Particle systems

[Fenerit]

I can't wait for this...

[duds26]

Please make the transparency physically correct,
by that I mean that if the model is thicker the transparency goes down, opacy rises.
If the model is thinner the transparency goes up, opacity decreases.
(Anim8or is implementing this at the moment.)


So for addon makers it would look like this:

Transparency
Border = 0.8 0.7 0.6 (unit % light that stays when light enters or exit material, rest of the light is lost, doesn't happen in real life but could be useful for addon makers)
Loose = 0.002 0.003 0.004 (unit: %/distance, how much of the light goes away when it goes through a certain distance of a material, preferably m, km or lightyear)
Min = 0.0000001 0.0000001 0.0000001 (unit: %, percentage of light that comes in and is able to pass through always, even if the material is so thick that the loss of light becomes bigger or equal than 1(Border + Loose*distance), doesn't happen in real life but could be useful to addon makers)

(The use of three numbers is for RGB values. In real life the light more or less absorbed depending on the wavelength of the light. )


Handy resources:
http://en.wikipedia.org/wiki/Volume_rendering
http://animationphysics.wordpress.com/


http://www.pbrt.org/reviews.php <-- very usefull book about physically based rendering

[selden]

Duds,

Please provide an example of Celestia doing the wrong thing.

[duds26]

Oops, didn't know Celestia was rendering it the right way.

Thought I had seen this in an addon about the outer solar system.
It looked equaly dense in the middle as in the edges,
and that is not how it's in the real world.

[duds26]

There are no big changes to the ssc file for the add-on shown in the video. Instead of loading an ordinary mesh, a Celestia particle system is specified instead. The particle system file is an ASCII text file that defines particle colors, textures, initial positions, and initial velocities.

These look very nice Chris, but I'm just curious about the definitions you describe here.
You are defining the particles, and their properties, but do these definitions include an ending option? In other words, it looks (from the videos) as if the motion is constant.
Please forgive the dumb question, but from your explanation it doesn't seem to have any ending. Is this in the works, or are the effects something you'd have to turn on and off?
Also, take the Buran Launch video here. Can the effect be modified so that the particles can be told to settle down eventually? Do you understand what I mean? Would you/we have to
define a different particle routine in order to show the smoke and dust settling down after the launch? This is probably not important since most people would view the actual
model on its trajectory, but what happens to the view after the spacecraft has left the pad?

In fact, there needs to be some discussion about whether particle systems belong in Celestia at all. The videos in this thread are demonstrations of what's possible.
Used carefully, some phenomena can be simulated realistically with particle systems; abused, they can turn the Solar System into a disco

If these systems can be used to turn Celestia into a disco routine, I'm almost positive that they will be. You would not believe some of the material that already gets submitted to the ML for use with our favorite universe-exploring software. Ask Ulrich...

Just my two-cents worth.

Everybody should be free of what they want to put in their addon, if the solar system becomes a disco then so be it. lol
Besides, otherwise there can't be made an addon for a surfaceobject that is a disco on earth, then it needs those effects to be a disco.

[Fenerit]

Beautiful work Chris. I think this system (along with non linear path development) is critical in Celestia. The visualization possibilities are endless. Those videos on Youtube are beautiful. Will we be able to do non glowing particles as well?

By non-linear paths, I take it that you mean animation support?

Non-glowing particles are possible. The smoke in the Buran liftoff is one example. For realism, very important thing will be the ability to specify some scattering properties for the particles. It could be as simple as specifying a phase parameter.

BTW, if you only have one dimensional force motion, how did you do Tvashtar?

In that example, each particle is affected by a constant force along the local z-axis of the particle system, resulting in parabolic motion. The motion of the particles would be more accurately modeled by using a central 1/r^2 force, but I don't think that anyone would notice the difference visually.

--Chris

I'm not sure of this, but just to keep the topic alive, for an eruptive volcano the settings could be similar:

Code: Select all

   Emitter
    {
        Texture "smoketex.png"
        StartColor [ 0.8 0.5 0.3 ]
        EndColor [ 0 0 0 ]
        StartOpacity 1.0
        EndOpacity 0.6

        StartSize 0.4
        EndSize 0.04

        Rate 10
        Lifetime 30

        InitialPosition {
            Constant [ 0 0 0 ]
        }
        InitialVelocity {
            Cone { MinAngle 30 MaxAngle 45 MinSpeed 0.04 MaxSpeed 0.08 }
        }

        Acceleration [ 0 0 0.3 ]

   Wind [ 0.011 0.012 0.01]
   Gravity [0.05 0.05 0.015]

        MinRotationRate 0.01
        MaxRotationRate 0.05
    }

Wind as spread and gravity as falloff . A strong gravity could simulating the reboil of magma.