=====================================
64#4 - 4x8 FONT DRIVER FOR 64 COLUMNS
=====================================

  Routine to print text in 64 columns with 4x8 characters for
  the ZX-Spectrum, that can be accessed from Sinclair BASIC
  using PRINT #4.


=====
USAGE
=====

  To create the channel and attach it to stream #4, load the code
  from tape and execute it only once, as follows:

CLEAR 64867: LOAD ""CODE : RANDOMIZE USR 64868


  Afterwards, you can use PRINT #4 to print text in 64 columns:

PRINT #4;AT 4,7;"4x8 FONT DRIVER"'"by Andrew, Crisis, and Einar"
FOR f=32 TO 127: PRINT #4;CHR$ f;: NEXT f


  This channel supports regular ASCII characters (from 32 to
  127), AT control codes, and you can also use apostrophe as
  carriage return.


============
TECH DETAILS
============

* To choose another address, just change the ORG statement and
  re-assemble the code.


* To choose another channel number, just change the value of
  symbol STR_NUM and recompile the code.


* To use this stream directly in assembly, execute the code
  (only once) to create the stream, then simply open channel #4
  and use RST 10 as usual, for instance:

        call    64874           ; create channel
        ...
        ld      a, 0x04
        call    0x1601          ; open channel #4
        ...
        ld      hl, STRING
LOOP:   ld      a, (hl)
        or      a
        ret     z
        rst     0x10            ; print register A
        inc     hl
        jr      LOOP
        ret
STRING: defb  '4x8 Font Driver', 0x00


* To also include your own custom 4x8 characters, just add
  their definitions at the end of the 4x8 font table (7 bytes
  for each pair). In this case, it's better to re-assemble
  the code at another address so the additional characters
  won't overlap the UDG area. Afterwards, use them as usual:

FOR f=32 TO 255: PRINT #4;CHR$ f;: NEXT f


=======================
OPTIONAL COMMA OPERATOR
=======================

  The "comma operator" is disabled by default. When enabled, it
  can be used to move the cursor to next column multiple of 16,
  as follows:

PRINT #4;AT 5,9;"ENTIRE";AT 5,3;"HELLO","WORLD!"


  It has 2 possible implementations:

* Option 1 works as "fast comma", jumping directly to target
  column. Thus the example above will produce this result:

    HELLO ENTIRE WORLD!


* Option 2 works as "standard comma", erasing characters along
  the way. Thus the example above will produce this result:

    HELLO        WORLD!


  To enable the "comma operator", uncomment the chosen option in
  the source code, change the compile address accordingly (so the
  enlarged code won't overlap the UDG area) and recompile it.


=========================
OPTIONAL INVERSE OPERATOR
=========================

  The "inverse operator" is also disabled by default. When
  enabled, each character can be printed as inversed.

  It has 2 possible implementations:

* Option 1 works as "standard inverse", using "INVERSE 1" to
  activate inverse mode, and "INVERSE 0" to deactivate. This is
  the easiest method for BASIC programming. The only drawback is
  that channel #4 does not automatically deactivate it, since it
  cannot detect that the PRINT statement has finished. Thus you
  have to explicitly disable it yourself afterwards, as follows:

PRINT #4; INVERSE 1;AT 7,1;"Hello World!"; INVERSE 0


* Option 2 works as "ZX81 inverse" since it's similar to the ZX81
  character set where the highest bit in each character indicates
  if it's inversed. This is the easiest method for Assembly
  programming but it also works in BASIC, just add 128 to the
  character value to obtain its inverse. For instance:

FOR f=32 to 127: PRINT #4; CHR$ (f+128);: NEXT f


=====
FONTS
=====

The same routine is available on tape using different fonts:

"64#4 Owen" - Uses default font designed by Andrew Owen.

"64#4 Minix" - Uses font "Minix" designed by Einar Saukas.

"64#4 n-Bot" - Uses font "NanoBot" designed by Einar Saukas.

"64#4 Omni1" - Uses font "Omni 1" designed by Einar Saukas.

"64#4 Omni2" - Uses font "Omni 2" designed by Einar Saukas.


=======
LICENSE
=======

You can freely use this tool and/or these fonts in your programs,
or adapt this code and/or fonts according to your needs, the only
requirement is that you must clearly indicate that you are using
this material, or alternatively provide the following link in 
your documentation:

http://www.worldofspectrum.org/infoseekid.cgi?id=0027130

The condition above also applies to any derivative work based on
this material, thus you are still required to credit "64#4" even 
if you are only using it indirectly, such as including in your 
program the <print64.bas> library from Boriel ZX BASIC Compiler 
(that is based on this).


=======
CREDITS
=======

Original implementation (657 bytes) by
  Andrew Owen.

Reduced 4x7 font storage (602 bytes) by
  Chris 'Crisis' Born.

Optimized reimplementation (494 bytes) and documentation by
  Einar Saukas.

Interface 1 compatibility fix (500 bytes) by
  J.G.Harston.

Stream initialization based on code by
  Ian Beardsmore from Your Spectrum issue 7, September 1984.

Channel wrapper based on code by
  Tony Samuels from Your Spectrum issue 20, November 1985.

Further information available at the following thread:
  http://www.worldofspectrum.org/forums/showthread.php?t=14526