started a new branch for a material development cycle. new features: glass preview in the VPL renderer, more documentation

doc/macros.sty

@@ -43,22 +43,16 @@
 	}
 	
 \newcommand{\renderings}[1]{
-	\begin{figure}[h]
+	\begin{figure}[h!]
 		\centering
 		\hfill
 		#1
 	\end{figure}
 }
 
-\newcommand{\rendering}[2]{
+\newcommand{\rendering}[2]{\subfigure[#1]{\fbox{\includegraphics[width=0.4\textwidth]{images/#2}}}\hfill}
-	\subfigure[#1]{\fbox{\includegraphics[width=0.4\textwidth]{images/#2}}}
+\newcommand{\medrendering}[2]{ \subfigure[#1]{\fbox{\includegraphics[width=0.3\textwidth]{images/#2}}}\hfill}
-	\hfill
+\newcommand{\smallrendering}[2]{ \subfigure[#1]{\fbox{\includegraphics[width=0.2\textwidth]{images/#2}}}\hfill}
-}
-
-\newcommand{\smallrendering}[2]{
-	\subfigure[#1]{\fbox{\includegraphics[width=0.2\textwidth]{images/#2}}}
-	\hfill
-}
 
 \newcommand{\parameter}[3]{
 		\small\texttt{#1} & \small #2 & \small #3\\

include/mitsuba/hw/glrenderer.h

@@ -159,7 +159,7 @@ public:
 	void setColorMask(bool value);
 
 	/// Set the current fixed-function pipeline color
-	void setColor(const Spectrum &spec);
+	void setColor(const Spectrum &spec, Float alpha = 1.0f);
 
 	/// Push a view transformation onto the matrix stack
 	void pushTransform(const Transform &trafo);

include/mitsuba/hw/renderer.h

@@ -207,7 +207,7 @@ public:
 	virtual void setColorMask(bool value) = 0;
 
 	/// Set the current fixed-function pipeline color
-	virtual void setColor(const Spectrum &spec) = 0;
+	virtual void setColor(const Spectrum &spec, Float alpha = 1.0f) = 0;
 
 	/// Push a view transformation onto the matrix stack
 	virtual void pushTransform(const Transform &trafo) = 0;

include/mitsuba/hw/vpl.h

@@ -25,15 +25,17 @@
 MTS_NAMESPACE_BEGIN
 
 /**
- * This class is responsible for the on-demand creation of
+ * \brief This class is responsible for the on-demand creation of
- * GPU shaders to render meshes with a particular material
+ * GPU shaders to render meshes that are illuminated by a virtual 
- * illuminated by a virtual point light source. For each
+ * point light source. 
- * encountered BSDF-VPL pair, a custom piece of code describing
+ *
- * the characteristic light transport between them is created 
+ * For each encountered BSDF-VPL pair, a custom piece of code 
+ * describing the characteristic light transport between them is created 
  * and cached. To avoid generating a potentially huge (N squared) 
  * number of very similar programs, the implementation passes some 
  * properties using uniforms, in which case already existing code 
- * can be reused and we get something more like lower case n squared.
+ * can be reused and we get something more like lower case n squared
+ * (where lower n is the number of material types).
  */
 class MTS_EXPORT_HW VPLShaderManager : public Object {
 public:
@@ -55,9 +57,12 @@ public:
 	/// Release bound resources
 	void unbind();
 
-	/// Return all bound triangle meshes
+	/// Return all bound opaque triangle meshes
 	inline const std::vector<std::pair<const TriMesh *, Transform> > &getMeshes() const { return m_meshes; }
 
+	/// Return all bound transparent triangle meshes
+	inline const std::vector<std::pair<const TriMesh *, Transform> > &getTransparentMeshes() const { return m_transparentMeshes; }
+
 	/// Return the shadow cube map for debugging purposes
 	inline GPUTexture *getShadowMap() { return m_shadowMap; }
 
