diff --git a/hyperweb.cpp b/hyperweb.cpp
index 2d2b5f9e..d9eafa73 100644
--- a/hyperweb.cpp
+++ b/hyperweb.cpp
@@ -112,16 +112,6 @@ EX void offer_choose_file(reaction_t r) {
     });
   }
 
-// -- demo --
-
-#if CAP_URL
-EX void open_url(string s) {
-  EM_ASM_({
-    window.open(UTF8ToString($0, 1000));
-    }, s.c_str());
-  }
-#endif
-
 //    window.open(Pointer_stringify($0));
 bool demoanim;
 
diff --git a/rogueviz/heatx.cpp b/rogueviz/heatx.cpp
new file mode 100644
index 00000000..0a4cc51b
--- /dev/null
+++ b/rogueviz/heatx.cpp
@@ -0,0 +1,145 @@
+#include "rogueviz.h"
+#include <unordered_map>
+
+// heat equation simulation
+// https://twitter.com/ZenoRogue/status/1208409387733307392
+
+// run with e.g.
+// -geo 1 -canvas 0 -smart 1 -smartlimit 999999 -heatx
+// -tes tessellations/sample/marjorie-rice.tes heat_scale=0.02 -canvas 0 -smart 1 -smartlimit 999999 -heatx
+
+namespace hr {
+
+namespace heatx {
+
+const int NOT_STARTED = 999999;
+const int OFF = 999998;
+
+int last_steps = NOT_STARTED;
+
+std::unordered_map<cell*, double> m1, m2, m3;
+
+ld delta = 0.01;
+
+int mode = 1;
+
+int qsteps = 2000;
+
+ld frac_per_frame = .001;
+
+ld frac;
+
+ld scale = 0.05;
+
+void advance_heat_wave() {
+
+  if(euclid && GDIM == 2)
+    pconf.scale = scale / max(frac, .15);
+
+  int steps = mode == 2 ? (frac * qsteps) : (frac * frac * qsteps);
+
+  if(steps != last_steps) {
+    celllister cl(cwt.at, 400, 20000, nullptr);
+    if(steps < last_steps) {
+      last_steps = 0;
+      m1.clear();
+      m2.clear();
+      for(cell *c: cl.lst) m1[c] = 0;
+      m2 = m1;
+      m1[cwt.at] = 1;
+      }
+    while(last_steps < steps) {
+      switch(mode) {
+        case 0:
+          // heat: average of adjacent
+          for(cell *c: cl.lst) {
+            ld v = m1[c];
+            forCellEx(c2, c) {
+              if(m1.count(c2)) v += m1[c2]; else v += m1[c];
+              }
+            v /= (1 + c->type);
+            m2[c] = v;
+            }
+          swap(m1, m2);
+          break;
+        case 1:
+          // heat: transfer to adjacent
+          for(auto& p: m2) p.second = 0;
+          for(cell *c: cl.lst) {
+            ld v = m1[c] / (1 + c->type);
+            m2[c] += v;
+            forCellEx(c2, c) {
+              if(m1.count(c2)) m2[c2] += v; else m2[c] += v;
+              }
+            }
+          swap(m1, m2);
+          break;
+        case 2:
+          // wave
+          for(cell *c: cl.lst) {
+            m3[c] = 0;
+            forCellEx(c2, c) {
+              if(m1.count(c2)) m3[c] += (m1[c2] - m1[c]);
+              }
+            }
+          for(cell *c: cl.lst) {
+            m1[c] += m2[c] * delta + m3[c] * delta * delta / 2;
+            m2[c] += m3[c] * delta;
+            }
+          break;
+        }
+      last_steps++;
+      }
+    ld maxv = 0;
+    for(auto p: m1) maxv = max(maxv, abs(p.second));
+    for(cell *c: cl.lst) {
+      ld x = m1[c] / maxv;
+      if(mode == 2) {
+        if(x < 0) c->landparam = gradient(0x001010, 0x1010FF, -1, x, 0);
+        else c->landparam = gradient(0x1010FF, 0xFFFFFF, 0, x, 1);
+        }
+      else {
+        if(x < 1/2.) c->landparam = gradient(0x001010, 0xFF1010, 0, x, 1/2.);
+        else c->landparam = gradient(0xFF1010, 0xFFFF10, 1/2., x, 1.);
+        if(x > .2 && x < .3) c->landparam |= 0x4040;
+        }
+      }
+    }
+  
+  // return false;
+  }
+
+void enable() {
+  using rogueviz::rv_hook;
+  rv_hook(hooks_frame, 100, advance_heat_wave);
+  rv_hook(anims::hooks_anim, 100, [] {
+     if(inHighQual) {
+       frac = std::fmod(ticks, anims::period) * 1. / anims::period;
+       }
+     else {
+       frac += frac_per_frame;
+       if(frac > 1) frac--;
+       }
+     });
+  rv_hook(shot::hooks_take, 100, [] { 
+     advance_heat_wave(); calcparam(); models::configure(); 
+     });
+  rv_hook(hooks_drawcell, 100, [] (cell *c, const shiftmatrix& V) {
+    if(WDIM == 3) 
+      queuepoly(face_the_player(V), cgi.shRing, darkena(c->landparam_color, 0, 0xFF));
+    return false;
+    });
+  rogueviz::cleanup.push_back([] { m1.clear(); m2.clear(); m3.clear(); last_steps = OFF; });
+  last_steps = NOT_STARTED; frac = 0;
+  }
+
+auto heathook = arg::add3("-heatx", enable)
+  + addHook(hooks_configfile, 100, [] {
+    param_f(delta, "heat_delta");
+    param_i(qsteps, "heat_qsteps");
+    param_f(frac_per_frame, "heat_pf");
+    param_f(scale, "heat_scale");
+    });
+
+}
+}
diff --git a/rogueviz/rogueviz-all.cpp b/rogueviz/rogueviz-all.cpp
index da7f9b01..c0e59e44 100644
--- a/rogueviz/rogueviz-all.cpp
+++ b/rogueviz/rogueviz-all.cpp
@@ -36,6 +36,8 @@
 #include "hypcity.cpp"
 #include "hypocycloid.cpp"
 
