// Copyright Contributors to the Open Shading Language project.
// SPDX-License-Identifier: BSD-3-Clause
// https://github.com/AcademySoftwareFoundation/OpenShadingLanguage
//
// ubersurface.osl
// 
// 
// A demonstration of writing a production-like generalized surface shader in OSL
// This shader combines diffuse, specular, refractive and emissive closure to create
// a flexible material description.
//
// See the help metadata on the parameters for usage info.  Hopefully much of it is 
// self-explanatory.
//
// Author: Adam S. Martinez
// Date: August 5th, 2011
// Soundtrack: Gojira - Flying Whales
//
// August 2013:
// This update employs a simple material layering mechanism that allows
// two ubersurface shaders to connect and composite in a consistent manner.
// Connecting ubersurfaceB.Out_Ci to ubersurfaceA.Next_Layer results in 
// the appearance of ubersurfaceA over ubersurfaceB.
//
// In this logic, opacity of 0 will pass through the top layer and call the
// Next_Layer.  Refractive materials will filter Next_Layer according to 
// the Refraction_Color.
//
// See testsuite/render-material-layer for an example.
// 
// Note:  This shader uses the "absorption" closure keyword for 
// the microfacet_beckmann_refraction closure.  This is currently 
// unsupported by the testrender application.
//


// The TEXTURE_PARAMS macro defines a set of parameters common to all texture maps.  
// The metadata provides parameter display hints to host applications. These metadata
// blocks are in The Foundry's Katana format.
#define TEXTURE_PARAMS(MAPNAME) \
    string Texture_ ## MAPNAME ## _Name = ""\
        [[ string widget = "filename", string help = "A texture file name", \
           string page = #MAPNAME ".Texture"]],\
    float  Texture_ ## MAPNAME ## _Blur    = 0.0\
        [[ string help = "The blur amount, as a portion of the image size.", \
           string page = #MAPNAME ".Texture"]],  \
    float  Texture_ ## MAPNAME ## _Width   = 1.0 \
        [[ string help = "A multiplier on the surface derivatives.  Lower \
           numbers cause larger resolution mip levels to be used.", \
           string page = #MAPNAME ".Texture"]], \
    string Texture_ ## MAPNAME ## _Wrap_Mode = "periodic"\
        [[ string widget = "popup", \
           string options = "black|clamp|file|mirror|periodic",\
           string help = "The U and V wrap mode for this texture. ", \
           string page = #MAPNAME ".Texture"]],\
    float Texture_ ## MAPNAME ## _Scale_U = 1.0\
        [[ string help = "Scales the U texture coordinate prior to texture lookup.", \
           string page = #MAPNAME ".Texture"]], \
    float Texture_ ## MAPNAME ## _Scale_V = 1.0\
        [[ string help = "Scales the V texture coordinate prior to texture lookup.", \
           string page = #MAPNAME ".Texture"]], \
    int Texture_ ## MAPNAME ## _Flip_U = 0\
        [[ string help = "Flips the U texture coordinate prior to texture lookup.", \
           string widget = "checkBox", \
           string page = #MAPNAME ".Texture"]], \
    int Texture_ ## MAPNAME ## _Flip_V = 0\
        [[ string help = "Flips the V texture coordinate prior to texture lookup.", \
           string widget = "checkBox", \
           string page = #MAPNAME ".Texture"]],

// The evaluate texture function manipulates the texture coordinates and executes the texture() call
// because this function gets called via a macro (defined below), the results are stored in the output
// parameter 'result.'
void evaluateTexture( string texfile, float blur, float width, string wrap, float scale_u, 
                      float scale_v, int flip_u, int flip_v, float uu, float vv, output color result)
{
    if(texfile != "")
    {
        float u_tex = uu ;
        float v_tex = vv ;

        if(flip_u)
            u_tex = 1.0 - u_tex;

        if(flip_v)
            v_tex = 1.0 - v_tex;

        u_tex *= scale_u;
        v_tex *= scale_v;

        result = texture(texfile, u_tex, v_tex, "width", width, "blur", blur, "swrap", wrap, "twrap", wrap);
    }
}

