Render SpriteBatch + ParticleEffect in 3D space in libgdx?

Question

I am using libgdx version 0.9.9. I want to render a fire effect using ParticleEffect in 3D space along with other 3D models.

Logical flow of my code:

1. ModelBatch Begin
2. Render all 3D models in Bullet World using ModelBatch
3. ModelBatch End
4. SpriteBatch Begin
5. Render the fire effect using ParticleEffect (effect.draw) using SpriteBatch
6. SpriteBatch End
7. Draw the HUD using Stage

The problem: The fire effect is rendering fine at a point in 3D space. But when I rotate the camera so that a 3D model lies between the camera and the fire effect the fire effect renders over the 3D model instead of being hidden behind the 3D model.

Things that I have tried:

1. I have tried rendering the SpriteBatch first and then the 3D models: In this case the fire effect is not visible. I am guessing that the 3D models (layer) is rendering over the fire effect (layer) and hence the effect is not visible.
2. I tried rendering the SpriteBatch between steps 1 and 3 i.e. rendering the SpriteBatch between modelbatch.begin and modelbatch.end. In this case the fire effect is not visible at all.
3. I have tried rendering the Particle Effect as an Actor (added to HUD Stage). As expected the fire effect renders as part of the topmost HUD layer and the same problem remains.
4. I have tried exploring Decals but found that Particle Effect doesn't work with DebcalBatch. I didn't want to display an animated fire .gif over the Decal and hence didn't try it.

Has anyone faced similar problem? Any suggested workaround to make ParticleEffect behave as part of the 3D world so that it gets hidden when blocked by other 3D models? I have seen a video posted by Xoppa on youtube about 3D particles in libgdx but there are no steps / solution mentioned. Any help will be highly appreciated.

Answer 1

The reason SpriteBatch was not being displayed in the following rendering order:

1. Render particle effect using SpriteBatch
2. Render 3D Models

was because the 3d models consisted of a Skydome that was overlapping the SpriteBatch, thus hiding it completely. I took out the Skydome from the set of 3D models rendered in step # 2 above and am rendering it before the particle effect.

Following rendering order is working fine for me:

1. Render Skydome using ModelBatch
2. Render particle effect using SpriteBatch
3. Render rest of the models using ModelBatch

With this the particle effect is in front of the sky but behind the 3d models.

Answer 2

You will need to render the spritebatch first if you want the fire to appear on behind and not on top. The problem would seem to be that the screen is clearing itself when it renders in 3D. There's a few ways you could approach this.

You can try to make sure that only the first process clears the screen.

This is the code:

Gdx.graphics.getGL20().glClearColor( 1, 0, 0, 1 );
Gdx.graphics.getGL20().glClear( GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT );

Unfortunately if your 3D renderer is calling that internally and you don't have control over it, then you're in a bit of a bind. (I'm not sure how much library code or your own code you're using)

I would suggest rendering both to frame buffer objects instead, and then you can just render the images from the two frame buffer objects onto the screen as 2D textures. You can then use blending between those if you want, or you can set the alpha or disable blending such that one is on top of the other, just make sure you render them in whatever order you want.

http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/graphics/glutils/FrameBuffer.html