source: downloads/Samples/Media/materials/programs/OffsetMappingVp.glsl @ 1

attribute vec3 tangent;

uniform vec4 lightPosition; // object space 
uniform vec4 lightPosition1; // object space 
uniform vec4 eyePosition;   // object space 
uniform vec4 spotDirection; // object space
uniform vec4 spotDirection1; // object space
uniform mat4 worldViewProj; // not actually used but here for compat with HLSL
uniform mat4 worldMatrix;
uniform mat4 texViewProj1;
uniform mat4 texViewProj2;


varying vec3 tangentEyeDir;
varying vec3 tangentLightDir[2];
varying vec3 tangentSpotDir[2];
varying vec4 shadowUV[2];

void main()
{
        gl_Position = ftransform();

        vec4 worldPos = worldMatrix * gl_Vertex;

        shadowUV[0] = texViewProj1 * worldPos;
        shadowUV[1] = texViewProj2 * worldPos;

        // pass the main uvs straight through unchanged 
        gl_TexCoord[0] = gl_MultiTexCoord0;

        // calculate tangent space light vector 
        // Get object space light direction 
    vec3 lightDir = normalize(lightPosition.xyz -  (gl_Vertex.xyz * lightPosition.w));
        vec3 lightDir1 = normalize(lightPosition1.xyz -  (gl_Vertex.xyz * lightPosition1.w));
        
        vec3 eyeDir = (eyePosition - gl_Vertex).xyz; 

        // Calculate the binormal (NB we assume both normal and tangent are 
        // already normalised) 
        vec3 binormal = cross(gl_Normal, tangent); 

        // Form a rotation matrix out of the vectors 
        mat3 rotation = mat3(tangent, binormal, gl_Normal); 
    
        // Transform the light vector according to this matrix 
        tangentLightDir[0] = normalize(rotation * lightDir); 
        tangentLightDir[1] = normalize(rotation * lightDir1); 
        // Invert the Y on the eye dir since we'll be using this to alter UVs and
        // GL has Y inverted
        tangentEyeDir = normalize(rotation * eyeDir) * vec3(1, -1, 1); 

        tangentSpotDir[0] = normalize(rotation * -spotDirection.xyz);
        tangentSpotDir[1] = normalize(rotation * -spotDirection1.xyz);  
}