Landscape Effect

ImGui_Party_Landscape.inl

#define V ImVec2
#define F float
#define D 2048
F m[D*D],I,O,w,x,y,z,h,u,v,l;int q,i,j,T,M;F&A(int x,int y){return m[(x&(D-1))+(y&(D-1))*D];}
F S(F x,F y){I=A(x*D,y*D);return 1-I*I*9;}
void L(F& x,F a,F c){x=sqrt(1.-exp(-a*I*(1.-O)-c*O));}
#define R ((rand()%98)/49.-1)*l
void FX(ImDrawList*d,V a,V b,V B,ImVec4 o,F t){
if(!q){q=1;m[0]=0;l=.5;
for(T=D;T>1;l=l/2,T=T/2){M=T/2;for(j=0;j<D;j+=T){for(i=0;i<D;i+=T){w=A(i,j);x=A(i+T,j);y=A(i,j+T);z=A(i+T,j+T);
A(i+M,j)=(w+x)/2+R;A(i+M,j+T)=(y+z)/2+R;A(i,j+M)=(w+y)/2+R;A(i+T,j+M)=(x+z)/2+R;A(i+M,j+M)=(w+x+y+z)/4+R;}}}}
V s=a,e=b;o.w=1;for(i=64;i--;){s.y=e.y;e.y=a.y+B.y*i/150;d->AddRectFilled(s,e,0xffff6000+i*771);}
for(i=0;i<B.x;i++){s.x=e.x=a.x+i;e.y=s.y=b.y;w=(i/B.x)*2-1;h=S(.5,t*.2)-.5;
for(j=0;j<400;j++){z=j/400.;z=z*z*500;x=w*z;u=x/300+.5;v=z/300+t*.2;l=S(u,v);y=(l-h)*32;s.y=a.y+B.y*(y/(z+.1)+.25);
if(s.y<e.y){I=l-S(u+.01,v+.005)+.01;I=I*(I>0)*30+.2;O=1.0-exp(-z*3e-4);L(o.x,.6,2);L(o.y,.25,4);L(o.z,.15,10);d->AddLine(s,e,ImColor(o));e.y=s.y;}}}}

how did you come up with this?