// The following is a float version of the above.  Note that the texture() call will return a float value 
// representing the first channel found in the texture file.
void evaluateTexture( string texfile, float blur, float width, string wrap, float scale_u, 
                      float scale_v, int flip_u, int flip_v, float uu, float vv, output float result)
{
    if(texfile != "")
    {
        float u_tex = uu ;
        float v_tex = vv ;

        if(flip_u)
            u_tex = 1.0 - u_tex;

        if(flip_v)
            v_tex = 1.0 - v_tex;

        u_tex *= scale_u;
        v_tex *= scale_v;

        result = texture(texfile, u_tex, v_tex, "width", width, "blur", blur, "swrap", wrap, "twrap", wrap);
    }
}

// This macro allows us to easily call the evaluateTexture functions using the texture parameters defined by the 
// TEXTURE_PARAMS macro.  The parameters are the map definition, which must have an equivalent TEXTURE_PARAMS 
// call in the parameter list, and a storage variable for the texture lookup result.
#define TEXTURE_EVAL(MAPNAME, RESULT)\
    evaluateTexture(\
    Texture_ ## MAPNAME ## _Name,\
    Texture_ ## MAPNAME ## _Blur,\
    Texture_ ## MAPNAME ## _Width,\
    Texture_ ## MAPNAME ## _Wrap_Mode,\
    Texture_ ## MAPNAME ## _Scale_U,\
    Texture_ ## MAPNAME ## _Scale_V,\
    Texture_ ## MAPNAME ## _Flip_U,\
    Texture_ ## MAPNAME ## _Flip_V,\
    In_U,\
    In_V,\
    RESULT);

// The Shader
surface
ubersurface
(
    float   Opacity = 1
       [[   string help = "The overall opacity of the surface", 
            string page = "Opacity",
            float UImin = 0, float UImax = 1]],

    TEXTURE_PARAMS(Opacity)

    float   Kbump = 0
       [[   string help = "The amount to bump the surface by", 
            string page = "Bump"]],

    TEXTURE_PARAMS(Bump)

    float   Kd = 0.5
       [[   string help = "Diffuse closure weight", 
            string page = "Diffuse",
            float UImin = 0, float UImax = 1]],

    color   Diffuse_Color = 1
       [[   string help = "Diffuse closure color", 
            string page = "Diffuse"]],

    TEXTURE_PARAMS(Diffuse)

    float   IOR = 1.33
       [[   string help = "The index of refraction for specular effects.", 
            string page = "Specular"]],

    float   Roughness = 0.2
       [[   string help = "The surface roughness for specular effects. A value of 0 forces perfect reflection/refraction.", 
            string page = "Specular",
            float UImin = 0, float UImax = 1]],


    float   Ks = 0.5
       [[   string help = "Specular closure weight", 
            string page = "Specular",        
            float UImin = 0, float UImax = 1]],

    color   Specular_Color = 1
       [[   string help = "Specular closure color", 
            string page = "Specular"]],

    TEXTURE_PARAMS(Specular)

    float   Kt = 0
       [[   string help = "Transmissive, or refraction, closure weight.", 
            string page = "Refraction",   
            float UImin = 0, float UImax = 1]],

    color   Refraction_Color = 1
       [[   string help = "Refraction closure color", 
            string page = "Refraction"]],        

    TEXTURE_PARAMS(Refraction)

    color   Absorption_Color = 0
       [[   string help = "Color to absorb inside a refractive volume.", 
            string page = "Refraction"]],

    float   Ke = 0
       [[   string help = "Emissive, or incandescent, closure weight.", 
            string page = "Emission"]],   

    color   Emission_Color = 1
       [[   string help = "Emissive closure color.", 
            string page = "Emission"]],   

    TEXTURE_PARAMS(Emission)

    // These parameters are provided to use shading variables from external shaders
    normal In_Normal = N,

    float  In_U = u,

    float  In_V = v,

    // Shader Layering
    output closure color Out_Ci = 0,
    closure color Next_Layer = 0

