diff --git a/rogueviz/hypocycloid.cpp b/rogueviz/hypocycloid.cpp
new file mode 100644
index 00000000..b50cdd1c
--- /dev/null
+++ b/rogueviz/hypocycloid.cpp
@@ -0,0 +1,96 @@
+// compile with mymake rogueviz/hypocycloid
+
+// for https://twitter.com/ZenoRogue/status/1358464890978127875 :
+// hyper -shot-1000 -noscr -canvas i -noplayer -geo 1 circ1=1 circ2=2 show=.05 lw=20 -zoom .9 -animvideo 360 cycloid-2-euc.mp4
+// for https://twitter.com/ZenoRogue/status/1358464962088337410 :
+// hyper -shot-1000 -noscr -canvas i -noplayer -geo 0 "circ1=0../0..4../0..|4../0..0../0" "circ2=0../0..8../0..|8../0..0../0" show=.05 lw=3 loops=10 -zoom .9 -animvideo 3600 cycloid-2-hyp.mp4
+// for https://twitter.com/ZenoRogue/status/1358465029876690948 :
+// hyper -shot-1000 -noscr -canvas i -noplayer -geo 0 "circ1=0../0..8../0..|8../0..0../0" "circ2=0../0..32../0..|32../0..0../0" prec=3600 show=.05 lw=3 loops=10 -zoom .9 -animvideo 3600 cycloid-4-hyp.mp4
+
+// for https://twitter.com/ZenoRogue/status/1358506225990828033 :
+// hyper -shot-1000 -noscr -canvas i -noplayer -geo 2 "circ1=0../0...5../0..|.5../0..0../0" "circ2=0../0..1../0..|1../0..0../0" show=.05 lw=3 loops=10 -zoom .9 -animvideo 1200 cycloid-2-sph.mp4
+
+// for https://twitter.com/ZenoRogue/status/1358505146553159682 :
+// hyper -shot-1000 -noscr -canvas i -noplayer -geo 0 circ1=1 circ2=2 show=.1 lw=5 -zoom .9 "ratio=2../0..8../0..|8../0..2../0" prec=3600 -animvideo 3600 half-radius.mp4
+
+#include "../hyper.h"
+
+namespace hr {
+
+ld circ1 = 0.5; /* circumference of the small circle (actually, circumference divided by 2pi) */
+ld circ2 = 1;   /* circumference of the large circle (actually, circumference divided by 2pi) */
+
+ld show = 0.02; /* radius of the blue circle which shows the moving point */
+
+ld lw = 3;      /* linewidth multiplier */
+
+ld loops = 1;   /* with loops=k, the circle goes around k times during the full animation */
+
+ld ratio = 0;   /* if set to non-zero, circ1 and circ2 are assigned so that the ratio of radii is ratio */
+
+int prec = 360; /* precision */
+
+void circ_frame() {
+  ld t = (1. * prec * ticks) / anims::period * loops;
+  
+  if(ratio) {
+    ld min = 0;
+    ld max = 10;
+    for(int it=0; it<100; it++) {
+      ld x = (min + max) / 2;
+      ld f = sin_auto(2*x) - ratio * sin_auto(x);
+      if(f > 0 ^ spherical) max = x;
+      else min = x;
+      }
+    circ1 = sin_auto(min);
+    circ2 = sin_auto(2*min);
+    }
+  
+  ld rad1 = asin_auto(circ1);
+  ld rad2 = asin_auto(circ2);
+  
+  vid.linewidth *= lw;
+  
+  shiftmatrix at = shiftless(Id); //  * xpush(rad2);
+  
+  ld kdegree = 2 * M_PI / prec;
+  
+  if(1) {
+    for(int i=0; i<=prec; i++)
+      curvepoint(spin(i*kdegree) * xpush(rad2) * C0);      
+    queuecurve(at, 0xFF0000FF, 0x200000FF, PPR::LINE);
+    }
+
+  for(int i=0; i<=prec; i++)
+    curvepoint(spin(t*kdegree) * xpush(rad2-rad1) * spin(i*kdegree) * xpush(rad1) * C0);
+  queuecurve(at, 0x00FF00FF, 0x002000FF, PPR::LINE);
+  
+  for(int q=0; q<360; q+=36) queueline(
+    at * spin(t*kdegree) * xpush(rad2-rad1) * C0, 
+    at * spin(t*kdegree) * xpush(rad2-rad1) * spin(q*degree-t*kdegree*circ2/circ1) * xpush(rad1) * C0,
+    0xFFD500FF, 4);
+  
+  for(int i=0; i<=prec; i++)
+    curvepoint(spin(i*kdegree) * xpush(rad2-rad1) * spin(-i*kdegree*circ2/circ1) * xpush(rad1) * C0);
+
+  queuecurve(at, 0xFFFFFFFF, 0, PPR::LINE);
+
+  for(int i=0; i<=prec; i++)
+    curvepoint(spin(t*kdegree) * xpush(rad2-rad1) * spin(-t*kdegree*circ2/circ1) * xpush(rad1) * spin(i*kdegree) * xpush(show) * C0);
+  queuecurve(at, 0xFFFFFFFF, 0xFFFF, PPR::LINE);    
+
+  vid.linewidth /= lw;
+  }
+
+auto shot_hooks = addHook(hooks_frame, 100, circ_frame)
+  + addHook(hooks_configfile, 100, [] {
+    param_f(circ1, "circ1");
+    param_f(circ2, "circ2");
+    param_f(show, "show");
+    param_f(loops, "loops");
+    param_f(ratio, "ratio");
+    param_i(prec, "prec");
+    param_f(lw, "lw");
+    });
+
+}