What is a normal?

[Sastraxi]

I haven't found many good tutorials on the uses of surrace normals or what they're for. All I can basically figure is that it is a ray that is perpendicular to the surface, but I have no idea how to calculate them or why we need them.

Could anyone shed some light on the topic?

[Zaei]

Originally posted by Sastraxi
Could anyone shed some light on the topic?

Funny you put it that way. Face Normals are vectors that point in the direction that a face is pointing. Vertex Normals is the averaged normal of all faces that share that vertex. Normals are usually used for, well, lighting. You can calculate the angle between a ray from a light to a vertex, and that vertex's normal, and use that to calculate the amount of light that hits that vertex, and thus, its intensity.

There is a tutorial about lighting over on directx4vb (you know the address). There is a function to calculate face normals in that tutorial.

Z.

[Sastraxi]

Ah, so that's where I got it from. Thanks for that. Oh, and I don't want to start another thread but how do you do light maps? I don't believe he covered that one at his site.

[Sastraxi]

One last thing- I need to know actual code for the Vector Subtract and Cross Product and Normalise functions, I don't want to have DirectX as a dependancy for those 3 functions.

[Zaei]

Lightmaps are simply an extra texture blended (additive) on top of the regular texture to give the appearance of light in an area.

Vector Subtract is easy:

given vector A and vector B, and result vector r:
r.x = A.x - B.x
r.y = A.y - B.y
r.z = A.z - B.z

Vector Normalize is also fairly easy:

Given vetor A and result vector r:
mag = sqrt((A.x)^2 + (A.y)^2 + (A.z)^2)
r.x = A.x / mag
r.y = A.y / mag
r.z = A.z / mag

Cross Product:

Given vector A, vector B, and result vertor r:
r.x = A.y * B.z - A.z * B.y
r.y = A.z * B.x - A.x * B.z
r.z = A.x * B.y - A.y * B.z

Z.