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rgibson11

OpenGL Weird light behaviour in bump mapping shader

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I implemented a test bump map shader from some tutorials and it produces great results, except the light, it is being affected by the camera direction. I want it to be fixed in global space. I cant find what seems to be the problem.

Vert:

uniform mat4 World;
uniform mat4 View;
uniform mat4 Proj;

attribute vec3 tangent;
attribute vec3 bitangent;

struct lightDataType
{
vec4 ambient;
vec4 diffuse;
vec4 specular;
vec4 position; // Position in eye coordinates
};

varying vec3 tbnDirToLight; // Direction to light in tangent space
varying vec3 tbnHalfVector; // Half vector in tangent space

uniform vec3 mEye; //Camera eye in global space?

void main (void)
{
mat4 VP = (Proj * View);
mat4 WVP = (Proj * View * World);
mat4 WV = (View * World);
mat4 W = World;
mat4 V = View;
mat4 P = Proj;

gl_Position = WVP * vec4(gl_Vertex.x, gl_Vertex.y, gl_Vertex.z, 1.0);

gl_TexCoord[0] = gl_MultiTexCoord0;

lightDataType light;
light.position = vec4(0, 5, 0, 1); //Not sure what goes here

vec3 mvNormal = vec3(WV * vec4(gl_Normal, 1.0)); //If its 0 at the end it produces incorrect results
vec3 mvTangent = vec3(WV * vec4(tangent, 1.0));
vec3 mvBinormal = vec3(WV * vec4(bitangent, 1.0));

vec3 mvVertex = vec3(WV * gl_Vertex);

//vec3 mvDirToEye = mEye - mvVertex;
vec3 mvDirToEye = -mvVertex;

vec3 tbnDirToEye;
tbnDirToEye.x = dot(mvDirToEye, mvTangent);
tbnDirToEye.y = dot(mvDirToEye, mvBinormal);
tbnDirToEye.z = dot(mvDirToEye, mvNormal);

vec3 mvDirToLight = vec3(light.position) - mvVertex;
tbnDirToLight.x = dot(mvDirToLight, mvTangent);
tbnDirToLight.y = dot(mvDirToLight, mvBinormal);
tbnDirToLight.z = dot(mvDirToLight, mvNormal);

tbnHalfVector = normalize(tbnDirToEye + tbnDirToLight);
}



Frag:

uniform sampler2D texUnit0; //Diffuse
uniform sampler2D texUnit1; //Normal
uniform sampler2D texUnit2; //Opacity, not used here
uniform sampler2D texUnit3; //Specular

struct lightDataType
{
vec4 ambient;
vec4 diffuse;
vec4 specular;
vec4 position;
};

varying vec3 tbnDirToLight;
varying vec3 tbnHalfVector;

void main(void)
{
lightDataType light;
light.ambient = vec4(0.4, 0.4, 0.4, 1.0);
light.diffuse = vec4(0.4, 0.4, 0.4, 1.0);
light.specular = vec4(0.45, 0.45, 0.45, 1.0);
float shininess = 100.0;

vec4 baseColour = texture2D(texUnit0, gl_TexCoord[0].xy);
vec3 normal = normalize(texture2D(texUnit1, gl_TexCoord[0].xy).xyz * 2.0 - 1.0);

//normal.y = -normal.y; //UNCOMMENT IF WRONG

vec4 ambient = light.ambient * baseColour;

vec3 tbnNormDirToLight = normalize(tbnDirToLight);
float diffuseIntensity = max(dot(tbnNormDirToLight, normal), 0.0);
vec4 diffuse = light.diffuse * baseColour * diffuseIntensity;
vec4 specular = vec4(0.0, 0.0, 0.0, 0.0);
if(diffuseIntensity > 0.0)
{
vec4 specularColour = texture2D(texUnit3, gl_TexCoord[0].xy);
float specularModifier = max(dot(normal, normalize(tbnHalfVector)), 0.0);
specular = light.specular * specularColour * pow(specularModifier, shininess);
}

gl_FragColor = clamp(ambient + diffuse + specular, 0.0, 1.0);
gl_FragColor.a = baseColour.a;
}



Im pretty sure its some mistake to do with opengl spaces, pls help.

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A vertex shader transforms vertices from world space into clipping coordinates space (screen space) (with the modelview-projection matrix), but also needs to transform the vectors, if they are fixed in world space. This is not evident, but you need another matrix to transform vectors : the normal matrix (gl_NormalMatrix). This is explained in the orange book, ch. 6.2.

When I want my light source to be fixed in global space (i.e. turning with the scene) I add the line :

LightPosition = vec3(gl_NormalMatrix * LightPosition);

And just remove it when I want the light fixed in screen coordinates (always coming from the same apparent direction)

I also apply this transformation to the normal, tangent and binormal vectors :

vec3 t,n,b;
n = vec3(gl_Normal);
n = normalize(gl_NormalMatrix * n);
t = Tangent;
t = normalize(gl_NormalMatrix * t);
b = cross(n, t);

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