bsdf.cpp

/***************************************************************************
 * Copyright 1998-2018 by authors (see AUTHORS.txt)                        *
 *                                                                         *
 *   This file is part of LuxCoreRender.                                   *
 *                                                                         *
 * Licensed under the Apache License, Version 2.0 (the "License");         *
 * you may not use this file except in compliance with the License.        *
 * You may obtain a copy of the License at                                 *
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 *     http://www.apache.org/licenses/LICENSE-2.0                          *
 *                                                                         *
 * Unless required by applicable law or agreed to in writing, software     *
 * distributed under the License is distributed on an "AS IS" BASIS,       *
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.*
 * See the License for the specific language governing permissions and     *
 * limitations under the License.                                          *
 ***************************************************************************/

#include "slg/bsdf/bsdf.h"
#include "slg/scene/scene.h"

using namespace luxrays;
using namespace slg;
using namespace std;

// Used when hitting a surface
void BSDF::Init(const bool fixedFromLight, const Scene &scene, const Ray &ray,
		const RayHit &rayHit, const float passThroughEvent, const PathVolumeInfo *volInfo) {
	hitPoint.fromLight = fixedFromLight;
	hitPoint.passThroughEvent = passThroughEvent;

	hitPoint.p = ray(rayHit.t);
	hitPoint.fixedDir = -ray.d;

	// Get the scene object
	sceneObject = scene.objDefs.GetSceneObject(rayHit.meshIndex);
	hitPoint.objectID = sceneObject->GetID();
	
	// Get the triangle
	mesh = sceneObject->GetExtMesh();

	// Initialized local to world object space transformation
	mesh->GetLocal2World(ray.time, hitPoint.localToWorld);

	// Get the material
	material = sceneObject->GetMaterial();

	// Interpolate face normal
	hitPoint.geometryN = mesh->GetGeometryNormal(ray.time, rayHit.triangleIndex);
	hitPoint.shadeN = mesh->InterpolateTriNormal(ray.time, rayHit.triangleIndex, rayHit.b1, rayHit.b2);
	hitPoint.intoObject = (Dot(ray.d, hitPoint.geometryN) < 0.f);

	// Set interior and exterior volumes
	volInfo->SetHitPointVolumes(hitPoint,
			material->GetInteriorVolume(hitPoint, hitPoint.passThroughEvent),
			material->GetExteriorVolume(hitPoint, hitPoint.passThroughEvent),
			scene.defaultWorldVolume);

	// Interpolate color
	hitPoint.color = mesh->InterpolateTriColor(rayHit.triangleIndex, rayHit.b1, rayHit.b2);

	// Interpolate alpha
	hitPoint.alpha = mesh->InterpolateTriAlpha(rayHit.triangleIndex, rayHit.b1, rayHit.b2);

	// Check if it is a light source
	if (material->IsLightSource())
		triangleLightSource = scene.lightDefs.GetLightSourceByMeshAndTriIndex(rayHit.meshIndex, rayHit.triangleIndex);
	else
		triangleLightSource = NULL;

	// Interpolate UV coordinates
	hitPoint.uv = mesh->InterpolateTriUV(rayHit.triangleIndex, rayHit.b1, rayHit.b2);

	// Compute geometry differentials
	mesh->GetDifferentials(hitPoint.localToWorld, rayHit.triangleIndex, hitPoint.shadeN,
		&hitPoint.dpdu, &hitPoint.dpdv,
		&hitPoint.dndu, &hitPoint.dndv);

	// Apply bump or normal mapping
	material->Bump(&hitPoint);

	// Build the local reference system
	frame = hitPoint.GetFrame();
}

// Used when hitting a volume scatter point
void BSDF::Init(const bool fixedFromLight, const Scene &scene, const luxrays::Ray &ray,
		const Volume &volume, const float t, const float passThroughEvent) {
	hitPoint.fromLight = fixedFromLight;
	hitPoint.passThroughEvent = passThroughEvent;

	hitPoint.p = ray(t);
	hitPoint.fixedDir = -ray.d;

	sceneObject = NULL;
	mesh = NULL;
	material = &volume;

	hitPoint.geometryN = Normal(-ray.d);
	hitPoint.shadeN = hitPoint.geometryN;
	CoordinateSystem(Vector(hitPoint.shadeN), &hitPoint.dpdu, &hitPoint.dpdv);
	hitPoint.dndu = hitPoint.dndv = Normal(0.f, 0.f, 0.f);

	hitPoint.intoObject = true;
	hitPoint.interiorVolume = &volume;
	hitPoint.exteriorVolume = &volume;

	hitPoint.color = Spectrum(1.f);
	hitPoint.alpha = 1.f;

	triangleLightSource = NULL;

	hitPoint.uv = UV(0.f, 0.f);
	
	hitPoint.objectID = 0;

