Some gravity particles

[User137]

I realized today that while 3D is great, is not necessary to simulate the gravity particle effect, or should you call it "anti-gravity". This can be done in 2D, with big gain in performance, and better results to look at.

Now after testing it a little, it didn't seem to work somehow, or maybe i'm missing something. I also think that i'm able to rid of Sqrt() completely.

    for i:=FFirst to FLast do
      with star[i] do
        for j:=i+1 to count-1 do begin
          xx:=v.x-star[j].v.x;
          yy:=v.y-star[j].v.y;
          d:=xx*xx+yy*yy;
          if d>0 then begin
            d:=(G_FORCE*G_FORCE)/(d*d*d); // Compiler should optimize the constant multiplication to 1 value
            // If not, just remove multiplication and change G_FORCE value
            if star[j].positive<>positive then d:=-d;
            vec.x:=(star[j].v.x-v.x)*d;
            vec.y:=(star[j].v.y-v.y)*d;
            movement.x:=movement.x+vec.x;
            movement.y:=movement.y+vec.y;
            star[j].movement.x:=star[j].movement.x-vec.x;
            star[j].movement.y:=star[j].movement.y-vec.y;
          end;
        end;

The particles scatter endlessly, with no clear groupings done as was in 3D. I have tried with many different parameters. I wouldn't want to make boundaries to the "universe", where particles would bounce backwards, but i might have to. I also tried with every particle being same polarity, and they still did not group. It's not because of removal of sqrt(), that was almost last step in my tests, improvement to calculation time i'd say.

[SilverWarior]

Based on the code it seems you are only applying force to [j] particle and not to [i] particle at the same time.
Haven't you been calculating force between two particle once and then applying that force to both of your particles at once?

[User137]

Based on the code it seems you are only applying force to [j] particle and not to [i] particle at the same time.
Haven't you been calculating force between two particle once and then applying that force to both of your particles at once?

If i set NUM_TOTAL = 2; and 2 opposite particles, they start pushing eachother away in opposite direction, as should. Same code as before, i just commented Z-related lines. "with star[i] do" on second quoted line refers to "i" particle.

I didn't do the math before, i was thinking it might still be relatively same effect.

sqrt(4)*sqrt(4)*sqrt(4)
= 2*2*2 = 8

= sqrt(4*4*4)
= sqrt(64) = 8

X/Sqrt(Y)
= (X*X)/Y , if Y>=0

[imcold]

X/Sqrt(Y)
= (X*X)/Y , if Y>=0

Um, no. Trivially proven by X=1, Y=2.

[User137]

Oh crap... this is how it actually goes:
X / Sqrt(Y)
= (X*Sqrt(Y)) / Y
which puts us back to square 1... on why doesn't it work, or works like that even when using sqrt? I have tried decreasing, but also increasing the G_FORCE to compensate lack of particle density in depth direction. But at the same time there is a more uniform force pulling every direction, from the overall system.

[imcold]

If you scratch one dimension, you have to reduce the divisor - scratch one multiplication. Then it could be reduced further, this should work nicely:

d = G_FORCE / d

[User137]

Remember there were originally 2 multiplications in optimized version, so now it becomes 1 and that looks like working well

d:=G_FORCE/(d*d);

I still want to give boundaries to the world though, and see what it'd be like. Kind of like how subsection would settle, and i expect a little plasma-like effect. Some days later perhaps.

edit: Decided to code them straight away. (No plasma, but something more boring )

            // Rectangular collision
            {if v.x<-10 then movement.x:=abs(movement.x)
            else if v.x>10 then movement.x:=-abs(movement.x);
            if v.y<-10 then movement.y:=abs(movement.y)
            else if v.y>10 then movement.y:=-abs(movement.y); }
            // Circular collision
            if v.x*v.x+v.y*v.y>100 then
              movement:=reflect(movement, vector2f(-v.x*0.1,-v.y*0.1));

[imcold]

The modified "d" calculation doesn't produce the same values as the previous equation if you take out the sqrt, so the effect has to be different.

dist = sqrt(v)
d = G_FORCE / (dist*dist*dist) = G_FORCE  / (sqrt(v) * sqrt(v) * sqrt(v))

power:

d^2 = G_FORCE*G_FORCE / (v * v * v)
d = sqrt(d^2)