Cycles: Use curve approximation for blackbody instead of lookup table

Now we calculate color in range 800..12000 using an approximation a/x+bx+c for R and G and ((at + b)t + c)t + d) for B.
Max absolute error for RGB for non-lut function is less than 0.0001, which is enough to get the same 8 bit/channel color as for OSL with a noticeable performance difference.
However there is a slight visible difference between previous non-OSL implementation because of lookup table interpolation and offset-by-one mistake.
The previous implementation gave black color outside of soft range (t > 12000), now it gives the same color as for 12000.

Also blackbody node without input connected is being converted to value input at shader compile time.

Reviewers: dingto, sergey

Reviewed By: dingto

Subscribers: nutel, brecht, juicyfruit

Differential Revision: https://developer.blender.org/D1280

9 files changed, 10 insertions, 212 deletions

diff --git a/intern/cycles/render/CMakeLists.txt b/intern/cycles/render/CMakeLists.txt
index 2dc6962633d..4e8a1794813 100644
--- a/intern/cycles/render/CMakeLists.txt
+++ b/intern/cycles/render/CMakeLists.txt
@@ -18,7 +18,6 @@ set(SRC
 	attribute.cpp
 	background.cpp
 	bake.cpp
-	blackbody.cpp
 	buffers.cpp
 	camera.cpp
 	film.cpp
@@ -47,7 +46,6 @@ set(SRC_HEADERS
 	attribute.h
 	bake.h
 	background.h
-	blackbody.h
 	buffers.h
 	camera.h
 	film.h
diff --git a/intern/cycles/render/blackbody.cpp b/intern/cycles/render/blackbody.cpp
deleted file mode 100644
index 9f77f69a964..00000000000
--- a/intern/cycles/render/blackbody.cpp
+++ /dev/null
@@ -1,140 +0,0 @@
-/*
- * Adapted from Open Shading Language with this license:
- *
- * Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
- * All Rights Reserved.
- *
- * Modifications Copyright 2013, Blender Foundation.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- * * Redistributions of source code must retain the above copyright
- *   notice, this list of conditions and the following disclaimer.
- * * Redistributions in binary form must reproduce the above copyright
- *   notice, this list of conditions and the following disclaimer in the
- *   documentation and/or other materials provided with the distribution.
- * * Neither the name of Sony Pictures Imageworks nor the names of its
- *   contributors may be used to endorse or promote products derived from
- *   this software without specific prior written permission.
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#include "blackbody.h"
-#include "util_color.h"
-#include "util_math.h"
-
-#include "kernel_types.h"
-
-CCL_NAMESPACE_BEGIN
-
-vector<float> blackbody_table_build()
-{
-	/* quoted from OSLs opcolor.cpp
-	In order to speed up the blackbody computation, we have a table
-	storing the precomputed BB values for a range of temperatures.  Less
-	than BB_DRAPER always returns 0.  Greater than BB_MAX_TABLE_RANGE
-	does the full computation, we think it'll be rare to inquire higher
-	temperatures.
-
-	Since the bb function is so nonlinear, we actually space the table
-	entries nonlinearly, with the relationship between the table index i
-	and the temperature T as follows:
-	i = ((T-Draper)/spacing)^(1/xpower)
-	T = pow(i, xpower) * spacing + Draper
-	And furthermore, we store in the table the true value raised ^(1/5).
-	I tuned this a bit, and with the current values we can have all
-	blackbody results accurate to within 0.1% with a table size of 317
-	(about 5 KB of data).
-	*/
-
-	const float cie_colour_match[81][3] = {
-		{0.0014f,0.0000f,0.0065f}, {0.0022f,0.0001f,0.0105f}, {0.0042f,0.0001f,0.0201f},
-		{0.0076f,0.0002f,0.0362f}, {0.0143f,0.0004f,0.0679f}, {0.0232f,0.0006f,0.1102f},
-		{0.0435f,0.0012f,0.2074f}, {0.0776f,0.0022f,0.3713f}, {0.1344f,0.0040f,0.6456f},
-		{0.2148f,0.0073f,1.0391f}, {0.2839f,0.0116f,1.3856f}, {0.3285f,0.0168f,1.6230f},
-		{0.3483f,0.0230f,1.7471f}, {0.3481f,0.0298f,1.7826f}, {0.3362f,0.0380f,1.7721f},
-		{0.3187f,0.0480f,1.7441f}, {0.2908f,0.0600f,1.6692f}, {0.2511f,0.0739f,1.5281f},
-		{0.1954f,0.0910f,1.2876f}, {0.1421f,0.1126f,1.0419f}, {0.0956f,0.1390f,0.8130f},
-		{0.0580f,0.1693f,0.6162f}, {0.0320f,0.2080f,0.4652f}, {0.0147f,0.2586f,0.3533f},
-		{0.0049f,0.3230f,0.2720f}, {0.0024f,0.4073f,0.2123f}, {0.0093f,0.5030f,0.1582f},
-		{0.0291f,0.6082f,0.1117f}, {0.0633f,0.7100f,0.0782f}, {0.1096f,0.7932f,0.0573f},
-		{0.1655f,0.8620f,0.0422f}, {0.2257f,0.9149f,0.0298f}, {0.2904f,0.9540f,0.0203f},
