Cycles: Cleanup MultiGGX closure implementation

The implementation originally handled four different cases:
Regular glossy, glass, metallic fresnel glossy and diffuse.

However, only the first two are actually used currently. Therefore, this commit
removes the other two, which allows to simplify the code.

Additionally, due to the Principled BSDF, the function arguments are now
identical for glossy and glass, which allows to get rid of some ugly #ifdefs.

1 files changed, 28 insertions, 86 deletions

diff --git a/intern/cycles/kernel/closure/bsdf_microfacet_multi_impl.h b/intern/cycles/kernel/closure/bsdf_microfacet_multi_impl.h
index 16d900088cb..2eb2457c9e5 100644
--- a/intern/cycles/kernel/closure/bsdf_microfacet_multi_impl.h
+++ b/intern/cycles/kernel/closure/bsdf_microfacet_multi_impl.h
@@ -26,24 +26,16 @@
  * the balance heuristic isn't necessarily optimal anymore.
  */
 ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
-        float3 wi,
-        float3 wo,
-        const bool wo_outside,
-        const float3 color,
-        const float alpha_x,
-        const float alpha_y,
-         ccl_addr_space uint *lcg_state
-#ifdef MF_MULTI_GLASS
-        , const float eta
-        , bool use_fresnel
-        , const float3 cspec0
-#elif defined(MF_MULTI_GLOSSY)
-         , float3 *n, float3 *k
-         , const float eta
-         , bool use_fresnel
-         , const float3 cspec0
-#endif
-)
+	float3 wi,
+	float3 wo,
+	const bool wo_outside,
+	const float3 color,
+	const float alpha_x,
+	const float alpha_y,
+	ccl_addr_space uint *lcg_state,
+	const float eta,
+	bool use_fresnel,
+	const float3 cspec0)
 {
 	/* Evaluating for a shallower incoming direction produces less noise, and the properties of the BSDF guarantee reciprocity. */
 	bool swapped = false;
@@ -77,44 +69,29 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
 	/* Analytically compute single scattering for lower noise. */
 	float3 eval;
 	float3 throughput = make_float3(1.0f, 1.0f, 1.0f);
+	const float3 wh = normalize(wi+wo);
 #ifdef MF_MULTI_GLASS
 	eval = mf_eval_phase_glass(-wi, lambda_r, wo, wo_outside, alpha, eta);
 	if(wo_outside)
 		eval *= -lambda_r / (shadowing_lambda - lambda_r);
 	else
 		eval *= -lambda_r * beta(-lambda_r, shadowing_lambda+1.0f);
-
-	float F0 = fresnel_dielectric_cos(1.0f, eta);
-	if(use_fresnel) {
-		throughput = interpolate_fresnel_color(wi, normalize(wi + wo), eta, F0, cspec0);
-
-		eval *= throughput;
-	}
-#elif defined(MF_MULTI_DIFFUSE)
-	/* Diffuse has no special closed form for the single scattering bounce */
-	eval = make_float3(0.0f, 0.0f, 0.0f);
 #else /* MF_MULTI_GLOSSY */
-	const float3 wh = normalize(wi+wo);
 	const float G2 = 1.0f / (1.0f - (lambda_r + 1.0f) + shadowing_lambda);
 	float val = G2 * 0.25f / wi.z;
 	if(alpha.x == alpha.y)
 		val *= D_ggx(wh, alpha.x);
 	else
 		val *= D_ggx_aniso(wh, alpha);
-	if(n && k) {
-		eval = fresnel_conductor(dot(wh, wi), *n, *k) * val;
-	}
-	else {
-		eval = make_float3(val, val, val);
-	}
+	eval = make_float3(val, val, val);
+#endif
 
 	float F0 = fresnel_dielectric_cos(1.0f, eta);
 	if(use_fresnel) {
 		throughput = interpolate_fresnel_color(wi, wh, eta, F0, cspec0);
 
-		eval = throughput * val;
+		eval *= throughput;
 	}
-#endif
 
 	float3 wr = -wi;
 	float hr = 1.0f;
@@ -129,13 +106,6 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
 		float3 wm = mf_sample_vndf(-wr, alpha, make_float2(lcg_step_float_addrspace(lcg_state),
 		                                                   lcg_step_float_addrspace(lcg_state)));
 
