Fast Vector scale

AdamB

Anyone got any good tips for a fast Geom::Vector3d scale? Along with a few others, its a function thats sorely missing in the API. Initially, I trivially did:

def scale(s)
	Geom::Vector3d.new(self.x * s,self.y * s, self.z * s)
end

However, this is waaay slower than the Vector3d#length function which (must) do slightly more work. I'm currently using (brace yourself for the horror):

vec = (vtmp = aVector; vtmp.length = vtmp.length * aNewLength; vtmp)

where aVector and aNewLength are effective parameters.

Its actually faster..but just so ugly.

tbd

why this testcase doesnt work ? I am missing something ?

later edit: duh, vtmp = v.clone otherwise it will change the original vector
from my tests scale2 is like 26-30% speed increase


def scale(v,s)
  Geom;;Vector3d.new(v.x * s,v.y * s, v.z * s)
end

def scale2(v,s)  
  vtmp = v; 
  vtmp.length = vtmp.length * s
  vtmp
end

v1 = Geom;;Vector3d.new(5,1,5)
n1 = 10

t1 = Time.now
begin
  50000.times do |x|
    scale2(v1,n1)   
  end
rescue => err
 p err
end
p Time.now - t1

AdamB

yes, that my point - that the internal function (length) that does something like *Math.sqrt(v.dot(v))*is faster than 3 scalar multiplies.. A bit sad.

Adam

tbd

because the internal function length is done in C world and those 3 scalar multiplies in Ruby world (which of course is slower)