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I'm trying to create a galaxy simulation using opengl with the compute shader and when I start my simulation, the galaxy with the spiral arms doesn't form, instead it goes into chaos. I noticed that the particles in the center are not spinning fast enough Does anyone had this problem before ?

I tried to:

  • change mass and smooth value
  • using verlet integration
  • change velocity initial value
  • change the number of particles

here is the code:

#version 430 core

layout (local_size_x = 128, local_size_y = 1, local_size_z = 1) in;

struct Particle
{
    vec4 position;
    vec4 velocity;
    vec4 acceleration;
};

layout (std430, binding = 0) buffer ParticleBuffer {
    Particle p[];
};

uniform float dt;
uniform float accuracy;

  const float mass = 1e-5;
  const float csmooth = 1e-6;

vec3 compute_force(vec3 posi){
    vec3 f = vec3(0);
    for(int i = 0; i<accuracy*p.length(); i++){
        if(posi != p[i].position.xyz){
            vec3 v = p[i].position.xyz - posi;
            float d = length(v);
            f+= mass*v/(pow(d,3)+csmooth);
        }
    }
    return f;
}

void main() {
    uint index = gl_GlobalInvocationID.x;

    vec3 pos = p[index].position.xyz;
    vec3 vel = p[index].velocity.xyz;
    vec3 accel = p[index].acceleration.xyz;

    vec3 newPos = pos+vel*dt + accel*(dt*dt*0.5);
    vec3 newAccel = compute_force(pos);
    vec3 newVel = vel + (accel+newAccel) *(dt*0.5);

    p[index].position.xyz = newPos;
    p[index].velocity.xyz = newVel;
    p[index].acceleration.xyz = newAccel;
}
```
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    $\begingroup$ I am not sure, but please try to delete the accelerations term out of the newPos calculation... $\endgroup$
    – Thomas
    Commented Nov 4, 2022 at 23:04
  • $\begingroup$ seems like nothing really changed $\endgroup$
    – Sedenion
    Commented Nov 6, 2022 at 12:10
  • $\begingroup$ Can you go more into detail, how the particles behavior is? Are they 'jumping' or are they all go through a single position? $\endgroup$
    – Thomas
    Commented Nov 6, 2022 at 13:40
  • $\begingroup$ The velocity therm also looks strange to me: only add one acceleration value. I think 'accel' is the correct one. $\endgroup$
    – Thomas
    Commented Nov 6, 2022 at 13:45
  • $\begingroup$ BTW you are using the Euler numeric integration algorithm. It's accuracy is very bad... A better integrater is the 'Runge-Kutta' algorithm $\endgroup$
    – Thomas
    Commented Nov 6, 2022 at 13:49

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