Erakis

10-29-2001, 09:23 AM

Hello.

Your web site in very interresting (Congratulation !)

I have some problem with (Normals computing).

I already have a vectorial algebra course (School - Mathematic) and I well understand the way of calculating the normal vectors of one facet.

But my problem is knowing which facets do I choose among all those available when I built an object ?

EXEMPLE :

Suppose I want to draw a sphere like this one: http://astronomy.swin.edu.au/pbourke/opengl/sphere/

AND calculating normals facets MANUALLY...

The Problem

Is it better to compute each coords of sphere inside an array and use it after to compute the normal or I could compute it in same time.

I don't understand, cause to compute a normals facets, I need 3 vectors but in this exemple there are only 2 vectors at each glBegin(...) / glEnd.

How can I create the third vector ?

After picking the 3 vector, If understand well I have to do this :

Subtract 2 vector from the 3 vector by a matrix soustraction operation.

Do the Cross product of the result

Normalize the lenght of the result vector.

Could you help me just a little bit cause I don't find any docs on internet.

The docs I found, just related the way to compute normal but not USE it.

Martin

eraquila@bigfoot.com

PS : Thank to help me and excuse me to disturb you.

Your web site in very interresting (Congratulation !)

I have some problem with (Normals computing).

I already have a vectorial algebra course (School - Mathematic) and I well understand the way of calculating the normal vectors of one facet.

But my problem is knowing which facets do I choose among all those available when I built an object ?

EXEMPLE :

Suppose I want to draw a sphere like this one: http://astronomy.swin.edu.au/pbourke/opengl/sphere/

AND calculating normals facets MANUALLY...

The Problem

Is it better to compute each coords of sphere inside an array and use it after to compute the normal or I could compute it in same time.

I don't understand, cause to compute a normals facets, I need 3 vectors but in this exemple there are only 2 vectors at each glBegin(...) / glEnd.

How can I create the third vector ?

After picking the 3 vector, If understand well I have to do this :

Subtract 2 vector from the 3 vector by a matrix soustraction operation.

Do the Cross product of the result

Normalize the lenght of the result vector.

Could you help me just a little bit cause I don't find any docs on internet.

The docs I found, just related the way to compute normal but not USE it.

Martin

eraquila@bigfoot.com

PS : Thank to help me and excuse me to disturb you.