diff --git a/CMakeLists.txt b/CMakeLists.txt
index 62d09c25..10aa5f8f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -137,8 +137,8 @@ target_compile_options (
 # python3 (for building python binding)
 ###############################################################################
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/src/ext/pybind11/tools")
-set(KRR_PYTHON_EXECUTABLE "" CACHE STRING "Path to selected python executable")
-set(Python_ROOT_DIR ${KRR_PYTHON_EXECUTABLE})
+set(KRR_PYTHON_PATH "" CACHE STRING "Path to selected python executable")
+set(Python_ROOT_DIR ${KRR_PYTHON_PATH})
 find_package(Python COMPONENTS Interpreter Development)
 if (Python_FOUND)
 	set(KRR_ENABLE_PYTHON ON)
diff --git a/README.md b/README.md
index 1db84b8f..03898511 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,13 @@ git clone --recursive https://github.com/cuteday/KiRaRay.git
 
 #### Building
 
-This project uses cmake to build, Make sure cuda is installed and added to PATH, and `OptiX_INSTALL_DIR` environment variable points to the OptiX installation directory.
+This project uses cmake to build, make sure CUDA is installed and added to PATH. Several optional variables are available for building configuration.
+
+| Variable                | Default     | Description                                                  |
+| ----------------------- | ----------- | ------------------------------------------------------------ |
+| `OptiX_INSTALL_DIR`     | auto-detect | When auto-detection failed to find the correct OptiX path, this variable needs to be manually specified to point to the OptiX installation. |
+| `KRR_RENDER_SPECTRAL`   | ON          | Whether to build spectral render. If turned OFF, the RGB renderer is build. |
+| `KRR_PYTHON_PATH` | auto-detect | Manually specify this to enable Python binding for a specific version of Python. |
 
 #### Running
 
@@ -54,8 +60,6 @@ build/src/kiraray.exe common/configs/example_cbox.json
 
 > The two necessary entries in the configuration are `model` (specifying the relative path to the scene file) and `passes` (describing the render pipeline). Once compiled, directly run `kiraray` without specifying configuration (this [example configuration](common/configs/example_cbox.json) will be used) to get a feel for this toy renderer.
 
-</details>
-
 #### Usage
 
 **Camera controlling.** Dragging `LeftMouse` for orbiting, dragging `Scroll` or `Shift+LeftMouse` for panning. `Scroll` for zooming in/out.
diff --git a/common/scripts/README.md b/common/scripts/README.md
index 023d0024..b373d2ca 100644
--- a/common/scripts/README.md
+++ b/common/scripts/README.md
@@ -1,6 +1,6 @@
 # KiRaRay Python Binding
 
-The python binding should be compiled with the same version of Python as the binding is intended to be used. To specify the python version, set the `KRR_PYTHON_EXECUTABLE` variable to the folder that containing the python executable.
+The python binding should be compiled with the same version of Python as the binding is intended to be used. To specify the python version, set the `KRR_PYTHON_PATH` variable to the folder that containing the python executable.
 
 > After Python 3.8, the search paths of DLL dependencies has been reset. Only the system paths, the directory containing the DLL or PYD file are searched for load-time dependencies. Instead, a new function os.add_dll_directory() was added to supply additional search paths. 
 Necessary DLL paths are exported from `pykrr_common`, see [krr.py](krr.py) for details.
diff --git a/src/main/kiraray.cpp b/src/main/kiraray.cpp
index 41068800..fd2872f8 100644
--- a/src/main/kiraray.cpp
+++ b/src/main/kiraray.cpp
@@ -14,7 +14,7 @@ extern "C" int main(int argc, char *argv[]) {
 			   "Switch to Release build for normal performance!");
 #endif
 
-	string configFile = "common/configs/test/cboxexplosion.json";
+	string configFile = "common/configs/example_cbox.json";
 	if (argc < 2){
 		Log(Warning, "No config file specified, using default config file: %s", configFile.c_str());
 	} else {
diff --git a/src/render/materials/disney.h b/src/render/materials/disney.h
index 8f38c278..70d9dead 100644
--- a/src/render/materials/disney.h
+++ b/src/render/materials/disney.h
@@ -4,6 +4,7 @@
 #include "common.h"
 
 #include "render/shared.h"
+#include "render/sampling.h"
 
 #include "util/math_utils.h"
 
