diff --git a/demo3.cpp b/demo3.cpp
index 6c46a5e..2124541 100644
--- a/demo3.cpp
+++ b/demo3.cpp
@@ -24,6 +24,25 @@ Player player;
 char floorColor = 0;
 Vector2D selectedSquare; ///< Coords of tile selected for editing.
 
+/**
+  Represents one terrain change against the implicit terrain.
+*/
+class Change
+{
+public:
+  Vector2D mCoords;
+  Unit mHeight;
+  uint8_t mColor;
+};
+
+#define MAX_CHANGES 32
+
+Change changes[MAX_CHANGES];
+
+bool editReleased = false;
+bool editing = false;
+uint16_t changeIndex = 0;
+
 #define HEIGHT_PROFILE_LENGTH 256
 const int8_t heightProfile[] = {
 9,9,9,10,10,10,11,11,12,13,13,14,14,14,15,15,15,16,16,16,16,16,15,15,15,14,14,
@@ -129,6 +148,10 @@ const unsigned char imageBackground[] =
 
 Unit floorHeightAt(int16_t x, int16_t y)
 {
+  for (uint16_t i = 0; i < MAX_CHANGES; ++i)
+    if (changes[i].mCoords.x == x && changes[i].mCoords.y == y)
+      return changes[i].mHeight;
+
   return (heightProfile[absVal(x) % HEIGHT_PROFILE_LENGTH] +
          heightProfile[absVal(y + 20) % HEIGHT_PROFILE_LENGTH]) *
          UNITS_PER_SQUARE;
@@ -148,7 +171,7 @@ inline void pixelFunc(PixelInfo pixel)
 
   if (pixel.isWall)
   {
-    c = pixel.hit.square.x != selectedSquare.x || pixel.hit.square.y != selectedSquare.y ? 50 : 30;
+    c = pixel.hit.square.x != selectedSquare.x || pixel.hit.square.y != selectedSquare.y || (editing && pokitto.frameCount % 2) == 0 ? 50 : 30;
     
     intensity = pixel.depth / (UNITS_PER_SQUARE * 3);
     intensity += pixel.hit.direction % 2 == 0 ? 2 : 0;
@@ -196,7 +219,7 @@ void draw()
   c.computeTextureCoords = 0;
 
   render(player.mCamera,floorHeightAt,0,0,pixelFunc,c);
-
+/*
 pokitto.display.setColor(rgbToIndex(7,7,3));
 pokitto.display.setCursor(1,1);
 pokitto.display.print(player.mCamera.position.x);
@@ -204,11 +227,9 @@ pokitto.display.print(" ");
 pokitto.display.print(player.mCamera.position.y);
 pokitto.display.print(" ");
 pokitto.display.print(player.mCamera.direction);
-
+*/
 }
 
-bool runReleased = false;
-
 int main()
 {
   initGeneral();
@@ -217,6 +238,13 @@ int main()
 
   player.setPositionSquare(4,5);
 
+  for (uint16_t i = 0; i < MAX_CHANGES; ++i)
+  {
+    changes[i].mCoords.x = 0;
+    changes[i].mCoords.y = 0;
+    changes[i].mHeight = floorHeightAt(0,0);
+  }
+
   uint32_t previousTime = 0;
   uint32_t dt;
 
@@ -276,25 +304,47 @@ int main()
 
       if (pokitto.cBtn())
       {
-        if (runReleased)
+        if (editReleased)
         {
-          player.mRunning = !player.mRunning;
-          runReleased = false;
+          editing = !editing;
+
+          changeIndex = (changeIndex + 1) % MAX_CHANGES;
+
+          for (uint16_t i = 0; i < MAX_CHANGES; ++i)
+            if (changes[i].mCoords.x == selectedSquare.x &&
+                changes[i].mCoords.y == selectedSquare.y)
+            {
+              changeIndex = i;
+              break;
+            }
+
+          changes[changeIndex].mHeight = floorHeightAt(selectedSquare.x,selectedSquare.y);
+          changes[changeIndex].mCoords.x = selectedSquare.x;
+          changes[changeIndex].mCoords.y = selectedSquare.y;
+          editReleased = false;
         }
       }
       else
-        runReleased = true;
+        editReleased = true;
 
       if (pokitto.upBtn())
       {
-        if (aButton)
+        if (editing)
+        {
+          changes[changeIndex].mHeight += 100;
+        }
+        else if (aButton)
           player.mCamera.shear = min(player.mCamera.shear + 10,60);
         else
           moveOffset = d;
       }
       else if (pokitto.downBtn())
       {
-        if (aButton)
+        if (editing)
+        {
+          changes[changeIndex].mHeight -= 100;
+        }
+        else if (aButton)
           player.mCamera.shear = max(player.mCamera.shear - 10,-60);
         else
         {
@@ -344,7 +394,7 @@ int main()
         if (player.mCamera.height - CAMERA_COLL_HEIGHT_BELOW -
           floorHeightAt(camX,camY) < 2)
           player.mVericalSpeed = JUMP_SPEED; // jump
-      }     
+      } 
 
       player.mVericalSpeed -= (dt * GRAVITY_ACCELERATION) / 1000; // gravity
     }