[osl/en] Added OSL and covered almost everything (#4857)

* added OSL language

Added most of the basics

* Update osl.html.markdown

* Updated Datatypes

* Added some functions

* Update osl.html.markdown

* Added Pattern Generations, Calculus, Texture and Light functions

* Final

* fixed 80 words

* Added Examples

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+---
+language: osl
+filename: learnosl.osl
+contributors:
+  - ["Preetham Pemmasani", "https://github.com/Preetham-ai"]
+---
+
+OSL (Open Shading Language) is a programming language designed by Sony for Arnold Renderer used for creating shaders.
+
+[Read more here.](https://raw.githubusercontent.com/imageworks/OpenShadingLanguage/master/src/doc/osl-languagespec.pdf)
+
+```c
+
+
+// Single-line comments start with //
+
+/* Multi line comments are preserved. */
+
+// Statements can be terminated by ;
+divide(1,2);
+
+///////////////
+// 1. Basics //
+///////////////
+
+// Declating variables
+color Blue; // Initializing a variable
+int _num = 3;
+float Num = 3.00;
+float c[3] = {0.1, 0.2, 3.14}; // Array
+
+// Math works as you would expect
+3 + 1;   // 4
+74 - 3;   // 71
+20 * 2; // 40
+75/3;  // 25.0
+
+// And modulo division only works with integers
+10 % 2; // 0
+31 % 4; // 1
+
+// Bitwise operations only works with integers
+- 0 // 1 (Unary Negation)
+~ 00100011 // 11011100 (bitwise Compliment)
+1 << 2; // 4 (shift Left)
+12 >> 1; // 3 (shift Right)
+1 & 0; // 0 (bitwise AND)
+1 | 0; // 1 (bitwise OR)
+1 ^ 1; // 0 (bitwise XOR)
+
+// We also have booleans
+true;
+false;
+
+// Booleans can't be compared to integers
+true == 1 // Error
+false == 0 // Error
+
+// Negation uses the ! symbol
+!0; // 1
+!1; // 0
+!2; // 0
+//... and so on
+
+// Relation Operators are defined like:
+0 == 0 // true (equal to)
+0 != 1 // true (not equal to)
+5 < 3 // false (less then)
+3 <= 3 // true (less than or equal to)
+69 > 69 // false (greater than)
+99 >= 52 // true (greater than or equal)
+
+
+// Functions are same as C and C++
+float sum(float a, float b){
+	return a+b;
+}
+
+int subtract(int a, int b){
+	return a-b;
+}
+
+sum(2,3); // 5
+
+////////////////
+// 2. Shaders //
+////////////////
+
+// Shaders explain the custom behavior of materials and light
+// Shader's syntax is similar to the main function in C
+// The inputs and the outputs should be initialized to default types
+shader multiply(float a = 0.0,
+				float b = 0.0, 
+				output float c = 0.0){
+    c = a*b;
+}
+
+// Double brackets[[ ]] is used to classify metadata of a shader
+surface plastic
+	[[ string help = "Realistic wood shader" ]]
+(
+	color Plastic = color (0.7, 0.5, 0.3) [[ string help = "Base color" ]],
+	float Reflectivity = 0.5 [[ float min = 0, float max = 1 ]],
+){...}
+
+///////////////////////////////////////
+// Metadata Types
+///////////////////////////////////////
+
+[[ string label = "IOR" ]] // Display-name in UI of the parameter
+[[ string help = "Change Refractive Index" ]] // Info about the parameter
+[[ string help = "widget" // Gives widgets to input the parameter
+	string widget = "number" ]] // input float or int
+	string widget = "string" ]] // String input
+	string widget = "boolean" ]] // yes/no (or) 1/0
+	string widget = "popup", options = "smooth|rough" ]] // Drop-down list
+	// enum Drop-down list can also be made
+	string widget = "mapper", options = "smooth:0|rough:1" ]]
+	string widget = "filename" ]] // Input files externally
+	string widget = "null" ]] // null input
+
+[[ float min = 0.0 ]] // Minimum value of parameter
+[[ float max = 0.5 ]] // Maximum value of parameter
+[[ int slider = 3.0   // Adds a slider as an input
+	int slidermin = -1]] // minimum value of the slider
+	int slidermax = 3]] // maximum value of the slider
+	int slidercenter = 2]] // origin value of the slider
+
+[[ float sensitivity = 0.5 ]] // step size for incrementing the parameter
+[[ string URL = www.example.com/ ]] // URL of shader's documentation 
+
+	
+
+// There are different types of shaders
+
+/* Surface shaders determine the basic material properties of a surface and
+how it reacts to light */
+// Light shaders are a type of SURFACE shaders used for emissive objects.
