Vector cross product

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Vector cross product #87216 08/23/06 16:56 08/23/06 16:56
Joined: Jan 2002 Posts: 4,225 Germany / Essen Uhrwerk OP Expert
Uhrwerk OP Expert Joined: Jan 2002 Posts: 4,225 Germany / Essen	Hello everybody. I am missing a function that calculates the crossproduct of two vectors. The function to calculate the dot product is already available in vec_dot(). I know the function is easy to program yourself, but an engine internal function could be much more effective, couldn't it? Always learn from history, to be sure you make the same mistakes again...

Re: Vector cross product [Re: Uhrwerk] #87217 08/23/06 17:18 08/23/06 17:18
Joined: Oct 2003 Posts: 246 A Alberto Member
Alberto Member A Joined: Oct 2003 Posts: 246	I agree, the dot product function is even much simpler than the cross product one. They simply forgot it , I guess

Re: Vector cross product [Re: Alberto] #87218 08/24/06 20:50 08/24/06 20:50
Joined: Jul 2001 Posts: 6,904 H HeelX Senior Expert
HeelX Senior Expert H Joined: Jul 2001 Posts: 6,904	Code: function vec_cross (&a, &b) { temp[0] = a[1] * b[2] - a[2] * b[1]; temp[1] = a[2] * b[0] - a[0] * b[2]; temp[2] = a[0] * b[1] - a[1] * b[0]; return(temp); }

Re: Vector cross product [Re: Uhrwerk] #87219 08/25/06 13:14 08/25/06 13:14
Joined: Jan 2002 Posts: 4,225 Germany / Essen Uhrwerk OP Expert
Uhrwerk OP Expert Joined: Jan 2002 Posts: 4,225 Germany / Essen	Quote: I know the function is easy to program yourself, but an engine internal function could be much more effective, couldn't it? Code: function vec_cross (&ret, &a, &b) { ret[0] = a[1] * b[2] - a[2] * b[1]; ret[1] = a[2] * b[0] - a[0] * b[2]; ret[2] = a[0] * b[1] - a[1] * b[0]; } vec_dot is even simpler: Code: function vec_cross (&a, &b) { return(a[0] * b[0] + a[1] * b[1] + a[2] * b[2]); } Always learn from history, to be sure you make the same mistakes again...

Re: Vector cross product [Re: Uhrwerk] #87220 08/25/06 13:28 08/25/06 13:28
Joined: May 2002 Posts: 7,441 ventilator Senior Expert
ventilator Senior Expert Joined: May 2002 Posts: 7,441	but it's better to implement these functions with something else than vars if they are supposed to work correctly with non-normalized vectors too.

Re: Vector cross product [Re: ventilator] #87221 08/25/06 15:07 08/25/06 15:07
Joined: Jan 2002 Posts: 4,225 Germany / Essen Uhrwerk OP Expert
Uhrwerk OP Expert Joined: Jan 2002 Posts: 4,225 Germany / Essen	The vetors don't need to be normalized. The cross product returns a vector standing upright on the given twos with the length of the parallelogram, build by the two given vectors. If you used normalized vectors the length would be always the same. In case you want to implement that, just insert a "vec_normalize(ret,1);" at the end of the function vec_cross. Always learn from history, to be sure you make the same mistakes again...

Re: Vector cross product [Re: Uhrwerk] #87222 08/25/06 15:16 08/25/06 15:16
Joined: May 2002 Posts: 7,441 ventilator Senior Expert
ventilator Senior Expert Joined: May 2002 Posts: 7,441	yes, but the calculations are unsafe because of the limited var range. if the vectors are too long you could get bogus results.

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