Calculating Tangent attribute bumpmapping

[rrarunan]

From the GLSL bumpmapping tutorial :

       The line :-

       "The new thing is the T vector which is also provided by the 3d engine
       but as a vertex attribute (attribute key word in GLSL code)."

       I\'ve looked at a lot of references and I\'m still looking for a way to     :?:
       calculate the TANGENT , T Vector given a vertex and normal..

       Can anyone please help me?

[JeGX]

Hi rrarunan,

the calculation of the tangent vector is not an easy task.
But here is a little piece of GLSL code that shows you how to calculate the tangent and binormal vectors from the vertex normal only:

Code: [Select]


vec3 tangent;
vec3 binormal;

vec3 c1 = cross( gl_Normal, vec3(0.0, 0.0, 1.0) );
vec3 c2 = cross( gl_Normal, vec3(0.0, 1.0, 0.0) );

if( length(c1)>length(c2) )
{
tangent = c1;
}
else
{
tangent = c2;
}

tangent = normalize(tangent);

binormal = cross(gl_Normal, tangent);
binormal = normalize(binormal);


This piece of code is a part of a forthcoming tutorial.  
Hope that will help you!

[rrarunan]

Thanks for the code..  I really appreciate it..

 I just have two quick questions..

a)  does this mean , I can just pass the normal per-vertex and find the tangent and bi-normal vectors for the tangent space transformation?

b) While texturing the cube (I'm using a cube), do I have to texture it with just the colorMap or both the color and the normal maps..

- Arunan

 :?

[JeGX]

a - yes, per vertex-normal is enough to find tangent and bi-normal vectors.
b - you only need the color map to texture your cube. The normal map is only used to orientate the per-pixel normal used in diffuse and specular calculations.

[rrarunan]

Thank you for the info..

Arunan