+// Displacement shaders alter the geometry using position and normals.
+// Volume shaders adds a medium like air/smoke/dust into the scene.
+
+volume multiply(float a = 0.0, float b = 0.0, output float c = 0.0){
+    c = 2*a+b; 
+}
+
+////////////////////////////////////////
+// 3. Data Types and Global Variables //
+////////////////////////////////////////
+
+// Data Types
+
+// 1. The void type indicates a function that doesn't return any value
+
+// 2. int (Integer)
+	int x = -12; // Minimum size of 32-bits
+	int new2 = 0x01cf; // Hexadecimal can also be specified
+
+	///////////////////////////////////////
+	// Order of Evaluation
+	///////////////////////////////////////
+
+	// From top to bottom, top has higher precedence
+	//--------------------------//
+	//        Operators         //
+	//--------------------------//
+	// int++, int--             //
+	// ++ int --int - ~ !       //
+	// * / %                    //
+	// + -                      //
+	// << >>                    //
+	// < <= > >=                //
+	// == !=                    //
+	// &                        //
+	// ^                        //
+	// |                        //
+	// &&                       //
+	// ||                       //
+	// ?:                       //
+	// = += -= *= /=            //
+	//--------------------------//
+
+// 3. float (Floating-point number)
+	float A = 2.3; // minimum  IEEE 32-bit float
+	float Z = -4.1e2; // Z = -4.1 * 10^2
+
+	// Order of evaluation is similar to int.
+	// Operations like ( ~ ! % << >> ^ | & && || ) aren't available in float
+
+// 4. string
+	// The syntax is similar to C
+	string new = "Hello World";
+	// some Special characters:
+	/*
+	'\"'; // double quote
+	'\n'; // newline character
+	'\t'; // tab character (left justifies text)
+	'\v'; // vertical tab
+	'\\'; // back slash
+	'\r'; // carriage return
+	'\b'; // backspace character
+	*/
+
+	// Strings are concatenated with whitespace
+	"Hello " "world!"; // "Hello world!"
+	// concat function can also be used
+	string concat ("Hello ","World!"); // "Hello world!"
+
+	// printf function is same as C
+	int i = 18;
+	printf("I am %d years old",i); // I am 18 years old
+
+	// String functions can alse be used
+	int strlen (string s); // gives the length of the string
+	int len = strlen("Hello, World!"); // len = 13
+
+	// startswith returns 1 if string starts with prefix, else returns 0
+	int starts = startswith("The quick brown fox", "The"); // starts = 1
+
+	// endswith returns 1 if string starts with suffix, else returns 0
+	int ends = endswith("The quick brown fox", "fox"); // ends will be 1
+
+// 5. color (Red, Green, Blue)
+	color p = color(0,1,2); // black
+	color q = color(1); // white ( same as color(1,1,1) )
+	color r = color("rgb", 0.23, 0.1, 0.8); // explicitly specify in RGB
+	color s = color("hsv", 0.23, 0.1, 0.8); // specify in HSV
+	// HSV stands for (Hue, Saturation, Luminance)
+	// HSL stands for (Hue, Saturation, Lightness)
+	// YIQ, XYZ and xyY formats can also be used
+	// We can also access the indivudual values of (R,G,B)
+	float Red = p[0]; // 0 (access the red component)
+	float Green = p[1]; // 1 (access the green component)
+	float Blue = p[2]; // 2 (access the blue component)
+
+	// They can also be accessed like this
+	float Red = p.r; // 0 (access the red component)  
+	float Green = p.g; // 1 (access the green component) 
+	float Blue = p.b; // 2 (access the blue component)
+
+	// Math operators work like this with decreasing precedence
+	color C = (3,2,3) * (1,0,0); // (3, 0, 0)
+	color D = (1,1,1) * 255; // (255, 255, 255)
+	color E = (25,5,125) / 5; // (5, 1, 25)
+	color F = (30,40,50) / (3,4,5); // (10, 10, 10)
+	color A = (1,2,3) + (1,0,0); // (2, 2, 3)
+	color B = (1,2,3) - (1,0,0); // (0, 2, 3)