-		{0.3597f,0.9803f,0.0134f}, {0.4334f,0.9950f,0.0087f}, {0.5121f,1.0000f,0.0057f},
-		{0.5945f,0.9950f,0.0039f}, {0.6784f,0.9786f,0.0027f}, {0.7621f,0.9520f,0.0021f},
-		{0.8425f,0.9154f,0.0018f}, {0.9163f,0.8700f,0.0017f}, {0.9786f,0.8163f,0.0014f},
-		{1.0263f,0.7570f,0.0011f}, {1.0567f,0.6949f,0.0010f}, {1.0622f,0.6310f,0.0008f},
-		{1.0456f,0.5668f,0.0006f}, {1.0026f,0.5030f,0.0003f}, {0.9384f,0.4412f,0.0002f},
-		{0.8544f,0.3810f,0.0002f}, {0.7514f,0.3210f,0.0001f}, {0.6424f,0.2650f,0.0000f},
-		{0.5419f,0.2170f,0.0000f}, {0.4479f,0.1750f,0.0000f}, {0.3608f,0.1382f,0.0000f},
-		{0.2835f,0.1070f,0.0000f}, {0.2187f,0.0816f,0.0000f}, {0.1649f,0.0610f,0.0000f},
-		{0.1212f,0.0446f,0.0000f}, {0.0874f,0.0320f,0.0000f}, {0.0636f,0.0232f,0.0000f},
-		{0.0468f,0.0170f,0.0000f}, {0.0329f,0.0119f,0.0000f}, {0.0227f,0.0082f,0.0000f},
-		{0.0158f,0.0057f,0.0000f}, {0.0114f,0.0041f,0.0000f}, {0.0081f,0.0029f,0.0000f},
-		{0.0058f,0.0021f,0.0000f}, {0.0041f,0.0015f,0.0000f}, {0.0029f,0.0010f,0.0000f},
-		{0.0020f,0.0007f,0.0000f}, {0.0014f,0.0005f,0.0000f}, {0.0010f,0.0004f,0.0000f},
-		{0.0007f,0.0002f,0.0000f}, {0.0005f,0.0002f,0.0000f}, {0.0003f,0.0001f,0.0000f},
-		{0.0002f,0.0001f,0.0000f}, {0.0002f,0.0001f,0.0000f}, {0.0001f,0.0000f,0.0000f},
-		{0.0001f,0.0000f,0.0000f}, {0.0001f,0.0000f,0.0000f}, {0.0000f,0.0000f,0.0000f}
-	};
-
-	const double c1 = 3.74183e-16; // 2*pi*h*c^2, W*m^2
-	const double c2 = 1.4388e-2;   // h*c/k, m*K
-								   // h is Planck's const, k is Boltzmann's
-	const float dlambda = 5.0f * 1e-9f;  // in meters
-
-	/* Blackbody table from 800 to 12k Kelvin (319 entries (317+2 offset) * 3) */
-	vector<float> blackbody_table(956);
-
-	float X, Y, Z;
-
-	/* ToDo: bring this back to what OSL does with the lastTemperature limit ? */
-	for(int i = 0;  i <= 317;  ++i) {
-		double Temperature = pow((double)i, (double)BB_TABLE_XPOWER) * (double)BB_TABLE_SPACING + (double)BB_DRAPER;
-		X = 0;
-		Y = 0;
-		Z = 0;
-
-		/* from OSL "spectrum_to_XYZ" */
-		for(int n = 0; n < 81; ++n) {
-			float lambda = 380.0f + 5.0f * n;
-			double wlm = lambda * 1e-9f;   // Wavelength in meters
-			// N.B. spec_intens returns result in W/m^2 but it's a differential,
-			// needs to be scaled by dlambda!
-			float spec_intens = float((c1 * pow(wlm, -5.0)) / (exp(c2 / (wlm * Temperature)) -1.0));
-			float Me = spec_intens * dlambda;
-
-			X += Me * cie_colour_match[n][0];
-			Y += Me * cie_colour_match[n][1];
-			Z += Me * cie_colour_match[n][2];
-		}
-		
-		/* Convert from xyz color space */
-		float3 col = xyz_to_rgb(X, Y, Z);
-
-		/* Clamp to zero if values are smaller */
-		col = max(col, make_float3(0.0f, 0.0f, 0.0f));
-
-		col.x = powf(col.x, 1.0f / BB_TABLE_YPOWER);
-		col.y = powf(col.y, 1.0f / BB_TABLE_YPOWER);
-		col.z = powf(col.z, 1.0f / BB_TABLE_YPOWER);
-
-		/* Store in table in RRRGGGBBB format */
-		blackbody_table[i] = col.x;
-		blackbody_table[i+319*1] = col.y;
-		blackbody_table[i+319*2] = col.z;	
-	}
-
-	return blackbody_table;
-}
-CCL_NAMESPACE_END
diff --git a/intern/cycles/render/blackbody.h b/intern/cycles/render/blackbody.h
deleted file mode 100644
index 6b752a227fa..00000000000
--- a/intern/cycles/render/blackbody.h
+++ /dev/null
@@ -1,28 +0,0 @@
-/*
- * Copyright 2011-2013 Blender Foundation
- *
- * 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
- *
- * 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.
- */
-
-#ifndef __BLACKBODY_H__
-#define __BLACKBODY_H__
-
-#include "util_vector.h"
-
-CCL_NAMESPACE_BEGIN
-
-vector<float> blackbody_table_build();
-
-CCL_NAMESPACE_END
-
-#endif /* __BLACKBODY_H__ */
diff --git a/intern/cycles/render/graph.h b/intern/cycles/render/graph.h
index 301938aa158..7817a4cdc6d 100644
--- a/intern/cycles/render/graph.h
+++ b/intern/cycles/render/graph.h
@@ -194,7 +194,6 @@ public:
 	virtual bool has_surface_emission() { return false; }
 	virtual bool has_surface_transparent() { return false; }
 	virtual bool has_surface_bssrdf() { return false; }
-	virtual bool has_converter_blackbody() { return false; }
 	virtual bool has_bssrdf_bump() { return false; }
 	virtual bool has_spatial_varying() { return false; }
 	virtual bool has_object_dependency() { return false; }
diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index 8529855ff2e..d17d531aa77 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -3652,9 +3652,17 @@ void BlackbodyNode::compile(SVMCompiler& compiler)
 	ShaderInput *temperature_in = input("Temperature");
 	ShaderOutput *color_out = output("Color");
 
