From cb09876c8162f01a0a7068345f34a9ed31d0cd12 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Sat, 27 Mar 2010 22:29:54 +0000
Subject: [PATCH] Compute offsets of Bezier curves to keep rails at constant
 separation

---
 include/BezierCurve.hpp | 15 +++++++++++++++
 src/Points.cpp          |  5 ++++-
 src/SBend.cpp           |  7 ++++++-
 src/SlopeTrack.cpp      |  5 ++++-
 src/TrackCommon.cpp     | 22 +++++++++++++++-------
 5 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/include/BezierCurve.hpp b/include/BezierCurve.hpp
index 78e88bc..3f1ac70 100644
--- a/include/BezierCurve.hpp
+++ b/include/BezierCurve.hpp
@@ -106,6 +106,21 @@ struct BezierCurve {
           + p[3].z * 3 * t * t
           );
    }
+
+   // Value of the function at a constant radius in the Z-plane
+   Vector<T> offset(T t, T p) const
+   {
+      Vector<T> v = (*this)(t);
+      const Vector<T> d = deriv(t);
+
+      const T o =
+         p / sqrt((d.x * d.x) + (d.z * d.z));
+
+      v.x += o * d.z;
+      v.z -= o * d.x;
+
+      return v;
+   }
 };
 
 // Generate Bezier curves
diff --git a/src/Points.cpp b/src/Points.cpp
index 913a009..3623967 100644
--- a/src/Points.cpp
+++ b/src/Points.cpp
@@ -189,7 +189,10 @@ void Points::render() const
    else if (myAxis == axis::Y)
       glRotatef(270.0f, 0.0f, 1.0f, 0.0f);
 
-   renderRailMesh(reflected ? reflectMesh : railMesh);
+   glPushMatrix();
+   glTranslatef(-0.5f, 0.0f, 0.0f);
+   (reflected ? reflectMesh : railMesh)->render();
+   glPopMatrix();
 
    glPushMatrix();
    glRotatef(90.0f, 0.0f, 1.0f, 0.0f);
diff --git a/src/SBend.cpp b/src/SBend.cpp
index 65a2ef4..f977619 100644
--- a/src/SBend.cpp
+++ b/src/SBend.cpp
@@ -106,7 +106,12 @@ void SBend::render() const
    if (axis == axis::Y)
       glRotatef(-90.0f, 0.0f, 1.0f, 0.0f);
 
-   renderRailMesh(railMesh);
+   glPushMatrix();
+   
+   glTranslatef(-0.5f, 0.0f, 0.0f);
+   railMesh->render();
+   
+   glPopMatrix();
    
    for (float i = 0.1f; i < curve.length; i += 0.25f) {
       glPushMatrix();
diff --git a/src/SlopeTrack.cpp b/src/SlopeTrack.cpp
index 78d3473..8c31ae7 100644
--- a/src/SlopeTrack.cpp
+++ b/src/SlopeTrack.cpp
@@ -111,7 +111,10 @@ void SlopeTrack::render() const
    if (axis == axis::Y)
       glRotatef(-90.0f, 0.0f, 1.0f, 0.0f);
 
-   renderRailMesh(railMesh);
+   glPushMatrix();
+   glTranslatef(-0.5f, 0.0f, 0.0f);
+   railMesh->render();
+   glPopMatrix();
 
    // Draw the sleepers
    glTranslatef(-0.5f, 0.0f, 0.0f);
diff --git a/src/TrackCommon.cpp b/src/TrackCommon.cpp
index 0c6b15f..995ed43 100644
--- a/src/TrackCommon.cpp
+++ b/src/TrackCommon.cpp
@@ -118,17 +118,16 @@ namespace {
       theRailMesh = makeMesh(buf);
    }
 
-   // Generate a rail mesh from a Bezier curve
-   IMeshPtr generateBezierRailMesh(const BezierCurve<float>& aFunc)
+   void buildOneBezierRail(const BezierCurve<float>& func,
+      IMeshBufferPtr buf, float p)
    {
-      IMeshBufferPtr buf = makeMeshBuffer();
-      
       const float step = 0.1f;
 
       for (float t = 0.0f; t < 1.0f; t += step) {
-         Vector<float> v1 = aFunc(t);
-         Vector<float> v2 = aFunc(t + step);
-         
+
+         Vector<float> v1 = func.offset(t, p);
+         Vector<float> v2 = func.offset(t + step, p);
+              
          v1.z -= RAIL_WIDTH / 2.0f;
          v2.z -= RAIL_WIDTH / 2.0f;
 
@@ -153,6 +152,15 @@ namespace {
             makeVector(v2.x, v2.y + track::RAIL_HEIGHT, v2.z + RAIL_WIDTH),
             METAL);
       }
+   }
+
+   // Generate a rail mesh from a Bezier curve
+   IMeshPtr generateBezierRailMesh(const BezierCurve<float>& func)
+   {
+      IMeshBufferPtr buf = makeMeshBuffer();
+      
+      buildOneBezierRail(func, buf, GAUGE/2.0f);
+      buildOneBezierRail(func, buf, -GAUGE/2.0f);
 
       return makeMesh(buf);
    }
-- 
2.39.2