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From: Richard Ashbery <basura@invalid.addr.uk>
Newsgroups: comp.sys.acorn.programmer
Subject: Instability in rectangular cursor
Date: Fri, 13 Nov 2020 13:17:57 +0000 (GMT)
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Are there any BASIC programmers out there who may have missed my
posting on ROOL > Forums > General about an issue with a routine that
simply animates a rectangular cursor across the screen by moving the
mouse? The mouse overlays another horizontal rectangle but in so doing
results in instability and spoils the rendering. Any solutions would
be welcome.

MODE 1920,1080,32
PX%=0
PY%=0
REPEAT
  GCOL 0,0,255
  RECTANGLE FILL 0,0,3838,100
  MOUSE MX%,MY%,MB%
  GCOL 255,0,0
  RECTANGLE FILL PX%-50,PY%,100
  IF MX%<PX% THEN : PX%=PX%-1 : ENDIF
  IF MX%>PX% THEN : PX%=PX%+1 : ENDIF
UNTIL0