From b1fd9bac57bfb31a94baed36c1f962284c4ddb35 Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Sat, 18 Apr 2026 20:45:51 +0200
Subject: [PATCH] backed-map:: implemented relative_backed_matrix

---
 backed-map.cpp | 21 +++++++++++++++++++++
 reg3.cpp       |  9 +--------
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/backed-map.cpp b/backed-map.cpp
index ac144bac..8d1a6b60 100644
--- a/backed-map.cpp
+++ b/backed-map.cpp
@@ -19,6 +19,8 @@ struct backed_map {
   void rebase(heptagon*& backer, transmatrix& T);
   void handle_precision_errors(heptagon *actual);
 
+  transmatrix relative_backer_matrix(heptagon *h2, heptagon *h1, const hyperpoint& hint);
+
   geometry_information *alt_cgip[2];
 
   geometry_information *find_alt_cgip();
@@ -189,6 +191,25 @@ void backed_map::swapdim() {
   alt_cgip[1] = nullptr;
   }
 
+transmatrix backed_map::relative_backer_matrix(heptagon *h2, heptagon *h1, const hyperpoint& hint) {
+  #if CAP_BT
+  if(mhyperbolic && GDIM == 3) {
+    dynamicval<eGeometry> g(geometry, gBinary3);
+    dynamicval<hrmap*> cm(currentmap, current_altmap);
+    return currentmap->relative_matrix(h2, h1, hint);
+    }
+  #endif
+  if(mhyperbolic && GDIM == 2) {
+    dynamicval<int> uc(cgip->use_count, cgip->use_count+1);
+    dynamicval<eGeometry> g(geometry, gNormal);
+    dynamicval<eVariation> gv(variation, eVariation::pure);
+    dynamicval<geometry_information*> gi(cgip, find_alt_cgip());
+    dynamicval<hrmap*> cm(currentmap, current_altmap);
+    return currentmap->relative_matrix(h2, h1, hint);
+    }
+  return Id;
+  }
+
 bool show_map_stress;
 
 void draw_stress_map() {
diff --git a/reg3.cpp b/reg3.cpp
index e95712b7..4b4bb3ff 100644
--- a/reg3.cpp
+++ b/reg3.cpp
@@ -1689,14 +1689,7 @@ EX namespace reg3 {
     transmatrix relative_matrixh(heptagon *h2, heptagon *h1, const hyperpoint& hint) override {
       auto p1 = bm.where[h1];
       auto p2 = bm.where[h2];
-      transmatrix T = Id;
-      #if CAP_BT
-      if(hyperbolic) { 
-        dynamicval<eGeometry> g(geometry, gBinary3);
-        dynamicval<hrmap*> cm(currentmap, bm.current_altmap);
-        T = currentmap->relative_matrix(p2.first, p1.first, hint);
-        }
-      #endif
+      transmatrix T = bm.relative_backer_matrix(p2.first, p1.first, hint);
       T = inverse(p1.second) * T * p2.second;      
       if(elliptic && T[LDIM][LDIM] < 0) T = centralsym * T;
       return T;