even cooler starfield... simulate gravity between stars

diff --git a/misc/tools/spherefunc2skybox.c b/misc/tools/spherefunc2skybox.c
index 1f5481c3eb8269e2a1c3dab3f1d357aabad5dbb6..201cefb955c5446652816170cb0f56b83f355df1 100644 (file)
--- a/misc/tools/spherefunc2skybox.c
+++ b/misc/tools/spherefunc2skybox.c
@@ -147,17 +147,32 @@ struct
        double darkness;
        double power;
        double density;
+       int g;
+       double gpower;
+       double gfactor;
+       double gdpower;
 }
 color_starfield_parms;
+typedef struct
+{
+       double x, y, z, e;
+       double R, G, B, A;
+} starfield_t;
+starfield_t *starfield = NULL;
+int starfield_cmp(const void *a_, const void *b_)
+{
+       const starfield_t *a = a_;
+       const starfield_t *b = b_;
+       if(a->z < b->z)
+               return -1;
+       if(a->z > b->z)
+               return +1;
+       return 0;
+}
 void color_starfield(double x, double y, double z, double *r, double *g, double *b)
 {
-       static struct
-       {
-               double x, y, z, e;
-               double R, G, B, A;
-       } *starfield = NULL;
-       int i;
-       double f;
+       int i, j, k;
+       double f, mindot, d;
 
        if(!starfield)
        {
@@ -176,12 +191,6 @@ void color_starfield(double x, double y, double z, double *r, double *g, double
                                  + starfield[i].z * starfield[i].z;
                        }
                        while(r > 1);
-                       r = sqrt(r);
-                       starfield[i].x /= r;
-                       starfield[i].y /= r;
-                       starfield[i].z /= r;
-
-                       starfield[i].e = color_starfield_parms.density * pow(rnd(), -color_starfield_parms.power);
 
                        starfield[i].R = rnd();
                        starfield[i].G = rnd();
@@ -191,15 +200,39 @@ void color_starfield(double x, double y, double z, double *r, double *g, double
                        starfield[i].G /= f;
                        starfield[i].B /= f;
                        starfield[i].A = rnd();
+                       starfield[i].e = color_starfield_parms.density * pow(rnd(), -color_starfield_parms.power);
+               }
+               fprintf(stderr, "Gravitating starfield...\n");
+               for(k = 0; k < color_starfield_parms.g; ++k)
+               {
+                       i = rand() % color_starfield_parms.n;
+                       j = rand() % color_starfield_parms.n;
+                       f = pow(rnd(), color_starfield_parms.gpower);
+                       f = f * color_starfield_parms.gfactor;
+                       d = pow(starfield[j].x - starfield[i].x, 2)
+                         + pow(starfield[j].y - starfield[i].y, 2)
+                         + pow(starfield[j].z - starfield[i].z, 2);
+                       f *= pow(1 / (1 + d), color_starfield_parms.gdpower);
+                       starfield[i].x += f * (starfield[j].x - starfield[i].x);
+                       starfield[i].y += f * (starfield[j].y - starfield[i].y);
+                       starfield[i].z += f * (starfield[j].z - starfield[i].z);
+                       double r = starfield[i].x * starfield[i].x + starfield[i].y * starfield[i].y + starfield[i].z * starfield[i].z;
+                       r = sqrt(r);
+                       starfield[i].x /= r;
+                       starfield[i].y /= r;
+                       starfield[i].z /= r;
                }
+               fprintf(stderr, "Sorting starfield...\n");
+               qsort(starfield, sizeof(*starfield), color_starfield_parms.n, starfield_cmp);
                fprintf(stderr, "Done.\n");
        }
 
        *r = *g = *b = 0;
+       mindot = pow(1/256.0, 1.0/color_starfield_parms.density);
        for(i = 0; i < color_starfield_parms.n; ++i)
        {
                double dot = x * starfield[i].x + y * starfield[i].y + z * starfield[i].z;
-               if(dot <= 0)
+               if(dot <= mindot)
                        continue;
                double f = pow(dot, starfield[i].e) * starfield[i].A;
                *r += starfield[i].R * f;
@@ -355,6 +388,10 @@ int main(int argc, char **argv)
                color_starfield_parms.darkness = argc<= 5 ? 0.4 : atof(argv[5]);
                color_starfield_parms.power = argc<= 6 ? 2.5 : atof(argv[6]);
                color_starfield_parms.density = argc<= 7 ? 60000 : atof(argv[7]);
+               color_starfield_parms.g = argc<= 8 ? 10000000 : atoi(argv[8]);
+               color_starfield_parms.gpower = argc<= 9 ? 3 : atoi(argv[9]);
+               color_starfield_parms.gfactor = argc<= 10 ? 0.9 : atof(argv[10]);
+               color_starfield_parms.gdpower = argc<= 11 ? 15 : atof(argv[11]);
        }
        else
        {