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ic0de

Whats wrong with my bump-map shader?

5 posts in this topic

so I wrote a normal mapping shader in glsl but it doesn't appear to work, the normal map screws lighting up royally.

here's my shader :

vertex:
[code]


varying vec3 v;

void main(void)
{

v = vec3(gl_ModelViewMatrix * gl_Vertex);

gl_TexCoord[0] = gl_MultiTexCoord0;
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}
[/code]

fragment:
[code]

varying vec2 vTexCoord;

varying vec3 v;

uniform sampler2D Texture;
uniform sampler2D normalTexture;

void main(void)
{

vec3 normal = normalize(texture2D(normalTexture, gl_TexCoord[0].st).rgb * 2.0 - 1.0);
normal = normalize (normal);

vec3 lightpos = normalize(gl_LightSource[0].position.xyz - v);
vec3 eyevec = normalize(-v);
vec3 reflection = normalize(-reflect(lightpos, normal));
vec4 ambient, specular, diffuse;
vec4 texcolor = texture2D(Texture, vec2(gl_TexCoord[0]));

vec4 finalcolor;

float L_Term = dot(normal, lightpos);

ambient = (gl_FrontLightModelProduct.sceneColor * gl_FrontMaterial.ambient) + gl_FrontLightProduct[0].ambient * gl_FrontMaterial.ambient;

if(L_Term > 0.0)
{

specular = gl_LightSource[0].specular * gl_FrontMaterial.specular * (pow( max(dot(reflection, eyevec), 0.0), gl_FrontMaterial.shininess ));

diffuse = gl_FrontLightProduct[0].diffuse * gl_FrontMaterial.diffuse * max(dot(normal, lightpos), 0.0);

finalcolor = (texcolor) * (ambient + specular + diffuse);

}
else
{
finalcolor = (texcolor) * ambient;
}

gl_FragColor = finalcolor;
}

[/code]

so what did I do wrong?
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At the moment, your code is written to use world-space normal-maps. Is that intended?

You don't have vertex streams for normals/tangents/binormals, which means you're unable to properly decode a tangent-space normal map (the kind where flat areas a bluish).

Also, your calculation of eyevec seems suspect - this should be a vector between the pixel and the eye, but it seems as if you're getting a direction between the origin and the eye.
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[quote name='Hodgman' timestamp='1323233970' post='4891345']
At the moment, your code is written to use world-space normal-maps. Is that intended?

You don't have vertex streams for normals/tangents/binormals, which means you're unable to properly decode a tangent-space normal map (the kind where flat areas a bluish).

Also, your calculation of eyevec seems suspect - this should be a vector between the pixel and the eye, but it seems as if you're getting a direction between the origin and the eye.
[/quote]

Thanks

How can I calculate the tangent/binormal? Can I do this inside the shader? And also what would be the "correct" way to calculate eyevec
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you need to provide tangents
you can find binormal with cross(normal, tangent)

and eye vector is usually v_eye = normalize(-positon.xyz) * tbnMatrix; in the vertex shader
where position is the world-space position of vertices

youll have to do the same to v_light... v_light = normalize(lightposition.xyz) * tbn;
aka converting it to tangent / texture space

youll have to rotate normal, tangent and binormal, using gl_NormalMatrix
and normalize them, you can do that in the same line as you make the tbn matrix:

tbn matrix is: mat3 tbn = gl_NormalMatrix * mat3(tangent, binormal, normal);

notice how i multiply matrix AT THE END, instead of the usual at the start
its the same as transpose of tbn * vector
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[quote name='Kaptein' timestamp='1323273568' post='4891488']
you need to provide tangents
you can find binormal with cross(normal, tangent)

and eye vector is usually v_eye = normalize(-positon.xyz) * tbnMatrix; in the vertex shader
where position is the world-space position of vertices

youll have to do the same to v_light... v_light = normalize(lightposition.xyz) * tbn;
aka converting it to tangent / texture space

youll have to rotate normal, tangent and binormal, using gl_NormalMatrix
and normalize them, you can do that in the same line as you make the tbn matrix:

tbn matrix is: mat3 tbn = gl_NormalMatrix * mat3(tangent, binormal, normal);

notice how i multiply matrix AT THE END, instead of the usual at the start
its the same as transpose of tbn * vector
[/quote]

I read somewhere that I could find the tangent in the vertex shader like so:

[code]
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);
[/code]

Is this sufficient to use in my bump map shader
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probably not, you most likely will have to provide tangents along with normals... using attributes
its probably best if you move from standard vertex struct to a user defined one, using vertexattrib and VAOs
if theres anything you need help with on that part i can post some of my code and compare it
openGL is hillariously undocumented, and more often than not i seem to be reading the specifications for each and every thing i have to use =)

either way, make sure you have tangents to start with and go from there
im sure someone can explain why trying to make tangents is a bad idea, but i dont know why...
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