1 files changed, 75 insertions, 0 deletions
diff --git a/engine/src/terrain/com/jme3/terrain/geomipmap/lodcalc/util/EntropyComputeUtil.java b/engine/src/terrain/com/jme3/terrain/geomipmap/lodcalc/util/EntropyComputeUtil.java
new file mode 100644
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--- /dev/null
+++ b/engine/src/terrain/com/jme3/terrain/geomipmap/lodcalc/util/EntropyComputeUtil.java
@@ -0,0 +1,75 @@
+package com.jme3.terrain.geomipmap.lodcalc.util;
+
+import com.jme3.bounding.BoundingBox;
+import com.jme3.collision.CollisionResults;
+import com.jme3.math.Matrix4f;
+import com.jme3.math.Ray;
+import com.jme3.math.Vector3f;
+import com.jme3.scene.Mesh;
+import com.jme3.scene.VertexBuffer;
+import com.jme3.scene.VertexBuffer.Type;
+import com.jme3.util.BufferUtils;
+import java.nio.FloatBuffer;
+import java.nio.IntBuffer;
+
+/**
+ * Computes the entropy value δ (delta) for a given terrain block and
+ * LOD level.
+ * See the geomipmapping paper section
+ * "2.3.1 Choosing the appropriate GeoMipMap level"
+ *
+ * @author Kirill Vainer
+ */
+public class EntropyComputeUtil {
+
+    public static float computeLodEntropy(Mesh terrainBlock, IntBuffer lodIndices){
+        // Bounding box for the terrain block
+        BoundingBox bbox = (BoundingBox) terrainBlock.getBound();
+
+        // Vertex positions for the block
+        FloatBuffer positions = terrainBlock.getFloatBuffer(Type.Position);
+
+        // Prepare to cast rays
+        Vector3f pos = new Vector3f();
+        Vector3f dir = new Vector3f(0, -1, 0);
+        Ray ray = new Ray(pos, dir);
+
+        // Prepare collision results
+        CollisionResults results = new CollisionResults();
+
+        // Set the LOD indices on the block
+        VertexBuffer originalIndices = terrainBlock.getBuffer(Type.Index);
+
+        terrainBlock.clearBuffer(Type.Index);
+        terrainBlock.setBuffer(Type.Index, 3, lodIndices);
+
+        // Recalculate collision mesh
+        terrainBlock.createCollisionData();
+
+        float entropy = 0;
+        for (int i = 0; i < positions.capacity() / 3; i++){
+            BufferUtils.populateFromBuffer(pos, positions, i);
+
+            float realHeight = pos.y;
+
+            pos.addLocal(0, bbox.getYExtent(), 0);
+            ray.setOrigin(pos);
+
+            results.clear();
+            terrainBlock.collideWith(ray, Matrix4f.IDENTITY, bbox, results);
+
+            if (results.size() > 0){
+                Vector3f contactPoint = results.getClosestCollision().getContactPoint();
+                float delta = Math.abs(realHeight - contactPoint.y);
+                entropy = Math.max(delta, entropy);
+            }
+        }
+
+        // Restore original indices
+        terrainBlock.clearBuffer(Type.Index);
+        terrainBlock.setBuffer(originalIndices);
+
+        return entropy;
+    }
+
+}