dPds works !

This was posted on the renderman forums, so i'm pretty sure its common knowledge.
Basically if you are in need of a consistent local basis transform for the usual stuff like normal maps and mapped anisotropic direction, you'll need a reliable tangent vector, sometimes referred to (by me, mainly) as dPds.

The RSL code is as follows:


void dPdst( float ss,tt; point PP;
output varying vector dPds;
output varying vector dPdt; )
{
float Dus = Du(ss);
float Dut = Du(tt);
float Dvs = Dv(ss);
float Dvt = Dv(tt);
vector DuP = Du(PP);
vector DvP = Dv(PP);
float det = (Dus*Dvt-Dvs*Dut);
dPds = (DuP*Dvt - DvP*Dut) / det;
dPdt = (DvP*Dus - DuP*Dvs) / det;
}


9 things i hate about my iPhone

These are the 10 9 most irritating things about my iPhone that stop at 'quite good' where it could have been truly great.

1 - Battery Life : shocking.
2 - Its expensive. Very very expensive.
3 - It can't bluetooth photos to non-iPhones. Basic stuff, and it can't even do that.
4 - You can't use your own sound files for ring tones. You have to buy them
5 - You can't copy files, such as pdfs, to it for offline reading. That's rubbish!!
5 - The calendar can't repeat on useful intervals such as 'last working day of month' or 'first tuesday in month'. Basic, basic, *basic* functionality that it can't even do.
6 - The pin number screen-lock is so irritating. If I want my data secure, I have to keep unlocking it all the time, even with the least annoying unlock option. Its so annoying when you are in a hurry.
7 - Touch sensitive keypad and predictive text frequently cause typos. The more of a hurry you are in, the worse it gets since it is so over-sensitive to mis-keying (or not adding the letter even when you hit a button with your finger).
8 - You can't write your own software for it unless you have a mac. Why should that be? Its not even running OSX !
9 - The sim card slot is like a chinese maths puzzle.


And that ladies and gentlemen, is why I think Apple are such smug bastards.