Oberon/Text

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Programmatical Access to a Text[edit]

A Text can be manipulated using procedures in the Texts module; visible for S3 and for V5. Also summarized for S3 in DEFINITION Texts.

To read a Text programmatically, a RECORD termed a Reader is opened on the Text at a specified offset. (A Reader is a RECORD; not a procedure.) With reader open, the Read(reader, ch) procedure retrieves a character each time it is executed. The font of a character is referenced in the Objects.Library of the Reader. The Reader also has fields, col, the color of the character and voff, vertical offset of the character. After an execution of Read(reader, ch), the freshly read character is available in ch and attributes are in the components of reader. This assumes that the object read was a character as evidenced by (reader.lib IS Fonts.Font) being TRUE. Each execution of Read() advances reader through the Text by one character until the end is reached and reader.eot becomes TRUE.

How Text Works[edit]

These tables show the structure of records in memory representing a Text. When Texts.Store() records a Text in a file for a storage medium, the information in the record structure is serialized. In the inverse process, Texts.Load() deserializes the information to the record structure of the Text in memory.

Click on a hyperlink to see the module where a type is defined.

In Oberon V2[edit]

The Type Text
Type Fields of TextDesc Types of Fields Notes
Texts.Text, a pointer to a Texts.TextDesc len LONGINT Length of text, in bytes.
changed BOOLEAN Flag indicating a revision.
notify Texts.Notifier Pointer to a method to notify interested clients of state changes.
trailer Texts.Piece Pointer to the Sentinel node in the list of pieces.
pce Texts.Piece Last found piece.
org LONGINT Offset in [0,len) of first character in last found piece.
Texts.Piece
Type Fields of PieceDesc Types of Fields Notes
Texts.Piece, a pointer to a Texts.PieceDesc f Files.File Pointer, to file.
off LONGINT Integer offset in Text of first character in Piece.
len LONGINT Number of bytes in Piece.
fnt Fonts.Font Pointer to a font.
col INTEGER  
voff INTEGER Vertical offset of characters in pixels.
prev Texts.Piece Pointer to previous piece of Text.
next Texts.Piece Pointer to next piece of Text.

In S3[edit]

TextDesc is an extension of Objects.ObjDesc. The fields added to make TextDesc are distinguished from the fields inherited from ObjDesc by a differing background color.

The Type Text
Type Fields of
TextDesc
Types of Fields Notes
Texts.Text, a pointer to a Texts.TextDesc stamp LONGINT Integer
dlink Objects.Object Pointer
slink Objects.Object Pointer
lib Objects.Library Pointer
ref INTEGER  
handle Objects.Handler Pointer
len LONGINT Length of text.
obs Objects.Library Pointer
trailer Texts.Piece Pointer to Sentinel node in list of pieces.
org LONGINT Offset in [0,len) of first character in last found piece.
pce Texts.Piece Last found piece.
Objects.Library in the table above
Type Fields of LibDesc Types of Fields Notes
Objects.Library, a pointer to a LibDesc next Objects.Library Pointer
ind Objects.Index Pointer
f Files.File Pointer
R Files.Rider Pointer
name Objects.Name  
dict Objects.Dictionary Pointer
maxref INTEGER  
GName POINTER  
Texts.Piece
Type Fields of PieceDesc Types of Fields Notes
Texts.Piece, a pointer to a Texts.PieceDesc f Files.File Pointer
off LONGINT Integer
len LONGINT  
obj Objects.Object Pointer
lib Objects.Library Pointer
ref INTEGER  
col SHORTINT  
voff SHORTINT  
prev Piece Pointer
next Piece Pointer

In the Oberon Subsystem of A2[edit]

TextDesc is an extension of Objects.ObjDesc. The fields added to make TextDesc are distinguished from the fields inherited from ObjDesc by differing background colors.

The Type Text
Type Fields of
TextDesc
Types of Fields Notes
Texts.Text, a pointer to a Texts.TextDesc stamp LONGINT Integer
dlink Objects.Object Pointer
slink Objects.Object Pointer
lib Objects.Library Pointer
ref INTEGER  
handle Objects.Handler Pointer
len LONGINT Length of text.
obs Objects.Library Pointer
trailer Texts.Piece Pointer to Sentinel node in list of pieces.
org LONGINT Offset in [0,len) of first character in last found piece.
pce Texts.Piece Last found piece.
Objects.Library in the table above
Type Fields of LibDesc Types of Fields Notes
Objects.Library, a pointer to a LibDesc next Objects.Library Pointer
ind Objects.Index Pointer
f Files.File Pointer
R Files.Rider Pointer
name Objects.Name  
dict Objects.Dictionary Pointer
maxref INTEGER  
GName POINTER  
Texts.Piece
Type Fields of PieceDesc Types of Fields Notes
Texts.Piece, a pointer to a Texts.PieceDesc f Files.File Pointer
off LONGINT Integer
len LONGINT  
obj Objects.Object Pointer
lib Objects.Library Pointer
ref INTEGER  
col SHORTINT  
voff SHORTINT  
prev Piece Pointer
next Piece Pointer

In Oberon V5[edit]

The Type Text
Type Fields of TextDesc Types of Fields Notes
Texts.Text, a pointer to a Texts.TextDesc len INTEGER[1] Length of text, in bytes.
changed BOOLEAN Flag indicating a revision.
notify Texts.Notifier Pointer to a method to notify interested clients of state changes.
trailer Texts.Piece Pointer to the Sentinel node in the list of pieces.
pce Texts.Piece Last found piece.
org INTEGER Offset in [0,len) of first character in last found piece.
Texts.Piece
Type Fields of PieceDesc Types of Fields Notes
Texts.Piece, a pointer to a Texts.PieceDesc f Files.File Pointer, to file.
off INTEGER Integer offset in Text of first character in Piece.
len INTEGER Number of bytes in Piece.
fnt Fonts.Font Pointer to a font.
col INTEGER  
voff INTEGER Vertical offset of characters in pixels.
prev Texts.Piece Pointer to previous piece of Text.
next Texts.Piece Pointer to next piece of Text.

Texts.FindPiece and the cache[edit]

For a given Text, T, and offset pos in [0, T.len), procedure Texts.FindPiece has the task of locating the piece containing pos. At each execution, FindPiece could begin at offset 0 and add lengths of pieces until the piece containing pos is located. In reality, better efficiency is obtained by use of a cache based upon T.pce and T.org. When FindPiece completes a search, the pointer to the found piece is recorded in T.pce; the offset of the first character of that piece is recorded in T.org. The next execution of FindPiece begins at that cached location. With a result from FindPiece often being near the preceeding result, this

strategy avoids repeated summation of lengths from the beginning of the first piece.

  1. In V5 the only integer type is INTEGER. Cf. LONGINT in V2.