Blender 3D : Glass material with Open Shading Language.

Open Shading Language (OSL) is a small but rich language for programmable shading in advanced renderers and other applications, ideal for describing materials, lights, displacement, and pattern generation.

OSL was originally developed by Sony Pictures Imageworks for use in its in- house renderer used for feature film animation and visual effects, released as open source so it could be used by other visual effects and animation studios and rendering software vendors. Now it's the de facto standard shading language for VFX and animated features, used across the industry in many commercial and studio- proprietary renderers. Because of this, the work on OSL received an Academy Award for Technical Achievement in 2017 ..., see the GitHub project.

Today I'll show you how to use this option with Blender 3D to create a glass-like material for an object and render it with Blender 3D.

Open the Blender 3D application and set the render to Cycles, CPU and check Open Shading Language, see the next image:

Add an object, add a new material remove the Principled BSDF node

Create a file named Glass_001.osl select this file in the material area for the object.

You can see in the image above how I set the material with a Script node.

Add this source code in the file and render the scene:

#include "stdosl.h"

#define IOR_THRESHOLD 1.000001

float FresnelDielectric(vector i, normal n, float eta)
{
    float c = fabs(dot(i, n));
    float g = eta * eta - 1 + c * c;
    float result = 1.0;
    
    if (g > 0) {
        g = sqrt(g);
        float a = (g - c) / (g + c);
        float b = (c * (g + c) - 1) / (c * (g + c) + 1);
        result = 0.5 * a * a * (1 + b * b);
    }
    
    return result;
}


surface Glass(
    color diffuse_col = 0.8, 
    float ior = 1.45, 
    output closure color bsdf = 0)
{
    float real_ior = max(ior, IOR_THRESHOLD);
    float eta = backfacing()? 1.0 / real_ior : real_ior;
    float fr = FresnelDielectric(I, N, eta);
    
    bsdf = diffuse_col * (fr * reflection(N) + (1.0 - fr) * refraction(N, eta));
}

Blender 3D - Open Shading Language tutorial - part 001 .

Using this tutorial about Open Shading Language, you can try a glass shader. The source code show a simple use for Fresnel equations. The backfacing() and raytype() are two functions that provide the shader some information about the state of the renderer and the scene at the time of evaluation. I used just backfacing(), because is a raw example of this Fresnel equations. As you can see the I, N, eta inputs from Fresnel_Dielectric() is used to get a result variable fr. The all result of this shader is bsdf like a equation. See the next code:

#define IOR_THRESHOLD 1.000000001

float Fresnel_Dielectric(vector i, normal n, float eta)
{
//see https://en.wikipedia.org/wiki/Fresnel_equations
    float c = fabs(dot(i, n));
    float g = eta * eta - 1 + c * c;
    float result = 1.0;
    
    if (g > 0) {
        g = sqrt(g);
        float a = (g - c) / (g + c);
        float b = (c * (g + c) - 1) / (c * (g + c) + 1);
        result = 0.5 * a * a * (1 + b * b);
    }
    
    return result;
}

shader glass(
    color diffuse_col = 1.8, 
    float ior = 1.45, 
    output closure color bsdf = 0)
{
    float real_ior = max(ior, IOR_THRESHOLD);
    float eta = backfacing()? 1.0 / real_ior : real_ior;
    float fr = Fresnel_Dielectric(I, N, eta);
    
    bsdf = diffuse_col * (fr * reflection(N) + (1.0 - fr) * refraction(N, eta));
}

Blender 3D - Open Shading Language tutorial.

Today, I will show you how to use the Open Shading Language with Blender 3D version 2.79.
Use the Scripting area from Screen layout and Cycles for rendering.
Select from Render tab and check the option:Open Shading Language.
Add your object to test this tool.
For example you can use the default Cube.
Add a material to this object.
The Scripting area from Screen layout come with editor text.
Use Templates - > Open Shading Language -> Empty Shader and add this OSL script:

shader marble (color Col = .5, float freq = 1.0,  
           output color result = 0)  
{  
float sum = 0;  
float freq_value = freq;  

point pixel_shader = transform ("object", P);  
for (int i = 0; i < 6; i++)   
{  
    sum = sum + 1/freq_value * abs(.5 - noise( 4 * freq_value * pixel_shader)) ;  
    freq_value = 2 * freq_value;  
}  
result = Col * sum;  
}  

Save this script into your folder . Add a OSL script interface into Node Editor using : Add -> Script -> Script.
This will come with a open dialog icon to add your OSL script.
Link result to Color from your material Diffuse BSDF. All this steps I tell you is on the next image: