
IndexedFaceSet
10 vertices per face. 5000 faces. Less than 15,000 indices.
10 vertices per face. 5000 faces. 15,000 indices in any index field.
IndexedLineSet
15,000 total vertices. 15,000 indices in any index field.
15,000 total vertices. 15,000 indices in any index field.
Inline
No restrictions.
Full support except as for all groups. url references VRML files conforming to the base profile
LOD
Restrictions as for all groups.
At least first 4 level/range combinations interpreted, and
support as for all groups. Implementations may disregard level distances.
25 eventIns. 25 eventOuts. 25 fields.
No scripting language support required.
Shape
No restrictions.
Full support.
Sound
No restrictions.
2 active sounds. Linear distance attenuation. No spatialization. See 7.3.4.
Sphere
No restrictions.
Full support.
SphereSensor
No restrictions.
Full support.
SpotLight
No restriction
Ignore beamWidth. Ignore radius. Linear attenuation.
Switch
Restrictions as for all groups.
Full support except as for all groups.
Text
100 characters per string. 100 strings.
100 characters per string. 100 strings.
TextureCoordinate
15,000 coordinates.
15,000 coordinates.
TextureTransform
No restrictions.
Full support.
TimeSensor
No restrictions.
Ignored if cycleInterval < 0.01 second.
TouchSensor
No restrictions.
Full support.
Transform
Restrictions as for all groups.
Full support except as for all groups.
Viewpoint
No restrictions.
Ignore fieldOfView. Ignore description.
VisibilitySensor
No restrictions.
Always visible.
WorldInfo
No restrictions.
Ignored.
7.3.4 Sound priority, attenuation, and spatialization
7.3.4.1 Sound priority
If the browser does not have the resources to play all of the currently
active sounds, it is recommended that the browser sort the active sounds
into an ordered list using the following sort keys in the order specified:
decreasing priority;
for sounds with priority > 0.5, increasing (now-startTime);
decreasing intensity at viewer location (intensity ×
intensity attenuation);
where priority is the priority field of the Sound node,
now represents the current time, startTime is the startTime
field of the audio source node specified in the source field, and
intensity attenuation refers to the intensity multiplier derived from the
linear decibel attenuation ramp between inner and outer ellipsoids.
It is important that sort key 2 be used for the high priority (event
and cue) sounds so that new cues will be heard even when the browser is
"full" of currently active high priority sounds. Sort key 2 should
not be used for normal priority sounds, so selection among them will be
based on sort key 3 (intensity at the location of the viewer).
The browser shall play as many sounds from the beginning of this sorted
list as it can given available resources and allowable latency between rendering.
On most systems, the resources available for MIDI streams are different
from those for playing sampled sounds, thus it may be beneficial to maintain
a separate list to handle MIDI data.
7.3.4.2 Sound attenuation and spatialization
In order to create a linear decrease in loudness as the viewer moves
from the inner to the outer ellipsoid of the sound, the attenuation must
be based on a linear decibel ramp. To make the falloff consistent across
browsers, the decibel ramp is to vary from 0 dB at the minimum ellipsoid
to -20 dB at the outer ellipsoid. Sound nodes with an outer ellipsoid that
is ten times larger than the minimum will display the inverse square intensity
dropoff that approximates sound attenuation in an anechoic environment.
Browsers may support spatial localization of sounds whose spatialize
field is TRUE as well as their underlying sound libraries will allow. Browsers
shall at least support stereo panning of non-MIDI sounds based on the angle
between the viewer and the source. This angle is obtained by projecting
the Sound location (in global space) onto the XZ plane of the viewer.
Determine the angle between the Z-axis and the vector from the viewer to
the transformed location, and assign a pan value in the range [0.0,
1.0] as depicted in Figure 7.1. Given this pan
value, left and right channel levels can be obtained using the following
equations:
Using this technique, the loudness of the sound is modified by the intensity
field value, then distance attenuation to obtain the unspatialized audio
output. The values in the unspatialized audio output are then scaled by
leftPanFactor and rightPanFactor to determine the final left and right output
signals. The use of more sophisticated localization techniques is encouraged,
but not required (see E.[SNDB]).
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7.1 Introduction