Unfamiliar syntax

[fafner]

I downloaded some code for triangle-box intersection, and it contains a way of defining functions I haven't really seen used before. Here's an example:

#define CROSS(dest, v1, v2) \

		  dest[0]=v1[1]*v2[2]-v1[2]*v2[1]; \

		  dest[1]=v1[2]*v2[0]-v1[0]*v2[2]; \

		  dest[2]=v1[0]*v2[1]-v1[1]*v2[0];

When I try to compile this I get several error messages like:

error: C++ requires a type specifier for all declarations
                  dest[0]=v1[1]*v2[2]-v1[2]*v2[1]; \

and

error: use of undeclared identifier 'v1'
                  dest[0]=v1[1]*v2[2]-v1[2]*v2[1]; \

Is this a maybe a C-thing? Does anyone know how I can get past this without rewriting the entire file?

Thanks,
Fafner

[ne555]

remove the empty lines.

> Is this a maybe a C-thing?
that's called a `macro', it would simply do text substitution (use at your own risk)
In C++ you may use templates

[fafner]

Thanks, removing the lines solved it :) I know about macros, I've just never used them and so had no idea about the empty line thing.

[Duthomhas]

Off the top of my head:

template <typename T>
inline
void CROSS( T& dest[ 3 ], T& v1[ 3 ], T& v2[ 3 ] )
{
  dest[0] = (v1[1] * v2[2]) - (v1[2] * v2[1]);
  dest[1] = (v1[2] * v2[0]) - (v1[0] * v2[2]);
  dest[2] = (v1[0] * v2[1]) - (v1[1] * v2[0]);
}

That'll properly compute the cross product of any two 3D vectors with a (presumably) floating point element type.

Remember that order matters. Mix the two input vectors and your normal (dest) vector will point in the opposite direction.

Hope this helps.

[vaportrack]

vector will point in the opposite

Yep cw vs ccw