+	// Operators like ( - == != ) are also used
+
+	// Color Functions
+	color blackbody (1500) // Gives color based on temperature (in Kelvin)
+	float luminance (0.5, 0.3, 0.8) // 0.37 gives luminance cd/m^2
+	// Luminance is calculated by 0.2126R+0.7152G+0.0722B
+	color wavelength color (700) // (1, 0, 0) Gives color based on wavelength
+	color transformc ("hsl", "rgb") // converts one system to another
+
+// 6. point (x,y,z) is position of a point in the 3D space
+// 7. vector (x,y,z) has length and direction but no position
+// 8. normal (x,y,z) is a special vector perpendicular to a surface
+	// These Operators are the same as color and have the same precedence
+	L = point(0.5, 0.6, 0.7);
+	M = vector(30, 100, 70);
+	N = normal(0, 0, 1);
+
+	// These 3 types can be assigned to a coordinate system
+	L = point("object", 0.5, 0.6, 0.7); // relative to local space
+	M = vector("common", 30, 100, 70); // relative to world space
+	// There's also ("shader", "world", "camera", "screen", "raster", "NDC")
+
+	float x = L[0]; // 0.5 (access the x-component)  
+	float y = L[1]; // 0.6 (access the y-component)  
+	float z = L[2]; // 0.7 (access the z-component)
+
+	// They can also be accessed like this
+	float x = M.x; // 30 (access the x-component)
+	float y = M.y; // 100 (access the y-component)
+	float z = M.z; // 70 (access the z-component)
+
+	float a = dot ((1,2,3), (1,2,3)); // 14 (Dot Product)
+	vector b = cross ((1,2,3), (1,2,3)); // (0,0,0) (Cross Product)
+	float l = length(L); // 1.085 (length of vector)
+	vector normalize (vector L); // (0.460, 0.552, 0.644) Normalizes the vector
+
+	point p0 = point(1, 2, 3);
+	point p1 = point(4, 5, 6);
+	point Q = point(0, 0, 0);
+
+	// Finding distance between two points
+	float len = distance(point(1, 2, 3), point(4, 5, 6)); // 5.196
+	// Perpendicular distance from Q to line joining P0 and P1
+	float distance (point P0, point P1, point Q); // 2.45
+
+
+// 9. matrix
+	// Used for transforming vectors between different coordinate systems.
+	// They are usually 4x4 (or) 16 floats
+	matrix zero = 0; // makes a 4x4 zero matrix
+	/* 0.0, 0.0, 0.0, 0.0,
+       0.0, 0.0, 0.0, 0.0,
+       0.0, 0.0, 0.0, 0.0,
+       0.0, 0.0, 0.0, 0.0 */
+	
+	matrix ident = 1; // makes a 4x4 identity matrix
+	/* 1.0, 0.0, 0.0, 0.0,
+	   0.0, 1.0, 0.0, 0.0,
+	   0.0, 0.0, 1.0, 0.0,
+	   0.0, 0.0, 0.0, 1.0 */
+		
+	matrix m = 7; // Maked a 4x4 scalar matrix with scaling factor of 7
+	/* 7.0, 0.0, 0.0, 0.0,
+	   0.0, 7.0, 0.0, 0.0,
+	   0.0, 0.0, 7.0, 0.0,
+	   0.0, 0.0, 0.0, 7.0 */
+	
+	float x = m[1][1]; // 7
+	
+	// matrices can be constructed using floats in row-major order
+	// matrices are usually 4x4 with 16 elements
+	matrix myMatrix = matrix(1.0, 0.0, 0.0, 0.0,    // Row 1
+                             0.0, 2.0, 0.0, 0.0,    // Row 2
+                             0.0, 0.0, 3.0, 0.0,    // Row 3
+                             0.0, 0.0, 0.0, 4.0);	// Row 4
+
+	// matrix transformations are easy to implement
+	matrix a = matrix ("shader", 1); // converted shader to common
+	matrix m = matrix ("object", "world"); // converted object to world
+
+	// Operations that can be used with decreasing precedence are:
+	// ( - * / == !=)
+
+	float determinant (matrix M) // 24 (returns the determinant of the matrix)
+	float transpose (matrix M) // returns the transpose of the matrix
+	/* 1.0, 0.0, 0.0, 0.0,
+       0.0, 2.0, 0.0, 0.0,
+       0.0, 0.0, 3.0, 0.0,
+       0.0, 0.0, 0.0, 4.0 */
+
+// 10. array 
+	// Arrays in OSL are similar to C
+	float a[5]; // initialize array a with size 5
+	int b[3] = {90,80,70}; // declare array with size 3
+	int len = arraylength(b); // 3
+	int f = b[1]; // 80
+	float anotherarray[3] = b; // arrays can be copied if same type
+
+// 11. struct (Structures)
+	// Structures in OSL are similar to C and C++.
