From abb9de15be1ad022a288827ffbcdb01e94ac3eb8 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Mon, 18 Jan 2010 07:42:46 +0000
Subject: [PATCH] Render an actual L-system tree!

---
 src/LTree.cpp     | 90 ++++++++++++++++++++++++++++++++++++++---------
 src/LTreeDemo.cpp | 10 +++++-
 2 files changed, 83 insertions(+), 17 deletions(-)

diff --git a/src/LTree.cpp b/src/LTree.cpp
index a9baa2c..8a0ed8a 100644
--- a/src/LTree.cpp
+++ b/src/LTree.cpp
@@ -22,14 +22,21 @@
 #include <vector>
 #include <ostream>
 #include <iterator>
+#include <algorithm>
+#include <stdexcept>
+#include <sstream>
+
+#include <GL/gl.h>
 
 namespace lsystem {
 
    enum Token {
       X = 'X',   // Only used for replacement
       F = 'F',   // Draw forward
-      L = 'L',   // Turn left N degrees
-      R = 'R',   // Turn right N degrees
+      L = '-',   // Turn left N degrees
+      R = '+',   // Turn right N degrees
+      B = '[',   // Push position
+      E = ']',   // Pop position
    };
 
    typedef list<Token> TokenList;
@@ -62,7 +69,6 @@ namespace lsystem {
          ostream_iterator<char>(os));
       return os;
    }
-   
 }
 
 lsystem::Rule::Rule(Token lhs, const char* tokenStr)
@@ -72,7 +78,6 @@ lsystem::Rule::Rule(Token lhs, const char* tokenStr)
       rhs.push_back((Token)*tokenStr++);
 }
 
-
 lsystem::LSystem::LSystem(const Rule* rules, int nRules, Token start)
    : rules(rules), nRules(nRules), start(start)
 {
@@ -101,6 +106,8 @@ void lsystem::evolve(LSystem& l)
    } while (it != l.state.end());
 }
 
+using namespace lsystem;
+
 // Trees generated by L-systems
 class LTree : public IScenery {
 public:
@@ -110,28 +117,79 @@ public:
    void render() const;
    void setPosition(float x, float y, float z);
 private:
+   struct RenderState {
+      RenderState()
+         : x(0.0f), y(0.0f), z(0.0f)
+      {}
+      
+      float x, y, z;
+   };
+   
+   void interpret(Token t, RenderState& rs) const;
+
+   LSystem ls;
+   
+   static const Rule rules[];
+};
+
+const Rule LTree::rules[] = {
+   Rule(X, "F-[[X]+X]+F[+FX]-X"),
+   Rule(F, "FF"),
 };
 
 LTree::LTree()
+   : ls(rules, 2, X)
 {
-   using namespace lsystem;
-   
-   Rule rules[] = {
-      Rule(X, "F-[[X]+X]+F[+FX]-X"),
-      Rule(F, "FF"),
-   };
-   LSystem l(rules, 2, X);
-
-   debug() << "Initial: " << l;
+   debug() << "Initial: " << ls;
    for (int n = 0; n < 5; n++) {
-      evolve(l);
-      debug() << "n=" << n << ": " << l;
+      evolve(ls);
+      debug() << "n=" << n << ": " << ls;
    }
 }
 
-void LTree::render() const
+void LTree::interpret(Token t, RenderState& rs) const
 {
+   const float SEGMENT_LEN = 0.01f;
+   
+   switch (t) {
+   case 'F':
+      glBegin(GL_LINES);
+      glVertex3f(0.0f, 0.0f, 0.0f);
+      glVertex3f(0.0f, SEGMENT_LEN, 0.0f);
+      glEnd();
+      glTranslatef(0.0f, SEGMENT_LEN, 0.0f);
+      break;
+   case 'X':
+      // Ignored
+      break;
+   case '-':
+      glRotatef(25.0, 0.0f, 0.0f, 1.0f);
+      break;
+   case '+':
+      glRotatef(-25.0, 0.0f, 0.0f, 1.0f);
+      break;
+   case '[':
+      glPushMatrix();
+      break;
+   case ']':
+      glPopMatrix();
+      break;
+   default:
+      {
+         ostringstream ss;
+         ss << "Bad token in LTree: " << static_cast<char>(t);
+         throw runtime_error(ss.str());
+      }
+   }
+}
 
+void LTree::render() const
+{
+   using namespace placeholders;
+   
+   RenderState rs;
+   for_each(ls.state.begin(), ls.state.end(),
+      bind(&LTree::interpret, this, _1, rs));
 }
 
 void LTree::setPosition(float x, float y, float z)
diff --git a/src/LTreeDemo.cpp b/src/LTreeDemo.cpp
index da40114..89ff054 100644
--- a/src/LTreeDemo.cpp
+++ b/src/LTreeDemo.cpp
@@ -19,6 +19,8 @@
 #include "ILogger.hpp"
 #include "IScenery.hpp"
 
+#include <GL/gl.h>
+
 class LTreeDemo : public IScreen {
 public:
    LTreeDemo();
@@ -37,16 +39,22 @@ public:
       MouseButton button) {}
    
 private:
+   ISceneryPtr ltree;
 };
 
 LTreeDemo::LTreeDemo()
 {
-   makeLTree();
+   ltree = makeLTree();
 }
 
 void LTreeDemo::display(IGraphicsPtr context) const
 {
+   glDisable(GL_LIGHTING);
+   glDisable(GL_TEXTURE_2D);
+   
+   glTranslatef(0.0f, 0.0f, -5.0f);
 
+   ltree->render();
 }
 
 void LTreeDemo::overlay() const
-- 
2.39.2