Rendering ring of particles around entity that faces direction of entity travel

[ryanshah]

I currently spawn a ring of particles around my entity when it is spawned, however depending on how the player is facing to cast the entity the particle ring does not always appear in front of the player. I know this is something to do with the z position (vz), but I dont 100% understand how to set it in this case. For example in some directions it appears fine, but in some the ring is effectively flipped 90 degrees so all I can see is a line of particles instead of the ring.

@Override
  public void tick() {
  if (this.world.isRemote || (this.shootingEntity == null || !this.shootingEntity.removed) && this.world.isBlockLoaded(new BlockPos(this.getPosX(), this.getPosY(), this.getPosZ()))) {
    super.tick();
    ++this.ticksInAir;

    RayTraceResult raytraceresult = ProjectileHelper.func_234618_a_(this, entity -> entity.isAlive() && entity != this.shootingEntity);
    if (raytraceresult.getType() != RayTraceResult.Type.MISS && !net.minecraftforge.event.ForgeEventFactory.onProjectileImpact(this, raytraceresult)) {
      this.onImpact(raytraceresult);
    }

    Vector3d vec3d = this.getMotion();
    this.setPosition(getPosX() + vec3d.x, getPosY() + vec3d.y, getPosZ() + vec3d.z);
    //ProjectileHelper.rotateTowardsMovement(this, 0.2f);

    float f = this.getMotionFactor();

    double radius = 1.25D;
    double d0 = this.getPosX() - vec3d.x;
    double d1 = this.getPosY() - vec3d.y;
    double d2 = this.getPosZ() - vec3d.z;

    for(double angle = 0.0D; angle < 2 * Math.PI; angle += 4d / 180d * (2 * Math.PI)) {
      double vx = d0 + MathHelper.cos((float)angle) * radius;
      double vy = d1 + MathHelper.sin((float)angle) * radius;
      double vz = d2 + MathHelper.sin((float) angle) * radius;

      this.world.addParticle(ParticleTypes.SMOKE, vx, vy, vz, vec3d.x, vec3d.y, vec3d.z);
    }

    this.setMotion(vec3d.add(this.accelerationX, this.accelerationY, this.accelerationZ).scale(f));
    //this.setPosition(this.getPosX(), this.getPosY(), this.getPosZ());
  } else {
    this.remove();
  }
}

 

Edited April 29, 2021 by ryanshah
updated code

[Draco18s]

You are rotating around vector3.UP (that is, the axis that points vertically) and then doing something weird by adding the same value to Y and Z (this literally makes no sense) and what you want to do is rotate around a vector that points in the direction the player is facing.

 

https://stackoverflow.com/q/31225062

[ryanshah]

I'm still not sure I totally understand. For reference I have updated the OP to contain the tick method so you can what posX etc. I am referencing in this question.

[MFMods]

are you sure you understand the geometry in that code? adding sine to Z and cosine to X gives you a circle. but why are you adding anything to Y? that gives you a spiral (not a vertical one, also, but you didn't want any kind).

 

and are you sure you get the part about incrementing the angle? because that code would be much simpler if you did - you'd make a constant holding the number of particles and just divide 2pi by N.

Edited April 29, 2021 by MFMods

[Draco18s]

  On 4/29/2021 at 11:57 AM, ryanshah said:

double vx = d0 + MathHelper.cos((float)angle) * radius;

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does not equal

  Quote

double vx = d0*(d0*x + d1*y + d2*z)*(1d - MathHelper.cos(angle)) + x*MathHelper.cos(angle) + (-d2*y + d1*z)*MathHelper.sin(angle);

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same goes for the other three values.

You need to rotate around the direction of travel to get the effect you want and right now you're rotating around a fixed vector.

  On 4/29/2021 at 11:57 AM, ryanshah said:

4d / 180d * (2 * Math.PI)

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A constant, divided by a constant, multiplied by a constant times a constant.
Sounds like a constant to me. Specifically Math.PI/22.5d. Or you could just do an integer loop from 1 to 45 and multiply the loop index by that constant instead of doing a loop over a double.