+#include "heatx.cpp"
+
 #include "notknot.cpp"
 
 #include "inner-maps.cpp"
diff --git a/sysconfig.h b/sysconfig.h
index f2f28651..a93165ea 100644
--- a/sysconfig.h
+++ b/sysconfig.h
@@ -79,6 +79,10 @@
 #define CAP_GMP 0
 #endif
 
+#ifndef CAP_URL
+#define CAP_URL 1
+#endif
+
 #define CAP_FRAMELIMIT (!ISMOBWEB)
 
 #if ISMOBILE
@@ -339,6 +343,8 @@
 #define hyper fake_hyper // avoid "hyper" typedef in <_mingw.h>
 #define WIN32_LEAN_AND_MEAN // avoid "rad1" macro in <windows.h>
 #define NOMINMAX // avoid "min" and "max" macros in <windows.h>
+#include <windows.h>
+#include <shellapi.h>
 #endif
 
 #include <stdio.h>
diff --git a/util.cpp b/util.cpp
index 702357ac..b315f472 100644
--- a/util.cpp
+++ b/util.cpp
@@ -703,4 +703,25 @@ EX bool file_exists(string fname) {
   return access(fname.c_str(), F_OK) != -1;
   }
 
+EX void open_url(string s) {
+  #if ISWEB
+  EM_ASM_({
+    window.open(UTF8ToString($0, 1000));
+    }, s.c_str());
+  #else
+
+#ifdef WINDOWS  
+  ShellExecute(0, 0, s.c_str(), 0, 0, SW_SHOW);
+#endif
+
+#ifdef LINUX
+  system(("xdg-open "+s).c_str());
+#endif
+
+#ifdef MAC
+  system(("open "+s).c_str());
+#endif
+#endif
+  }
+  
 }