vect.go

package chipmunk

import "fmt"

type Vect struct {
  X, Y Float
}

func vect(x, y Float) *Vect {
  return &Vect{x, y}
}

func (v *Vect) Add(o *Vect) *Vect {
  return &Vect{v.X + o.X, v.Y + o.Y}
}

func (v *Vect) Neg() *Vect {
  return &Vect{-v.X, -v.Y}
}

func (v *Vect) Sub(o *Vect) *Vect {
  return &Vect{v.X - o.X, v.Y - o.Y}
}

func (v *Vect) Mult(s Float) *Vect {
  return &Vect{v.X * s, v.Y * s}
}

func (v *Vect) Dot(o *Vect) Float {
  return v.X*o.X + v.Y*o.Y
}

func (v *Vect) Cross(o *Vect) Float {
  return v.X*o.Y - v.Y*o.X
}

func (v *Vect) Perp() *Vect {
  return &Vect{-v.Y, v.X}
}

func (v *Vect) RPerp() *Vect {
  return &Vect{v.Y, -v.X}
}

func (v *Vect) Project(o *Vect) *Vect {
  return o.Mult(v.Dot(o) / o.Dot(o))
}

func (v *Vect) Rotate(o *Vect) *Vect {
  return &Vect{v.X*o.X - v.Y*o.Y, v.X*o.Y + v.Y*o.X}
}

func (v *Vect) Unrotate(o *Vect) *Vect {
  return &Vect{v.X*o.X + v.Y*o.Y, v.Y*o.X - v.X*o.Y}
}

func (v *Vect) LengthSq() Float {
  return v.Dot(v)
}

func (v *Vect) Lerp(o *Vect, t Float) *Vect {
  return v.Mult(1.0 - t).Add(o.Mult(t))
}

func (v *Vect) Normalize() *Vect {
  return v.Mult(1.0 / v.Length())
}

func (v *Vect) NormalizeSafe() (normalized *Vect) {
  if v.X == 0.0 && v.Y == 0.0 {
    normalized = &Vect{0.0, 0.0}
  } else {
    normalized = v.Normalize()
  }

  return
}

func (v *Vect) Clamp(length Float) (clamped *Vect) {
  if v.Dot(v) > length*length {
    clamped = v.Normalize().Mult(length)
  } else {
    clamped = v
  }
  return
}

func (v *Vect) LerpConst(o *Vect, d Float) *Vect {
  return v.Add(o.Sub(v).Clamp(d))
}

func (v *Vect) Dist(o *Vect) Float {
  return v.Sub(o).Length()
}

func (v *Vect) DistSq(o *Vect) Float {
  return v.Sub(o).LengthSq()
}

func (v *Vect) Near(o *Vect, dist Float) bool {
  return v.DistSq(o) < dist*dist
}

func (v *Vect) Length() Float {
  return v.Dot(v).Sqrt()
}

func (v *Vect) Slerp(o *Vect, t Float) (slerp *Vect) {
  omega := v.Dot(o).Acos()
  if !(omega.IsNaN() || omega == 0.0) {
    denom := 1.0 / omega.Sin()
    slerp = v.Mult(((1.0 - t) * omega).Sin() * denom).
      Add(o.Mult(((t * omega) * denom).Sin()))
  } else {
    slerp = v
  }
  return
}

func (v *Vect) SlerpConst(o *Vect, a Float) *Vect {
  angle := v.Dot(o).Acos()
  return v.Slerp(o, a.Min(angle)/angle)
}

func VectorForAngle(a Float) *Vect {
  return &Vect{a.Cos(), a.Sin()}
}

func (v *Vect) ToAngle() Float {
  return v.Y.Atan2(v.X)
}

func (v *Vect) String() string {
  return fmt.Sprintf("(%.3f, %.3f)", v.X, v.Y)
}