Points and Vectors in 3D

[Simon]

On 12/03/2011 20:51, Caligo wrote:
> Given everything that D offers, what would be the best way to implement
> a Point and a Vector type?  The same (x, y, z) can be used to represent
> vectors, but a point represents a position, whereas a vector represents
> a direction.  So, would you define two different structs for each? or
> define and implement an interface?  a fixed array or POD members?

I've done lots of 3d over the years and used quite a lot of different 
libraries and I've come to prefer code that makes a distinction between 
points and vectors. Makes code easier to read and more type safe, though 
it's a bit more inconvenient when you need to mix things up.

I use:

struct pt {
   float[3] _vals;
}

struct vec {
   float[3] _vals;
}

Using the float[3] allows you to use vector ops:

pt	p0;
vec	v;

p0._vals[] += v._vals[];

You don't want an interface; you don't get anything more value type than 
points & vectors. In a modern 3d models you could be dealing with a 1/2 
million vertices.

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