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#ifndef TESSELLATION_NPATCH_GLSLLIB
#define TESSELLATION_NPATCH_GLSLLIB

struct NPatchTessPatch
{
    float b210;
    float b120;
    float b021;
    float b012;
    float b102;
    float b201;
    float b111;
    float n110;
    float n011;
    float n101;
    float t110;
    float t011;
    float t101;
};

#if TESSELLATION_CONTROL_SHADER
layout (vertices = 3) out;

layout(location=15) out NPatchTessPatch tcTessPatch[];

// global setup in main
vec3 ctWorldPos[3];
vec3 ctNorm[3];
vec3 ctTangent[3];

uniform vec3 camera_position;
uniform vec2 distanceRange;
uniform float disableCulling;

float isBackFace()
{
    vec3 faceNormal = normalize( cross( ctWorldPos[2] - ctWorldPos[0], ctWorldPos[1] - ctWorldPos[0] ) );

    vec3 ncd = normalize( ctWorldPos[0] - camera_position );

    return sign( 0.2 + dot(faceNormal, ncd) ); // 0.2 is a conservative offset to account for curved surfaces
}

float adaptiveCameraFactor( in float minTess, in float maxTess )
{
    float distanceValue0 = distance( camera_position, ctWorldPos[0] );
    float distanceValue1 = distance( camera_position, ctWorldPos[1] );
    float distanceValue2 = distance( camera_position, ctWorldPos[2] );

    float range = distanceRange[1] - distanceRange[0];

    vec3 edgeDistance;
    edgeDistance[0] = ((distanceValue1 + distanceValue2) / 2.0) / range;
    edgeDistance[1] = ((distanceValue2 + distanceValue0) / 2.0) / range;
    edgeDistance[2] = ((distanceValue0 + distanceValue1) / 2.0) / range;

    edgeDistance = clamp( edgeDistance, vec3(0.0), vec3(1.0) );

    //float af = mix( minTess, maxTess,  1.0 - edgeDistance[gl_InvocationID] );
    float af = 1.0 - edgeDistance[gl_InvocationID];
    af = clamp( af*af*maxTess , minTess, maxTess );

    return af;
}

float adaptiveFeatureFactor( in float minTess, in float maxTess )
{
    vec3 adaptValue;
    adaptValue[0] = clamp( dot(ctNorm[1], ctNorm[2]), -1.0, 1.0 );
    adaptValue[1] = clamp( dot(ctNorm[2], ctNorm[0]), -1.0, 1.0 );
    adaptValue[2] = clamp( dot(ctNorm[0], ctNorm[1]), -1.0, 1.0 );

    //float af = min( adaptValue[0], min(adaptValue[1], adaptValue[2]) );
    // map [-1, +1] range to [0, 1] range
    float af = (adaptValue[gl_InvocationID] + 1.0) / 2.0;

    af = mix( minTess, maxTess,  1.0 - af );

    return af;
}

float getwij(int i, int j)
{
    return dot(gl_in[j].gl_Position.xyz - gl_in[i].gl_Position.xyz, ctNorm[i]);
}

float getvij(int i, int j)
{
    vec3 pji = gl_in[j].gl_Position.xyz - gl_in[i].gl_Position.xyz;
    vec3 nij = ctNorm[i] + ctNorm[j];

    return 2.0*dot(pji, nij)/dot(pji, pji);
}

void tessShader ( in float tessEdge, in float tessInner )
{
    // setup control points
    // notations and formulas see http://alex.vlachos.com/graphics/CurvedPNTriangles.pdf
    // note we compute separate x,y,z component for each invocation
    float b300 = gl_in[0].gl_Position[gl_InvocationID];
    float b030 = gl_in[1].gl_Position[gl_InvocationID];
    float b003 = gl_in[2].gl_Position[gl_InvocationID];
    float n200 = ctNorm[0][gl_InvocationID];
    float n020 = ctNorm[1][gl_InvocationID];
    float n002 = ctNorm[2][gl_InvocationID];
    float t200 = ctTangent[0][gl_InvocationID];
    float t020 = ctTangent[1][gl_InvocationID];
    float t002 = ctTangent[2][gl_InvocationID];