[ryanshah]

  On 4/29/2021 at 2:44 PM, MFMods said:

are you sure you understand the geometry in that code? adding sine to Z and cosine to X gives you a circle. but why are you adding anything to Y? that gives you a spiral (not a vertical one, also, but you didn't want any kind).

 

and are you sure you get the part about incrementing the angle? because that code would be much simpler if you did - you'd make a constant holding the number of particles and just divide 2pi by N.

Expand  

I am adding to Y instead of Z for the angle to have my ring appear upwards infront of the player, otherwise it just appears flat.

[ryanshah]

  On 4/29/2021 at 2:52 PM, Draco18s said:

does not equal

same goes for the other three values.

You need to rotate around the direction of travel to get the effect you want and right now you're rotating around a fixed vector.

A constant, divided by a constant, multiplied by a constant times a constant.
Sounds like a constant to me. Specifically Math.PI/22.5d. Or you could just do an integer loop from 1 to 45 and multiply the loop index by that constant instead of doing a loop over a double.

Expand  

I'll do some constant refactoring later. For now, I have the current code:

 

double radius = 1.25D;
double u = this.getPosX() - vec3d.x;
double v = this.getPosY() - vec3d.y;
double w = this.getPosZ() - vec3d.z;

for(double angle = 0.0D; angle < 2 * Math.PI; angle += 4d / 180d * (2 * Math.PI)) {
  double mod = (u * getPosX()) + (v * getPosY()) + (w * getPosZ());
  double vx = u * mod * (1d - MathHelper.cos((float)angle)) + getPosX() * MathHelper.cos((float)angle) + (-w * getPosY() + v*getPosZ()) * MathHelper.sin((float)angle);
  double vy = v * mod * (1d - MathHelper.cos((float)angle)) + getPosY() * MathHelper.cos((float)angle) + (w * getPosX() - u*getPosZ()) * MathHelper.sin((float)angle);
  double vz = w * mod * (1d - MathHelper.cos((float)angle)) + getPosZ() * MathHelper.cos((float)angle) + (-v * getPosX() + u*getPosY()) * MathHelper.sin((float)angle);

  this.world.addParticle(ParticleTypes.SMOKE, vx, vy, vz, vec3d.x, vec3d.y, vec3d.z);
}

 

But where would I include the radius of the ring?

Edited April 29, 2021 by ryanshah
updated code

[Draco18s]

vx, vy, and vz represent a unit vector. Multiply by the desired magnitude.

Edited April 29, 2021 by Draco18s

[ryanshah]

  On 4/29/2021 at 4:13 PM, Draco18s said:

vx, vy, and vz represent a unit vector. Multiply by the desired magnitude.

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Thanks for the help so far, I think I'm nearly there..

float radius = 2f;
// Get origins
double u = this.getPosX() - vec3d.x;
double v = this.getPosY() - vec3d.y;
double w = this.getPosZ() - vec3d.z;

Vector3d facing = new Vector3d(getPosX(), getPosY(), getPosZ());

for(double angle = 0.0D; angle < 2 * Math.PI; angle += 4d / 180d * (2 * Math.PI)) {
  double c = (u * facing.x) + (v * facing.y) + (w * facing.z); // constant
  double vx = u * c * (1d - MathHelper.cos((float)angle)) + facing.x * MathHelper.cos((float)angle) + (-w * facing.y + v*facing.z) * MathHelper.sin((float)angle);
  double vy = v * c * (1d - MathHelper.cos((float)angle)) + facing.y * MathHelper.cos((float)angle) + (w * facing.x - u*facing.z) * MathHelper.sin((float)angle);
  double vz = w * c * (1d - MathHelper.cos((float)angle)) + facing.z * MathHelper.cos((float)angle) + (-v * facing.x + u*facing.y) * MathHelper.sin((float)angle);
  this.world.addParticle(ParticleTypes.SMOKE, getPosX() + vx * radius, getPosY() + vy * radius, getPosZ() + vz * radius, vec3d.x, vec3d.y, vec3d.z);
}

So to my understanding, I first get the origin (0, 0, 0) and i want to do the transforms over the unit vector and then apply the vx,vy,vz offsets multiplied by the radius of the circle to the original position. However, nothing here is showing. I think I might have the wrong unit vector to use..