Challenge - starfield simulation

[Carl Gundel]

This is already less than 1K, but how small can it be? 

dim st(9,1)
gosub [setup]
timer 20, [cycle]
[cycle]
for c=0 to n
xold=st(c,0)
yold=st(c,1)
st(c,0)=xold*1.23
st(c,1)=yold*1.23

x=int(st(c,0))
y=int(st(c,1))
if abs(x)<15 and abs(y)<15 then
gosub [clearStar]
else
if abs(x)>200 or abs(y)>200 then
st(c,0)=(rnd(1)-0.5)*3
st(c,1)=(rnd(1)-0.5)*3
else
gosub [drawStar]
end if
end if
next c
wait
goto [cycle]

[clearStar]
#starfield "color black ; place "; xCenter + xold; " "; yCenter + yold
#starfield "\."
return

[drawStar]
gosub [clearStar]
#starfield "color white ; place "; xCenter + x; " "; yCenter + y
#starfield "\."
return

[setup]
input"# stars (1-10)";n
n=n-1
for x=0 to n
st(x,0)=(rnd(1)-0.5)*200
st(x,1)=(rnd(1)-0.5)*200
next x
open "starfield" for graphics as #starfield
#starfield "home ; posxy xCenter yCenter"
#starfield "down ; fill black ; backcolor black"
#starfield "trapclose [quit]"
return

[quit]
close #starfield
end

[Rod]

440 bytes

dim s(99,3)
open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;backcolor black;trapclose [q]"
[l]
scan
for i=0 to 99
s(i,2)=s(i,0):s(i,3)=s(i,1):s(i,0)=s(i,0)*1.23+.01:s(i,1)=s(i,1)*1.23
if abs(s(i,0))>DisplayWidth/2 then s(i,0)=(rnd(0)-0.5)*3 : s(i,1)=(rnd(0)-0.5)*3
#s "color black;place ";x+s(i,2);" ";y+s(i,3);" ;\."
#s "color white;place ";x+s(i,0);" ";y+s(i,1);" ;\."
next
goto [l]

[q]
close #s
end


[tsh73]

385
dim s(99,3):open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;trapclose [q];size 2;rule xor"
[l]scan:for i=0 to 99
s(i,2)=s(i,0):s(i,3)=s(i,1):s(i,0)=s(i,0)*1.23+.01:s(i,1)=s(i,1)*1.23
if abs(s(i,0))>DisplayWidth/2 then s(i,0)=(rnd(0)-0.5)*3:s(i,1)=(rnd(0)-0.5)*3
#s "set ";x+s(i,2);" ";y+s(i,3);";set ";x+s(i,0);" ";y+s(i,1)
next
goto [l]
[q] close #s:end


[Rod]

tsh73 clever!

[David Drake]

Feb 18, 2020 3:40:46 GMT -5 Rod said:

tsh73 clever!

I agree.  tsh73 did a fine job with this.

[Carl Gundel]

Feb 18, 2020 2:51:23 GMT -5 tsh73 said:

385
dim s(99,3):open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;trapclose [q];size 2;rule xor"
[l]scan:for i=0 to 99
s(i,2)=s(i,0):s(i,3)=s(i,1):s(i,0)=s(i,0)*1.23+.01:s(i,1)=s(i,1)*1.23
if abs(s(i,0))>DisplayWidth/2 then s(i,0)=(rnd(0)-0.5)*3:s(i,1)=(rnd(0)-0.5)*3
#s "set ";x+s(i,2);" ";y+s(i,3);";set ";x+s(i,0);" ";y+s(i,1)
next
goto [l]
[q] close #s:end


Nice.

Slightly smaller still at 374 bytes.  Who needs END?  Standing on the shoulders of giants. 

dim s(99,3):open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;trapclose [q];size 2;rule xor"
while 1:scan
s(i,2)=s(i,0):s(i,3)=s(i,1):s(i,0)=s(i,0)*1.2+.01:s(i,1)=s(i,1)*1.2
if abs(s(i,0))>DisplayWidth/2 then s(i,0)=(rnd(0)-.5)*3:s(i,1)=(rnd(0)-.5)*3
#s "set ";x+s(i,2);" ";y+s(i,3);";set ";x+s(i,0);" ";y+s(i,1)
i=(i+1)mod 100
wend
[q] close #s


[Rod]