@@ -301,26 +302,31 @@ class DisneyBsdf {
 	KRR_CALLABLE BSDFSample sample(Vector3f wo, Sampler &sg,
 								   TransportMode mode = TransportMode::Radiance) const {
 		BSDFSample sample;
-		float comp = sg.get1D();
-		if (comp < pDiffuse) {
-			Vector3f wi = cosineSampleHemisphere(sg.get2D());
-			if (wo[2] < 0) wi[2] *= -1;
-			sample.pdf	 = pdf(wo, wi);
-			sample.f	 = f(wo, wi);
-			sample.wi	 = wi;
-			sample.flags = BSDF_DIFFUSE_REFLECTION;
-		} else if (comp < pDiffuse + pSpecRefl) {
-			sample = microfacetBrdf.sample(wo, sg, mode);
-			sample.pdf *= pSpecRefl;
-			if (pDiffuse && sample.isNonSpecular()) {
-				// TODO: validate if you should disable other components when sampled an delta component.
-				sample.f += disneyDiffuse.f(wo, sample.wi);
-				sample.f += disneyRetro.f(wo, sample.wi);
-				sample.pdf += pDiffuse * AbsCosTheta(sample.wi) * M_INV_PI;
+		int comp = sampleDiscrete({pDiffuse, pSpecRefl, pSpecTrans}, sg.get1D());
+		switch (comp) {
+			case 0: {
+				Vector3f wi = cosineSampleHemisphere(sg.get2D());
+				if (wo[2] < 0) wi[2] *= -1;
+				sample.pdf	 = pdf(wo, wi);
+				sample.f	 = f(wo, wi);
+				sample.wi	 = wi;
+				sample.flags = BSDF_DIFFUSE_REFLECTION;
+				break;
+			} case 1: {
+				sample = microfacetBrdf.sample(wo, sg, mode);
+				sample.pdf *= pSpecRefl;
+				if (pDiffuse && sample.isNonSpecular()) {
+					// NOTE: disable other components when sampled an delta component.
+					sample.f += disneyDiffuse.f(wo, sample.wi);
+					sample.f += disneyRetro.f(wo, sample.wi);
+					sample.pdf += pDiffuse * AbsCosTheta(sample.wi) * M_INV_PI;
+				}
+				break;
+			} case 2: {
+				sample = microfacetBtdf.sample(wo, sg, mode);
+				sample.pdf *= pSpecTrans;
+				break;
 			}
-		} else if (pSpecTrans > 0) {
-			sample = microfacetBtdf.sample(wo, sg, mode);
-			sample.pdf *= pSpecTrans;
 		}
 		return sample;
 	}
diff --git a/src/render/materials/principled.h b/src/render/materials/principled.h
index c651f2e5..ced3b1ab 100644
--- a/src/render/materials/principled.h
+++ b/src/render/materials/principled.h
@@ -157,42 +157,45 @@ class PrincipledBsdf {
 	KRR_CALLABLE BSDFSample sample(Vector3f wo, Sampler &sg,
 								   TransportMode mode = TransportMode::Radiance) const {
 		BSDFSample sample{};
-		float comp = sg.get1D();
-		if (comp < pDiffuse) {
-			Vector3f wi = cosineSampleHemisphere(sg.get2D());
-			if (wo[2] < 0)
-				wi[2] *= -1;
-			sample.pdf	 = pdf(wo, wi, mode);
-			sample.f	 = f(wo, wi, mode);
-			sample.wi	 = wi;
-			sample.flags = BSDF_DIFFUSE_REFLECTION;
-		} else if (comp < pDiffuse + pMetal) {
-			sample = metalBrdf.sample(wo, sg, mode);
-			sample.pdf *= pMetal;
-			if (pDiffuse > 0) {
-				sample.f += weightDiffuse * disneyDiffuse.f(wo, sample.wi);
-				sample.f += weightDiffuse * disneyRetro.f(wo, sample.wi);
-				sample.pdf += pDiffuse * AbsCosTheta(sample.wi) * M_INV_PI;
-			}
-			if (pGlass > 0) {
-				sample.f += weightGlass * glassBsdf.f(wo, sample.wi, mode);
-				sample.pdf += pGlass * glassBsdf.pdf(wo, sample.wi, mode);
-			}
-		} else if (pGlass > 0) {
-			sample = glassBsdf.sample(wo, sg);
-			if (!sample.f.any() || sample.pdf == 0)
-				return {};
-			sample.pdf *= pGlass;
-			if (SameHemisphere(wo, sample.wi)) {
+		int comp = sampleDiscrete({pDiffuse, pMetal, pGlass}, sg.get1D());
+		switch (comp) {
+			case 0: {
+				Vector3f wi = cosineSampleHemisphere(sg.get2D());
+				if (wo[2] < 0) wi[2] *= -1;
+				sample.pdf	 = pdf(wo, wi, mode);
+				sample.f	 = f(wo, wi, mode);
+				sample.wi	 = wi;
+				sample.flags = BSDF_DIFFUSE_REFLECTION;
+				break;
+			} case 1: {
+				sample = metalBrdf.sample(wo, sg, mode);
+				sample.pdf *= pMetal;
 				if (pDiffuse > 0) {
 					sample.f += weightDiffuse * disneyDiffuse.f(wo, sample.wi);
 					sample.f += weightDiffuse * disneyRetro.f(wo, sample.wi);
 					sample.pdf += pDiffuse * AbsCosTheta(sample.wi) * M_INV_PI;
 				}
-				if (pMetal > 0) {
-					sample.f += weightMetal * metalBrdf.f(wo, sample.wi, mode);
-					sample.pdf += pMetal * metalBrdf.pdf(wo, sample.wi, mode);
+				if (pGlass > 0) {
+					sample.f += weightGlass * glassBsdf.f(wo, sample.wi, mode);
+					sample.pdf += pGlass * glassBsdf.pdf(wo, sample.wi, mode);
+				}
+				break;
+			} case 2: {
+				sample = glassBsdf.sample(wo, sg);
+				if (!sample.f.any() || sample.pdf == 0) return {};
+				sample.pdf *= pGlass;
+				if (SameHemisphere(wo, sample.wi)) {
+					if (pDiffuse > 0) {
+						sample.f += weightDiffuse * disneyDiffuse.f(wo, sample.wi);
+						sample.f += weightDiffuse * disneyRetro.f(wo, sample.wi);
+						sample.pdf += pDiffuse * AbsCosTheta(sample.wi) * M_INV_PI;
+					}
+					if (pMetal > 0) {
+						sample.f += weightMetal * metalBrdf.f(wo, sample.wi, mode);
+						sample.pdf += pMetal * metalBrdf.pdf(wo, sample.wi, mode);
+					}
 				}
+				break;
 			}
 		}
 		return sample;