	// Build the local reference system
	frame.SetFromZ(hitPoint.shadeN);
}

bool BSDF::IsCameraInvisible() const {
	return (sceneObject) ? sceneObject->IsCameraInvisible() : false;
}

u_int BSDF::GetObjectID() const {
	return (sceneObject) ? sceneObject->GetID() : std::numeric_limits<u_int>::max();
}

Spectrum BSDF::Evaluate(const Vector &generatedDir,
		BSDFEvent *event, float *directPdfW, float *reversePdfW) const {
	const Vector &eyeDir = hitPoint.fromLight ? generatedDir : hitPoint.fixedDir;
	const Vector &lightDir = hitPoint.fromLight ? hitPoint.fixedDir : generatedDir;

	const float dotLightDirNG = Dot(lightDir, hitPoint.geometryN);
	const float absDotLightDirNG = fabsf(dotLightDirNG);
	const float dotEyeDirNG = Dot(eyeDir, hitPoint.geometryN);
	const float absDotEyeDirNG = fabsf(dotEyeDirNG);

	if (!IsVolume()) {
		// These kind of tests make sense only for materials

		if ((absDotLightDirNG < DEFAULT_COS_EPSILON_STATIC) ||
				(absDotEyeDirNG < DEFAULT_COS_EPSILON_STATIC))
			return Spectrum();

		const float sideTest = dotEyeDirNG * dotLightDirNG;
		if (((sideTest > 0.f) && !(material->GetEventTypes() & REFLECT)) ||
				((sideTest < 0.f) && !(material->GetEventTypes() & TRANSMIT)))
			return Spectrum();
	}

	const Vector localLightDir = frame.ToLocal(lightDir);
	const Vector localEyeDir = frame.ToLocal(eyeDir);
	const Spectrum result = material->Evaluate(hitPoint, localLightDir, localEyeDir,
			event, directPdfW, reversePdfW);
	assert (!result.IsNaN() && !result.IsInf());

	// Adjoint BSDF (not for volumes)
	if (hitPoint.fromLight && !IsVolume())
		return result * (absDotEyeDirNG / absDotLightDirNG);
	else
		return result;
}

Spectrum BSDF::ShadowCatcherSample(Vector *sampledDir,
		float *pdfW, float *absCosSampledDir, BSDFEvent *event) const {
	// Just continue to trace the ray
	*sampledDir = -hitPoint.fixedDir;
	*absCosSampledDir = AbsDot(*sampledDir, hitPoint.geometryN);

	*pdfW = 1.f;
	*event = SPECULAR | TRANSMIT;
	const Spectrum result(1.f);

	// Adjoint BSDF
	if (hitPoint.fromLight) {
		const float absDotFixedDirNG = AbsDot(hitPoint.fixedDir, hitPoint.geometryN);
		const float absDotSampledDirNG = AbsDot(*sampledDir, hitPoint.geometryN);
		return result * (absDotSampledDirNG / absDotFixedDirNG);
	} else
		return result;
}

Spectrum BSDF::Sample(Vector *sampledDir,
		const float u0, const float u1,
		float *pdfW, float *absCosSampledDir, BSDFEvent *event) const {
	Vector localFixedDir = frame.ToLocal(hitPoint.fixedDir);
	Vector localSampledDir;

	const Spectrum result = material->Sample(hitPoint,
			localFixedDir, &localSampledDir, u0, u1, hitPoint.passThroughEvent,
			pdfW, absCosSampledDir, event);
	if (result.Black())
		return result;

	*sampledDir = frame.ToWorld(localSampledDir);

	// Adjoint BSDF
	if (hitPoint.fromLight) {
		const float absDotFixedDirNG = AbsDot(hitPoint.fixedDir, hitPoint.geometryN);
		const float absDotSampledDirNG = AbsDot(*sampledDir, hitPoint.geometryN);
		return result * (absDotSampledDirNG / absDotFixedDirNG);
	} else
		return result;
}

void BSDF::Pdf(const Vector &sampledDir, float *directPdfW, float *reversePdfW) const {
	const Vector &eyeDir = hitPoint.fromLight ? sampledDir : hitPoint.fixedDir;
	const Vector &lightDir = hitPoint.fromLight ? hitPoint.fixedDir : sampledDir;
	Vector localLightDir = frame.ToLocal(lightDir);
	Vector localEyeDir = frame.ToLocal(eyeDir);

	material->Pdf(hitPoint, localLightDir, localEyeDir, directPdfW, reversePdfW);
}

Spectrum BSDF::GetPassThroughTransparency() const {
	const Vector localFixedDir = frame.ToLocal(hitPoint.fixedDir);

	return material->GetPassThroughTransparency(hitPoint, localFixedDir, hitPoint.passThroughEvent);
}

Spectrum BSDF::GetEmittedRadiance(float *directPdfA, float *emissionPdfW) const {
	return triangleLightSource ?
		triangleLightSource->GetRadiance(hitPoint, directPdfA, emissionPdfW) :
		Spectrum();
}