-	compiler.stack_assign(temperature_in);
 	compiler.stack_assign(color_out);
-	compiler.add_node(NODE_BLACKBODY, temperature_in->stack_offset, color_out->stack_offset);
+
+	if(temperature_in->link == NULL) {
+		float3 color = svm_math_blackbody_color(temperature_in->value.x);
+		compiler.add_node(NODE_VALUE_V, color_out->stack_offset);
+		compiler.add_node(NODE_VALUE_V, color);
+	}
+	else {
+		compiler.stack_assign(temperature_in);
+		compiler.add_node(NODE_BLACKBODY, temperature_in->stack_offset, color_out->stack_offset);
+	}
 }
 
 void BlackbodyNode::compile(OSLCompiler& compiler)
diff --git a/intern/cycles/render/nodes.h b/intern/cycles/render/nodes.h
index ee984773dcf..686fb5e2fd7 100644
--- a/intern/cycles/render/nodes.h
+++ b/intern/cycles/render/nodes.h
@@ -549,8 +549,6 @@ public:
 class BlackbodyNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(BlackbodyNode)
-	
-	bool has_converter_blackbody() { return true; }
 };
 
 class MathNode : public ShaderNode {
diff --git a/intern/cycles/render/shader.cpp b/intern/cycles/render/shader.cpp
index 496fd0f0cb9..971cd5097de 100644
--- a/intern/cycles/render/shader.cpp
+++ b/intern/cycles/render/shader.cpp
@@ -15,7 +15,6 @@
  */
 
 #include "background.h"
-#include "blackbody.h"
 #include "device.h"
 #include "graph.h"
 #include "light.h"
@@ -32,7 +31,6 @@
 
 CCL_NAMESPACE_BEGIN
 
-vector<float> ShaderManager::blackbody_table;
 vector<float> ShaderManager::beckmann_table;
 
 /* Beckmann sampling precomputed table, see bsdf_microfacet.h */
@@ -149,7 +147,6 @@ Shader::Shader()
 	has_surface_transparent = false;
 	has_surface_emission = false;
 	has_surface_bssrdf = false;
-	has_converter_blackbody = false;
 	has_volume = false;
 	has_displacement = false;
 	has_bssrdf_bump = false;
@@ -243,7 +240,6 @@ void Shader::tag_used(Scene *scene)
 ShaderManager::ShaderManager()
 {
 	need_update = true;
-	blackbody_table_offset = TABLE_OFFSET_INVALID;
 	beckmann_table_offset = TABLE_OFFSET_INVALID;
 }
 