)
{

    // Nshading will store a modified N if bump mapping is used
    normal Nshading = In_Normal;

    // Determine opacity and prepare a transparent closure
    float opacity = 1;
    TEXTURE_EVAL(Opacity, opacity)
    opacity *= Opacity;
    closure color transparencyClosure =  transparent() * (1.0-opacity);

    // For material layering we have to keep some extra stuff around...
    color refractionFilter = 1;

    // Test for shadow rays and exit early, supplying only the transparency closure.
    if(raytype("shadow")) {
        Out_Ci = transparencyClosure;

	//Naive layering of in shadow context
	if(isconnected(Next_Layer)){
	   Out_Ci = Out_Ci + Next_Layer;
	}

    } else {
    	// Storage for weighted closures that we will accumulate at the end of this 'beauty' block 
        closure color diffuseClosure	= 0;
    	closure color specularClosure	= 0;
	closure color emissionClosure	= 0;
    	closure color refractionClosure = 0;
	
	// Determine index of refraction based on which side we have hit.
	float eta = IOR;
	if(backfacing()) eta = 1.0/IOR;

	// Bump
	if(Kbump) {
            float bumpTexture = 0;
    	    TEXTURE_EVAL(Bump, bumpTexture)
            bumpTexture *= Kbump;
            if(bumpTexture) {
	        point Pbump = P + normalize(Nshading) * bumpTexture;
                Nshading = normalize(calculatenormal(Pbump));
    	    }
	}

    	// Diffuse
	if(Kd) {
            color diffuseTexture = color(1);
    	    TEXTURE_EVAL(Diffuse, diffuseTexture)
            diffuseClosure = diffuse(Nshading) * Kd * Diffuse_Color * diffuseTexture;
        }

    	// Specular
        if(Ks) {
            if(Roughness <= 0.005) {
	        specularClosure = reflection(Nshading, eta);
            } else {
        	specularClosure = microfacet("beckmann", Nshading, Roughness, eta, 0);
	    }

    	    color specularTexture = color(1);
            TEXTURE_EVAL(Specular, specularTexture)
	    specularClosure *= specularTexture * Ks * Specular_Color;
	}

    	// Emission 
	if(Ke) {
            // Because emission() returns a radiance that, integrated over all
            // angles, yields a power density of 1, we multiply by the desired
            // total power and divide by the total surface area.  In this
            // manner, the 'Ke' parameter gives the total power of the light
            // (e.g., in Watts) independently of its physical size or shape
            // (which may be changed to affect shadow softness without altering
            // overall illumination).  N.B.: The total power is BEFORE Emission_Color
            // filters the color!
	    color emissionTexture = color(1);
    	    TEXTURE_EVAL(Emission, emissionTexture)
	    emissionClosure = emission() * (Ke / surfacearea()) * Emission_Color * emissionTexture;
    	}
	

	// Refraction
    	refractionFilter = 1.0-opacity;
	if(Kt) {
	    if(Roughness <= 0.005) {
                refractionClosure = refraction(Nshading, eta, "absorption", Absorption_Color);
    	    } else {
                refractionClosure = microfacet("beckmann", Nshading, vector(0), Roughness, Roughness,  eta, 1, "absorption", Absorption_Color);
            }

	    color refractionTexture = color(1);
    	    TEXTURE_EVAL(Refraction, refractionTexture)
	    refractionClosure *= refractionTexture * Kt * Refraction_Color;
	    // Attenuate diffuse by inverse of refraction Kt. 
	    diffuseClosure *= 1.0-Kt;
	    refractionFilter = mix(color(1), refractionTexture * Refraction_Color, Kt*opacity );
    	}

	// Accumulate and output
    	Out_Ci = ((diffuseClosure + specularClosure + emissionClosure) * opacity);

	if(isconnected(Next_Layer))
	{
	   Out_Ci = Next_Layer * refractionFilter + Out_Ci;
	} else {
	   Out_Ci = Out_Ci + (refractionClosure*opacity) + transparencyClosure;
	}
    }

    Ci = Out_Ci;

}


