Re: [Quesa-develop] Re: Quesa - Optimization ideas.

[Roger H. <rog...@mi...>]

On Thursday, February 12, 2004, at 05:50  pm, Dair Grant wrote:

>> You know, if you added a fourth redundant dimension to the Cartesian
>> coordinate system, you could load points, vectors, etc. as true 
>> altivec
>> vectors and perform a number of operations VERY quickly, albeit at the
>> cost of some unused memory.  Hmm...
>
> Right now QD3D vectors and colours are always three components.
>
> This is something we might want to change, or at least add the option
> that you can specify points as quads and colours as argb (rather than
> distinct diffuse colour + diffuse transparency colour).

I may be saying the obvious as we are all at different points in out 
understanding
of graphics/coordinate geometry, but when I saw the AltiVec 
specification I
thought it was ideal for 3D work because a 3D vector has an implied Z 
of zero
and a point has an implied Z of one. If you do a matrix multiply by a 
vector
the bottom ( translation ) row gets multiplied by zero and has no effect
whilst for a point it gets multiplied by one and added on. If you take 
the average
of a number of points their Zs get added together and normally you 
divide by
the number of points, bringing the Z back to one. Of course the implied 
divide
by Z does it for you anyway. The other advantage is that C typing does 
not get
in the way. For points, ( A + B ) / 2  is not normally allowed, though 
you can do
A + ( B - A ) / 2 using standard routines as B - A gives a vector.

Using 4 coordinates, point = point + vector also works automatically
as lots of other stuff. Do we really need point3D and vector3D on the 
G4? I don't
think so unless we have millions of them to pack into as small a space 
as
possible. Of course we have to make it all work on other machines, like 
G3 too in a
transparent way and that's the challenge.

Roger.