Extreme unstable of particles

[f1nalspace]

I am playing around with the particles in jbox2d.
At first glance it was working fine, creating a few particles for one group works and was running stable.
Now i creating more groups, but joining it together and even with two groups, it gets unstable very fast - particles jump like crazy.

I am creating particles like this, doing nothing special and later render it using opengl.
And yes i am creating particle groups for every lava tile in my map.

        world.setParticleRadius(0.1f * worldScale);
        world.setParticleDamping(0.2f);
        world.setParticleDensity(0.1f);

        ParticleGroup lastGroup = null;
        Vec2f tileFluidExt = new Vec2f(1f * worldScale * 0.5f, 1f * worldScale * 0.5f);
        Transform pxf = new Transform();
        pxf.setIdentity();
        CircleShape pshape = new CircleShape();
        for (int y = 0; y < tileFluidsLayer.getHeight(); y++) {
            for (int x = 0; x < tileFluidsLayer.getWidth()-1; x++) {
                int tile = tileFluidsLayer.getTile(x, y);
                if (tile == tileFluidsSet.getFirstId() + TileFluid.LAVA) {
                    final Vec2f fluidPos = createTilePosition(new Vec2f(x + 0.5f, y + 0.5f), tileFluidExt);
                    ParticleGroupDef pgf = new ParticleGroupDef();
                    pshape = new CircleShape();
                    pshape.m_radius = (1f - 0.2f) * worldScale;
                    pxf.setIdentity();
                    world.destroyParticlesInShape(pshape, pxf);
                    pgf.shape = pshape;
                    pgf.flags = ParticleType.b2_viscousParticle;
                    pgf.position.set(fluidPos.getX(), fluidPos.getY());
                    ParticleGroup newGroup = world.createParticleGroup(pgf);
                    if (lastGroup != null) {
                        world.joinParticleGroups(lastGroup, newGroup);
                    }
                    lastGroup = newGroup;
                }
            }
        }

[dmurph]

This is solved by #26

[f1nalspace]

Even with the c++ version of liquidfun 1.1, it has the exact same problem. Gets unstable after the second group has been added. So upgrading to 1.1 is great, but wont solve my issue at all.

[dmurph]

Ah, so that would be an issue with liquidfun then. Maybe some of the following would work:

• only create particles for the edges of the lava
• disable all particles not on edges, maybe make them static
• have particles not on edges be solid shapes until they are needed as lava, and then dynamically switch them

Most of these will be pretty difficult though. Having large stable bodies of particles is going to be an issue with most particle simulations, so you'll probably have to figure out a way of 'faking' it.

[f1nalspace]

Its not a matter of size/count, with just 100 particles 25 each groups - but joined together) it will get unstable, like crazy. Maybe it does not like Chain-Shapes... Yeah i see what is now coming. I may have no choice but create the particle simulation myself. I was planning to simulate ~200k particles - and all may have different properties (mass, stiffness, viscosity etc.)

[dmurph]

What do you mean joined together?
Yeah if you're planning on 200k, then you'll probably want your own simulation. You can try using of of the guts of LiquidFun, the Voronoi diagram they use is pretty cool.

[dmurph]

(ah, nvm, I see what you mean by joined together)