Matrix Star

Author: Roberto Capuano
Category: Christmas Challenge
System:   MSX
Language: BASIC
Len source code: 289
Len exe file: 243
Len code only: 243
Instructions:
Connect to WebMSX at https://webmsx.org/
press ALT-B, copy and paste the source from TXT file
type "RUN"
In alternative mount star.dsk as drive A:
load"a:star.bas"
run
Description:
Program writes the star shape in video memory as sequence of bytes. Each byte is shifted with a random number. 
At each iteration the shift range is reduced. 
10 cls: SCREEN1:KEYOFF:DEFINTA-Z: BA=6144
Clear Screen, switch to 32 column mode, set BA as base video address
15 for RA=5 TO 0 step -1
At each iteration reduces random range
20 FOR L=0TO12:for J=0 TO A:B=16-L:C=B-4:
Star shapes is divided in 4 triangles up to 12 rows.
30 VPOKE BA+(4+J)*32+L,42+RND(1)*RA
31 VPOKE BA+(C+J)*32+B,42+RND(1)*RA
32 VPOKE BA+(C+J)*32+L,42+RND(1)*RA
33 VPOKE BA+(4+J)*32+B,42+RND(1)*RA
Writes in video memory 4 characters at times
40 :NEXT J:A=A+1:NEXT L:A=0:NEXT RA
close loops
Comments:
The idea was to render the star using a Matrix effect. A full screen version is too slow to entertain.