+	struct RGBA { // Defining a structure
+		color rgb;
+		float alpha;
+	};
+
+	
+	RGBA col; // Declaring a structure
+	RGBA b = { color(0.1, 0.2, 0.3), 1 }; // Can also be declared like this
+
+	r.rgb = color (1, 0, 0); // Assign to one field
+	color c = r.rgb; // Read from a structure field
+
+// 12. closure
+	// Closure is used to store data that aren't considered when it executes.
+	// It cannot be manipulated or read.
+	// A null closure can always be assigned.
+	// OSL currently only supports color as their closure.
+
+	// A few examples of closures are:
+
+	// Diffuse BSDF closures:
+	closure color oren_nayar_diffuse_bsdf(normal N, color alb, float roughness)
+	closure color burley_diffuse_bsdf(normal N, color alb, float roughness);
+
+	// Dielectric BSDF closure:
+	closure color dielectric_bsdf(normal N, vector U, color reflection_tint,
+	    color transmission_tint, float roughness_x, float roughness_y,
+	    float ior, string distribution);
+
+	// Conductor BSDF closure:
+	closure color conductor_bsdf(normal N, vector U, float roughness_x,
+	    float roughness_y, color ior, color extinction, string distribution);
+
+	// Generalized Schlick BSDF closure:
+	closure color generalized_schlick_bsdf(normal N, vector U,
+	    color reflection_tint, color transmission_tint,
+	    float roughness_x, float roughness_y, color f0, color f90,
+	    float exponent, string distribution);
+
+	// Translucent BSDF closure:
+	closure color translucent_bsdf(normal N, color albedo);
+
+	// Transparent BSDF closure:
+	closure color transparent_bsdf();
+
+	// Subsurface BSSRDF closure:
+	closure color subsurface_bssrdf();
+
+	// Sheen BSDF closure:
+	closure color sheen_bsdf(normal N, color albedo, float roughness);
+
+	// Anisotropic VDF closure: (Volumetric)
+	closure color anisotropic_vdf(color albedo, color extinction,
+	    float anisotropy);
+
+	// Medium VDF closure: (Volumetric)
+	closure color medium_vdf(color albedo, float transmission_depth,
+	    color transmission_color, float anisotropy, float ior, int priority);
+
+	closure color uniform edf(color emittance); // Emission closure
+	closure color holdout(); // Holdout Hides objects beneath it
+
+	// BSDFs can be layered using this closure
+	closure color layer (closure color top, closure color base);
+
+
+
+// Global Variables
+// Contains info that the renderer knows
+// These variables need not be declared
+
+point P // Position of the point you are shading
+vector I // Incident ray direction from viewing position to shading position
+normal N // Normal of the surface at P
+normal Ng // Normal of the surface at P irrespective of bump mapping
+float u // UV 2D x - parametric coordinate of geometry
+float v // UV 2D y - parametric coordinate of geometry
+vector dPdu // change of P with respect to u tangent to the surface
+vector dPdv // change of P with respect to v tangent to the surface
+float time // Current time
+float dtime // Time covered
+vector dPdtime // change of P with respect to time
+
+/////////////////////
+// 4. Control flow //
+/////////////////////
+
+// Conditionals in OSL are just like in C or C++.
+
+// If/Else
+if (5>2){
+	int x = s;
+	int l = x;
+}
+else{
+	int x = s + l; 
+}
+
+// 'while' loop
+int i = 0;
+while (i < 5) {
+    i += 1;
+    printf("Current value of i: %d\n", i);
+}
+
+// 'do-while' loop is where test happens after the body of the loop
+int i = 0;
+do {
+    printf("Current value of i: %d\n", i);
+    i += 1;
+} while (i < 5);
+
+// 'for' loop
+for (int i = 0; i < 5; i += 1) {
+    printf("Current value of i: %d\n", i);
+}
+
+/////////////////////
+// 5. Functions //
+/////////////////////
+
+// Math Constants
+	M_PI // π
+	M_PI_35 // π/35
+	m_E // e
+	M_LN2 // ln 2
+	M_SQRT2 // √2
+	M_SQRT1_2 // √(1/2)
+
+// Geometry Functions
+	vector N = vector(0.1, 1, 0.2); // Normal vector
+	vector I = vector(-0.5, 0.2, 0.8); // Incident vector
+
+	// Faceforward tells the direction of vector
+	vector facing_dir = faceforward(N, I); // facing_dir = (-0.5, 0.2, 0.8)
+
+	// faceforward with three arguments
+	vector ref = vector(0.3, -0.7, 0.6); // Reference normal
+	facing_dir = faceforward(N, I, ref); // facing_dir = (0.5, -0.2, -0.8)
+
+	// reflect gives the reflected vector along normal
+	vector refl = reflect(I, N); // refl = (-0.7, -0.4, 1.4)\
+
+	// refract gives the refracted vector along normal
+	float ior = 1.5; // Index of refraction
+	vector refr = refract(I, N, ior); // refr = (-0.25861, 0.32814, 0.96143)
+
+	/* Fresnel computes the Reflection (R) and Transmission (T) vectors, along
+	with the scaling factors for reflected (Kr) and transmitted (Kt) light. */
+	float Kr, Kt;
+	vector R, T;
+	fresnel(I, N, ior, Kr, Kt, R, T);
+/* Kr = 0.03958, Kt = 0.96042
+	R = (-0.19278, -0.07711, 0.33854)
+	T = (-0.25861, 0.32814, 0.96143) */
+
+	// Rotating a point along a given axis
+	point Q = point(1, 0, 0);
+	float angle = radians(90); // 90 degrees
+	vector axis = vector(0, 0, 1);
+	point rotated_point = rotate(Q, angle, axis);
+	// rotated_point = point(0, 1, 0)
+
+	// Rotating a point along a line made by 2 points
+	point P0 = point(0, 0, 0);
+	point P1 = point(1, 1, 0);
+	angle = radians(45); // 45 degrees
+	Q = point(1, 0, 0);
+	rotated_point = rotate(Q, angle, P0, P1);
+	// rotated_point = point(0.707107, 0.707107, 0)
+
+	// Calculating normal of surface at point p
+	point p1 = point(1, 0, 0); // Point on the sphere of radius 1
+	vector normal1 = calculatenormal(p1);
+	// normal1 = vector(1, 0, 0)
+
+	// Transforming units is easy
+	float transformu ("cm", float x) // converts to cm
+	float transformu ("cm", "m", float y) // converts cm to m
+
+// Displacement Functions
+	void displace (float 5); // Displace by 5 amp units
+	void bump (float 10); // Bump by 10 amp units
+
+
+// Noise Generation
+
+	type noise (type noise (string noisetype, float u, float v, ...)); // noise
+	type noise (string noisetype, point p,...); // point instead of coordinates
+	/* some noises are ("perlin", "snoise", "uperlin", "noise", "cell", "hash"
+	"simplex", "usimplex", "gabor", etc) */
+	
+	// Noise Names
+
+	// 1. Perlin Noise (perlin, snoise):
+	// Creates smooth, swirling noise often used for textures.
+	// Range: [-1, 1] (signed)
+	color cloud_texture = noise("perlin", P);
+
+	// 2. Simplex Noise (simplex, usimplex):
+	// Similar to Perlin noise but faster.
+	// Range: [-1, 1] (signed) for simplex, [0, 1] (unsigned) for usimplex
+	float bump_amount = 0.2 * noise("simplex", P * 5.0);
+
+	// 3. UPerlin Noise (uperlin, noise):
+	// Similar to peril
+	// Range: [0, 1] (unsigned)
+	color new_texture = noise("uperlin", P);
+	
+	// 4. Cell Noise (cell):
+	// Creates a blocky, cellular and constant values within each unit block
+	// Range: [0, 1] (unsigned)
+	color new_texture = noise("cell", P);
+
+	// 5. Hash Noise (hash):
+	// Generates random, uncorrelated values at each point.
