source: data/branches/Shader_HS18/programs/GLSL120/OffsetMappingVp.glsl

#version 120

uniform vec4 lightPosition; // object space
uniform vec3 eyePosition;   // object space
uniform mat4 worldViewProj; // not actually used but here for compat with HLSL

varying vec3 oEyeDir;
varying vec3 oLightDir;
varying vec3 oHalfAngle;
varying vec4 oUv0;

attribute vec3 normal;
attribute vec3 tangent;
attribute vec4 uv0;
attribute vec4 position;

/* Vertex program that moves light and eye vectors into texture tangent space at vertex */

void main()
{
    // Calculate output position
    gl_Position = worldViewProj * position;

    // Pass the main uvs straight through unchanged
    oUv0 = uv0;

    vec3 lightDir = lightPosition.xyz - (position.xyz * lightPosition.w);

    vec3 eyeDir = eyePosition - position.xyz;

    // Calculate the binormal (NB we assume both normal and tangent are
    // already normalised)
    // NB looks like nvidia cross params are BACKWARDS to what you'd expect
    // this equates to NxT, not TxN
    vec3 localbinormal = cross(tangent, normal);

    // Form a rotation matrix out of the vectors, column major for glsl es
        mat3 TBN = mat3(vec3(tangent[0], localbinormal[0], normal[0]),
                                                vec3(tangent[1], localbinormal[1], normal[1]),
                                                vec3(tangent[2], localbinormal[2], normal[2]));
    

    // Transform the light vector according to this matrix
    oLightDir = normalize(TBN * lightDir);
    oEyeDir = normalize(TBN * eyeDir);
    oHalfAngle = normalize(oEyeDir + oLightDir);
}