From 5c476344f7f7a289cc4cb195622e8f789ee2ff18 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Sun, 28 Feb 2010 16:47:29 +0000
Subject: [PATCH] Only allow track to be placed on level ground

---
 include/IMap.hpp  |  6 ++++++
 include/Maths.hpp |  7 +++++++
 src/Editor.cpp    | 13 +++++++++++--
 src/Map.cpp       | 40 ++++++++++++++++++++++++++++++++++++----
 4 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/include/IMap.hpp b/include/IMap.hpp
index 115f3db..7246c70 100644
--- a/include/IMap.hpp
+++ b/include/IMap.hpp
@@ -109,6 +109,12 @@ public:
    // Get the height above ground at a particular point
    virtual float heightAt(float x, float y) const = 0;
 
+   // Given a tile and an axis, return a vector indicating the slope
+   // along that axis. `level' is set if the slope is the same across
+   // the tile
+   virtual Vector<float> slopeAt(Point<int> where,
+      track::Direction axis, bool& level) const = 0;
+
    // Place a tree, building, etc. at a location
    virtual void addScenery(Point<int> where, ISceneryPtr s) = 0;
    
diff --git a/include/Maths.hpp b/include/Maths.hpp
index 4005667..90a0a6b 100644
--- a/include/Maths.hpp
+++ b/include/Maths.hpp
@@ -112,6 +112,13 @@ struct Vector {
    {
       return !(v == *this);
    }
+
+   bool approxEqual(const Vector<T>& rhs, T delta) const
+   {
+      return (abs(rhs.x - x) < delta)
+         && (abs(rhs.y - y) < delta)
+         && (abs(rhs.z - z) < delta);
+   }
    
    T x, y, z;
 };
diff --git a/src/Editor.cpp b/src/Editor.cpp
index 407f6f1..ef2388f 100644
--- a/src/Editor.cpp
+++ b/src/Editor.cpp
@@ -233,8 +233,17 @@ bool Editor::drawTrackTile(const Point<int>& aPoint, const track::Direction& anA
       }
    }
    else {
-      map->setTrackAt(aPoint, makeStraightTrack(anAxis));
-      return true;
+      bool level;
+      Vector<float> slope = map->slopeAt(aPoint, anAxis, level);
+
+      if (level) {
+         map->setTrackAt(aPoint, makeStraightTrack(anAxis));
+         return true;
+      }
+      else {
+         warn() << "Track must be placed on level ground";
+         return false;
+      }
    }
 }
 
diff --git a/src/Map.cpp b/src/Map.cpp
index 3eed064..f5fff54 100644
--- a/src/Map.cpp
+++ b/src/Map.cpp
@@ -110,6 +110,8 @@ public:
    IStationPtr extendStation(Point<int> aStartPos,
       Point<int> aFinishPos);
    float heightAt(float x, float y) const;
+   Vector<float> slopeAt(Point<int> where, track::Direction axis,
+      bool& level) const;
    void addScenery(Point<int> where, ISceneryPtr s);
    
    // ISectorRenderable interface
@@ -888,10 +890,10 @@ void Map::tileVertices(int x, int y, int* indexes) const
 {
    assert(x >= 0 && x < myWidth && y >= 0 && y < myDepth);
           
-   indexes[3] = x + (y * (myWidth+1));
-   indexes[2] = (x+1) + (y * (myWidth+1));
-   indexes[1] = (x+1) + ((y+1) * (myWidth+1));
-   indexes[0] = x + ((y+1) * (myWidth+1));          
+   indexes[3] = x + (y * (myWidth+1));         // (X, Y)
+   indexes[2] = (x+1) + (y * (myWidth+1));     // (X+1, Y)
+   indexes[1] = (x+1) + ((y+1) * (myWidth+1)); // (X+1, Y+1)
+   indexes[0] = x + ((y+1) * (myWidth+1));     // (X, Y+1)
 }
 
 // True if changing the height of this tile will affect
@@ -968,6 +970,36 @@ float Map::heightAt(float x, float y) const
    return avg / 4.0f;
 }
 
+Vector<float> Map::slopeAt(Point<int> where,
+   track::Direction axis, bool &level) const
+{
+   int indexes[4];
+   tileVertices(where.x, where.y, indexes);
+
+   // This is slightly consfusing since the track Y axis
+   // is the Z axis in the height map
+
+   Vector<float> v1, v2;
+
+   if (axis == axis::X) {
+      v1 = heightMap[indexes[2]].pos - heightMap[indexes[3]].pos;
+      v2 = heightMap[indexes[1]].pos - heightMap[indexes[0]].pos;
+   }
+   else {
+      v1 = heightMap[indexes[0]].pos - heightMap[indexes[3]].pos;
+      v2 = heightMap[indexes[1]].pos - heightMap[indexes[2]].pos;
+   }
+
+   level = v1.approxEqual(v2, 0.001f);
+
+   debug() << "slopeAt where=" << where
+           << " axis=" << axis
+           << " v1=" << v1 << " v2=" << v2
+           << " level=" << level;
+
+   return v1;
+}
+
 void Map::changeAreaHeight(const Point<int>& aStartPos,
    const Point<int>& aFinishPos,
    float aHeightDelta)
-- 
2.39.2