@@ -178,7 +183,7 @@ private:
 		int param_shadowMap, param_vplPos, param_camPos, param_vplPower;
 		int param_vplN, param_vplS, param_vplT, param_vplWi, param_vplUV;
 		int param_nearClip, param_invClipRange, param_minDist;
-		int param_diffuseSources, param_diffuseReceivers;
+		int param_diffuseSources, param_diffuseReceivers, param_alpha;
 
 		inline VPLProgramConfiguration() { }
 
@@ -272,6 +277,7 @@ private:
 	ref<GPUProgram> m_backgroundProgram;
 	VPLDependencyNode m_backgroundDependencies;
 	std::vector<std::pair<const TriMesh *, Transform> > m_meshes;
+	std::vector<std::pair<const TriMesh *, Transform> > m_transparentMeshes;
 	std::vector<std::pair<const GPUGeometry *, Transform> > m_drawList;
 };
 

include/mitsuba/render/shader.h

@@ -28,10 +28,12 @@ class Renderer;
 class GPUProgram;
 
 /**
- * Abstract hardware resource -- provides support for functionality,
+ * \brief Abstract hardware resource. 
- * which can alternatively also live on the GPU. By default, the
+ *
- * method 'createShader' just returns NULL, which means that the
+ * Implementations provides support for functionality that are also able to 
- * BSDF/Light source/Texture/.. cannot be used with a GPU-based renderer.
+ * live on the GPU. By default, the method 'createShader' just returns \c NULL,
+ * which means that the BSDF/Light source/Texture/.. has not yet been ported
+ * to the GPU-based renderer.
  */
 class MTS_EXPORT_RENDER HWResource {
 public:
@@ -41,8 +43,10 @@ public:
 };
 
 /**
- * Shader base class for use with a VPL-style renderer. Could implement
+ * \brief Shader base class for use with a VPL-style renderer.
- * one of various things, such as a BSDF, a light source, or a texture.
+ *
+ * Subclasses can implement one of various things, such as a BSDF, 
+ * a light source, or a texture.
  */
 class MTS_EXPORT_RENDER Shader : public Object {
 public:
@@ -52,59 +56,65 @@ public:
 		ELuminaireShader
 	};
 
-	/**
+	enum EFlags {
-	 * Return the type of shader represented by this instance
+		ETransparent = 0x01
-	 */
+	};
+
+	// Return the type of shader represented by this instance
 	inline EShaderType getType() const { return m_type; }
 
-	/**
+	/// Return a list of flags
-	 * List other shaders, on which this instance depends
+	inline uint32_t getFlags() const { return m_flags; }
-	 */
+
+
+	// List other shaders, on which this instance depends
 	virtual void putDependencies(std::vector<Shader *> &deps);
 
 	/**
-	 * Is this shader complete? This is mainly useful to
+	 * \brief Is this shader complete? 
-	 * check whether all dependencies could be constructed
+	 *
-	 * successfully. The default implementation returns true
+	 * This is mainly useful to check whether all dependencies 
+	 * could be constructed successfully. The default 
+	 * implementation returns \c true.
 	 */
 	virtual bool isComplete() const;
 
 	/**
-	 * Generate a string version of this shader's evaluation
+	 * \brief Generate a string version of this shader's evaluation
-	 * routine. The appended string should assign the name
+	 * routine. 
-	 * 'evalName' to this function. The function names of 
+	 *
-	 * depedencies (as specified by 'putDependencies'), are
+	 * The appended string should assign the name \c evalName to this 
-	 * supplied in the parameter 'depNames' in identical order.
+	 * function. The function names of depedencies (as specified by 
+	 * \ref putDependencies), are supplied in the parameter \c depNames
+	 * in identical order.
 	 */
 	virtual void generateCode(std::ostringstream &oss,
 			const std::string &evalName,
 			const std::vector<std::string> &depNames) const = 0;
 
