Wiki refresh (Hello Terrain) (#159)

I am going through the beginner wiki pages and updating them so they are the same as the source code files in jme3test/helloworld.

In this we update TerrainQuad and mat_terrain, add in a 2.b creating a random height map, and then add a control.setLodCalculator to step 5. 

jme3test/helloworld source code:
https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-examples/src/main/java/jme3test/helloworld/HelloTerrain.java

docs/modules/tutorials/pages/beginner/hello_terrain.adoc

@@ -22,7 +22,6 @@ package jme3test.helloworld;
 
 import com.jme3.app.SimpleApplication;
 import com.jme3.material.Material;
-import com.jme3.renderer.Camera;
 import com.jme3.terrain.geomipmap.TerrainLodControl;
 import com.jme3.terrain.heightmap.AbstractHeightMap;
 import com.jme3.terrain.geomipmap.TerrainQuad;
@@ -31,16 +30,11 @@ import com.jme3.terrain.heightmap.HillHeightMap; // for exercise 2
 import com.jme3.terrain.heightmap.ImageBasedHeightMap;
 import com.jme3.texture.Texture;
 import com.jme3.texture.Texture.WrapMode;
-import java.util.ArrayList;
-import java.util.List;
 
 /** Sample 10 - How to create fast-rendering terrains from heightmaps,
 and how to use texture splatting to make the terrain look good.  */
 public class HelloTerrain extends SimpleApplication {
 
-  private TerrainQuad terrain;
-  Material mat_terrain;
-
   public static void main(String[] args) {
     HelloTerrain app = new HelloTerrain();
     app.start();
@@ -51,7 +45,7 @@ public class HelloTerrain extends SimpleApplication {
     flyCam.setMoveSpeed(50);
 
     /** 1. Create terrain material and load four textures into it. */
-    mat_terrain = new Material(assetManager,
+    Material mat_terrain = new Material(assetManager,
             "Common/MatDefs/Terrain/Terrain.j3md");
 
     /** 1.1) Add ALPHA map (for red-blue-green coded splat textures) */
@@ -79,11 +73,21 @@ public class HelloTerrain extends SimpleApplication {
     mat_terrain.setTexture("Tex3", rock);
     mat_terrain.setFloat("Tex3Scale", 128f);
 
-    /** 2. Create the height map */
+    /* 2.a Create a custom height map from an image */
     AbstractHeightMap heightmap = null;
     Texture heightMapImage = assetManager.loadTexture(
             "Textures/Terrain/splat/mountains512.png");
     heightmap = new ImageBasedHeightMap(heightMapImage.getImage());
+    
+    /* 2.b Create a random height map */
+//      HillHeightMap heightmap = null;
+//      HillHeightMap.NORMALIZE_RANGE = 100;
+//      try {
+//          heightmap = new HillHeightMap(513, 1000, 50, 100, (byte) 3);
+//      } catch (Exception ex) {
+//          ex.printStackTrace();
+//      }
+
     heightmap.load();
 
     /** 3. We have prepared material and heightmap.
@@ -95,7 +99,7 @@ public class HelloTerrain extends SimpleApplication {
      * 3.5) We supply the prepared heightmap itself.
      */
     int patchSize = 65;
-    terrain = new TerrainQuad("my terrain", patchSize, 513, heightmap.getHeightMap());
+    TerrainQuad terrain = new TerrainQuad("my terrain", patchSize, 513, heightmap.getHeightMap());
 
     /** 4. We give the terrain its material, position & scale it, and attach it. */
     terrain.setMaterial(mat_terrain);
@@ -105,6 +109,7 @@ public class HelloTerrain extends SimpleApplication {
 
     /** 5. The LOD (level of detail) depends on were the camera is: */
     TerrainLodControl control = new TerrainLodControl(terrain, getCamera());
+    control.setLodCalculator( new DistanceLodCalculator(patchSize, 2.7f) ); // patch size, and a multiplier
     terrain.addControl(control);
   }
 }
@@ -228,8 +233,8 @@ Load four textures into this material. The first one, `Alpha`, is the alphamap t
 
 [source,java]
 ----
-mat_terrain.setTexture("Alpha",
-    assetManager.loadTexture("Textures/Terrain/splat/alphamap.png"));
+mat_terrain.setTexture("Alpha", assetManager.loadTexture(
+          "Textures/Terrain/splat/alphamap.png"));
 ----
 
 The three other textures are the layers that you have previously decided to paint: grass, dirt, and road. You create texture objects and load the three textures as usual. Note how you assign them to their respective texture layers (Tex1, Tex2, and Tex3) inside the Material!
@@ -290,9 +295,9 @@ Here's the code:
 
 [source]
 ----
-terrain = new TerrainQuad(
+TerrainQuad terrain = new TerrainQuad(
   "my terrain",               // name
-  65,                         // tile size
+  patchSize,                  // tile size
   513,                        // block size
   heightmap.getHeightMap());  // heightmap
 
@@ -331,6 +336,7 @@ JME3 includes an optimization that adjusts the level of detail (LOD) of the rend
 ----
 
     TerrainLodControl control = new TerrainLodControl(terrain, getCamera());
+    control.setLodCalculator( new DistanceLodCalculator(patchSize, 2.7f) ); // patch size, and a multiplier
     terrain.addControl(control);
 
 ----