more precise torus-rug rendering

fieldpattern.cpp

@@ -720,6 +720,66 @@ fpattern& getcurrfp() {
   return fp43;
   }
 
+// extra information for field quotient extra configuration
+
+struct primeinfo {
+  int p;
+  int cells;
+  bool squared;
+  };  
+
+struct fgeomextra {
+  eGeometry base;
+  vector<primeinfo> primes;
+  int current_prime_id;
+  fgeomextra(eGeometry b, int i) : base(b), current_prime_id(i) {}
+  };
+
+vector<fgeomextra> fgeomextras = {
+  fgeomextra(gNormal, 3),
+  fgeomextra(gOctagon, 1),
+  fgeomextra(g45, 0),
+  fgeomextra(g46, 3),
+  fgeomextra(g47, 0)
+  };
+
+int current_extra = 0;
+
+void nextPrime(fgeomextra& ex) {
+  dynamicval<eGeometry> g(geometry, ex.base);
+  int nextprime;
+  if(size(ex.primes))
+    nextprime = ex.primes.back().p + 1;
+  else
+    nextprime = 2;
+  while(true) {
+    fieldpattern::fpattern fp(0);
+    fp.Prime = nextprime;
+    if(fp.solve() == 0) {
+      fp.build();
+      ex.primes.emplace_back(primeinfo{nextprime, size(fp.matrices) / S7, (bool) fp.wsquare});
+      break;
+      }
+    nextprime++;
+    }
+  }
+
+void nextPrimes(fgeomextra& ex) {
+  while(size(ex.primes) < 4) 
+    nextPrime(ex);
+  }
+
+void enableFieldChange() {
+  fgeomextra& gxcur = fgeomextras[current_extra];
+  fieldpattern::quotient_field_changed = true;
+  nextPrimes(gxcur);
+  dynamicval<eGeometry> g(geometry, gQuotient2);
+  ginf[geometry].sides = ginf[gxcur.base].sides;
+  ginf[geometry].vertex = ginf[gxcur.base].vertex;
+  ginf[geometry].distlimit = ginf[gxcur.base].distlimit;
+  fieldpattern::current_quotient_field.init(gxcur.primes[gxcur.current_prime_id].p);
+  }
+
 }
 
 #define currfp fieldpattern::getcurrfp()
@@ -727,3 +787,4 @@ fpattern& getcurrfp() {
 int currfp_gmul(int a, int b) { return currfp.gmul(a,b); }
 int currfp_inverses(int i) { return currfp.inverses[i]; }
 int currfp_distwall(int i) { return currfp.distwall[i]; }
+