What is the word on using gl_NormalMatrix inside a fragment shader in OpenGL 2.0 ? I am using NVIDIA Quadro FX 500 with 61.76 driver gl_NormalMatrix does not seem to have any effect for transforming vectors or even points. Any advice would be of help. Thanks!

a code snippet would be helpfull....

Fragment Shader:-
-----------------
uniform sampler2D decalTexture;
uniform sampler2D bumpMapTexture;
uniform samplerCube cubeMapTexture;

varying vec2 texCoord;

varying vec3 T, B, N;
varying vec3 V, L;
varying vec3 cmV;


void main(void)
{
T = normalize(T);
B = normalize(B);
N = normalize(N);

V = normalize(V);
L = normalize(L);

cmV = normalize(cmV);

vec3 view, light, half;

/* Transform V & L to tangent-space and compute half vector */
view.x = dot(T, V);
view.y = dot(B, V);
view.z = dot(N, V);

light.x = dot(T, L);
light.y = dot(B, L);
light.z = dot(N, L);

half = normalize(light + view);

/* Fetch the Decal color and tangent-space normal */
vec3 decal = vec3 (texture2D(decalTexture, texCoord));
vec3 normal = vec3 (texture2D(bumpMapTexture, texCoord));

normal.x = 2.0 * normal.x - 1.0;
normal.y = 2.0 * normal.y - 1.0;
normal.z = 2.0 * normal.z - 1.0;

/* Compute Diffuse and Specular components */
float ndotl = max(dot(normal, light), 0.0);
float ndoth = pow(max(dot(normal, half), 0.0), 60.0);

/* Transform normal from Tangent-space to World space */
vec3 t = vec3(T.x, B.x, N.x);
vec3 b = vec3(T.y, B.y, N.y);
vec3 n = vec3(T.z, B.z, N.z);

vec3 cmNormal;
cmNormal.x = dot(t, normal);
cmNormal.y = dot(b, normal);
cmNormal.z = dot(n, normal);

/* Transform normal from World space to cubemap space */
cmNormal = vec3 (gl_NormalMatrix * cmNormal);
cmNormal = normalize(cmNormal);

vec3 refVector = reflect(-cmV, cmNormal);

vec3 refColor = vec3 (textureCube(cubeMapTexture, refVector));

vec3 fColor;
fColor.x = ndotl * (decal.x + refColor.x) + ndoth;
fColor.y = ndotl * (decal.y + refColor.y) + ndoth;
fColor.z = ndotl * (decal.z + refColor.z) + ndoth;

gl_FragColor = vec4 (vec3(fColor), 1.0);
}

----------------------------------------------------------------
I implemented the same method using ARB Vertex/fragment programs and it works perfectly.

The reason I declared T, B, N as varying is because I am not able to fetch the BumpMap normal inside the vertex shader.

I tested the rest of the stuff like (diffuse, specular, bumpshading) by changing the argument fColor in the last statment:

gl_FragColor = vec4 (vec3(fColor), 1.0);

to ndotl, ndoth respectively.

I tried using gl_NormalMatrix, glModelViewMatrix and even glTextureMatrix[0] (by loading the Inverse of the modelview transform into the texture unit 0 texture matrix stack). All gave the same effect no change.

Any clue would of great help, Thank you!

---------------------------------------------------------------
Below is the vertex and fragment shader for cube environment mapping which works perfectly.

Vertex Shader:-
---------------
varying vec3 N;
varying vec3 V;


void main(void)
{
gl_Position = ftransform();

vec3 vertex = vec3 (gl_ModelViewMatrix * gl_Vertex);

V = normalize(-vertex);

N = vec3 (gl_NormalMatrix * gl_Normal);
}

Fragment Shader:-
------------------
uniform samplerCube cubeMapTexture;

varying vec3 N;
varying vec3 V;


void main(void)
{
vec3 view = normalize(V);
vec3 normal = normalize(N);

vec3 refVector = reflect(-view, normal);

vec3 refColor = vec3 (textureCube(cubeMapTexture, refVector));

gl_FragColor = vec4 (vec3(refColor), 1.0);
}
----------------------------------------------------------------

The orange book (OpenGL Shading Language) says it can be accessed and used in both the vertex and fragment shaders.

So if I can't access texture units inside a vertex shader and gl_normalMatrix does not have any effect inside the fragment shader, how do I get to implement my reflective bump mapping ?

I guess the only way is to send the gl_NormalMatrix from the application to tha gragment program as a uniform variable.

Did NVIDIA comment on this anywhere ?

Thanks!

gl_NormalMatrix is a built-in variable in glsl. Take a look at section 7.5 of the OpenGL shading language specification.

gl_NormalMatrix is the inverse transpose of the upper 3x3 part of the modelview matrix.

James,

Thank you for the pointer, I know it is a built-in variable.

What I am saying is it is not working inside the fragment shader like it does inside the vertex shader. Do you know why ?

Thanks!

I'm sorry, I should probably have read your post more thoroughly first...
I have a radeon 9600, and use RenderMonkey for coding GLSL shaders all the time. I consistently use gl_NormalMatrix, and there's no problem...

Here's some code that does per-pixel Phong shading:

Vertex shader:


Fragment shader:


Here gl_NormalMatrix is used to transform the normal vectors in the vertex shader. If you remove gl_NormalMatrix, you're going to get some weird and wrong results. Why don't you try it?