vectors.lua

--Methods for handling math between 2D vectors
-- Vectors are tables with x,y variables inside

-- Contributors: WarrenM

-- Add v1 to v2
function v_addv( v1, v2 )
  return { x = v1.x + v2.x, y = v1.y + v2.y }
end

-- Subtract v2 from v1
function v_subv( v1, v2 )
  return { x = v1.x - v2.x, y = v1.y - v2.y }
end

-- Multiply v by scalar n
function v_mults( v, n )
  return { x = v.x * n, y = v.y * n }
end

-- Divide v by scalar n
function v_divs( v, n )
  return { x = v.x / n, y = v.y / n }
end

-- Gets magnitude of v, squared (faster than v_mag)
function v_magsqr( v )
  return ( v.x * v.x ) + ( v.y * v.y )
end

-- Compute magnitude of v
function v_mag( v )
  return sqrt( ( v.x * v.x ) + ( v.y * v.y ) )
end

-- Normalizes v into a unit vector
function v_normalize( v )
  local len = v_mag( v )
  return { x = v.x / len, y = v.y / len }
end

-- Computes dot product between v1 and v2
function v_dot( v1, v2 )
   return ( v1.x * v2.x ) + ( v1.y * v2.y )
end

-- Computes the reflection vector between vector v and normal n
-- NOTE : assumes v and n are normalized
function v_reflect( v, n )
  local dot = v_dot( v, n )
  local wdnv = v_mults( v_mults( n, dot ), 2.0 )
  local refv = v_subv( v, wdnv )
  return refv
end