From 5136a24da2eccd0013ee2754eda821f0838c380d Mon Sep 17 00:00:00 2001
From: zyxkad <zyxkad@gmail.com>
Date: Sat, 25 Nov 2023 20:12:05 -0700
Subject: [PATCH] add MagnetField

---
 engine.go | 17 ++++++++++++++-
 force.go  | 65 +++++++++++++++++++++++++++++++++++++++----------------
 motion.go | 15 +++++++++++++
 3 files changed, 77 insertions(+), 20 deletions(-)
 create mode 100644 motion.go

diff --git a/engine.go b/engine.go
index 2bcda09..1870709 100644
--- a/engine.go
+++ b/engine.go
@@ -1,5 +1,20 @@
 package molecular
 
+type Config struct {
+	MinSpeed float64
+	MaxSpeed float64
+}
+
 type Engine struct {
-	//
+	cfg Config
+}
+
+func NewEngine(cfg Config) *Engine {
+	return &Engine{
+		cfg: cfg,
+	}
+}
+
+func (e *Engine) Config() Config {
+	return e.cfg
 }
diff --git a/force.go b/force.go
index 9b49589..1c3f31a 100644
--- a/force.go
+++ b/force.go
@@ -1,39 +1,66 @@
 package molecular
 
-import (
-	"math"
-)
-
 const (
-	G = 6.674e-11   // The gravitational constant is 6.674×10−11 N⋅m2/kg2
-	C = 299792458.0 // The speed of light
+	G = 6.674e-11 // The gravitational constant is 6.674×10−11 N⋅m2/kg2
 )
 
-func RelativeDeltaTime(t float64, speed float64) float64 {
-	return t / math.Sqrt(1-speed*speed/C*C)
+type GravityField struct {
+	mass float64
 }
 
-type ForceField struct {
-	pos  Vec
-	mass float64
+func NewGravityField(pos Vec, mass float64) *GravityField {
+	return &GravityField{
+		mass: mass,
+	}
 }
 
-func (f *ForceField) Mass() float64 {
+func (f *GravityField) Mass() float64 {
 	return f.mass
 }
 
-func (f *ForceField) SetMass(mass float64) {
+func (f *GravityField) SetMass(mass float64) {
 	f.mass = mass
 }
 
-// FieldAt returns the acceleration at the pos due to the force field
-func (f *ForceField) FieldAt(pos Vec) Vec {
-	acc := f.pos.Subbed(pos)
-	l := acc.Len()
+// FieldAt returns the acceleration at the distance due to the gravity field
+func (f *GravityField) FieldAt(distance Vec) Vec {
+	l := distance.Len()
 	if l == 0 {
 		return ZeroVec
 	}
+	distance.Negate()
 	// normalize 1 / l and G * m / l ^ 2
-	acc.ScaleN(G * f.mass / (l * l * l))
-	return acc
+	distance.ScaleN(G * f.mass / (l * l * l))
+	return distance
+}
+
+// MagnetField represents a simulated magnetic field.
+// For easier calculate, it's not the real magnetic field.
+// Since the magnetic field disappears easily, the cubic distance is used
+type MagnetField struct {
+	power float64 // in m^3 / s^2
+}
+
+func NewMagnetField(power float64) *MagnetField {
+	return &MagnetField{
+		power: power,
+	}
+}
+
+func (f *MagnetField) Power() float64 {
+	return f.power
+}
+
+func (f *MagnetField) SetPower(power float64) {
+	f.power = power
+}
+
+func (f *MagnetField) FieldAt(distance Vec) Vec {
+	l := distance.Len()
+	if l == 0 {
+		return ZeroVec
+	}
+	// normalize will scale with factor 1 / l, so we merge two steps into one
+	distance.ScaleN(f.power / (l * l * l))
+	return distance
 }
diff --git a/motion.go b/motion.go
new file mode 100644
index 0000000..a6905e3
--- /dev/null
+++ b/motion.go
@@ -0,0 +1,15 @@
+package molecular
+
+import (
+	"math"
+)
+
+const (
+	C = 299792458.0 // The speed of light
+)
+
+// RelativeDeltaTime returns the actuall time that relative to the obeserver (server),
+// with given speed and the time relative to the moving object
+func RelativeDeltaTime(t float64, speed float64) float64 {
+	return t / math.Sqrt(1-speed*speed/C*C)
+}