fixed particle not positioned in the center

src/main/kotlin/com/bytedice/bde_particles/math/main.kt

@@ -5,12 +5,10 @@ import net.minecraft.util.hit.HitResult
 import net.minecraft.util.math.Vec3d
 import net.minecraft.world.RaycastContext
 import net.minecraft.world.World
+import org.joml.Vector2f
 import org.joml.Vector3f
 import org.joml.Vector4f
-import kotlin.math.asin
-import kotlin.math.atan2
-import kotlin.math.cos
-import kotlin.math.sin
+import kotlin.math.*
 import kotlin.random.Random
 
 
@@ -89,4 +87,62 @@ fun quatToEuler(quat: Vector4f): Vector3f {
   val yaw = atan2(siny_cosp, cosy_cosp)
 
   return Vector3f(roll, pitch, yaw)
+}
+
+
+fun randomInCircle(r: Float) : Vector2f {
+  val randRadius = r * sqrt(randomFloatBetween(0.0f, 1.0f))
+  val randAngle  = randomFloatBetween(0.0f, Math.PI.toFloat() * 2)
+
+  val randomPos = Vector2f(randRadius * cos(randAngle), randRadius * sin(randAngle))
+  return randomPos
+}
+
+
+fun randomInSphere(r: Float) : Vec3d {
+  val randRadius = r * Random.nextDouble().pow(1.0 / 3.0)
+
+  val phi = Random.nextDouble(0.0, 2 * Math.PI)
+
+  val cosTheta = Random.nextDouble(-1.0, 1.0)
+  val theta = acos(cosTheta)
+
+  val x = randRadius * sin(theta) * cos(phi)
+  val y = randRadius * sin(theta) * sin(phi)
+  val z = randRadius * cos(theta)
+
+  return Vec3d(x, y, z)
+}
+
+
+fun randomInRect(w: Float, h: Float) : Vector2f {
+  return Vector2f(randomFloatBetween(0.0f, w), randomFloatBetween(0.0f, h))
+}
+
+
+fun transformOffsetByQuat(offset: Vector3f, rotation: Vector4f): Vector3f {
+  val x = offset.x
+  val y = offset.y
+  val z = offset.z
+
+  val qx = rotation.x.toDouble()
+  val qy = rotation.y.toDouble()
+  val qz = rotation.z.toDouble()
+  val qw = rotation.w.toDouble()
+
+  val t2 = qw * x + qy * z - qz * y
+  val t3 = qw * y + qz * x - qx * z
+  val t4 = qw * z + qx * y - qy * x
+  val t5 = -qx * x - qy * y - qz * z
+
+  val newX = t2 * qw + t5 * -qx + t3 * -qz - t4 * -qy
+  val newY = t3 * qw + t5 * -qy + t4 * -qx - t2 * -qz
+  val newZ = t4 * qw + t5 * -qz + t2 * -qy - t3 * -qx
+
+  return Vector3f(newX.toFloat(), newY.toFloat(), newZ.toFloat())
+}
+
+
+fun transformOffsetByScale(offset: Vector3f, scale: Vector3f): Vector3f {
+  return offset.mul(scale)
 }

src/main/kotlin/com/bytedice/bde_particles/particle/Particle.kt

@@ -2,8 +2,7 @@ package com.bytedice.bde_particles.particle
 
 import com.bytedice.bde_particles.DisplayEntity
 import com.bytedice.bde_particles.DisplayEntityProperties
-import com.bytedice.bde_particles.math.eulerToQuat
-import com.bytedice.bde_particles.math.randomFloatBetween
+import com.bytedice.bde_particles.math.*
 import net.minecraft.server.world.ServerWorld
 import net.minecraft.util.math.Vec3d
 import org.joml.Vector3f
@@ -20,7 +19,7 @@ class Particle(particleParams: ParticleParams) {
     randomFloatBetween(particleParams.rotVelRandom.first.y, particleParams.rotVelRandom.second.x),
     randomFloatBetween(particleParams.rotVelRandom.first.z, particleParams.rotVelRandom.second.z)
   )
-  val size = Vector3f(
+  val scale = Vector3f(
     randomFloatBetween(particleParams.sizeRandom.first.x, particleParams.sizeRandom.second.x),
     randomFloatBetween(particleParams.sizeRandom.first.y, particleParams.sizeRandom.second.x),
     randomFloatBetween(particleParams.sizeRandom.first.z, particleParams.sizeRandom.second.z)
@@ -31,16 +30,23 @@ class Particle(particleParams: ParticleParams) {
   var isInit = false
 
   fun init(pos: Vec3d) {
+    val offset = Vector3f(-0.5f, -0.5f, -0.5f)
+    val quatRot = eulerToQuat(this.rot)
+
+    val scaleOffset = transformOffsetByScale(offset, this.scale)
+    val rotOffset = transformOffsetByQuat(scaleOffset, quatRot)
+
     val properties = DisplayEntityProperties(
       pos          = pos,
       blockType    = this.params.blockCurve[0],
-      leftRotation = eulerToQuat(rot),
-      scale        = size
+      translation  = rotOffset,
+      leftRotation = quatRot,
+      scale        = this.scale
     )
     
-    blockDisplay = DisplayEntity(properties)
+    this.blockDisplay = DisplayEntity(properties)
 
-    isInit = true
+    this.isInit = true
   }
 
 

src/main/kotlin/com/bytedice/bde_particles/particle/ParticleParams.kt

@@ -5,7 +5,7 @@ import org.joml.Vector3f
 
 data class ParticleParams (
   //val shape: Shape, // add later, start with single point
-  val blockCurve:   Array<String>            = arrayOf("minecraft:black_concrete", "minecraft:green_concrete"),
+  val blockCurve:   Array<String>            = arrayOf("minecraft:purple_concrete"),
   val rotRandom:    Pair<Vector3f, Vector3f> = Pair(Vector3f(0.0f, 0.0f, 0.0f), Vector3f(360.0f, 360.0f, 360.0f)),
   val rotVelRandom: Pair<Vector3f, Vector3f> = Pair(Vector3f(1.0f, 1.0f, 1.0f), Vector3f(5.0f, 5.0f, 5.0f)),
   val rotVelCurve:  Array<Vector3f>          = arrayOf(Vector3f(1.0f, 1.0f, 1.0f), Vector3f(0.0f, 0.0f, 0.0f)),