More mitsuba-related bugfixes

 It think something's wrong with specular part of instr_eval_execute(),
    point lights end up extremely bright in ditt scene

Author: Crisspl

include/irr/builtin/glsl/sampling/cos_weighted.glsl

@@ -5,7 +5,7 @@
 
 vec3 irr_glsl_projected_hemisphere_generate(in vec2 _sample)
 {
-    vec2 p = irr_glsl_concentricMapping(_sample);
+    vec2 p = irr_glsl_concentricMapping(_sample*0.99999+0.000005);
 
     float z = sqrt(max(0.0, 1.0 - p.x*p.x - p.y*p.y));
 

include/irr/builtin/material_compiler/glsl/common.glsl

@@ -918,7 +918,8 @@ irr_glsl_LightSample irr_bsdf_cos_generate(in MC_precomputed_t precomp, in instr
 			out_microfacet.inner = irr_glsl_calcAnisotropicMicrofacetCache(currInteraction.inner, s);
 			finalizeMicrofacet(out_microfacet);
 
-			rem = albedo*irr_glsl_oren_nayar_cos_remainder_and_pdf(localPdf, s, currInteraction.inner.isotropic, ax2);
+			const float NdotL = irr_glsl_conditionalAbsOrMax(is_bsdf, s.NdotL, 0.0);
+			rem = albedo*irr_glsl_oren_nayar_cos_remainder_and_pdf_wo_clamps(localPdf, ax2, dot(currInteraction.inner.isotropic.V.dir, s.L), NdotL, NdotV);
 			localPdf *= is_bsdf ? 0.5 : 1.0;
 		} else
 #endif
@@ -927,8 +928,8 @@ irr_glsl_LightSample irr_bsdf_cos_generate(in MC_precomputed_t precomp, in instr
 		{
 			localPdf = 1.0;
 
-			const float TdotV2 = currInteraction.inner.TdotV * currInteraction.inner.TdotV;
-			const float BdotV2 = currInteraction.inner.BdotV * currInteraction.inner.BdotV;
+			const float TdotV2 = currInteraction.TdotV2;
+			const float BdotV2 = currInteraction.BdotV2;
 			const float NdotV2 = currInteraction.inner.isotropic.NdotV_squared;
 
 			const vec3 upperHemisphereLocalV = currInteraction.inner.isotropic.NdotV < 0.0 ? -localV : localV;

include/irr/builtin/shaders/loaders/mitsuba/instance_data_struct.glsl

@@ -11,6 +11,7 @@ struct InstanceData
 	vec3 normalMatrixRow2;
 	uint _padding;//not needed
 	uvec2 emissive;
+	float determinant;
 	uint front_prefetch_count;
 	uint front_nprecomp_count;
 	uint front_genchoice_count;

include/irr/ext/MitsubaLoader/CMitsubaLoader.h

@@ -53,6 +53,7 @@ class CMitsubaLoader : public asset::IAssetLoader
 				};
 			} normalMat;
 			uint64_t emissive;//uvec2, rgb19e7
+			float determinant;
 			uint32_t front_prefetch_count;
 			uint32_t front_nprecomp_count;
 			uint32_t front_genchoice_count;

src/irr/asset/material_compiler/CMaterialCompilerGLSLBackendCommon.cpp

@@ -29,6 +29,7 @@ namespace material_compiler
 				coat->eta = coat_blend->eta;
 				coat->ndf = coat_blend->ndf;
 				coat->shadowing = coat_blend->shadowing;
+				coat->thin = false;
 			}
 			cache->insert({ coat_blend, coat });
 

src/irr/ext/MitsubaLoader/CMitsubaLoader.cpp

@@ -284,7 +284,7 @@ void main()
 	mat2 dUV = mat2(dFdx(UV),dFdy(UV));
 
 	// "The sign of this computation is negated when the value of GL_CLIP_ORIGIN (the clip volume origin, set with glClipControl) is GL_UPPER_LEFT."
-	const bool front = !gl_FrontFacing;
+	const bool front = (!gl_FrontFacing) != (InstData.data[InstanceIndex].determinant < 0.0);
 	MC_precomputed_t precomp = precomputeData(front);
 #ifdef TEX_PREFETCH_STREAM
 	runTexPrefetchStream(getTexPrefetchStream(precomp), UV, dUV);
@@ -1704,6 +1704,7 @@ inline core::smart_refctd_ptr<asset::ICPUDescriptorSet> CMitsubaLoader::createDS
 			SInstanceData instData;
 
 			instData.tform = inst.tform;
+			instData.determinant = instData.tform.getPseudoDeterminant().x;
 			instData.tform.getSub3x3InverseTranspose(instData.normalMat.normalMatrix);
 			instData.emissive = core::rgb32f_to_rgb19e7(emissive.pointer);
 

src/irr/ext/MitsubaLoader/CMitsubaMaterialCompilerFrontend.cpp

@@ -417,14 +417,14 @@ auto CMitsubaMaterialCompilerFrontend::compileToIRTree(asset::material_compiler:
             if (bsdf->type == IR::CBSDFNode::ET_MICROFACET_DIELECTRIC)
             {
                 auto* dielectric = static_cast<const IR::CMicrofacetDielectricBSDFNode*>(bsdf);
-                if (!dielectric->thin) // do not copy thin dielectrics
-                {
-                    auto* copy = static_cast<IR::CMicrofacetDielectricBSDFNode*>(ir->copyNode(front));
+                auto* copy = static_cast<IR::CMicrofacetDielectricBSDFNode*>(ir->copyNode(front));
+                if (!copy->thin) //we're always outside in case of thin dielectric
                     copy->eta = IRNode::color_t(1.f) / copy->eta;
 
-                    return copy;
-                }
+                return copy;
             }
+            else if (bsdf->type == IR::CBSDFNode::ET_MICROFACET_DIFFTRANS)
+                return ir->copyNode(front);
         }
         [[fallthrough]]; // intentional
         default: