[boost] Geometry/Vec lib swizzle syntax prototype

From: Michael Fawcett (michael.fawcett_at_[hidden])
Date: 2006-12-01 09:01:22

I have uploaded a small prototype that demonstrates the syntax
mentioned in the thread below.  It is in the Vault under Math -
Geometry as swizzle_demo.zip.

http://article.gmane.org/gmane.comp.lib.boost.devel/149076/match=geometry+vector+lib+swizzle

Here's a small example showing its use:

float4 b(1, 2, 3, 4);

float4 a = b.xxxx(); // a is now 1, 1, 1, 1
a = b.wwwz(); // a is now 4, 4, 4, 3
a = b.yzzw(); // a is now 2, 3, 3, 4
a = b.wzyx(); // a is now 4, 3, 2, 1

float4 c(10, 20, 30, 40);
c.yz() = b.zy(); // c is now 10, 3, 2, 40

This mimics Cg, HLSL, and GLSL syntax closely.  The swizzle syntax is
implemented as function calls so that it doesn't increase the size of
the vector struct (important for using those structs directly for
graphics API calls).

The prototype code does not implement arithmetic operators for
simplicity's sake, but my local copy has it implemented.

This isn't meant as a full library, only a demonstration showing that
the swizzle syntax can be achieved rather simply using the Boost PP
and TypeTraits libraries.

One item that could be changed is the multiple template parameters to
the classes.  In the discussion that took place during the review of
Andy Little's library the prospect of heterogeneous vectors took
place.  In my opinion heterogeneous vectors work with little expense
to the library writer and transparently to the user.  It would also
"just work" with Andy's Quan library, or the other Units library being
developed.  This is pretty off-topic for the syntax that I am
demonstrating, I just wanted to mention that I hadn't removed it from
this demo.  It is in no way necessary, but removal would require the
macros to be changed a little bit.

I have only compiled using VS 7.1 and 8.0.

I am by no means a PP or template guru, so I would welcome your
thoughts and critiques.

--Michael Fawcett