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Elite on the BBC Micro

Drawing pixels: CTWOS [Elite-A, I/O processor]

Name: CTWOS [Show more] Type: Variable Category: Drawing pixels Summary: Ready-made single-pixel character row bytes for mode 5 Deep dive: Drawing colour pixels in mode 5
Context: See this variable in context in the source code References: This variable is used as follows: * CPIX2 calls CTWOS * DIL2 calls CTWOS * draw_tail calls CTWOS

Ready-made bytes for plotting one-pixel points in mode 5 (the bottom part of the split screen). See the dashboard routines SCAN, DIL2 and CPIX2 for details. There is one extra row to support the use of CTWOS+1,X indexing in the CPIX2 routine. The extra row is a repeat of the first row, and saves us from having to work out whether CTWOS+1+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 %10001000 EQUB %01000100 EQUB %00100010 EQUB %00010001 EQUB %10001000