    // compute tangent control points
    tcTessPatch[gl_InvocationID].b210 = (2.0*b300 + b030 - getwij(0,1)*n200)/3.0;
    tcTessPatch[gl_InvocationID].b120 = (2.0*b030 + b300 - getwij(1,0)*n020)/3.0;
    tcTessPatch[gl_InvocationID].b021 = (2.0*b030 + b003 - getwij(1,2)*n020)/3.0;
    tcTessPatch[gl_InvocationID].b012 = (2.0*b003 + b030 - getwij(2,1)*n002)/3.0;
    tcTessPatch[gl_InvocationID].b102 = (2.0*b003 + b300 - getwij(2,0)*n002)/3.0;
    tcTessPatch[gl_InvocationID].b201 = (2.0*b300 + b003 - getwij(0,2)*n200)/3.0;
    // compute center control point
    float E = ( tcTessPatch[gl_InvocationID].b210
              + tcTessPatch[gl_InvocationID].b120
              + tcTessPatch[gl_InvocationID].b021
              + tcTessPatch[gl_InvocationID].b012
              + tcTessPatch[gl_InvocationID].b102
              + tcTessPatch[gl_InvocationID].b201 ) / 6.0;

    float V = ( b300 + b030 + b003 ) / 3.0;
    tcTessPatch[gl_InvocationID].b111 = E + (E-V)*0.5;

    // compute normals
    tcTessPatch[gl_InvocationID].n110 = n200 + n020 - getvij(0,1) * (b030 - b300);
    tcTessPatch[gl_InvocationID].n011 = n020 + n002 - getvij(1,2) * (b003 - b030);
    tcTessPatch[gl_InvocationID].n101 = n002 + n200 - getvij(2,0) * (b300 - b003);
    // compute tangents
    tcTessPatch[gl_InvocationID].t110 = t200 + t020 - getvij(0,1) * (b030 - b300);
    tcTessPatch[gl_InvocationID].t011 = t020 + t002 - getvij(1,2) * (b003 - b030);
    tcTessPatch[gl_InvocationID].t101 = t002 + t200 - getvij(2,0) * (b300 - b003);

    // compute backface
    float bf = isBackFace();
    bf = max(disableCulling, bf);

    // adapative tessellation factor regarding features
    float af = adaptiveFeatureFactor( tessInner, tessEdge );

    //float cf = adaptiveCameraFactor( tessInner, tessEdge );

    // Calculate the tessellation levels
    gl_TessLevelInner[0] = af * bf;
    gl_TessLevelOuter[gl_InvocationID] = af * bf;
}

#endif

#if TESSELLATION_EVALUATION_SHADER
layout (triangles, fractional_odd_spacing, ccw) in;

layout(location=15) in NPatchTessPatch tcTessPatch[];

// global setup in main
vec3 ctNorm[3];
vec3 teNorm;
vec3 ctTangent[3];
vec3 teTangent;
vec3 teBinormal;

bool doLinear(int i, int j)
{
    /*
    vec3 edgeji = gl_in[j].gl_Position.xyz - gl_in[i].gl_Position.xyz;

    float di = sign( dot( ctNorm[i], edgeji ) );
    float dj = sign( dot( ctNorm[j], -edgeji ) );

    if ( di != dj )
        return false;
    else
        return true;*/

    // Always do linear normal interpolation for now
    // Seems to produce always good results unless we would produce
    // a s-shaped triangle.
    return true;
}

vec4 tessShader ( )
{
    // pre compute square tesselation coord
    vec3 tessSquared = gl_TessCoord * gl_TessCoord;
    vec3 tessCubed = tessSquared * gl_TessCoord;

