Drawing pixels: CTWOS

       Name: CTWOS                                                   [Show more]
       Type: Variable
   Category: Drawing pixels
    Summary: Ready-made single-pixel character row bytes for mode 2
    Context: See this variable in context in the source code
 Variations: See code variations for this variable in the different versions
 References: This variable is used as follows:
             * CPIX2 uses CTWOS
             * DIL2 uses CTWOS
             * SC48 uses CTWOS


 Ready-made bytes for plotting one-pixel points in mode 2 (the bottom part of
 the split screen).

 In mode 2, each character row is one byte, which is two pixels. Rows 0 and 1
 of the table contain a character row byte with just the left pixel plotted,
 while rows 2 and 3 contain a character row byte with just the right pixel
 plotted.

 In other words, looking up row X will return a character row byte with pixel
 X/2 plotted (if the pixels are numbered 0 and 1).

 There are two extra rows to support the use of CTWOS+2,X indexing in the CPIX2
 routine. The extra rows are repeats of the first two rows, and save us from
 having to work out whether CTWOS+2+X needs to be wrapped around when drawing a
 two-pixel dash that crosses from one character block into another. See CPIX2
 for more details.


.CTWOS

 EQUB %10101010
 EQUB %10101010
 EQUB %01010101
 EQUB %01010101
 EQUB %10101010
 EQUB %10101010