330/326 
Slight cheat down from 99 to 9 stars, sans dim, but faster! 326 without end.
open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;trapclose [q];rule xor"
[l]
scan:z(i)=x(i):w(i)=y(i):x(i)=x(i)*1.2+.01:y(i)=y(i)*1.2
if abs(x(i))>DisplayWidth/2 then x(i)=(rnd(0)-.5)*3:y(i)=(rnd(0)-.5)*3
#s "set ";x+z(i);" ";y+w(i);";set ";x+x(i);" ";y+y(i)
i=(i+1)mod 10
goto [l]
[q] close #s:end


[David Drake]

Eliminating the _fs_nsb and a little housekeeping gets the LOF down to 318.

open "" for graphics as #s:#s "home;posxy x y;down;fill black;trapclose [q];rule xor"
[l] scan:z(i)=x(i):w(i)=y(i):x(i)=x(i)*1.2+.01:y(i)=y(i)*1.2:if abs(x(i))>DisplayWidth/2 then x(i)=(rnd(0)-.5)*3:y(i)=(rnd(0)-.5)*3
#s "set ";x+z(i);" ";y+w(i);";set ";x+x(i);" ";y+y(i):i=(i+1)mod 10:goto [l]
[q] close #s:end


[Carl Gundel]

Feb 18, 2020 14:08:52 GMT -5 Rod said:

330/326 
Slight cheat down from 99 to 9 stars, sans dim, but faster! 326 without end.
open "" for graphics_fs_nsb as #s
#s "home;posxy x y;down;fill black;trapclose [q];rule xor"
[l]
scan:z(i)=x(i):w(i)=y(i):x(i)=x(i)*1.2+.01:y(i)=y(i)*1.2
if abs(x(i))>DisplayWidth/2 then x(i)=(rnd(0)-.5)*3:y(i)=(rnd(0)-.5)*3
#s "set ";x+z(i);" ";y+w(i);";set ";x+x(i);" ";y+y(i)
i=(i+1)mod 10
goto [l]
[q] close #s:end


Clever, but it's so fast now that it doesn't look like a starfield simulation.

[Rod]

You will never get anywhere in this universe unless you are travelling really really fast!

[Carl Gundel]

318 bytes. The loop is too fast so I moved a bunch of graphics command inside the loop to slow it down.
dim s(99,3):open "" for graphics_fs_nsb as #s
[l] #s "discard;fill black"
for i=0 to 99:scan:s(i,0)=s(i,0)*1.2+.01:s(i,1)=s(i,1)*1.2
if abs(s(i,0))>1000 then s(i,0)=(rnd(0)-.5)*3:s(i,1)=(rnd(0)-.5)*3
#s "home;posxy x y;down;trapclose [q];size 2;color white;set ";x+s(i,0);" ";y+s(i,1)
next:goto [l]
[q]close #s

This approach doesn't look as nice as the rule xor way, but it is smaller.

[Carl Gundel]

Adding two bytes to make it three times as many stars makes a huge improvement in how it looks. 320 bytes
dim s(299,3):open "" for graphics_fs_nsb as #s
[l] #s "discard;fill black"
for i=0 to 299:scan:s(i,0)=s(i,0)*1.2+.01:s(i,1)=s(i,1)*1.2
if abs(s(i,0))>1000 then s(i,0)=(rnd(0)-.5)*3:s(i,1)=(rnd(0)-.5)*3
#s "home;posxy x y;down;trapclose [q];size 2;color white;set ";x+s(i,0);" ";y+s(i,1)
next:goto [l]
[q]close #s

[Carl Gundel]

Thanks for all the interesting starfield simulation submissions guys. Nice work!

[tsh73]

312. With XOR we don't need other array for points.
dim x(99),y(99):open "" for graphics_fs as #s:#s "home;posxy x y;down;fill black;trapclose [q];rule xor"
[l] scan:#s "set ";x+x(i);" ";y+y(i):x(i)=x(i)*1.2+.01:y(i)=y(i)*1.2:if abs(x(i))>DisplayWidth/2 then x(i)=(rnd(0)-.5)*3:y(i)=(rnd(0)-.5)*3
#s "set ";x+x(i);" ";y+y(i):i=(i+1)mod 100:goto [l]
[q] close #s

[Carl Gundel]

301
dim x(99),y(99):open "" for graphics_fs as #s:#s "home;posxy x y;down;fill black;trapclose [q];rule xor"
[l] scan:#s "set ";x+x(i);" ";y+y(i):x(i)=x(i)*1.2+.01:y(i)=y(i)*1.2:if abs(x(i))>999 then x(i)=(rnd(0)-.5)*3:y(i)=(rnd(0)-.5)*3
#s "set ";x+x(i);" ";y+y(i):i=(i+1)mod 100:goto [l]
[q] close #s