From 1458929a5d7620a0f1a5db4a266e5c4ce8af1a0b Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Sat, 2 Oct 2021 19:49:29 +0200
Subject: [PATCH] clearer functions bt::bt_to_minkowski and bt::minkowski_to_bt

---
 binary-tiling.cpp | 20 ++++++++++++++++++--
 reg3.cpp          |  6 ++----
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/binary-tiling.cpp b/binary-tiling.cpp
index 9b31b67c..5cf619d3 100644
--- a/binary-tiling.cpp
+++ b/binary-tiling.cpp
@@ -827,6 +827,7 @@ EX namespace bt {
     return log(2) + log(-h[0]);
     }
   
+  /** you probably want minkowski_to_bt */
   EX hyperpoint deparabolic3(hyperpoint h) {
     h /= (1 + h[3]);
     hyperpoint one = point3(1,0,0);
@@ -837,6 +838,22 @@ EX namespace bt {
     return point3(log(2) + log(-h[0]), h[1] / co, h[2] / co);
     }
 
+  /** \brief convert BT coordinates to Minkowski coordinates 
+      in the BT coordinates, h[2] is vertical; the center of the horosphere in Klein model is (1,0,0) 
+      */
+
+  EX hyperpoint bt_to_minkowski(hyperpoint h) {
+    ld yy = log(2) / 2;
+    return parabolic3(h[0], h[1]) * xpush0(yy*h[2]);
+    }
+
+  /** \brief inverse of bt_to_minkowski */
+  EX hyperpoint minkowski_to_bt(hyperpoint h) {
+    h = bt::deparabolic3(h);
+    h = point3(h[1], h[2], h[0] / (log(2)/2));
+    return h;
+    }
+
 #if CAP_COMMANDLINE  
 auto bt_config = arg::add2("-btwidth", [] {arg::shift_arg_formula(vid.binary_width); });
 #endif
@@ -1177,8 +1194,7 @@ EX void create_faces() {
   if(kite::in()) {
     auto kv = kite::make_walls();
     for(auto& v: kv.first) for(auto& h: v) {
-      h = bt::deparabolic3(h);
-      h = point3(h[1], h[2], h[0] / (log(2)/2));
+      h = minkowski_to_bt(h);
       }
     for(int i=0; i<isize(kv.first); i++) {
       add_wall(i, kv.first[i]);
diff --git a/reg3.cpp b/reg3.cpp
index c27ae96d..092339ce 100644
--- a/reg3.cpp
+++ b/reg3.cpp
@@ -17,10 +17,8 @@ EX hyperpoint final_coords(hyperpoint h) {
   if(sn::in() || !bt::in()) 
     return ultra_normalize(h);
   #if CAP_BT
-  if(bt::in()) {
-    ld yy = log(2) / 2;
-    return bt::parabolic3(h[0], h[1]) * xpush0(yy*h[2]);
-    }
+  if(bt::in()) 
+    return bt::bt_to_minkowski(h);
   #endif
   return h;
   }