Thin film OSL shader

[^Lele^]

that's how it ought to be used.
Make sure you turn fresnel off, as it's got its own one!

[Morbid Angel]

makes sense...that's why I had to crank the shader fresnel! I'll correct it tomorrow.

[^Lele^]

lol! yeas, that'd make sense!
You can wire me a few hundred bucks at your own leisure

[Fredrik Averpil]

Wow!

Simon, who sits next to me in our office saw this and downloaded, gave it a test run ... and wow, just wow!
Thanks so much for sharing!

[Fredrik Averpil]

By the way - I totally missed this just because you're posting this in a max sub-forum. God knows how much goodies I've missed because of this (being a Maya user) ...

[^Lele^]

A particular use of the iridescence shader, coupled with a flakes normal texture, in a blend material, to generate a carpaint with iridescent flakes.
Scene and shaders are attached, just grab yourself an HDRI in place of mine.



OSL_carPaint_with_iridescence.zip

[^Lele^]

And a slightly tweaked, less pronounced, shader (chiefly, i changed each layer's influence, and the flakes' normals orientation variance).



A word of notice: you WILL need many AA Rays AND a reconstructive filter on the rendered image to make sure the flakes won't shimmer in an animation.
This is a need forced by the fact that the flakes map does no filtering on its own, so we have to burden VRay with it.
This last one was rendered with a fixed-12 and a sharp quadratic filter.

EDIT: made a mistake earlier. Corrected now, max 2014 scene added, along with the flakes OSL shader with descriptions for each spinner.

OSL_carPaint_with_iridescence_B.zip

[Joelaff]

Cool, Lele!

[pg1]

Seems to broken on 2015?

I get this error
In the material compiler output
Could not compile shader J:\Jobs\46761M_Mazda2Headlight_CP\3d\Projects\Maps \irridescence.osl (OSL to OSO)

[Morbid Angel]

Seems to broken on 2015?

I get this error
In the material compiler output
Could not compile shader J:\Jobs\46761M_Mazda2Headlight_CP\3d\Projects\Maps \irridescence.osl (OSL to OSO)

yup same here...any ideas?

[sharktacos]

yup same here...any ideas?

Don't know if this is relevant in Max, but in Maya the outputs and results need to be called "color". Try this:

/* Amplitude reflection coefficient (s-polarized) */
float rs(float n1, float n2, float cosI, float cosT) {
    return (n1 * cosI - n2 * cosT) / (n1 * cosI + n2 * cosT);
}
 
/* Amplitude reflection coefficient (p-polarized) */
float rp(float n1, float n2, float cosI, float cosT) {
    return (n2 * cosI - n1 * cosT) / (n1 * cosT + n2 * cosI);
}
 
/* Amplitude transmission coefficient (s-polarized) */
float ts(float n1, float n2, float cosI, float cosT) {
    return 2 * n1 * cosI / (n1 * cosI + n2 * cosT);
}
 
/* Amplitude transmission coefficient (p-polarized) */
float tp(float n1, float n2, float cosI, float cosT) {
    return 2 * n1 * cosI / (n1 * cosT + n2 * cosI);
}
 
// cosI is the cosine of the incident angle, that is, cos0 = dot(view angle, normal)
// lambda is the wavelength of the incident light (e.g. lambda = 510 for green)
// From http://www.gamedev.net/page/resources/_/technical/graphics-programming-and-theory/thin-film-interference-for-computer-graphics-r2962
float thinFilmReflectance(float cos0, float lambda, float thickness, float n0, float n1, float n2) {
    //float PI=3.1415926535897932384626433832795;
    float PI=M_PI;

    // compute the phase change term (constant)
    float d10 = (n1 > n0) ? 0 : PI;
    float d12 = (n1 > n2) ? 0 : PI;
    float delta = d10 + d12;
     
    // now, compute cos1, the cosine of the reflected angle
    float sin1 = pow(n0 / n1, 2) * (1 - pow(cos0, 2));
    if (sin1 > 1) return 1.0; // total internal reflection
    float cos1 = sqrt(1 - sin1);
     