 	/**
-	 * This function can optionally be implemented to resolve named 
+	 * \brief This function can optionally be implemented to resolve named 
 	 * program parameters to numerical IDs for increased performance.
-	 * The int array returned here will later be passed to bind().
+	 *
+	 * The int array returned here will later be passed to \ref bind().
 	 * The default implementation does nothing.
 	 */
 	virtual void resolve(const GPUProgram *program, const std::string &evalName,
 		std::vector<int> &parameterIDs) const;
 
 	/**
-	 * Configure the the associated GPU program. This
+	 * \brief Configure the the associated GPU program. 
-	 * function is typically used to bind textures and
+	 *
+	 * This function is typically used to bind textures and
 	 * to set program pararameters.
 	 */
 	virtual void bind(GPUProgram *program, const std::vector<int> &parameterIDs, 
 		int &textureUnitOffset) const;
 
-	/**
+	/// Release any bound resources.
-	 * Release any bound resources.
-	 */
 	virtual void unbind() const;
 
-	/**
+	/// Release all resources
-	 * Release all resources
-	 */
 	virtual void cleanup(Renderer *renderer);
 
 	MTS_DECLARE_CLASS()
@@ -113,8 +123,9 @@ protected:
 
 	/// Virtual destructor
 	virtual ~Shader();
-private:
+protected:
 	EShaderType m_type;
+	uint32_t m_flags;
 };
 
 MTS_NAMESPACE_END

src/bsdfs/dielectric.cpp

@@ -21,7 +21,7 @@
 
 MTS_NAMESPACE_BEGIN
 
-/*! \plugin{dielectric}{Ideal dielectric/glass material}
+/*! \plugin{dielectric}{Smooth dielectric material}
  *
  * \parameters{
  *     \parameter{intIOR}{\Float}{Interior index of refraction \default{1.5046}}
@@ -32,21 +32,59 @@ MTS_NAMESPACE_BEGIN
  *         factor used to modulate the transmittance component\default{1.0}}
  * }
  *
- * This plugin models an interface between two materials having mismatched 
+ * \renderings{
- * indices of refraction (e.g. a boundary between water and air).
+ *     \medrendering{Air-Water (IOR: 1$\leftrightarrow$1.33) interface, see \lstref{dielectric-water}}{bsdf_dielectric_water}
- * The microscopic surface structure of the surface is assumed to be perfectly 
+ *     \medrendering{Air-Diamond (IOR: 1$\leftrightarrow$2.419)}{bsdf_dielectric_diamond}
- * smooth, resulting in a degenerate BSDF described by a Dirac delta function.
+ *     \medrendering{Air-Glass (1$\leftrightarrow$1.504) interface with absorption, see \lstref{dielectric-glass}}{bsdf_dielectric_glass}
- * For non-smooth interfaces, please take a look at the \pluginref{roughglass}
+ * }
- * model. When using this plugin, it is crucial that the scene contains
+ *
- * meaningful and mutally compatible index of refraction change -- see
+ * This plugin models an interface between two dielectric materials having mismatched 
- * \figref{glass-explanation} for an example.
+ * indices of refraction (for instance, water and air). Exterior and interior IOR values
+ * can each be independently specified, where ``exterior'' refers to the side that contains 
+ * the surface normal. When no parameters are given, the plugin activates the defaults, which
+ * describe a borosilicate glass BK7/air interface.
+ *
+ * In this model, the microscopic surface structure of the surface is assumed to be perfectly 
+ * smooth, resulting in a degenerate\footnote{Meaning that for any given incoming ray of light,
+ * the model always scatters into a discrete set of directions, as opposed to a continuum.} 
+ * BSDF described by a Dirac delta function. For a similar model that describes a rough 
+ * surface microstructure, take a look at the \pluginref{roughglass} plugin. 
+ *
+ * \begin{xml}[caption=A simple air-to-water interface, label=lst:dielectric-water]
+ * <shape type="...">
+ *     <bsdf type="dielectric">
+ *         <float name="intIOR" value="1.33"/>
+ *         <float name="extIOR" value="1.0"/>
+ *     </bsdf>
+ * <shape>
+ * \end{xml}
+ *
+ * When using this model, it is crucial that the scene contains
+ * meaningful and mutally compatible indices of refraction changes---see
+ * \figref{glass-explanation} for a description of what this entails.
+ * 
+ * In many cases, we will want to additionally describe the \emph{medium} within a
+ * dielectric material. This requires the use of a rendering technique that is
+ * aware of media (e.g. the volumetric path tracer). An example of how one might
+ * describe a slightly absorbing piece of glass is given below:
+ *
+ * \begin{xml}[caption=A glass material with absorption, label=lst:dielectric-glass]
+ * <shape type="...">
+ *     <bsdf type="dielectric">
+ *         <float name="intIOR" value="1.504"/>
+ *         <float name="extIOR" value="1.0"/>
+ *     </bsdf>
+ *     <medium type="homogeneous" name="interior">
+ *			<rgb name="sigmaS" value="0, 0, 0"/>
+ *			<rgb name="sigmaA" value="4, 4, 2"/>
+ *     </medium>
+ * <shape>
+ * \end{xml}
  * 
- * The default settings of this plugin are set to a borosilicate glass BK7/air 
- * interface.
  */
-class Dielectric : public BSDF {
+class SmoothDielectric : public BSDF {
 public:
-	Dielectric(const Properties &props) 
+	SmoothDielectric(const Properties &props) 
 			: BSDF(props) {
 		/* Specifies the internal index of refraction at the interface */
 		m_intIOR = props.getFloat("intIOR", 1.5046f);
@@ -66,7 +104,7 @@ public:
 		m_usesRayDifferentials = false;
 	}
 
-	Dielectric(Stream *stream, InstanceManager *manager) 
+	SmoothDielectric(Stream *stream, InstanceManager *manager) 
 			: BSDF(stream, manager) {
 		m_intIOR = stream->readFloat();
 		m_extIOR = stream->readFloat();
@@ -81,7 +119,7 @@ public:
 		m_usesRayDifferentials = false;
 	}
 
-	virtual ~Dielectric() {
+	virtual ~SmoothDielectric() {
 		delete[] m_type;
 	}
 
@@ -339,7 +377,7 @@ public:
 
 	std::string toString() const {
 		std::ostringstream oss;
-		oss << "Dielectric[" << endl
+		oss << "SmoothDielectric[" << endl
 			<< "  intIOR = " << m_intIOR << "," << endl 
 			<< "  extIOR = " << m_extIOR << "," << endl
 			<< "  specularReflectance = " << indent(m_specularReflectance->toString()) << "," << endl
@@ -348,6 +386,8 @@ public:
 		return oss.str();
 	}
 
+	Shader *createShader(Renderer *renderer) const;
+
 	MTS_DECLARE_CLASS()
 private:
 	Float m_intIOR, m_extIOR;
@@ -355,7 +395,34 @@ private:
 	ref<Texture> m_specularReflectance;
 };
 
+/* Fake glass shader -- it is really hopeless to visualize
+   this material in the VPL renderer, so let's try to do at least 
+   something that suggests the presence of a transparent boundary */
+class SmoothDielectricShader : public Shader {
+public:
+	SmoothDielectricShader(Renderer *renderer) :
+		Shader(renderer, EBSDFShader) {
+		m_flags = ETransparent;
+	}
 
