DP Tool Club 8/CDASC08.ISO/VRAC/TVPROMPT.EXE/LETTERS.LIB

Text File | 1992-04-08 | 1KB | 34 lines

with CRT;

package Letters is
-- Copyright 1992 Tom Moran

  -- To be big enough to read on the teleprompter, we do 20 characters/line
  -- Thus each two bits in the letter pattern expand horizontally to 1 byte
  -- We could have taken 4 bits at a time, expanding to a word at a time,
  -- or even 8 bits to 32 bits, but it's simpler to deal with bytes in
  -- video ram than to fiddle about with double words, and this is more
  -- than adequate in speed.

  type Bit_Pairs is range 0 .. 3;
   for Bit_Pairs'size use 2;

  type Byte_Bit_Pairs is
    record
      A,B,C,D : Bit_Pairs;
    end record;
  for Byte_Bit_Pairs'Size use 8;
  for Byte_Bit_Pairs use
    record
      A at 0 range 6 .. 7;
      B at 0 range 4 .. 5;
      C at 0 range 2 .. 3;
      D at 0 range 0 .. 1;
    end record;

  -- Since we're using CGA it's OK to copy letter patterns from ROM
  subtype Line_Numbers is Integer range 0 .. 7;
  Pattern : array(Character, Line_Numbers) of Byte_Bit_Pairs;

end Letters;