    // compute cos2, the cosine of the final transmitted angle, i.e. cos(theta_2)
    // we need this angle for the Fresnel terms at the bottom interface
    float sin2 = pow(n0 / n2, 2) * (1 - pow(cos0, 2));
    if (sin2 > 1) return 1.0; // total internal reflection
    float cos2 = sqrt(1 - sin2);
     
    // get the reflection transmission amplitude Fresnel coefficients
    float alpha_s = rs(n1, n0, cos1, cos0) * rs(n1, n2, cos1, cos2); // rho_10 * rho_12 (s-polarized)
    float alpha_p = rp(n1, n0, cos1, cos0) * rp(n1, n2, cos1, cos2); // rho_10 * rho_12 (p-polarized)
     
    float beta_s = ts(n0, n1, cos0, cos1) * ts(n1, n2, cos1, cos2); // tau_01 * tau_12 (s-polarized)
    float beta_p = tp(n0, n1, cos0, cos1) * tp(n1, n2, cos1, cos2); // tau_01 * tau_12 (p-polarized)
         
    // compute the phase term (phi)
    float phi = (2 * PI / lambda) * (2 * n1 * thickness * cos1) + delta;
         
    // finally, evaluate the transmitted intensity for the two possible polarizations
    float ts = pow(beta_s, 2) / (pow(alpha_s, 2) - 2 * alpha_s * cos(phi) + 1);
    float tp = pow(beta_p, 2) / (pow(alpha_p, 2) - 2 * alpha_p * cos(phi) + 1);
     
    // we need to take into account conservation of energy for transmission
    float beamRatio = (n2 * cos2) / (n0 * cos0);
     
    // calculate the average transmitted intensity (if you know the polarization distribution of your
    // light source, you should specify it here. if you don't, a 50%/50% average is generally used)
    float t = beamRatio * (ts + tp) / 2;
     
    // and finally, derive the reflected intensity
    return 1 - t;
}
 
shader irridescence
[[ string description = "Thin film coating shader. Use as reflection color for the material, with Fresnel for the material OFF (this texture computes its own Fresnel)" ]]
(   
 float thicknessMin = 250 [[ string description = "Minimum thickness of the film, in nm" ]],
 float thicknessMax = 400 [[ string description = "Maximum thickness of the film, in nm" ]],
 string thickness = "test.png" [[ string description = "Texture map (usually noise) that determines the thickness of the film as fraction between the min and max" ]],
 float nmedium = 1 [[ string description = "Refractive index of the outer medium (typically air)" ]], // approximate refractive index of air   
 float nfilm = 1.5 [[ string description = "Refractive index of the thin film itself" ]] , // approximate refractive index of water   
 float ninternal = 1 [[ string description = "Refractive index of the material below the film" ]], // approximate refractive index of the lower material
 output color result = 0   
)   
{   
 float cos0 = abs(dot(I , N));
  
 color thickTex=texture(thickness, u, v);
 float t=(thickTex[0]+thickTex[1]+thickTex[2])/3.0;
 float thick=thicknessMin*(1.0-t)+thicknessMax*t;
  
 float red=thinFilmReflectance(cos0, 650, thick, nmedium, nfilm, ninternal);
 float green=thinFilmReflectance(cos0, 510, thick, nmedium, nfilm, ninternal);
 float blue=thinFilmReflectance(cos0, 475, thick, nmedium, nfilm, ninternal);
  
 result=color(red, green, blue);
}

[Macker]

Any news on building this into the Vray Shader? (perhaps under its own tab?)

I'm sure this could be used to create dichroic glass, could it not?

[DjordjeIlic]

Hi everyone.

I looking for some iridescent reflection....I tried OSL thin film,
but not working in Maya 2016-sp6.same osl working very well in max.

Thank you!
Djordje

[vlado]

Which V-Ray version and which OS?

Best regards,
Vlado

[sharktacos]

Instead of adding this to the VrayMtl (if folks are worried about clutter), how about having this as a new VrayTexture that ships with Vray?