Now drawing the robot's trajectory with a red line.

mainwindow.cpp

@@ -49,6 +49,27 @@ void MainWindow::renderRobot() {
   _scene.addPolygon(bot);
   _scene.addPolygon(right_wheel);
   _scene.addPolygon(left_wheel);
+
+  const QPointF* prev = NULL;
+  int j = 0;
+  for(QLinkedList<QPointF>::Iterator i = _pointList.begin(); i != _pointList.end(); i++, j++) {
+      if(prev) {
+          QLine line((int) prev->x(), (int) prev->y(), (int) (*i).x(), (int) (*i).y());
+          QPen pen(QBrush(QColor(255, 0, 0, 255 - (255. / POINT_LIST_SIZE * j))), 3);
+          _scene.addLine(line, pen);
+      }
+      prev = &(*i);
+  }
+
+  static int cpt = 0;
+  if(++cpt > ADD_POINT_EVERY) {
+      cpt = 0;
+      _pointList.prepend(pos);
+  }
+
+  while(_pointList.size() > POINT_LIST_SIZE) {
+      _pointList.removeLast();
+  }
 }
 
 void MainWindow::renderWorld() {

mainwindow.hpp

@@ -4,6 +4,7 @@
 #include <QMainWindow>
 #include "robot.hpp"
 #include <QGraphicsScene>
+#include <QLinkedList>
 
 namespace Ui {
 class MainWindow;
@@ -28,6 +29,10 @@ public slots:
     Robot& _robot;
 
     QGraphicsScene _scene;
+    QLinkedList<QPointF> _pointList;
+
+    static const int POINT_LIST_SIZE = 50;
+    static const int ADD_POINT_EVERY = 10;
 };
 
 #endif // MAINWINDOW_H