file_id.diz
xmas star 1.0
Author: David Payne
Category: Christmas Challenge 2022
System: BBC Micro
Language: BBC BASIC
Len source code: 60 bytes
Len exe file: 49 bytes
Len code only: 49 bytes
Instructions:
Open your web browser. Copy and paste the following URL:
https://bbcmic.ro/#%7B%22v%22%3A1%2C%22program%22%3A%221F.y%3D-8TO4%3AF.x%3D-4TOy%2B4%3AV.31%2Cx*SGNRND%2B8%2Cy*SGNRND%2B9%2C42%3AN.%2C%3ARUN%22%7D
the program will be run immediately. The xmas star looks nicer if you clear the screen first though, so to do this:
click on the BBC micro "screen" on the right
hit escape
enter CLS
enter RUN
Description:
Firstly note that the xmas star consists of 4 overlapping copies of the below triangle centred on the origin (the o).
One as below, one reflected in the x-axis, one reflected in the y-axis and one reflected in both of these axes.
*
**
***
****
*****
******
*******
********
****o****
**********
***********
************
*************
so the 1st version of the program simply draws the above triangle, which is translated onto the screen (i.e. x+8, y+9)
1FORy=-8TO4:FORx=-4TOy+4:VDU31,x+8,y+9,42:NEXT,
VDU31,x,y,42 is equivalent to PRINTTAB(x,y);"*";
the 2nd version "maps" each asterisk to one of the 4 triangles chosen at random. Put it all into an infinite loop and
the xmas star then magically appears:
1FORy=-8TO4:FORx=-4TOy+4:VDU31,x*SGN(RND)+8,y*SGN(RND)+9,42:NEXT,:RUN
the brackets are optional so may be removed, which gives:
1FORy=-8TO4:FORx=-4TOy+4:VDU31,x*SGNRND+8,y*SGNRND+9,42:NEXT,:RUN
finally, some of the keywords can be replaced by abbreviations (although this step doesn't affect the size of the program
in memory), which gives the final version:
1F.y=-8TO4:F.x=-4TOy+4:V.31,x*SGNRND+8,y*SGNRND+9,42:N.,:RUN
Comments:
I did also attempt this challenge in 6502 assembly language but I could not get close to the 49 bytes of the BASIC version.
1F.y=-8TO4:F.x=-4TOy+4:V.31,x*SGNRND+8,y*SGNRND+9,42:N.,:RUN