Even though this topic is solved, I would like to show how I did the grass generation for the terrain as I posted a screenshot in the last WIP screenshot thread.
I have been away the last two days, otherwise I would have replied to this topic earlier…
However, here is the app state. (Note that in my case another system (not shown here) will batch the grass afterwards!)
package de.gamedevbaden.crucified.appstates.view;
import com.jme3.app.Application;
import com.jme3.app.state.AbstractAppState;
import com.jme3.app.state.AppStateManager;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.FastMath;
import com.jme3.math.Vector2f;
import com.jme3.math.Vector3f;
import com.jme3.renderer.queue.RenderQueue;
import com.jme3.scene.Node;
import com.jme3.scene.Spatial;
import com.jme3.terrain.geomipmap.TerrainQuad;
import com.jme3.texture.Texture;
import com.jme3.texture.image.ImageRaster;
import java.util.ArrayList;
import java.util.List;
/**
* This app state will provide the functionality to generate grass for areas which are painted with a grass texture.
*/
public class TerrainGrassGeneratorAppState extends AbstractAppState {
private Spatial grassModel;
@Override
public void initialize(AppStateManager stateManager, Application app) {
this.grassModel = app.getAssetManager().loadModel("Models/Grass/SimpleGrass.j3o");
super.initialize(stateManager, app);
}
/**
* Will create one node which contains all the grass entities.
* Note: You should batch the grass afterwards, otherwise there might be a huge FPS drop for larger scenes.
* @param terrain the terrain you want generate grass for
* @param grassTexturePos the position of the texture (0 = first texture, 1 = second texture, ...)
* @return a node containing all grass batches.
*/
public Node createGrassForTerrain(TerrainQuad terrain, int grassTexturePos) {
if (terrain == null) {
return null;
}
// the following node will contain all grass batches
Node grassNode = new Node("GrassNode");
grassNode.setQueueBucket(RenderQueue.Bucket.Transparent);
// first we get the alpha map
Material terrainMaterial = terrain.getMaterial();
Texture alphaMap = terrainMaterial.getTextureParam("AlphaMap").getTextureValue();
Texture alphaMap_1 = terrainMaterial.getTextureParam("AlphaMap_1").getTextureValue();
Texture alphaMap_2 = terrainMaterial.getTextureParam("AlphaMap_2").getTextureValue();
// we get all alpha maps (there are maximum 3 alpha maps)
List<ImageRaster> rasterList = new ArrayList<>();
if (alphaMap != null) {
rasterList.add(ImageRaster.create(alphaMap.getImage()));
if (alphaMap_1 != null) {
rasterList.add(ImageRaster.create(alphaMap_1.getImage()));
if (alphaMap_2 != null) {
rasterList.add(ImageRaster.create(alphaMap_2.getImage()));
}
}
}
ImageRaster[] rasters = rasterList.toArray(new ImageRaster[rasterList.size()]);
Vector2f v = new Vector2f();
for (int z = 0; z < rasters[0].getHeight(); z++) {
for (int x = 0; x < rasters[0].getWidth(); x++) {
if (isThereGrass(x, z, rasters, grassTexturePos)) {
// place grass
Spatial grass = grassModel.clone();
v.set(x, z);
grass.setLocalTranslation(turnIntoTranslation(v, terrain));
grass.setLocalRotation(grass.getLocalRotation().fromAngles(new float[]{0, (float) (Math.random() * 180 * FastMath.DEG_TO_RAD), 0}));
grassNode.attachChild(grass);
}
}
}
return grassNode;
}
private boolean isThereGrass(int x, int z, ImageRaster[] raster, int posGrassTexture) {
float threshold = 0.7f; // the intensity of the grass texture which is needed to create grass
float otherThreshold = 0.1f; // the maximum allowed intensity of other textures at a certain position
// each alpha map can store information about 4 diffuse maps maximum
// we now want to get the texture with the grass
int mapNr = posGrassTexture / 4;
int colorPos = posGrassTexture % 4; // so we know if it's red, blue, green, or alpha channel
ImageRaster r = raster[mapNr];
ColorRGBA c = r.getPixel(x, z);
if (colorPos == 0) {
// red
if (c.getRed() >= threshold) {
// we now check if there are other textures "overprinting" this texture
if (c.getGreen() < otherThreshold && c.getBlue() < otherThreshold && c.getAlpha() < otherThreshold) {
// this texture is fine, we need to check the others as well
return isPixelVisible(mapNr, raster, otherThreshold, x, z);
}
}
} else if (colorPos == 1) {
// green
if (c.getGreen() >= threshold) {
if (c.getBlue() < otherThreshold && c.getAlpha() < otherThreshold) {
return isPixelVisible(mapNr, raster, otherThreshold, x, z);
}
}
} else if (colorPos == 2) {
// blue
if (c.getBlue() >= threshold) {
if (c.getAlpha() < threshold) {
return isPixelVisible(mapNr, raster, otherThreshold, x, z);
}
}
} else if (colorPos == 3) {
// alpha
if (c.getAlpha() >= threshold) {
return isPixelVisible(mapNr, raster, otherThreshold, x, z);
}
}
return false;
}
private boolean isPixelVisible(int mapNr, ImageRaster[] raster, float otherThreshold, int x, int z) {
// this method checks if the next textures overdraw the grass texture
// if they don't, the grass texture is the last one and because of that visible
if (mapNr+1 < raster.length) {
for (int i = mapNr+1; i < raster.length; i++) {
ImageRaster r2 = raster[i];
ColorRGBA c2 = r2.getPixel(x, z);
if (! (c2.getRed() < otherThreshold && c2.getGreen() < otherThreshold && c2.getBlue() < otherThreshold && c2.getAlpha() < otherThreshold)) {
// there is another texture overdrawing the desired (grass) texture, so the grass is not visible at this position
return false;
}
}
// we went through all other maps and did not return
// so there is no other texture overdrawing the grass texture, we can return true
return true;
} else {
// there aren't any more textures, so we can return true
return true;
}
}
private Vector3f turnIntoTranslation(Vector2f pixelPos, TerrainQuad terrain) {
float offset = terrain.getTerrainSize() / 2f;
float x = pixelPos.x - offset;
float z = (pixelPos.y - offset) * (-1);
float y = terrain.getHeight(new Vector2f(x,z));
return new Vector3f(x,y,z);
}
}
Maybe someone can make use of that 
Best regards
Domenic