@@ -340,7 +336,6 @@ void ShaderManager::device_update_common(Device *device,
 	uint shader_flag_size = scene->shaders.size()*4;
 	uint *shader_flag = dscene->shader_flag.resize(shader_flag_size);
 	uint i = 0;
-	bool has_converter_blackbody = false;
 	bool has_volumes = false;
 
 	foreach(Shader *shader, scene->shaders) {
@@ -367,8 +362,6 @@ void ShaderManager::device_update_common(Device *device,
 			flag |= SD_HETEROGENEOUS_VOLUME;
 		if(shader->has_bssrdf_bump)
 			flag |= SD_HAS_BSSRDF_BUMP;
-		if(shader->has_converter_blackbody)
-			has_converter_blackbody = true;
 		if(shader->volume_sampling_method == VOLUME_SAMPLING_EQUIANGULAR)
 			flag |= SD_VOLUME_EQUIANGULAR;
 		if(shader->volume_sampling_method == VOLUME_SAMPLING_MULTIPLE_IMPORTANCE)
@@ -394,23 +387,6 @@ void ShaderManager::device_update_common(Device *device,
 
 	/* lookup tables */
 	KernelTables *ktables = &dscene->data.tables;
-	
-	/* blackbody lookup table */
-	if(has_converter_blackbody && blackbody_table_offset == TABLE_OFFSET_INVALID) {
-		if(blackbody_table.size() == 0) {
-			thread_scoped_lock lock(lookup_table_mutex);
-			if(blackbody_table.size() == 0) {
-				blackbody_table = blackbody_table_build();
-			}
-		}
-		blackbody_table_offset = scene->lookup_tables->add_table(dscene, blackbody_table);
-		
-		ktables->blackbody_offset = (int)blackbody_table_offset;
-	}
-	else if(!has_converter_blackbody && blackbody_table_offset != TABLE_OFFSET_INVALID) {
-		scene->lookup_tables->remove_table(blackbody_table_offset);
-		blackbody_table_offset = TABLE_OFFSET_INVALID;
-	}
 
 	/* beckmann lookup table */
 	if(beckmann_table_offset == TABLE_OFFSET_INVALID) {
@@ -431,11 +407,6 @@ void ShaderManager::device_update_common(Device *device,
 
 void ShaderManager::device_free_common(Device *device, DeviceScene *dscene, Scene *scene)
 {
-	if(blackbody_table_offset != TABLE_OFFSET_INVALID) {
-		scene->lookup_tables->remove_table(blackbody_table_offset);
-		blackbody_table_offset = TABLE_OFFSET_INVALID;
-	}
-
 	if(beckmann_table_offset != TABLE_OFFSET_INVALID) {
 		scene->lookup_tables->remove_table(beckmann_table_offset);
 		beckmann_table_offset = TABLE_OFFSET_INVALID;
diff --git a/intern/cycles/render/shader.h b/intern/cycles/render/shader.h
index a1d697a7b7b..5bcb2c4e344 100644
--- a/intern/cycles/render/shader.h
+++ b/intern/cycles/render/shader.h
@@ -104,7 +104,6 @@ public:
 	bool has_volume;
 	bool has_displacement;
 	bool has_surface_bssrdf;
-	bool has_converter_blackbody;
 	bool has_bssrdf_bump;
 	bool has_heterogeneous_volume;
 	bool has_object_dependency;
@@ -173,10 +172,8 @@ protected:
 	AttributeIDMap unique_attribute_id;
 
 	thread_mutex lookup_table_mutex;
-	static vector<float> blackbody_table;
 	static vector<float> beckmann_table;
 
-	size_t blackbody_table_offset;
 	size_t beckmann_table_offset;
 };
 
diff --git a/intern/cycles/render/svm.cpp b/intern/cycles/render/svm.cpp
index 6f7cffa320f..d0bd34915df 100644
--- a/intern/cycles/render/svm.cpp
+++ b/intern/cycles/render/svm.cpp
@@ -393,10 +393,6 @@ void SVMCompiler::generate_node(ShaderNode *node, set<ShaderNode*>& done)
 			current_shader->has_heterogeneous_volume = true;
 	}
 
-	/* detect if we have a blackbody converter, to prepare lookup table */
-	if(node->has_converter_blackbody())
-		current_shader->has_converter_blackbody = true;
-
 	if(node->has_object_dependency()) {
 		current_shader->has_object_dependency = true;
 	}
@@ -716,7 +712,6 @@ void SVMCompiler::compile(Shader *shader, vector<int4>& global_svm_nodes, int in
 	shader->has_surface_transparent = false;
 	shader->has_surface_bssrdf = false;
 	shader->has_bssrdf_bump = false;
-	shader->has_converter_blackbody = false;
 	shader->has_volume = false;
 	shader->has_displacement = false;
 	shader->has_heterogeneous_volume = false;