ToonOutlines.osl

// Simple stylised shading node by Benjamin Mikhaiel
shader ToonOutlines(
    float thickness = 0.5,  //mindex's comma
    float tracedist = 50.0,
    float tracedistSteep = 100,
    float steepnessStrength = 1,
    float threshold = 0,
    float bias = -10,
    float Curvature = 0,
    float curvatureCrunch = 0,
    output color line = 1,
    output float dfDxOut = 0,
    output float dfDyOut = 0,
    output float fres = 0
)
{
    point points[4] = {point(-1.0, 1.0, 0.0),
                     point(1.0, 1.0, 0.0), 
                     point(-1.0, -1.0, 0.0),
                     point(1.0, -1.0, 0)};

    point finalPoints[8];

    point mainP = transform("world", "camera", P);
    //x left is -30? right is +30?
    //y up is +20? bottom is -20
    //z distance from camera 0 at cam, + value further away from camera



    fres = pow(1-clamp(dot(N, -normalize(I)), 0, 1), steepnessStrength);

    float scaledTraceDepth = mix(tracedistSteep, tracedist, fres);
    
    for (int i = 0; i < 4; i++)
    {
        // points around the position we want to check for an edge
        point samplePosition = mainP + (points[i] * thickness);
        // we then want to move the position towards the camera, so we need to move the bias distance along the vector to the camera.
        //back to world space?
        samplePosition = transform("camera", "world", samplePosition);
        finalPoints[i] = samplePosition - (normalize(I) * bias);
    }

        for (int i = 4; i < 8; i++)
    {
        // points around the position we want to check for an edge
        point samplePosition = mainP + (points[i - 4] * -thickness);
        // we then want to move the position towards the camera, so we need to move the bias distance along the vector to the camera.
        //back to world space?
        samplePosition = transform("camera", "world", samplePosition);
        finalPoints[i] = samplePosition - (normalize(I) * bias);
    }

    vector rayDir = normalize(I) * vector(-1.0, -1.0, -1.0);
    
    float traceXA = trace(finalPoints[0], rayDir, "maxdist", scaledTraceDepth);
    float traceXB = trace(finalPoints[1], rayDir, "maxdist", scaledTraceDepth);
    float traceYA = trace(finalPoints[2], rayDir, "maxdist", scaledTraceDepth);
    float traceYB = trace(finalPoints[3], rayDir, "maxdist", scaledTraceDepth);
    float traceXC = trace(finalPoints[4], rayDir, "maxdist", scaledTraceDepth);
    float traceXD = trace(finalPoints[5], rayDir, "maxdist", scaledTraceDepth);
    float traceYE = trace(finalPoints[6], rayDir, "maxdist", scaledTraceDepth);
    float traceYF = trace(finalPoints[7], rayDir, "maxdist", scaledTraceDepth);

    float dfDx = abs(traceXA - traceXB);
    float dfDy = abs(traceYB - traceYB);
    float dfDxB = abs(traceXC - traceXD);
    float dfDyB = abs(traceYE - traceYF);
    if (dfDx + dfDy + (Curvature - curvatureCrunch) > threshold)
    {
        line = 1;
    }
    else
    {
        line = 0;
    }

    if ((dfDxB + dfDyB) > threshold)
    {
        line += 1;
    }
    else
    {
        line += 0;
    }
}