Contact us Heritage collections Image license terms
HOME ACL Associates Technology Literature Applications Society Software revisited
Further reading □ Overview □ Paper 1 □ Paper 2 □ Paper 3 □ Paper 4 □ Paper 5 □ Paper 6 □ Paper 7 □ Paper 8 □ Paper 9 □ Paper 10 □ Paper 11 □ Paper 12 □ Paper 13 □ Paper 14 □ Paper 15 □ Paper 16 □ Paper 17 □ Paper 18 □ Paper 19 □ Paper 20 □ Paper 21 □ Paper 22 □ Paper 23 □ Paper 24 □ Paper 25 rev □ Paper 25 □ Paper 26 □ Paper 27 □ Paper 28 □ Paper 29 □ Paper 30 □ Paper 31 □ Paper 32 □ Paper 33 □ Paper 34 □ Paper 35 □ Paper E
ACD C&A INF CCD CISD Archives Contact us Heritage archives Image license terms

Search

   
⟶ ACL ⟶ Literature ⟶ Progress Reports ⟶ Technical Papers :: Literature: FR80 Technical Papers
⟶ ACL ⟶ Literature ⟶ Progress Reports ⟶ Technical Papers :: Literature: FR80 Technical Papers
ACL ACD C&A INF CCD CISD Archives
Further reading ⇓

□ Overview □ Paper 1 □ Paper 2 □ Paper 3 □ Paper 4 □ Paper 5 □ Paper 6 □ Paper 7 □ Paper 8 □ Paper 9 □ Paper 10 □ Paper 11 □ Paper 12 □ Paper 13 □ Paper 14 □ Paper 15 □ Paper 16 □ Paper 17 □ Paper 18 □ Paper 19 □ Paper 20 □ Paper 21 □ Paper 22 □ Paper 23 □ Paper 24 □ Paper 25 rev □ Paper 25 □ Paper 26 □ Paper 27 □ Paper 28 □ Paper 29 □ Paper 30 □ Paper 31 □ Paper 32 □ Paper 33 □ Paper 34 □ Paper 35 □ Paper E

Paper No 20: Multiple Fonts in Displayers

R E Thomas

11 December 1975

1. FONT ORGANISATION

The main character tables are stored in the upper bank. These are:

VCHTAB
Table of addresses pointing to the first word of a character. This table is reset on entry to the displayer and is altered whenever a new character code is set.
SPCTAB
This table converts character heights to scope points and seems independent of the actual font itself.
CHBOXH, CHBOXW
Character height and width (equals 16, 12 respectively for OCRB3 and GPO).
FONTNM
Font name (OCRB3 = 16, GPO = 17). This is not used.
FONTYP
Indicates whether courier angles are being used or not (OCRB3 = 0, GPO = 40).
CHSPMN
(124 for both fonts). This is not used.
CHSPBS
(160 for both fonts). This is used in width calculations.
CHSPMX
(250 for both fonts). This is not used.
CHVSTR
Table of characters, Address of next word past the last one is GHVEND.

Each character is preceded by two words for calculating height and width for proportional spacing. The first word (which is the address pointed to by the appropriate entry in VCHTAB) has the character. code as bottom 8 bits. The character definition then follows.

2. MULTIPLE FONT IMPLEMENTATION

Since the GPO font is the larger of the two, the two modified displayers are: 

FRFC and FMFC

The two existing fonts are saved as binary files in MON;FNT1 and FNT2 (OCRB3 and GPO respectively). The system allows for files FNT0 to FNT1. Each binary file (which has been created either by DEBUG or the Assembler) contains (in order): 

CHBOXH 
CHBOXW 
FONTNM 
FONTYP 
CHSPMN 
CHSPBS 
CHSPMX 
CHVSTR to CHVEND

The addresses stored in file are NOT significant. The data will be loaded correctly as long as the consecutive format specified above is maintained.

Other font files can be generated from the symbolic lists, as long as the resultant code is no longer than that occupied by the GPO font.

The data format 

232000 + N

(which is III select font order) has been implemented in these two displayers. N defines which font and must lie between 0 and 7 (to reference files FNT0 to FNT7 respectively). The execution of the command is as follows:

  1. Reset existing VCHTAB and return any space used for user-defined characters, new character codes, etc.
  2. Check that space is available above any picture definitions for a disc buffer. Exit with *DBF if no space.
  3. Find the specified font file. Exit with *DNF if not found.
  4. Read new font into core.
  5. Replace references to CHVEND so that they now point to the new font table end.
  6. Reset VCHTAB to the new error character location.
  7. Set up VCHTAB for the new characters that have been defined.
  8. Mirror the characters if necessary and set correct font type angles.
  9. (9) Obey "set character height zero" code so that new proportional space values can be set.

The user must reset the space and height commands again if the above does not give the desired height.

3. SETTING UP A FONT FILE

Font files (FNT0 to FNT7) can be set up in three ways:

  1. Dumped to file from a displayer by loading the displayer and zeroing all but the desired data: 
    FRFC$L 
0<CHBOXH$$Z 
CHVEND<37777$$Z 
$J HLT 
FNT2$F
  2. Assembled from a source file containing all the characters. This could be done from scratch if user-defined characters are used, but would involve a considerable amount of source input.
  3. Assembled from a source file, making use of the III source fonts. The file layout would be as follows: (for FNT1) 
    /FNT generation 
.NAME MON; FNT1 BINARY 
/defined set of all character names 
/required 
CC000l = = 0 
CC0002 = = 0 
etc 
/macro definition for proportional spacing 
.DEF ZZ 
0 
0 
.TERM 
/insert suitable source file 
.INSERT III164 OCRB3 
START

In cases 2 and 3, care must be taken to ensure that the font file generated is no larger than FNT2, so that the font will fit in FRFC.

4. POSSIBLE FUTURE MODIFICATIONS

  1. The host software packages can be modified to produce the following effects:
    1. Colour programs call FR rather than FC (since these two arc now identical).
    2. GPO font requests are for 'C' type displayers.
    3. OCRB3 font requests are also for 'C' type displayers, but with order 232001 inserted at the start. The routine HFONT would cause this to be issued and would then come after the graphics initialising routine (and be available anywhere in the program).
    Thus: 
      
Old    New   
FRFO   FRFC with 232001   
FRFC   FRFC   
FCFO   FRFC with 232001   
FCFC   FRFC   
FNFO   FMFC with 232001   
FHFC   FMFC
    Alternatively, GPO font could become the standard. This modification would mean that only two displayers would be required for maintenance.
  2. Further extensions to the character routines could include:
    1. A III control character to change font so that different fonts could be used easily in the same line (without specifically resetting the X,Y coordinates). However, there would be some difficulty in matching character sizes.
    2. A monitor command to change font could be implemented for stand-alone use of the displayer. This use is sufficiently infrequent not to make this worthwhile.
⇑ Top of page
© Chilton Computing and UKRI Science and Technology Facilities Council webmaster@chilton-computing.org.uk
Our thanks to UKRI Science and Technology Facilities Council for hosting this site