From bc01fddd7fa0f1fb5adddb90cf8c67a3e395456c Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Thu, 11 Jun 2009 20:30:27 +0100
Subject: [PATCH] Handle segment lengths greater than curve lengths

---
 src/Points.cpp      | 21 ++++++++++++++-------
 src/TrackCommon.cpp | 13 ++++++++++++-
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/src/Points.cpp b/src/Points.cpp
index 021ffa4..6cfeb47 100644
--- a/src/Points.cpp
+++ b/src/Points.cpp
@@ -122,8 +122,10 @@ track::TravelToken Points::getTravelToken(track::Position aPosition,
 }
 
 void Points::transform(const track::TravelToken& aToken, double aDelta) const
-{   
-   assert(aDelta < segmentLength(aToken));
+{
+   const float len = segmentLength(aToken);
+   
+   assert(aDelta < len);
 
    if (myX == aToken.position.x && myY == aToken.position.y) {
 
@@ -174,7 +176,12 @@ void Points::transform(const track::TravelToken& aToken, double aDelta) const
       // Curving onto the straight section
       float xTrans, yTrans, rotate;
 
-      const float fValue = 3.0f - aDelta;
+      // We have a slight problem in that the domain of the curve
+      // function is [0,3] but the delta is in [0,len] so we have
+      // to compress the delta into [0,3] here
+      const float curveDelta = aDelta * 3.0f / len;
+
+      const float fValue = 3.0f - curveDelta;
       const float curveValue = hypTanCurveFunc(fValue);
 
       // Calculate the angle that the tangent to the curve at this
@@ -183,23 +190,23 @@ void Points::transform(const track::TravelToken& aToken, double aDelta) const
       const float angle = radToDeg<float>(atanf(grad));
       
       if (myAxis == -axis::X && aToken.direction == axis::X) {
-         xTrans = aDelta - 2.0f;
+         xTrans = curveDelta - 3.0f + 1.0f;
          yTrans = amReflected ? curveValue : -curveValue;
          rotate = amReflected ? angle : -angle;
       }
       else if (myAxis == axis::X && aToken.direction == -axis::X) {
-         xTrans = 3.0f - aDelta;
+         xTrans = 3.0f - curveDelta;
          yTrans = amReflected ? -curveValue : curveValue;
          rotate = amReflected ? -angle : angle;
       }
       else if (myAxis == -axis::Y && aToken.direction == axis::Y) {
          xTrans = amReflected ? -curveValue : curveValue;
-         yTrans = aDelta - 2.0f;
+         yTrans = curveDelta - 3.0f + 1.0f;
          rotate = amReflected ? angle : -angle;
       }
       else if (myAxis == axis::Y && aToken.direction == -axis::Y) {
          xTrans = amReflected ? curveValue : -curveValue;
-         yTrans = 3.0f - aDelta;
+         yTrans = 3.0f - curveDelta;
          rotate = amReflected ? angle : -angle;
       }
       else
diff --git a/src/TrackCommon.cpp b/src/TrackCommon.cpp
index 27e808e..a205476 100644
--- a/src/TrackCommon.cpp
+++ b/src/TrackCommon.cpp
@@ -263,7 +263,18 @@ namespace {
 // The function that determines the curve of points and S-bends
 float hypTanCurveFunc(float x)
 {
-   return 0.5f * (1.0f + tanh(1.8f * x - 3.5f));
+   const float linearAbove = 2.7f;
+   const float wantOneAt = 2.9f;
+   if (x <= linearAbove)
+      // Use the curvey function   
+      return 0.5f * (1.0f + tanh(1.8f * x - 3.5f));
+   else {
+      // Interpolate linearly
+      const float fLinearAbove = hypTanCurveFunc(linearAbove);
+      const float m = (1.0f - fLinearAbove) / (wantOneAt - linearAbove);
+      
+      return m*(x - linearAbove) + fLinearAbove;
+   }
 }
 
 // The above function reflected about the x-axis
-- 
2.39.2