-#ifdef MF_MULTI_DIFFUSE
-		if(order == 0) {
-			/* Compute single-scattering for diffuse. */
-			const float G2_G1 = -lambda_r / (shadowing_lambda - lambda_r);
-			eval += throughput * G2_G1 * mf_eval_phase_diffuse(wo, wm);
-		}
-#endif
 #ifdef MF_MULTI_GLASS
 		if(order == 0 && use_fresnel) {
 			/* Evaluate amount of scattering towards wo on this microfacet. */
@@ -156,10 +126,8 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
 				phase = mf_eval_phase_glass(wr, lambda_r,  wo,  wo_outside, alpha, eta);
 			else
 				phase = mf_eval_phase_glass(wr, lambda_r, -wo, !wo_outside, alpha, 1.0f/eta);
-#elif defined(MF_MULTI_DIFFUSE)
-			phase = mf_eval_phase_diffuse(wo, wm);
 #else /* MF_MULTI_GLOSSY */
-			phase = mf_eval_phase_glossy(wr, lambda_r, wo, alpha, n, k) * throughput;
+			phase = mf_eval_phase_glossy(wr, lambda_r, wo, alpha) * throughput;
 #endif
 			eval += throughput * phase * mf_G1(wo_outside? wo: -wo, mf_C1((outside == wo_outside)? hr: -hr), shadowing_lambda);
 		}
@@ -181,25 +149,17 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
 			else if(use_fresnel && order > 0) {
 				throughput *= interpolate_fresnel_color(wi_prev, wm, eta, F0, cspec0);
 			}
-#elif defined(MF_MULTI_DIFFUSE)
-			wr = mf_sample_phase_diffuse(wm,
-			                             lcg_step_float_addrspace(lcg_state),
-			                             lcg_step_float_addrspace(lcg_state));
 #else /* MF_MULTI_GLOSSY */
 			if(use_fresnel && order > 0) {
 				throughput *= interpolate_fresnel_color(-wr, wm, eta, F0, cspec0);
 			}
-			wr = mf_sample_phase_glossy(-wr, n, k, &throughput, wm);
+			wr = mf_sample_phase_glossy(-wr, &throughput, wm);
 #endif
 
 			lambda_r = mf_lambda(wr, alpha);
 
-#if defined(MF_MULTI_GLOSSY) || defined(MF_MULTI_GLASS)
 			if(!use_fresnel)
 				throughput *= color;
-#else
-			throughput *= color;
-#endif
 
 			C1_r = mf_C1(hr);
 			G1_r = mf_G1(wr, C1_r, lambda_r);
@@ -215,18 +175,16 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_eval)(
  * escaped the surface in wo. The function returns the throughput between wi and wo.
  * Without reflection losses due to coloring or fresnel absorption in conductors, the sampling is optimal.
  */
-ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3 *wo, const float3 color, const float alpha_x, const float alpha_y, ccl_addr_space uint *lcg_state
-#ifdef MF_MULTI_GLASS
-	, const float eta
-	, bool use_fresnel
-	, const float3 cspec0
-#elif defined(MF_MULTI_GLOSSY)
-	, float3 *n, float3 *k
-	, const float eta
-	, bool use_fresnel
-	, const float3 cspec0
-#endif
-)
+ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(
+	float3 wi,
+	float3 *wo,
+	const float3 color,
+	const float alpha_x,
+	const float alpha_y,
+	ccl_addr_space uint *lcg_state,
+	const float eta,
+	bool use_fresnel,
+	const float3 cspec0)
 {
 	const float2 alpha = make_float2(alpha_x, alpha_y);
 
@@ -237,17 +195,11 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3
 	float C1_r = 1.0f;
 	float G1_r = 0.0f;
 	bool outside = true;
-#ifdef MF_MULTI_GLASS
-	float F0 = fresnel_dielectric_cos(1.0f, eta);
-	if(use_fresnel) {
-		throughput = interpolate_fresnel_color(wi, normalize(wi + wr), eta, F0, cspec0);
-	}
-#elif defined(MF_MULTI_GLOSSY)
+
 	float F0 = fresnel_dielectric_cos(1.0f, eta);
 	if(use_fresnel) {
 		throughput = interpolate_fresnel_color(wi, normalize(wi + wr), eta, F0, cspec0);
 	}
-#endif
 
 	int order;
 	for(order = 0; order < 10; order++) {
@@ -262,13 +214,8 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3
 		                                                   lcg_step_float_addrspace(lcg_state)));
 
 		/* First-bounce color is already accounted for in mix weight. */
-#if defined(MF_MULTI_GLASS) || defined(MF_MULTI_GLOSSY)
 		if(!use_fresnel && order > 0)
 			throughput *= color;
-#else
-		if(order > 0)
-			throughput *= color;
-#endif
 
 		/* Bounce from the microfacet. */
 #ifdef MF_MULTI_GLASS
@@ -294,10 +241,6 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3
 					throughput *= t_color;
 			}
 		}
-#elif defined(MF_MULTI_DIFFUSE)
-		wr = mf_sample_phase_diffuse(wm,
-		                             lcg_step_float_addrspace(lcg_state),
-		                             lcg_step_float_addrspace(lcg_state));
 #else /* MF_MULTI_GLOSSY */
 		if(use_fresnel) {
 			float3 t_color = interpolate_fresnel_color(-wr, wm, eta, F0, cspec0);
@@ -307,7 +250,7 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3
 			else
 				throughput *= t_color;
 		}
-		wr = mf_sample_phase_glossy(-wr, n, k, &throughput, wm);
+		wr = mf_sample_phase_glossy(-wr, &throughput, wm);
 #endif
 
 		/* Update random walk parameters. */
@@ -319,6 +262,5 @@ ccl_device_forceinline float3 MF_FUNCTION_FULL_NAME(mf_sample)(float3 wi, float3
 }
 
 #undef MF_MULTI_GLASS
-#undef MF_MULTI_DIFFUSE
 #undef MF_MULTI_GLOSSY
 #undef MF_PHASE_FUNCTION