-MTS_IMPLEMENT_CLASS_S(Dielectric, false, BSDF)
+	void generateCode(std::ostringstream &oss,
-MTS_EXPORT_PLUGIN(Dielectric, "Dielectric BSDF");
+			const std::string &evalName,
+			const std::vector<std::string> &depNames) const {
+		oss << "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
+			<< "    return vec3(0.08);" << endl
+			<< "}" << endl;
+		oss << "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
+			<< "    return vec3(0.08);" << endl
+			<< "}" << endl;
+	}
+	MTS_DECLARE_CLASS()
+};
+
+Shader *SmoothDielectric::createShader(Renderer *renderer) const { 
+	return new SmoothDielectricShader(renderer);
+}
+
+MTS_IMPLEMENT_CLASS(SmoothDielectricShader, false, Shader)
+MTS_IMPLEMENT_CLASS_S(SmoothDielectric, false, BSDF)
+MTS_EXPORT_PLUGIN(SmoothDielectric, "Smooth dielectric BSDF");
 MTS_NAMESPACE_END

src/bsdfs/roughglass.cpp

@@ -23,7 +23,7 @@
 
 MTS_NAMESPACE_BEGIN
 
-/*! \plugin{roughglass}{Rough dielectric/glass material}
+/*! \plugin{roughglass}{Rough dielectric material}
  * \parameters{
  *     \parameter{distribution}{\String}{
  *          Specifies the type of microfacet normal distribution 
@@ -58,13 +58,19 @@ MTS_NAMESPACE_BEGIN
  *         factor used to modulate the transmittance component\default{1.0}}
  * }
  *
+ * \renderings{
+ *     \medrendering{Beckmann, $\alpha$=0.2}{bsdf_dielectric_glass}
+ *     \medrendering{Beckmann, $\alpha$=0.3}{bsdf_dielectric_glass}
+ *     \medrendering{Beckmann, $\alpha$=0.4}{bsdf_dielectric_glass}
+ * }
+ *
  * This plugin implements a realistic microfacet scattering model for rendering
- * rough dielectric surfaces, such as ground glass. Microfacet theory
+ * rough interfaces between dielectric materials, such as a transition from air to ground glass. 
- * describes surfaces as an arrangement of unresolved and ideally specular 
+ * Microfacet theory describes surfaces as an arrangement of unresolved and ideally specular 
  * facets, whose normals are given by a specially chosen \emph{microfacet 
  * distribution}. By accounting for shadowing and masking effects between 
  * these facets, it is possible to reproduce the off-specular reflections 
- * peaks observed in measurements of real-world materials.
+ * peaks observed in real-world measurements of such materials.
  *
  * This plugin is essentially the ``roughened'' equivalent of the plugin
  * \pluginref{dielectric}. Its implementation is based on the paper 
@@ -95,7 +101,7 @@ public:
 		m_specularReflectance = new ConstantSpectrumTexture(
 			props.getSpectrum("specularReflectance", Spectrum(1.0f)));
 		m_specularTransmittance = new ConstantSpectrumTexture(
-			props.getSpectrum("specularTransmittance", Spectrum(1.9f)));
+			props.getSpectrum("specularTransmittance", Spectrum(1.0f)));
 
 		Float alpha;
 		if (props.hasProperty("alphaB")) {
@@ -763,6 +769,8 @@ public:
 		return oss.str();
 	}
 
+	Shader *createShader(Renderer *renderer) const;
+
 	MTS_DECLARE_CLASS()
 private:
 	EDistribution m_distribution;
@@ -772,6 +780,34 @@ private:
 	Float m_intIOR, m_extIOR;
 };
 
+/* Fake glass shader -- it is really hopeless to visualize
+   this material in the VPL renderer, so let's try to do at least 
+   something that suggests the presence of a transparent boundary */
+class RoughGlassShader : public Shader {
+public:
+	RoughGlassShader(Renderer *renderer) :
+		Shader(renderer, EBSDFShader) {
+		m_flags = ETransparent;
+	}
+
+	void generateCode(std::ostringstream &oss,
+			const std::string &evalName,
+			const std::vector<std::string> &depNames) const {
+		oss << "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
+			<< "    return vec3(0.08);" << endl
+			<< "}" << endl;
+		oss << "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
+			<< "    return vec3(0.08);" << endl
+			<< "}" << endl;
+	}
+	MTS_DECLARE_CLASS()
+};
+
+Shader *RoughGlass::createShader(Renderer *renderer) const { 
+	return new RoughGlassShader(renderer);
+}
+
+MTS_IMPLEMENT_CLASS(RoughGlassShader, false, Shader)
 MTS_IMPLEMENT_CLASS_S(RoughGlass, false, BSDF)
 MTS_EXPORT_PLUGIN(RoughGlass, "Rough glass BSDF");
 MTS_NAMESPACE_END

