Iso/iec jtc 1/sc 29 N

Image and video

The following image and video related nodes are used in ARAF: ImageTexture, MovieTexture.

ImageTexture

XSD Description

Functionality and semantics

As defined in ISO/IEC 14772-1:1997, section 6.22.

The ImageTexture node defines a texture map by specifying an image file and general parameters for mapping to geometry. Texture maps are defined in a 2D coordinate system (s, t) that ranges from [0.0, 1.0] in both directions. The bottom edge of the image corresponds to the S-axis of the texture map, and left edge of the image corresponds to the T-axis of the texture map. The lower-left pixel of the image corresponds to s=0, t=0, and the top-right pixel of the image corresponds to s=1, t=1.

The texture is read from the URL specified by the url field. When the url field contains no values ([]), texturing is disabled. Browsers shall support the JPEG and PNG image file formats. In addition, browsers may support other image formats (e.g. CGM) which can be rendered into a 2D image. Support for the GIF format is also recommended (including transparency).

The repeatS and repeatT fields specify how the texture wraps in the S and T directions. If repeatS is TRUE (the default), the texture map is repeated outside the [0.0, 1.0] texture coordinate range in the S direction so that it fills the shape. If repeatS is FALSE, the texture coordinates are clamped in the S direction to lie within the [0.0, 1.0] range. The repeatT field is analogous to the repeatS field.

MovieTexture

XSD Description

Functionality and semantics

As defined in ISO/IEC 14496-11 (BIFS), section 7.2.2.86.

The loop, startTime, and stopTime exposedFields and the isActive eventOut, and their effects on the MovieTexture node, are described in ISO/IEC 14496-11, section 7.1.1.1.6.2. The speed exposedField controls playback speed. It does not affect the delivery of the stream attached to the MovieTexture node. For streaming media, value of speed other than 1 shall be ignored.

A MovieTexture shall display frame or VOP 0 if speed is 0. For positive values of speed, the frame or VOP that an active MovieTexture will display at time now corresponds to the frame or VOP at movie time (i.e., in the movie’s local time base with frame or VOP 0 at time 0, at speed = 1): fmod (now - startTime, duration/speed) If speed is negative, then the frame or VOP to display is the frame or VOP at movie time: duration + fmod(now - startTime, duration/speed). A MovieTexture node is inactive before startTime is reached. If speed is non-negative, then the first VOP shall be used as texture, if it is already available. If speed is negative, then the last VOP shall be used as texture, if it is already available.

When a MovieTexture becomes inactive, the VOP corresponding to the time at which the MovieTexture became inactive shall persist as the texture. The speed exposedField indicates how fast the movie shall be played. A speed of 2 indicates the movie plays twice as fast. Note that the duration_changed eventOut is not affected by the speed exposedField. set_speed events shall be ignored while the movie is playing.

Textual information

The following text related nodes are used in ARAF: FontStyle, Text.

FontStyle

XSD Description

Functionality and semantics

As defined in ISO/IEC 14772-1:1997, section 6.20.

The FontStyle node defines the size, family, and style used for Text nodes, as well as the direction of the text strings and any language-specific rendering techniques used for non-English text.

The size field specifies the nominal height, in the local coordinate system of the Text node, of glyphs rendered and determines the spacing of adjacent lines of text. Values of the size field shall be greater than zero.

The spacing field determines the line spacing between adjacent lines of text. The distance between the baseline of each line of text is (spacing × size) in the appropriate direction (depending on other fields described below). Values of the spacing field shall be non-negative.

Font attributes are defined with the family and style fields. The browser shall map the specified font attributes to an appropriate available font as described below.

The family field contains a case-sensitive MFString value that specifies a sequence of font family names in preference order. The browser shall search the MFString value for the first font family name matching a supported font family. If none of the string values matches a supported font family, the default font family "SERIF" shall be used. All browsers shall support at least "SERIF" (the default) for a serif font such as Times Roman; "SANS" for a sans-serif font such as Helvetica; and "TYPEWRITER" for a fixed-pitch font such as Courier. An empty family value is identical to ["SERIF"].

