nuclear@0: #version 110
nuclear@0: 
nuclear@0: #define SQ(x)	((x) * (x))
nuclear@0: #define PI		3.141592653
nuclear@0: 
nuclear@0: /* -- Lambert's cosine law
nuclear@0:  * J. H. Lambert, Photometria sive de mensura de gratibus luminis, colorum et umbrae.
nuclear@0:  * Eberhard Klett, 1760.
nuclear@0:  */
nuclear@0: float lambert(vec3 norm, vec3 ldir)
nuclear@0: {
nuclear@0: 	return max(dot(norm, ldir), 0.0);
nuclear@0: }
nuclear@0: 
nuclear@0: /* -- Phong specular model
nuclear@0:  * B. T. Phong, "Illumination for Computer Generated Pictures"
nuclear@0:  * Communications of the ACM, 1975.
nuclear@0:  */
nuclear@0: float phong(vec3 view, vec3 norm, vec3 ldir, float spow)
nuclear@0: {
nuclear@0: 	vec3 lref = reflect(-ldir, norm);
nuclear@0: 	return pow(max(dot(lref, view), 0.0), spow);
nuclear@0: }
nuclear@0: 
nuclear@0: /* -- Blinn-Phong specular model
nuclear@0:  * J. F. Blinn, "Models of Light Reflection for Computer Synthesized Pictures"
nuclear@0:  * in Proceedings of SIGGRAPH 1977
nuclear@0:  */
nuclear@0: float blinn(vec3 norm, vec3 hvec, float spow)
nuclear@0: {
nuclear@0: 	return pow(max(dot(norm, hvec), 0.0), spow);
nuclear@0: }
nuclear@0: 
nuclear@0: /* -- Cook & Torrance model.
nuclear@0:  * R. L. Cook and K. E. Torrance, "A Reflectance Model for Computer Graphics"
nuclear@0:  * in Proceedings of SIGGRAPH 1981.
nuclear@0:  */
nuclear@0: float cook_torrance(vec3 view, vec3 norm, vec3 ldir, vec3 hvec, float rough, float ior)
nuclear@0: {
nuclear@0: 	float m = max(rough, 0.0001);
nuclear@0: 	
nuclear@0: 	// various useful dot products
nuclear@0: 	float ndoth = max(dot(norm, hvec), 0.0);
nuclear@0: 	float ndotv = max(dot(norm, view), 0.0);
nuclear@0: 	float ndotl = dot(norm, ldir);
nuclear@0: 	float vdoth = max(dot(view, hvec), 0.0);
nuclear@0: 	float ndoth_sq = SQ(ndoth);
nuclear@0: 
nuclear@0: 	// geometric term (shadowing/masking)
nuclear@0: 	float geom_a = (2.0 * ndoth * ndotv) / vdoth;
nuclear@0: 	float geom_b = (2.0 * ndoth * ndotl) / vdoth;
nuclear@0: 	float geom = min(1.0, min(geom_a, geom_b));
nuclear@0: 
nuclear@0: 	// beckmann microfacet distribution term
nuclear@0: 	float sin2_ang = 1.0 - ndoth_sq;	// sin^2(a) = 1 - cos^2(a)
nuclear@0: 	float tan2_ang = sin2_ang / ndoth_sq;	// tan^2(a) = sin^2(a) / cos^2(a)
nuclear@0: 	float d_mf = exp(-tan2_ang / SQ(m)) / (SQ(m) * SQ(ndoth_sq));
nuclear@0: 
nuclear@0: 	// fresnel term
nuclear@0: 	float c = vdoth;
nuclear@0: 	float g = sqrt(SQ(ior) + SQ(c) - 1.0);
nuclear@0: 	float ftmp = (c * (g + c) - 1.0) / (c * (g - c) + 1.0);
nuclear@0: 	float fres = 0.5 * (SQ(g - c) / SQ(g + c)) * (1.0 + SQ(ftmp));
nuclear@0: 
nuclear@0: 	return (fres / PI) * (d_mf / ndotl) * (geom / ndotv);
nuclear@0: }
nuclear@0: 
nuclear@0: /* -- Oren & Nayar model
nuclear@0:  * M. Oren and S. K. Nayar, "Generalization of Lambert's Reflectance Model"
nuclear@0:  * in Proceedings of SIGGRAPH 1994.
nuclear@0:  */
nuclear@0: float oren_nayar(vec3 view, vec3 norm, vec3 ldir, float rough)
nuclear@0: {
nuclear@0: 	float vdotn = max(dot(view, norm), 0.0);
nuclear@0: 	float ldotn = max(dot(ldir, norm), 0.0);
nuclear@0: 
nuclear@0: 	float theta_r = acos(vdotn);
nuclear@0: 	float theta_i = acos(ldotn);
nuclear@0: 	float cos_pr_minus_pi = dot(normalize(view - norm * vdotn), normalize(ldir - norm * ldotn));
nuclear@0: 	float alpha = max(theta_r, theta_i);
nuclear@0: 	float beta = min(theta_r, theta_i);
nuclear@0: 
nuclear@0: 	float sigma_sq = SQ(rough);
nuclear@0: 	float a = 1.0 - 0.5 * sigma_sq / (sigma_sq + 0.33);
nuclear@0: 	float b = 0.45 * sigma_sq / (sigma_sq + 0.09);
nuclear@0: 
nuclear@0: 	if(cos_pr_minus_pi >= 0.0) {
nuclear@0: 		b *= cos_pr_minus_pi * sin(alpha) * tan(beta);
nuclear@0: 	} else {
nuclear@0: 		b = 0.0;
nuclear@0: 	}
nuclear@0: 
nuclear@0: 	return ldotn * (a + b);
nuclear@0: }
nuclear@0: 
nuclear@0: /* TODO: need tangent/bitangent
nuclear@0: float ward(vec3 view, vec3 norm, vec3 ldir, vec3 hvec, vec3 tang, vec3 bitan, float ax, float ay)
nuclear@0: {
nuclear@0: 	float vdotn = dot(view, norm);
nuclear@0: 	float ldotn = dot(light, norm);
nuclear@0: }
nuclear@0: */