JME 3 Tutorial (12) - Hello Effects

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When you see one of the following in a game, then a particle system is likely behind it:

These things typically cannot be modeled by meshes. In very simple terms:

Particle effects can be animated (e.g. sparks, drops) and static (strands of grass, hair). Non-particle effects include bloom/glow, and motion blur/afterimage. In this tutorial we will look at animated particles (com.jme3.effect).

Sample Code

package jme3test.helloworld;
 
import com.jme3.app.SimpleApplication;
import com.jme3.effect.ParticleEmitter;
import com.jme3.effect.ParticleMesh;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.Vector3f;
 
/** Sample 11 - how to create fire, water, and explosion effects. */
public class HelloEffects extends SimpleApplication {
 
  public static void main(String[] args) {
    HelloEffects app = new HelloEffects();
    app.start();
  }
 
  @Override
  public void simpleInitApp() {
 
    ParticleEmitter fire = new ParticleEmitter("Emitter", ParticleMesh.Type.Triangle, 30);
    Material mat_red = new Material(assetManager, "Common/MatDefs/Misc/Particle.j3md");
    mat_red.setTexture("Texture", assetManager.loadTexture("Effects/Explosion/flame.png"));
    fire.setMaterial(mat_red);
    fire.setImagesX(2); fire.setImagesY(2); // 2x2 texture animation
    fire.setEndColor(  new ColorRGBA(1f, 0f, 0f, 1f));   // red
    fire.setStartColor(new ColorRGBA(1f, 1f, 0f, 0.5f)); // yellow
    fire.setInitialVelocity(new Vector3f(0, 2, 0));
    fire.setStartSize(1.5f);
    fire.setEndSize(0.1f);
    fire.setGravity(0);
    fire.setLowLife(0.5f);
    fire.setHighLife(3f);
    fire.setVelocityVariation(0.3f);
    rootNode.attachChild(fire);
 
    ParticleEmitter debris = new ParticleEmitter("Debris", ParticleMesh.Type.Triangle, 10);
    Material debris_mat = new Material(assetManager, "Common/MatDefs/Misc/Particle.j3md");
    debris_mat.setTexture("Texture", assetManager.loadTexture("Effects/Explosion/Debris.png"));
    debris.setMaterial(debris_mat);
    debris.setImagesX(3); debris.setImagesY(3); // 3x3 texture animation
    debris.setRotateSpeed(4);
    debris.setSelectRandomImage(true);
    debris.setInitialVelocity(new Vector3f(0, 4, 0));
    debris.setStartColor(new ColorRGBA(1f, 1f, 1f, 1f));
    debris.setGravity(6f);
    debris.setVelocityVariation(.60f);
    rootNode.attachChild(debris);
    debris.emitAllParticles();
 
  }
}

You should see an explosion that sends debris flying, and a fire. More example code

Texture Animation and Variation

Start by choosing a material texture for your effect. If you provide the emitter with a set of textures (see image), it can use them either for variation (random order), or as animation steps (fixed order).

Setting emitter textures works just as you have already learned in previous chapters. This time we use the Particle.j3md default material. In the following example, we have a closer look at the Debris effect.

    ...
    Material debris_mat = new Material(assetManager, "Common/MatDefs/Misc/Particle.j3md");
    debris_mat.setTexture("Texture", assetManager.loadTexture("Effects/Explosion/Debris.png"));
    debris.setMaterial(debris_mat);
    debris.setImagesX(3); // columns
    debris.setImagesY(3); // rows
    debris.setSelectRandomImage(true);
    ...
  1. Load the texture in the emitter's material.
  2. Tell the Emitter into how many animation steps (x*y) the texture is divided. 1x1 is default.
  3. Optionally, tell the Emitter whether the animation steps are to be at random, or in order.

As you see in the debris example, texture animations improve effects because each "flame" or "piece of debris" looks different. Also think of electric or magic effects, where you can create very interesting animations by using an ordered morphing series of lightning bolts; or flying leaves or snow flakes, for instance.

Default Particle Textures

The following effect textures are some of the example textures included in test-data.jar.

Texture Path Dimension Preview
Effects/Explosion/Debris.png 3*3
Effects/Explosion/flame.png 2*2
Effects/Explosion/shockwave.png 1*1
Effects/Explosion/smoketrail.png 1*3
Effects/Smoke/Smoke.png 1*15

Copy them into you assets/Effects directory to use them.

Creating Custom Textures

For your game, you will likely create custom textures. Look at the fire example again.

    ParticleEmitter fire = new ParticleEmitter("Emitter", ParticleMesh.Type.Triangle, 30);
    Material mat_red = new Material(assetManager, "Common/MatDefs/Misc/Particle.j3md");
    mat_red.setTexture("m_Texture", assetManager.loadTexture("Effects/Explosion/flame.png"));
    fire.setMaterial(mat_red);
    fire.setImagesX(2); // columns 
    fire.setImagesY(2); // rows
    fire.setEndColor(  new ColorRGBA(1f, 0f, 0f, 1f));   // red
    fire.setStartColor(new ColorRGBA(1f, 1f, 0f, 0.5f)); // yellow

Create a grayscale texture in a graphic editor, and save it to your assets/Effects directory. If you split up one image file into x*y animation steps, make sure each animation step is of equal size–just as you see in the examples here.

Emitter Parameters

A particle system is always centered around an emitter.

Use the setShape() method to change the EmitterShape:

Example: emitter.setShape(new EmitterPointShape(Vector3f.ZERO));

You create different effects by changing the emitter parameters:

Parameter Method (default value) Description
number setNumParticles() The maximum number of particles visible at the same time. Value is specified by user in constructor.
velocity setInitialVelocity() (Vector3f.ZERO) You must specify a vector how fast particles should move and it which start direction.
direction setVelocityVariation() (0.2f)
setFacingVelocity() (false)
setRandomAngle() (false)
setFaceNormal() (Vector3f.NAN)
setRotateSpeed() (0f)
Optional accessors that control in which direction particles face when flying.
lifetime setLowLife() (3f)
setHighLife() (7f)
Minimum and maximum time period before particles fade.
emission rate setParticlesPerSec() (20) How many new particles are emitted per second.
color setStartColor()
setEndColor() (gray)
Set to two different colors for gradient effects, or to same color.
size setStartSize() (0.2f)
setEndSize() (2f)
Set to two different values for shrink/grow effect, or to same size.
gravity setGravity() (0.1f) Whether particles falls down eventually. Set to 0f for zero-g effects.

You can find details about effect parameters in the user guide. Add and modify one paramter at a time, and try different values until you get the effect you want. Tip: Use the jMonkeyPlatform SceneComposer to preview effects settings (instructions: TODO).

Exercise

Can you "invert" the campfire into a small waterfall?

Conclusion

You have learned that many different effects can be created by changing the parameters and textures of one general emitter object.

Now we move on to the next exciting chapter – the simulation of physical objects. Let's shoot some cannon balls at a brick wall!

beginner, documentation, intro, transparency, effect

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