The style field specifies a case-sensitive SFString value that may be "PLAIN" (the default) for default plain type; "BOLD" for boldface type; "ITALIC" for italic type; or "BOLDITALIC" for bold and italic type. An empty style value ("") is identical to "PLAIN".

The horizontal, leftToRight, and topToBottom fields indicate the direction of the text. The horizontal field indicates whether the text advances horizontally in its major direction (horizontal = TRUE, the default) or vertically in its major direction (horizontal = FALSE). The leftToRight and topToBottom fields indicate direction of text advance in the major (characters within a single string) and minor (successive strings) axes of layout. Which field is used for the major direction and which is used for the minor direction is determined by the horizontal field.

For horizontal text (horizontal = TRUE), characters on each line of text advance in the positive X direction if leftToRight is TRUE or in the negative X direction if leftToRight is FALSE. Characters are advanced according to their natural advance width. Each line of characters is advanced in the negative Y direction if topToBottom is TRUE or in the positive Y direction if topToBottom is FALSE. Lines are advanced by the amount of size × spacing.

For vertical text (horizontal = FALSE), characters on each line of text advance in the negative Y direction if topToBottom is TRUE or in the positive Y direction if topToBottom is FALSE. Characters are advanced according to their natural advance height. Each line of characters is advanced in the positive X direction if leftToRight is TRUE or in the negative X direction if leftToRight is FALSE. Lines are advanced by the amount of size × spacing.

The justify field determines alignment of the above text layout relative to the origin of the object coordinate system. The justify field is an MFString which can contain 2 values. The first value specifies alignment along the major axis and the second value specifies alignment along the minor axis, as determined by the horizontal field. An empty justify value ("") is equivalent to the default value. If the second string, minor alignment, is not specified, minor alignment defaults to the value "FIRST". Thus, justify values of "", "BEGIN", and ["BEGIN" "FIRST"] are equivalent.

The major alignment is along the X-axis when horizontal is TRUE and along the Y-axis when horizontal is FALSE. The minor alignment is along the Y-axis when horizontal is TRUE and along the X-axis when horizontal is FALSE. The possible values for each enumerant of the justify field are "FIRST", "BEGIN", "MIDDLE", and "END". For major alignment, each line of text is positioned individually according to the major alignment enumerant. For minor alignment, the block of text representing all lines together is positioned according to the minor alignment enumerant.

The language field specifies the context of the language for the text string. Due to the multilingual nature of the ISO/IEC 10646-1:1993, the language field is needed to provide a proper language attribute of the text string. The format is based on RFC 1766: language[_territory].

The value for the language tag is based on ISO 639:1988 (e.g., 'zh' for Chinese, 'jp' for Japanese, and 'sc' for Swedish.) The territory tag is based on ISO 3166:1993 country codes (e.g., 'TW' for Taiwan and 'CN' for China for the 'zh' Chinese language tag). If the language field is empty (""), local language bindings are used.

The semantics of the FontStyle node are the ones specified above (ISO/IEC 14772-1:1997, section 6.20), with the exception that the field types are exposedField and the semantics of the size and spacing fields are as follows.

The size field defines the size of the EM box of a font (The EM is a relative measure of the height of the glyphs in a font defined in a device- and resolution-independent font design units). This value corresponds to the distance between two adjacent baselines of unadjusted text, set in a particular font. The value of the size field is conveyed using the same metric units that are used for a scene description. If a scene uses pixel-based metrics, the value of the size field is specified in pixels, otherwise it specifies the size in meters.

The spacing field defines the distance between two adjacent lines of text as the product of size and spacing. Special fonts provided in a font data stream can be accessed using the following syntax:

“OD:;FSID:”, where :

- is the numeric value of the objectDescriptorID of the associated font data stream,

- is the numeric value of the requested font subset as conveyed by fontSubsetID within the associated font data stream.

Text

XSD Description

Functionality and semantics

As defined in ISO/IEC 14772-1:1997, section 6.47.