    // combine control points
    vec3 b210 = vec3(tcTessPatch[0].b210, tcTessPatch[1].b210, tcTessPatch[2].b210);
    vec3 b120 = vec3(tcTessPatch[0].b120, tcTessPatch[1].b120, tcTessPatch[2].b120);
    vec3 b021 = vec3(tcTessPatch[0].b021, tcTessPatch[1].b021, tcTessPatch[2].b021);
    vec3 b012 = vec3(tcTessPatch[0].b012, tcTessPatch[1].b012, tcTessPatch[2].b012);
    vec3 b102 = vec3(tcTessPatch[0].b102, tcTessPatch[1].b102, tcTessPatch[2].b102);
    vec3 b201 = vec3(tcTessPatch[0].b201, tcTessPatch[1].b201, tcTessPatch[2].b201);
    vec3 b111 = vec3(tcTessPatch[0].b111, tcTessPatch[1].b111, tcTessPatch[2].b111);

    // combine control normals
    vec3 n110 = vec3(tcTessPatch[0].n110, tcTessPatch[1].n110, tcTessPatch[2].n110);
    vec3 n011 = vec3(tcTessPatch[0].n011, tcTessPatch[1].n011, tcTessPatch[2].n011);
    vec3 n101 = vec3(tcTessPatch[0].n101, tcTessPatch[1].n101, tcTessPatch[2].n101);

    // combine control tangents
    vec3 t110 = vec3(tcTessPatch[0].t110, tcTessPatch[1].t110, tcTessPatch[2].t110);
    vec3 t011 = vec3(tcTessPatch[0].t011, tcTessPatch[1].t011, tcTessPatch[2].t011);
    vec3 t101 = vec3(tcTessPatch[0].t101, tcTessPatch[1].t101, tcTessPatch[2].t101);

    // NPatch normal
    if ( doLinear( 0, 1 ) == true )
    {
        // linear normal
        teNorm = ctNorm[0] * gl_TessCoord[2]
                + ctNorm[1] * gl_TessCoord[0]
                + ctNorm[2] * gl_TessCoord[1];
        // NPatch tangent
        teTangent = ctTangent[0] * gl_TessCoord[2]
                  + ctTangent[1] * gl_TessCoord[0]
                  + ctTangent[2] * gl_TessCoord[1];
    }
    else
    {
        // quadratic normal
        teNorm = ctNorm[0] * tessSquared[2]
                + ctNorm[1] * tessSquared[0]
                + ctNorm[2] * tessSquared[1]
                + n110*gl_TessCoord[2] * gl_TessCoord[0]
                + n011*gl_TessCoord[0] * gl_TessCoord[1]
                + n101*gl_TessCoord[2] * gl_TessCoord[1];

        // NPatch tangent
        teTangent = ctTangent[0] * tessSquared[2]
                  + ctTangent[1] * tessSquared[0]
                  + ctTangent[2] * tessSquared[1]
                  + t110*gl_TessCoord[2] * gl_TessCoord[0]
                  + t011*gl_TessCoord[0] * gl_TessCoord[1]
                  + t101*gl_TessCoord[2] * gl_TessCoord[1];
    }

    // NPatch binormal
    teBinormal = cross( teNorm, teTangent );

    // npatch interpolated position
    vec3 finalPos = gl_in[0].gl_Position.xyz * tessCubed[2]
                   + gl_in[1].gl_Position.xyz * tessCubed[0]
                   + gl_in[2].gl_Position.xyz * tessCubed[1]
                   + b210 * 3.0 * tessSquared[2] * gl_TessCoord[0]
                   + b120 * 3.0 * tessSquared[0] * gl_TessCoord[2]
                   + b201 * 3.0 * tessSquared[2] * gl_TessCoord[1]
                   + b021 * 3.0 * tessSquared[0] * gl_TessCoord[1]
                   + b102 * 3.0 * tessSquared[1] * gl_TessCoord[2]
                   + b012 * 3.0 * tessSquared[1] * gl_TessCoord[0]
                   + b111 * 6.0 * gl_TessCoord[0] * gl_TessCoord[1] * gl_TessCoord[2];

    return vec4( finalPos, 1.0 );
}
#endif

#endif