src/integrators/vpl/vpl.cpp

@@ -54,6 +54,7 @@ public:
 	/// Draw the full scene using additive blending and shadow maps
 	void drawShadowedScene(const Scene *scene, const VPL &vpl) {
 	const std::vector<std::pair<const TriMesh *, Transform> > meshes = m_shaderManager->getMeshes();
+	const std::vector<std::pair<const TriMesh *, Transform> > transpMeshes = m_shaderManager->getTransparentMeshes();
 		const ProjectiveCamera *camera = static_cast<const ProjectiveCamera *>(scene->getCamera());
 		Point2 jitter(0.5f - m_random->nextFloat(), 0.5f - m_random->nextFloat());
 		Transform projectionTransform = camera->getGLProjectionTransform(jitter);
@@ -75,7 +76,29 @@ public:
 			m_shaderManager->unbind();
 		}
 		m_renderer->endDrawingMeshes();
+
 		m_shaderManager->drawBackground(clipToWorld, camPos, 1.0f);
+
+		if (transpMeshes.size() > 0) {
+			m_renderer->setDepthMask(false);
+			m_renderer->setBlendMode(Renderer::EBlendAlpha);
+			m_renderer->beginDrawingMeshes();
+			for (unsigned int j=0; j<transpMeshes.size(); j++) {
+				const TriMesh *mesh = transpMeshes[j].first;
+				bool hasTransform = !transpMeshes[j].second.isIdentity();
+				m_shaderManager->configure(vpl, mesh->getBSDF(), mesh->getLuminaire(),
+					camPos, !mesh->hasVertexNormals());
+				if (hasTransform)
+					m_renderer->pushTransform(transpMeshes[j].second);
+				m_renderer->drawTriMesh(mesh);
+				if (hasTransform)
+					m_renderer->popTransform();
+				m_shaderManager->unbind();
+			}
+			m_renderer->endDrawingMeshes();
+			m_renderer->setDepthMask(true);
+			m_renderer->setBlendMode(Renderer::EBlendNone);
+		}
 	}
 
 	bool preprocess(const Scene *scene, RenderQueue *queue, const RenderJob *job,

src/libhw/glrenderer.cpp

@@ -742,9 +742,11 @@ void GLRenderer::blitQuad(bool flipVertically) {
 	glGetIntegerv(GL_VIEWPORT, viewport);
 	Vector2 scrSize((float) viewport[2], (float) viewport[3]);
 	glMatrixMode(GL_PROJECTION);
+	glPushMatrix();
 	glLoadIdentity();
 	glOrtho(0, scrSize.x, scrSize.y, 0, -1, 1);
 	glMatrixMode(GL_MODELVIEW);
+	glPushMatrix();
 	glLoadIdentity();
 	const Float zDepth = -1.0f;
 	glBegin(GL_QUADS);
@@ -757,6 +759,9 @@ void GLRenderer::blitQuad(bool flipVertically) {
 	glTexCoord2f(0.0f, flipVertically ? 0.0f : 1.0f);
 	glVertex3f(0.0f, scrSize.y, zDepth);
 	glEnd();
+	glPopMatrix();
+	glMatrixMode(GL_PROJECTION);
+	glPopMatrix();
 }
 
 void GLRenderer::drawText(const Point2i &_pos, 
@@ -966,10 +971,10 @@ void GLRenderer::finish() {
 	m_queuedTriangles = 0;
 }
 
-void GLRenderer::setColor(const Spectrum &spec) {
+void GLRenderer::setColor(const Spectrum &spec, Float alpha) {
 	Float r, g, b;
 	spec.toLinearRGB(r, g, b);
-	glColor4f(r, g, b, 1);
+	glColor4f(r, g, b, alpha);
 }
 
 void GLRenderer::setBlendMode(EBlendMode mode) {

src/libhw/vpl.cpp

@@ -55,7 +55,7 @@ void VPLShaderManager::init() {
 			"varying float depth;\n"
 			"\n"
 			"void main() {\n"
-			"	depth = 0;\n" // avoid a (incorrect?) warning
+			"	depth = 0;\n" // avoid an (incorrect?) warning
 			"   for (int side = 0; side < 6; side++) {\n"
 			"	    gl_Layer = side;\n"
 			"       for (int i = 0; i < gl_VerticesIn; i++) {\n"
@@ -134,8 +134,12 @@ void VPLShaderManager::init() {
 					GPUGeometry *gpuGeo = m_renderer->registerGeometry(triMesh);
 					Shader *shader = triMesh->hasBSDF() ? 
 						m_renderer->registerShaderForResource(triMesh->getBSDF()) : NULL;
-					if (shader != NULL && !shader->isComplete())
+					if (shader != NULL && !shader->isComplete()) {
 						m_renderer->unregisterShaderForResource(triMesh->getBSDF());
+					} else if (shader->getFlags() & Shader::ETransparent) {
+						m_transparentMeshes.push_back(std::make_pair(triMesh.get(), instance->getWorldTransform()));
+						continue;
+					}
 					m_meshes.push_back(std::make_pair(triMesh.get(), instance->getWorldTransform()));
 					if (gpuGeo)
 						m_drawList.push_back(std::make_pair(gpuGeo, instance->getWorldTransform()));
@@ -146,8 +150,12 @@ void VPLShaderManager::init() {
 		GPUGeometry *gpuGeo = m_renderer->registerGeometry(triMesh);
 		Shader *shader = triMesh->hasBSDF() ? 
 			m_renderer->registerShaderForResource(triMesh->getBSDF()) : NULL;
-		if (shader != NULL && !shader->isComplete())
+		if (shader != NULL && !shader->isComplete()) {
 			m_renderer->unregisterShaderForResource(triMesh->getBSDF());
+		} else if (shader->getFlags() & Shader::ETransparent) {
+			m_transparentMeshes.push_back(std::make_pair(triMesh.get(), Transform()));
+			continue;
+		}
 		m_meshes.push_back(std::make_pair(triMesh.get(), Transform()));
 		if (gpuGeo)
 			m_drawList.push_back(std::make_pair(gpuGeo, Transform()));
@@ -353,7 +361,6 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 		: m_renderer->getShaderForResource(luminaire);
 	std::ostringstream oss;
 
-	
 	if (bsdfShader == NULL || vplShader == NULL ||
 		(luminaire != NULL && lumShader == NULL)) {
 		/* Unsupported! */
@@ -361,6 +368,13 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 		return;
 	}
 
+#if 0
+	if (bsdfShader->getFlags() & Shader::ETransparent) {
+		m_renderer->setColor(Spectrum(1.0f), 0.3f);
+		return;
+	}
+#endif
+
 	bool anisotropic = bsdf->getType() & BSDF::EAnisotropic;
 
 	m_targetConfig = VPLProgramConfiguration(vplShader, bsdfShader, 
@@ -464,7 +478,7 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 			<< "/* Uniform inputs */" << endl
 			<< "uniform samplerCube shadowMap;" << endl
 			<< "uniform vec3 vplPower, vplS, vplT, vplN, vplWi;" << endl
-			<< "uniform float nearClip, invClipRange, minDist;" << endl
+			<< "uniform float nearClip, invClipRange, minDist, alpha;" << endl
 			<< "uniform vec2 vplUV;" << endl
 			<< "uniform bool diffuseSources, diffuseReceivers;" << endl
 			<< "varying vec3 vertexColor;" << endl
@@ -546,7 +560,7 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 		} else {
 			oss << ";" << endl;
 		}
-		oss << "   gl_FragColor.a = 1.0;" << endl
+		oss << "   gl_FragColor.a = alpha;" << endl
 			<< "}" << endl;
 
