From 9bbd5f0e727c2e2e4ab66642d28ef3a5752f2a7e Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Thu, 11 Jun 2009 20:03:05 +0100
Subject: [PATCH] Turn onto curved bit of points

---
 include/Maths.hpp |  5 +++++
 maps/points.xml   |  2 +-
 src/Maths.cpp     | 14 ++++++++++++++
 src/Points.cpp    | 47 +++++++++++++++++++++++++++++++++++------------
 4 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/include/Maths.hpp b/include/Maths.hpp
index 3637e1d..64c9a25 100644
--- a/include/Maths.hpp
+++ b/include/Maths.hpp
@@ -18,6 +18,8 @@
 #ifndef INC_MATHS_HPP
 #define INC_MATHS_HPP
 
+#include "Platform.hpp"
+
 #include <cmath>
 #include <ostream>
 
@@ -190,6 +192,9 @@ struct Frustum {
 
 Frustum getViewFrustum();
 
+// A rough guess at the gradient at a point on a curve
+float approxGradient(function<float (float)> aFunc, float x);
+
 // Useful functions for converting to/from radians
 
 template <typename T>
diff --git a/maps/points.xml b/maps/points.xml
index 8c316e5..6c85879 100644
--- a/maps/points.xml
+++ b/maps/points.xml
@@ -2,7 +2,7 @@
 <map width="64" height="64">
 <name>No Name</name>
 
-<start x="37" y="15" dirX="-1" dirY="0"/>
+<start x="4" y="17" dirX="0" dirY="-1"/>
 
 <heightmap>maps/points.bin</heightmap>
 
diff --git a/src/Maths.cpp b/src/Maths.cpp
index 38b1e4f..f57521c 100644
--- a/src/Maths.cpp
+++ b/src/Maths.cpp
@@ -44,3 +44,17 @@ void drawNormal(const Vector<float>& aPosition,
    glPopAttrib();
    glPopAttrib();
 }
+
+// A rough guess at the gradient at a point on a curve
+float approxGradient(function<float (float)> aFunc, float x)
+{
+   const float delta = 0.01f;
+
+   const float x1 = x - delta;
+   const float x2 = x + delta;
+
+   const float y1 = aFunc(x1);
+   const float y2 = aFunc(x2);
+
+   return (y2 - y1) / (x2 - x1);
+}
diff --git a/src/Points.cpp b/src/Points.cpp
index dd047e0..ba557fb 100644
--- a/src/Points.cpp
+++ b/src/Points.cpp
@@ -146,6 +146,8 @@ void Points::transform(const track::TravelToken& aToken, double aDelta) const
       
       if (myAxis == axis::Y || myAxis == -axis::Y)
          glRotated(-90.0, 0.0, 1.0, 0.0);
+      
+      glTranslated(-0.5, 0.0, 0.0);
    }
    else if (aToken.position == straightEndpoint()) {
       debug() << "Section 2";
@@ -169,44 +171,63 @@ void Points::transform(const track::TravelToken& aToken, double aDelta) const
       
       if (myAxis == axis::Y || myAxis == -axis::Y)
          glRotated(-90.0, 0.0, 1.0, 0.0);
+      
+      glTranslated(-0.5, 0.0, 0.0);
    }
    else if (aToken.position == displacedEndpoint()) {
       // Curving onto the straight section
       debug() << "Section 3";
 
-      float xTrans, yTrans;
+      float xTrans, yTrans, rotate;
+
+      const float fValue = 3.0f - aDelta;
+      const float curveValue = hypTanCurveFunc(fValue);
+
+      // Calculate the angle that the tangent to the curve at this
+      // point makes to (one of) the axis at this point
+      const float grad = approxGradient(hypTanCurveFunc, fValue);
+      const float angle = radToDeg<float>(atanf(grad));
+      debug() << grad << " angle=" << angle;
       
       if (myAxis == -axis::X && aToken.direction == axis::X) {
          xTrans = aDelta - 2.0f;
 
          if (amReflected)
-            yTrans = hypTanCurveFunc(3.0f - aDelta);
+            yTrans = curveValue;
          else
-            yTrans = -hypTanCurveFunc(3.0f - aDelta);
+            yTrans = -curveValue;
+
+         rotate = amReflected ? angle : -angle;
       }
       else if (myAxis == axis::X && aToken.direction == -axis::X) {
          xTrans = 3.0f - aDelta;
          
          if (amReflected)
-            yTrans = -hypTanCurveFunc(3.0f - aDelta);
+            yTrans = -curveValue;
          else
-            yTrans = hypTanCurveFunc(3.0f - aDelta);
+            yTrans = curveValue;
+
+         rotate = amReflected ? -angle : angle;
       }
-      if (myAxis == -axis::Y && aToken.direction == axis::Y) {
+      else if (myAxis == -axis::Y && aToken.direction == axis::Y) {
          if (amReflected)
-            xTrans = -hypTanCurveFunc(3.0f - aDelta);
+            xTrans = -curveValue;
          else
-            xTrans = hypTanCurveFunc(3.0f - aDelta);
+            xTrans = curveValue;
          
          yTrans = aDelta - 2.0f;
+
+         rotate = amReflected ? angle : -angle;
       }
       else if (myAxis == axis::Y && aToken.direction == -axis::Y) {
          if (amReflected)
-            xTrans = hypTanCurveFunc(3.0f - aDelta);
+            xTrans = curveValue;
          else
-            xTrans = -hypTanCurveFunc(3.0f - aDelta);
+            xTrans = -curveValue;
          
          yTrans = 3.0f - aDelta;
+
+         rotate = amReflected ? angle : -angle;
       }
       else
          assert(false);
@@ -215,11 +236,13 @@ void Points::transform(const track::TravelToken& aToken, double aDelta) const
       
       if (myAxis == axis::Y || myAxis == -axis::Y)
          glRotated(-90.0, 0.0, 1.0, 0.0);
+      
+      glTranslated(-0.5, 0.0, 0.0);
+
+      glRotatef(rotate, 0.0f, 1.0f, 0.0f);
    }
    else
       assert(false);
-
-   glTranslated(-0.5, 0.0, 0.0);
    
    if (aToken.direction == -axis::X || aToken.direction == -axis::Y)
        glRotated(-180.0, 0.0, 1.0, 0.0);
-- 
2.39.2