Re: [boost] Small matrix/vector library (ET, swizzling, SSE)

From: Daniel Wesslén (daniel_at_[hidden])
Date: 2006-12-05 02:46:22

Michael Fawcett wrote:
> On 12/3/06, Daniel Wesslén <daniel_at_[hidden]> wrote:
>> Not all swizzlings are named, but if the one you happen to want is not
>> provided then it is easy to create:
>>
>> const indexer<bits::index_swizzle<0,0,2,0> > xxzx;
>> const indexer<bits::index_swizzle<3,2,1,0> > wzyx;
>> vector<4> v1, v2(1,2,3,4);
>> v1 = v2[xxzx]; // v1 = (1,1,3,1)
>> v1[xxzx] = v2; // error - v1[xxzx] is not a lvalue due to aliasing
>> v1[wzyx] = v2; // v1 = (4,3,2,1)
> 
> I really dislike that syntax.  Feel free to make use of the swizzle
> code generation macros I posted in the Vault.  They generate all
> possible combinations so users don't have to make instances of your
> index_swizzle classes.  You would want to replace the SWIZZLE_BODY
> macro with your own.  It simply takes in the next permutation as a
> sequence, e.g. (z)(w)(y).
> 
> The only downside is that there will be no compile-time error in
> situations like your //error line from above.
> 
> v1.xxzx() = v2; // compiles, but doesn't make too much sense

Fair enough. I much prefer my syntax to yours, but the main reason for 
posting was simply to present another way to do it - both syntax and 
implementation.

Obviously I could also generate all indexing objects, but in my 
experience (~3 years of using this library in computer graphics), xy and 
xyz are the only swizzlings (if you can even call them that) that's seen 
any significant use.

-- 
Daniel Wesslén