source: GTP/trunk/App/Demos/Illum/Ogre/Media/Towers/parallax.hlsl @ 2550

uniform float textureRepeat;
uniform sampler2D ColorMapSampler : register(s0);
uniform sampler2D DetailMapSampler   : register(s1);
uniform sampler2D BumpMapSampler  : register(s2);
#define PARALLAX_ITERATION 4
uniform float HEIGHT_SCALE;
uniform float HEIGHT_BIAS;

float3x3 TransfModelToTangent( in  float3 Tangent, in float3 Binormal, in float3 Normal ) {
        float T2 = dot(Tangent, Tangent);
        float B2 = dot(Binormal, Binormal);
        float N2 = dot(Normal, Normal);
        float BT = dot(Binormal, Tangent);
        float det = B2 * T2 - BT * BT;

        //return float3x3( (B2 * Tangent - BT * Binormal)/det, 
        //                 (T2 * Binormal - BT * Tangent)/det, 
        //                 Normal/N2 );
                                                        
        // simplified solution
        //return float3x3(Tangent/T2, Binormal/B2, Normal/N2); 
        // more simplified solution
        return float3x3(Tangent, Binormal, Normal);
}

float4 Illumination(float3 Light, float3 Normal, float3 View, float2 TexCoord, float2 TexCoord2)
{
        // Blinn lighting
        float3 Half = normalize(Light + View);
        float Diffuse = dot(Normal, Light);
        float Specular = dot(Normal, Half);
        float4 Lighting = lit(Diffuse, Specular, 16);
        float4 Color= tex2D(ColorMapSampler, TexCoord) * tex2D(DetailMapSampler, TexCoord2);

        return (Lighting.y + 0.1) * Color;
}

struct VS_OUTPUT {
    float4 hPosition : POSITION;     // point in normalized device space before homogeneous division
    float2 TexCoord  : TEXCOORD0;    // texture coordinates
    float2 TexCoord2  : TEXCOORD6;    // texture coordinates
    float3 mView     : TEXCOORD1;    // model space view vector
    float3 mLight    : TEXCOORD2;    // model space light vector
    float3 wTangent   : TEXCOORD3;       // model space tangent vector
    float3 wBinormal  : TEXCOORD4;       // model space binormal vector
    float3 wNormal    : TEXCOORD5;       // model space triangle normal vector
};

void DISCARD_BY_TEX(float2 Tex)
{
        if (Tex.x > textureRepeat || Tex.x < 0 || Tex.y > textureRepeat || Tex.y < 0)
                discard;
}

float2 PARALLAX_MAPPING_OFFSET_LIMIT(sampler2D heightMap, float2 TexCoord, float3 View)
{
    float4 Normal = tex2D(heightMap, TexCoord);
    float h = Normal.a * HEIGHT_SCALE + HEIGHT_BIAS;
    return TexCoord + h * View.xy;
}

float2 PARALLAX_MAPPING_ITER(sampler2D heightMap, float2 TexCoord, float3 View)
{
    for(int i = 0; i < PARALLAX_ITERATION; i++) {
                float4 Normal = tex2D(heightMap, TexCoord);
                float h = Normal.a * HEIGHT_SCALE + HEIGHT_BIAS;
                TexCoord += h * Normal.z * View;
        }
        return TexCoord.xy;
}

//------------------------------------------------------------------------------------
//
// ParallaxSlopeIterationPS: Iterative Parallax Mapping with Slope pixel shader
//
//------------------------------------------------------------------------------------
float4 ParallaxSlopeIterationPS(VS_OUTPUT IN) : COLOR
{
        //return tex2D(BumpMapSampler,IN.TexCoord).a;
        IN.wTangent = normalize(IN.wTangent);
        IN.wBinormal = normalize(IN.wBinormal);
        IN.wNormal = normalize(IN.wNormal);
        // get model space normal vector
        float3x3 ModelToTangent = TransfModelToTangent(IN.wTangent, IN.wBinormal, IN.wNormal );
        // needs normalization because of linear interpolation    
    float3 mLight = normalize( IN.mLight );
    float3 mView = normalize( IN.mView );
        float3 tView = normalize( mul(ModelToTangent, IN.mView ) );
     
    // performing parallax mapping
    float2 ParallaxTex = PARALLAX_MAPPING_OFFSET_LIMIT(BumpMapSampler, IN.TexCoord, tView);
        DISCARD_BY_TEX(ParallaxTex);
        
    // get model space normal vector
    //ParallaxTex = IN.TexCoord;
    float3 tNormal = tex2D(BumpMapSampler, ParallaxTex).rgb;
        // Normal vector should be transformed with the inverse transpose of TangentToModel
        // which is the transpose of ModelToTangent
    float3 mNormal = normalize( mul( tNormal, ModelToTangent ) ); 
        //mNormal = normalize(IN.wNormal);

    // illumination calculation

    return Illumination(mLight, mNormal, mView, ParallaxTex, IN.TexCoord2);
}