=====Loading BFont files=====

 8x8 bitmap character definitions (called BFonts) are defined with **VDU 23** and read with OSWORD 10. They can be saved as BFont files ([[http://mdfs.net/Apps/Font/img/|such as these]]) as the sequences of eight bytes that define each character.\\ \\  These BFont files can be loaded to define characters, and code using VDU similar to the following is often used:\\ 
<code bb4w>
      REM file loaded to mem%
      FOR C%=start% TO end%
        VDU 23,C%
        FOR B%=0 TO 7
          VDU ?(mem%+C%*8+B%)
        NEXT B%
      NEXT C%
</code>
\\  A more efficient way to do this is to notice that the **VDU 23,C%** can be done within the loop just before every eighth byte:\\ 
<code bb4w>
      FOR A%=0 TO len%-1
        IF (A% AND 7)=0 THEN VDU 23,(A% DIV 8)+start%
        VDU mem%?A%
      NEXT A%
</code>
\\  Bitmap fonts can also be saved as streams of **VDU 23** sequences. As these include the character number that is being defined **start%** is not needed, so it can be used as a flag so the same code can read 8-byte raw BFont files and 10-byte VDU sequence BFont files:\\ 
<code bb4w>
      REM BFont file loaded to mem%, length in len%
      REM start%=0 for VDU file, start%<>0 for raw file
      :
      FOR A%=0 TO len%
        IF start% THEN IF (A% AND 7)=0 THEN VDU 23,(A% DIV 8)+start%
        VDU mem%?A%
      NEXT A%
</code>
or:\\ 
<code bb4w>
    REM BFont file loaded to mem%, length in len%
    REM start%=0 for VDU file, start%<>0 for raw file
    :
    FOR A%=0 TO len%:IF start%:IF (A% AND 7)=0:VDU 23,(A% DIV 8)+start%
    VDU mem%?A%:NEXT A%
</code>
\\  If **len%** is not a whole multiple of 8 bytes with a raw BFont file, or a whole multiple of 10 bytes with a VDU BFont file then the code will end in the middle of a VDU sequence. You should test that **len%** is valid beforehand with code such as the following:\\ 
<code bb4w>
      IF (len% MOD 8)<>0 AND ?mem%<>23 AND (mem% MOD 10)<>0 THEN PRINT "Not a valid BFont file"
</code>
- [[https://www.wikispaces.com/user/view/jgharston|{{jgharston}}]] [[https://www.wikispaces.com/user/view/jgharston|jgharston]] Dec 26, 2013