c# - How to Draw Projectile Trajectory with Unity3d's built-in Physics Engine? -

i working on game fling projectile reacts physics forces. using built in unity physics in game, drawing trajectory of projectile before launched. so, i'm using linerenderer , simple physics class rolled compute positions:

public class slingphysics {     private vector3 halfgravity;     private float forcemultiplier;      public void init(vector3 gravity, float slingforce, float mass, float drag)     {         halfgravity = gravity / 2.0f;         forcemultiplier = slingforce / mass / (1 + drag);     }      public vector3 getposition(vector3 start, vector3 direction, float timedelta)     {         vector3 pos = direction * (timedelta * forcemultiplier);         pos.y += (halfgravity.y * timedelta * timedelta);         return start + pos;     }      /// <summary>     /// computes array of trajectory object positions time.     /// </summary>     /// <returns>number of positions filled buffer</returns>     /// <param name="startpos">starting position</param>     /// <param name="direction">direction (and magnitude) vector</param>     /// <param name="timeincrement">time increment of samples</param>     /// <param name="yfloor">minimum height, below clipped</param>     /// <param name="positions">buffer fill positions</param>     public int getpositions(vector3 startpos, vector3 direction, float timeincrement, float yfloor, vector3[] positions)     {         int maxitems = positions.length;         int = 0;         (; < maxitems; i++)         {             vector3 pos = getposition(startpos, direction, timeincrement * i);             if (pos.y < yfloor)                 break;             positions[i] = pos;         }         return i;     } } 

this works great , (somewhat surprisingly) matches actual trajectory projectile ends traveling when launched , governed unity physics engine.

but now, decided introduce drag on rigidbody , trajectory no longer perfect. continue try change physics model match unity doing, seems losing battle.

is there way precompute , draw trajectory using unity physics engine?

if not, how drag , angular drag implemented mathematically in unity physics?

is there documentation source unity's (5.3.4) physics implementation?

i continue try change physics model match unity doing

no, don't it. whenever unity updated, physics stuff break. example, unity 4 , 5 physics not the-same. had heavily modify unity 4 physics code make work properly.

the easiest solution problem not calculate @ all. way create two projectiles. projectile1 main projectile can seen , shot. projectile2 hidden projectile can't seen player.

on drag mode, shoot projectile2(hidden) store path or position(vector3) has traveled through in list. use stored path draw projectile trajectory.

you need shoot projectile2(hidden) once , store path. if during drag mode, finger, mouse or drag moves position, have clear list, re-shoot projectile2(hidden) once again, store position list , update projectile trajectory again.

when finger released, can shot projectile1(main projectile) visible player.

if using linerenderer, number of setvertexcount the-same number of list.count. drawing lines can done looping on positions in list.

the result the-same no matter how many times unity updated.