On 12/3/06, Daniel Wesslén <daniel@wesslen.org> 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 You could try to determine how the function was being used (read vs write) and only allow write masks for combinations where each vector component was only specified once: v1.xxzx() = v2; // fails to compile v1.wxzy() = v2; // compiles or you could throw an exception from the assignment operator if any of the invoking class's references were aliased. I much prefer the compile-time solution (if one exists?). --Michael Fawcett