 		program->setSource(GPUProgram::EFragmentProgram, oss.str());
@@ -572,6 +586,7 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 		m_targetConfig.param_minDist = program->getParameterID("minDist", false);
 		m_targetConfig.param_diffuseSources = program->getParameterID("diffuseSources", false);
 		m_targetConfig.param_diffuseReceivers = program->getParameterID("diffuseReceivers", false);
+		m_targetConfig.param_alpha = program->getParameterID("alpha", false);
 		m_current.program = program;
 		m_current.config = m_targetConfig;
 		m_programs[configName] = m_current;
@@ -589,11 +604,16 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 	program->setParameter(config.param_vplN, vpl.its.shFrame.n);
 	program->setParameter(config.param_vplS, vpl.its.shFrame.s);
 	program->setParameter(config.param_vplT, vpl.its.shFrame.t);
+	
+	program->setParameter(config.param_alpha, 
+		bsdfShader->getFlags() & Shader::ETransparent ? 0.5f : 1.0f);
+
 	if (vpl.type == ESurfaceVPL) {
 		program->setParameter(config.param_vplWi, vpl.its.wi);
 		program->setParameter(config.param_vplUV, vpl.its.uv);
 		program->setParameter(config.param_diffuseSources, m_diffuseSources);
 	}
+
 	Spectrum power = vpl.P;
 	if (m_diffuseSources && vpl.type == ESurfaceVPL)
 		power *= vpl.its.shape->getBSDF()->getDiffuseReflectance(vpl.its) * INV_PI;

src/librender/shader.cpp

@@ -21,7 +21,7 @@
 MTS_NAMESPACE_BEGIN
 	
 Shader::Shader(Renderer *renderer, EShaderType type)
-  : m_type(type) {
+  : m_type(type), m_flags(0) {
 }
 
 Shader::~Shader() {

src/qtgui/preview.cpp

@@ -473,6 +473,7 @@ void PreviewThread::run() {
 
 void PreviewThread::oglRenderVPL(PreviewQueueEntry &target, const VPL &vpl) {
 	const std::vector<std::pair<const TriMesh *, Transform> > meshes = m_shaderManager->getMeshes();
+	const std::vector<std::pair<const TriMesh *, Transform> > transpMeshes = m_shaderManager->getTransparentMeshes();
 
 	m_shaderManager->setVPL(vpl);
 
@@ -510,6 +511,26 @@ void PreviewThread::oglRenderVPL(PreviewQueueEntry &target, const VPL &vpl) {
 	m_renderer->endDrawingMeshes();
 	m_shaderManager->drawBackground(clipToWorld, camPos,
 		m_backgroundScaleFactor);
+	if (transpMeshes.size() > 0) {
+		m_renderer->setDepthMask(false);
+		m_renderer->setBlendMode(Renderer::EBlendAlpha);
+		m_renderer->beginDrawingMeshes();
+		for (size_t j=0; j<transpMeshes.size(); j++) {
+			const TriMesh *mesh = transpMeshes[j].first;
+			bool hasTransform = !transpMeshes[j].second.isIdentity();
+			m_shaderManager->configure(vpl, mesh->getBSDF(), 
+				mesh->getLuminaire(), camPos, !mesh->hasVertexNormals());
+			if (hasTransform)
+				m_renderer->pushTransform(transpMeshes[j].second);
+			m_renderer->drawTriMesh(mesh);
+			if (hasTransform)
+				m_renderer->popTransform();
+			m_shaderManager->unbind();
+		}
+		m_renderer->endDrawingMeshes();
+		m_renderer->setBlendMode(Renderer::EBlendNone);
+		m_renderer->setDepthMask(true);
+	}
 	m_framebuffer->releaseTarget();
 
 	target.buffer->activateTarget();