+	// Range: [0, 1] (unsigned)
+	color new_texture = noise("hash", P);
+
+	// Gabor Noise (gabor) 
+	// Gabor Noise is advanced version of Perin noies and gives more control
+	// Range: [-1, 1] (signed)
+	// Gabor Noise Parameters
+
+	// Anisotropic (default: 0)
+	// Controls anisotropy:
+	// 0: Isotropic (equal frequency in all directions)
+	// 1: Anisotropic with user-defined direction vector (defaults to (1,0,0))
+	/* 2: Hybrid mode,anisotropic along direction vector but radially isotropic
+	perpendicularly. */
+
+	// Direction (default: (1,0,0))
+	// Specifies the direction of anisotropy (used only if anisotropic is 1).
+
+	// bandwidth (default: 1.0)
+	// Controls the frequency range of the noise.
+
+	// impulses (default: 16)
+	// Controls the number of impulses used per cell, affecting detail level.
+
+	// do_filter (default: 1)
+	// Enables/disables antialiasing (filtering).
+
+	result = noise(
+        "gabor",
+        P,
+        "anisotropic", anisotropic,
+        "direction", direction,
+        "bandwidth", bandwidth,
+        "impulses", impulses,
+        "do_filter", do_filter
+    );
+
+	// Specific noises can also be used instead of passing them as types
+	// pnoise is periodic noise
+	float n1 = pnoise("perlin", 0.5, 1.0);
+	// 2D periodic noise with Gabor type
+	float n2 = pnoise("gabor", 0.2, 0.3, 2.0, 3.0);
+	// 2D non-periodic simplex noise
+	float n3 = snoise(0.1, 0.7);
+	// 2D periodic simplex noise
+	type psnoise (float u, float v, float uperiod, float vperiod);
+	float n4 = psnoise(0.4, 0.6, 0.5, 0.25);
+	// 2D cellular noise
+	float n5 = cellnoise(0.2, 0.8);
+	// 2D hash noise
+	int n6 = hash(0.7, 0.3);
+
+// Step Function
+	// Step Functions are used to compare input and threshold
+
+	// The type may be of float, color, point, vector, or normal.
+	type step (type edge, type x); // Returns 1 if x ≥ edge, else 0
+	color checker = step(0.5, P);  // P is a point on the surface
+	/* Pixels with P values below 0.5 will be black, those above or equal will
+	be white */
+	float visibility = step(10, distance(P, light_position));
+	// Light is fully visible within 10 units, completely invisible beyond
+
+	type linearstep (type edge0, type edge1, type x); /* Linearstep Returns 0
+	if x ≤ edge0, and 1 if x ≥ edge1, with linear interpolation */
+	color gradient = linearstep(0, 1, P);
+	// P is a point on the surface between 0 and 1
+	// Color will graduate smoothly from black to white as P moves from 0 to 1
+	float fade = linearstep(0.85, 1, N.z);  // N.z is the z-component
+	// Object edges with normals close to vertical (N.z near 1) will fade out
+	
+	type smoothstep (type edge0, type edge1, type x); /* smoothstep Returns 0
+	if x ≤ edge0, and 1 if x ≥ edge1, with Hermite interpolation */
+	float soft_mask = smoothstep(0.2, 0.8, noise(P));  /* noise(P) is a noisy
+	value between 0 and 1. soft_mask will vary smoothly between 0 and 1 based
+	on noise(P), with a smoother curve than linearstep */
+
+// Splines
+	// Splines are smooth curves based on a set of control points
+
+	/* The type of interpolation ranges from "catmull-rom", "bezier",
+	"bspline", "hermite", "linear", or "constant" */
+
+	// Spline with knot vector
+	float[] knots = {0, 0, 0, 0.25, 0.5, 0.75, 1, 1, 1};
+	point[] controls = {point(0),point(1, 2, 1),point(2, 1, 2),point(3, 3, 1)};
+	spline curve1 = spline("bezier", 0.5, len(knots), controls);
+	// curve1 is a Bezier spline evaluated at u = 0.5
+
+	// Spline with control points
+	spline curve2 = spline("catmull-rom", 0.25, point(0, 0, 0), point(1, 2, 1),
+	                       point(2, 1, 2), point(3, 3, 1));
