What is, How do you use it and what is it used for. Cheers Steve

The dot product (or scalar product) of two vectors is calculated like this:

if
v1 = (x1, y1, z1) and
v2 = (x2, y2, z2) then
v1.v2 = x1*x2 + y1*y2 + z1*z2

One useful thing you can do with it is determine the angle between two vectors. For this you use the following identity:

cos A = (v1.v2) / (|v1| * |v2|)

The angle between two vectors can be used for things like calculating how certain light sources affect the different polygons in your scene, or determining which polygons are facing ''away'' from the camera and thus don''t need to be drawn.

There''s probably all sorts of stuff that it is used with that I''m missing, but I haven''t done much 3D programming, I just know a lot of the math.

-Ironblayde
 Aeon Software

Down with Tiberia!
"All your women are belong to me." - Nekrophidius

Thanks For the Post

Anyway what does the pipe(|) sign mean?

Do you know where the formula of cross product come from? why is it:

out[x] = v1[y] * v2[z] - v1[z]* v2[y];
out[y] = v1[z] * v2[x] - v1[x]* v2[z];
out[z] = v1[x] * v2[y] - v1[y]* v2[x];

Sorry if this is basic maths questions but i am a newbie to 3D maths and only studying GCSE in the UK.

Thanks Alot

Steve

The pipe signs around the vector mean the length of that vector.



So, if your vector is like this:



VECTOR vec = < 0, 0, 5 >



then |vec| = 5, because the length of the vector is exactly five.

Thanks Alot