The Text node specifies a two-sided, flat text string object positioned in the Z=0 plane of the local coordinate system based on values defined in the fontStyle field (see ISO/IEC 14772-1:1997, section 6.20, FontStyle). Text nodes may contain multiple text strings specified using the UTF-8 encoding as specified by ISO 10646-1:1993 (see 2.[UTF8]). The text strings are stored in the order in which the text mode characters are to be produced as defined by the parameters in the FontStyle node.

The text strings are contained in the string field. The fontStyle field contains one FontStyle node that specifies the font size, font family and style, direction of the text strings, and any specific language rendering techniques used for the text.

The maxExtent field limits and compresses all of the text strings if the length of the maximum string is longer than the maximum extent, as measured in the local coordinate system. If the text string with the maximum length is shorter than the maxExtent, then there is no compressing. The maximum extent is measured horizontally for horizontal text (FontStyle node: horizontal=TRUE) and vertically for vertical text (FontStyle node: horizontal=FALSE). The maxExtent field shall be greater than or equal to zero.

The length field contains an MFFloat value that specifies the length of each text string in the local coordinate system. If the string is too short, it is stretched (either by scaling the text or by adding space between the characters). If the string is too long, it is compressed (either by scaling the text or by subtracting space between the characters). If a length value is missing (for example, if there are four strings but only three length values), the missing values are considered to be 0. The length field shall be greater than or equal to zero.

Specifying a value of 0 for both the maxExtent and length fields indicates that the string may be any length.

• 
  ISO 10646-1:1993 Character Encodings
  

Characters in ISO 10646 (see 2.[UTF8]) are encoded in multiple octets. Code space is divided into four units, as follows:

+-------------+-------------+-----------+------------+

| Group-octet | Plane-octet | Row-octet | Cell-octet |

+-------------+-------------+-----------+------------+

ISO 10646-1:1993 allows two basic forms for characters:

1. 
   UCS-2 (Universal Coded Character Set-2). This form is also known as the Basic Multilingual Plane (BMP). Characters are encoded in the lower two octets (row and cell).
   
2. 
   UCS-4 (Universal Coded Character Set-4). Characters are encoded in the full four octets.
   

In addition, three transformation formats (UCS Transformation Format or UTF) are accepted: UTF-7, UTF-8, and UTF-16. Each represents the nature of the transformation: 7-bit, 8-bit, or 16-bit. UTF-7 and UTF-16 are referenced in 2.[UTF8].

UTF-8 maintains transparency for all ASCII code values (0...127). It allows ASCII text (0x0..0x7F) to appear without any changes and encodes all characters from 0x80.. 0x7FFFFFFF into a series of six or fewer bytes.

If the most significant bit of the first character is 0, the remaining seven bits are interpreted as an ASCII character. Otherwise, the number of leading 1 bits indicates the number of bytes following. There is always a zero bit between the count bits and any data.

The first byte is one of the following. The X indicates bits available to encode the character:

0XXXXXXX only one byte 0..0x7F (ASCII)

110XXXXX two bytes Maximum character value is 0x7FF

1110XXXX three bytes Maximum character value is 0xFFFF

11110XXX four bytes Maximum character value is 0x1FFFFF

111110XX five bytes Maximum character value is 0x3FFFFFF

1111110X six bytes Maximum character value is 0x7FFFFFFF

All following bytes have the format 10XXXXXX.

As a two byte example, the symbol for a register trade mark is ® or 174 in ISO Latin-1 (see  ISO/IEC 8859-1:2012). It is encoded as 0x00AE in UCS-2 of ISO 10646. In UTF-8, it has the following two byte encoding: 0xC2, 0xAE.

• 
  Appearance
  

Textures are applied to text as follows. The texture origin is at the origin of the first string, as determined by the justification. The texture is scaled equally in both S and T dimensions, with the font height representing 1 unit. S increases to the right, and T increases up.

4.14, Lighting model, has details on VRML lighting equations and how Appearance, Material and textures interact with lighting.

The Text node does not participate in collision detection.