ASCII Eulerian Fluid Simulation in 2kB of Python

main.py

import os
timestep=1./60
gravity=-9.81
tg=timestep*gravity
s_x,s_y=10,20
u=v=[[.0 for A in range(s_y)]for A in range(s_x)]
pr=[[.0 for A in range(s_y)]for A in range(s_x)]
st=[[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],[0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1],[0,1,1,1,1,0,.1,0,0,.1,.1,.1,.1,.1,.1,.1,0,0,0,0],[0,1,1,1,1,1,.1,.1,.1,.1,.1,.1,.1,.1,.1,0,0,0,0,0],[0,1,1,1,1,1,.1,.1,.1,.1,.1,.1,.1,.1,.1,0,0,0,0,0],[0,.1,0,1,1,1,.1,.1,.1,.1,.1,.1,.1,.1,.1,0,0,0,0,0],[0,.1,0,.1,.1,.1,.1,.1,.1,.1,.1,.1,.1,.1,0,0,0,0,0,0],[0,.1,0,.2,.1,.1,.1,0,.1,.1,.1,.1,0,0,0,0,0,0,0,0],[0,.1,0,0,.2,.1,.1,0,.1,0,0,0,0,0,0,0,0,0,0,0],[0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0]]
C=1e3/timestep
loop=[(A,B)for A in range(1,len(u)-1)for B in range(1,len(u[0])-1)]
cl=lambda x,size:0 if x<=0 else size-1 if x>=size else x
sf=lambda i,j,field:((A:=cl(int(i-.5),s_x-1)),(C:=i-.5-A),(E:=cl(A+1,s_x-1)),(B:=cl(int(j-.5),s_y-1)),(D:=j-.5-B),(F:=cl(B+1,s_y-1)),(G:=1.-C),(H:=1.-D),G*H*field[A][B]+C*H*field[E][B]+C*D*field[E][F]+G*D*field[A][F])[-1]
ses='.',':','!','*','o','e','&','#','%','@'
for _ in range(2**10):
	u=[[A+tg for A in A]for A in u];v=[[A+tg for A in A]for A in v]
	for(i,j)in loop:
		l,r,t,b=u[i][j],u[i+1][j],v[i][j],v[i][j+1];ls,rs,ts,bs=st[i-1][j],st[i+1][j],st[i][j-1],st[i][j+1]
		if st[i][j]==0:continue
		s=ls+rs+ts+bs;d=l-r+t-b;p=-d/s*1.9;pr[i][j]+=p*C;u[i][j],v[i+1][j],u[i][j],v[i][j+1]=l+d*ls,r+d*rs,t+d*ts,b+d*bs
	for i in range(len(u)):u[i][0],u[i][s_y-1],v[0][j],v[s_x-1][j]=u[i][1],u[i][s_y-2],v[1][j],v[s_x-2][j]
	new_u=new_v=[[.0 for A in range(s_y)]for A in range(s_x)]
	for(i,j)in loop:
		if st[i][j]!=0 and st[i-1][j]!=0:x,y=i,j+.5;nu,nv=u[i][j],sum((v[i][j],v[i+1][j],v[i][j],v[i][j+1]))/4;x-=timestep*nu;y-=timestep*nv;new_u[i][j]=sf(x//1,y//1,u)
		if st[i][j]!=0 and st[i][j-1]!=0:x,y=i+.5,j;nu,nv=sum((u[i][j],u[i+1][j],u[i][j],u[i][j+1]))/4,v[i][j];x-=timestep*nu;y-=timestep*nv;new_v[i][j]=sf(x//1,y//1,v)
	u,v=new_u,new_v;os.system('clear')
	for line in pr:print(''.join([ses[min(int(abs(A)/C)//10,9)]for A in line]),flush=True)

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