+	// curve2 is a Catmull-Rom spline evaluated at u = 0.25
+
+	// Constant spline with a single float value
+	float value = 10;
+	u = 0.1;
+	spline curve5 = spline("constant", u, value);
+	// curve5 is a constant spline with value 10 evaluated at u = 0.1
+
+	// Hermite spline with point and vector controls
+	point q0 = point(0, 0, 0), q1 = point(3, 3, 3);
+	vector t0 = vector(1, 0, 0), t1 = vector(-1, 1, 1);
+	u = 0.75;
+	spline curve3 = spline("hermite", u, q0, t0, q1, t1);
+	// curve3 is a Hermite spline evaluated at u = 0.75
+
+	// Linear spline with float controls
+	float f0 = 0, f1 = 1, f2 = 2, f3 = 3;
+	u = 0.4;
+	spline curve4 = spline("linear", u, f0, f1, f2, f3);
+	// curve4 is a linear spline evaluated at u = 0.4
+	
+	// InverseSplines also exist
+	
+	// Inverse spline with control values
+	float y0 = 0, y1 = 1, y2 = 2, y3 = 3;
+	float v = 1.5;
+	float u1 = splineinverse("linear", v, y0, y1, y2, y3);
+	// u1 = 0.5 (linear interpolation between y1 and y2)
+
+	// Inverse spline with knot vector
+	float[] knots = {0, 0, 0, 0.25, 0.5, 0.75, 1, 1, 1};
+	float[] values = {0, 1, 4, 9};
+	v = 6;
+	float u2 = splineinverse("bezier", v, len(knots), values);
+	// u2 = 0.75 (Bezier spline inverse evaluated at v = 6)
+
+	// Inverse spline with constant value
+	v = 10;
+	float u3 = splineinverse("constant", v, 10);
+	// u3 = 0 (since the constant spline always returns 10)
+
+	// Inverse spline with periodic values
+	float y4 = 0, y5 = 1, y6 = 0;
+	v = 0.5;
+	float u4 = splineinverse("periodic", v, y4, y5, y6);
+	// u4 = 0.75 (periodic spline inverse evaluated at v = 0.5)
+
+
+
+// Calculus Operators
+	// Partial derivative of f with respect to x, y and z using Dx, Dy, Dz
+	float a = 3.14;
+	float dx = Dx(a); // partial derivative of a with respect to x
+
+	point p = point(1.0, 2.0, 3.0);
+	vector dp_dx = Dx(p); // partial derivative of p with respect to x
+
+	vector dv_dy = Dy(N); // partial derivative of normal with respect to y
+
+	color c = color(0.5, 0.2, 0.8);
+	color dc_dz = Dz(c); // partial derivative of c with respect to z
+	
+
+	float area (point p) // gives the surface area at the position p 
+
+	float filterwidth (float x) // gives the changes of x in adjacent samples
+
+// Texture Functions
+	// lookup for a texture at coordinates (x,y)
+	color col1 = texture("texture.png", 0.5, 0.2);
+	// Lookup color at (0.5, 0.2) in texture.png
+
+	// 3D lookup for a texture at coordinates (x,y)
+	color col3 = texture3d("texture3d.vdb", point(0.25, 0.5, 0.75));
+
+	// parameters are ("blur","width","wrap","fill","alpha","interp", ...)
+	color col2 = texture("texture.png",1.0,0.75,"blur",0.1,"wrap", "periodic");
+	// Lookup color at (1.0, 0.75) with blur 0.1 and periodic wrap mode
+	
+// Light Functions
+
+	float surfacearea (); // Returns the surface area of area light covers
+	int backfacing (); // Outputs 1 if the normals are backfaced, else 0
+	int raytype (string name); // returns 1 if the ray is a particular raytype
+
+	// Tracing a ray from a position in a direction
+	point pos = point(0, 0, 0); // Starting position of the ray
+	vector dir = vector(0, 0, 1); // Direction of the ray
+	int hit = trace(pos, dir); // returns 1 if it hits, else 0
+
+```
+### Further reading
+
+* [Blender Docs for OSL](https://docs.blender.org/manual/en/latest/render/shader_nodes/osl.html)
+* [C4D Docs for OSL](https://docs.otoy.com/cinema4d//OpenShadingLanguageOSL.html)
+* Open Shading Language on [Github](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage)
+* [Official OSL Documentation](https://open-shading-language.readthedocs.io/en/main/)
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