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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.Buffer;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.nio.ShortBuffer;
/**
* 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, Buffer 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);
if (lodIndices instanceof IntBuffer)
terrainBlock.setBuffer(Type.Index, 3, (IntBuffer)lodIndices);
else if (lodIndices instanceof ShortBuffer) {
terrainBlock.setBuffer(Type.Index, 3, (ShortBuffer) lodIndices);
}
// Recalculate collision mesh
terrainBlock.createCollisionData();
float entropy = 0;
for (int i = 0; i < positions.limit() / 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;
}
}