From 153cdc550c142325162668b81600321a29f450ae Mon Sep 17 00:00:00 2001
From: maj00r <maj00r@host>
Date: Fri, 23 Oct 2026 19:39:07 +0200
Subject: [PATCH] fix(sleepers): the fastenings of a rail part between two
 carved cuts where the part is laid, not twice as far out: both cuts carry its
 carved lines, taken once as the rails are laid, by one rule for both

---
 world/RailLayer.cpp         |  9 ++-------
 world/RailLayout.h          | 11 +++++++++++
 world/SleeperFastenings.cpp |  2 +-
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/world/RailLayer.cpp b/world/RailLayer.cpp
index 9ba6c119..4dfe7f3d 100644
--- a/world/RailLayer.cpp
+++ b/world/RailLayer.cpp
@@ -785,16 +785,12 @@ void TTrack::rail_layer::lay_cuts( gfx::vertex_array const &Shape, std::vector<r
             return ( A == null_handle ? B : A );
         }
         return ( tread_brightness( B, m_track.tread_band() ) > tread_brightness( A, m_track.tread_band() ) ? B : A ); };
-    knots::line offsets, extents, inner;
+    knots::line extents, inner;
     for( std::size_t i = 0; i <= Cuts.size(); ++i ) {
         auto const end { i < Cuts.size() ? Cuts[ i ].end : 1e9 };
         // a piece carved between two cuts has the same lines at both
         auto const own { i < Cuts.size() && false == ( i > 0 && Cuts[ i - 1 ].carved && Cuts[ i ].carved ) };
-        auto pieceoffsets { offsets };
-        if( own ) {
-            pieceoffsets.insert( pieceoffsets.end(), Cuts[ i ].endoffsets.begin(), Cuts[ i ].endoffsets.end() );
-        }
-        knots::sort( pieceoffsets );
+        auto const pieceoffsets { part_offsets( i > 0 ? &Cuts[ i - 1 ] : nullptr, i < Cuts.size() ? &Cuts[ i ] : nullptr ) };
         // the limits of the head from both ends can overlap along a short piece, as the planed wing rail of one frog and the cut of the next: the tighter of them holds
         auto const pieceextents { own ? knots::bound( extents, Cuts[ i ].endextents, true ) : extents };
         auto const pieceinner { own ? knots::bound( inner, Cuts[ i ].endinner, false ) : inner };
@@ -861,7 +857,6 @@ void TTrack::rail_layer::lay_cuts( gfx::vertex_array const &Shape, std::vector<r
             start = Cuts[ i ].start;
             startcap = Cuts[ i ].startcap;
             startbend = Cuts[ i ].startbend;
-            offsets = Cuts[ i ].startoffsets;
             extents = Cuts[ i ].startextents;
             inner = Cuts[ i ].startinner;
         }
diff --git a/world/RailLayout.h b/world/RailLayout.h
index 3e8379f5..ff667b82 100644
--- a/world/RailLayout.h
+++ b/world/RailLayout.h
@@ -164,6 +164,17 @@ struct rail_cut {
 struct rail_plan {
     std::vector<rail_cut> cuts;
 };
+// how far out a part of a rail between two cuts is laid: as it goes on from the one and comes to the other, once where both are carved, which
+// gives both its lines
+inline knots::line part_offsets( rail_cut const *Before, rail_cut const *After ) {
+
+    knots::line result { Before != nullptr ? Before->startoffsets : knots::line {} };
+    if( After != nullptr && false == ( Before != nullptr && Before->carved && After->carved ) ) {
+        result.insert( result.end(), After->endoffsets.begin(), After->endoffsets.end() );
+    }
+    knots::sort( result );
+    return result;
+}
 struct rail_tread {
     double from { 0.0 };
     double to { 0.0 };
diff --git a/world/SleeperFastenings.cpp b/world/SleeperFastenings.cpp
index b31318ad..9e282efa 100644
--- a/world/SleeperFastenings.cpp
+++ b/world/SleeperFastenings.cpp
@@ -94,7 +94,7 @@ fastened_rails::fastened_rails( TTrack &Track ) {
                     if( to - from < fastening_merge ) {
                         continue;
                     }
-                    auto const offsets { knots::sum( before != nullptr ? before->startoffsets : knots::line {}, after != nullptr ? after->endoffsets : knots::line {} ) };
+                    auto const offsets { track_rails::part_offsets( before, after ) };
                     auto const count { std::max( 1, static_cast<int>( std::ceil( ( to - from ) / fastening_step ) ) ) };
                     rail line;
                     line.track = track;