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The reason I'm asking this is because I saw an implementation which did it that way but I don't quiet understand it. I mean, usually I want to get the distance between two points in 3d space and if W is something other than 0 the result is not correct. The same when calculating lighting using the dot product.

float Vector::Length() const{
    return sqrtf(X * X + Y * Y + Z * Z + W * W);    //W necessary?
}

float Vector::Dot(const Vector& other) const{
    return X * other.X + Y * other.Y + Z * other.Z + W * other.W;
}

Edit: There are suggestions that my question is a duplicate of already existing ones. But the questions referred to are about whether you need the W component at all and for what. I know what I need it for, I'm just not sure about it's role in the operations I specified.

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    \$\begingroup\$ Possible duplicate of Do I need the 'w' component in my Vector class? \$\endgroup\$
    – Vaillancourt
    Apr 2, 2016 at 15:30
  • \$\begingroup\$ Or even this... \$\endgroup\$
    – Vaillancourt
    Apr 2, 2016 at 15:33
  • \$\begingroup\$ @AlexandreVaillancourt I don't think so. As you can read in my edit above, these questions are not the same as mine... \$\endgroup\$
    – lelgetrekt
    Apr 2, 2016 at 15:43
  • \$\begingroup\$ All right! I'll leave the link there just as a reference. \$\endgroup\$
    – Vaillancourt
    Apr 2, 2016 at 15:45
  • \$\begingroup\$ @aslg I think you have enough content there to make an answer :) \$\endgroup\$
    – Vaillancourt
    Apr 2, 2016 at 16:25

1 Answer 1

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The only reason you need to extend a vector to 4 dimensions (homogeneous coordinates, not 4-Dimensional space) is so that you can apply transforms or matrices (model, etc) to it. Unless you're explicitly making a game in a 4-Dimensional space you don't need to include the w component in the calculations you mentioned.

Indeed, as you noted, using a w different than 0 will of course yield wrong results for your typical 3D calculations.

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    \$\begingroup\$ I'd like to add that various transformations work out nicely if you represent points as coordinates with W = 1 and vectors (more accurately, "directions") as coordinates with W = 0. For example, a point will be affected under translation, but a direction will not be. \$\endgroup\$
    – jmegaffin
    Apr 2, 2016 at 20:32

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