Cycles / Blackbody node:

* First (brute force) implementation for SVM. This works and delivers the same result as OSL, but it's slow. 
* Code inside svm_blackbody.h inspired by a patch by Philipp Oeser (#35698), thanks. 

Ideas:
* Use a lookup table to perform the calculations on render/ level.
* Implement it as a RNA property only, and do the calculation like Sun/Sky precompute. 

5 files changed, 119 insertions, 4 deletions

diff --git a/intern/cycles/kernel/CMakeLists.txt b/intern/cycles/kernel/CMakeLists.txt
index 8b4466863e0..1dcf63f9e47 100644
--- a/intern/cycles/kernel/CMakeLists.txt
+++ b/intern/cycles/kernel/CMakeLists.txt
@@ -72,6 +72,7 @@ set(SRC_CLOSURE_HEADERS
 set(SRC_SVM_HEADERS
 	svm/svm.h
 	svm/svm_attribute.h
+	svm/svm_blackbody.h
 	svm/svm_camera.h
 	svm/svm_closure.h
 	svm/svm_convert.h
diff --git a/intern/cycles/kernel/shaders/node_blackbody.osl b/intern/cycles/kernel/shaders/node_blackbody.osl
index 7a6e71c298b..4a68eb973be 100644
--- a/intern/cycles/kernel/shaders/node_blackbody.osl
+++ b/intern/cycles/kernel/shaders/node_blackbody.osl
@@ -22,6 +22,10 @@ shader node_blackbody(
 	float Temperature = 1200.0,
 	output color Color = 0.0)
 {
-	Color = blackbody(Temperature);
+	color rgb = blackbody(Temperature);
+	
+	/* Scale by luminance */
+	float l = luminance(rgb);
+	Color = rgb /= l;
 }
 
diff --git a/intern/cycles/kernel/svm/svm.h b/intern/cycles/kernel/svm/svm.h
index 7f0bb3163a1..e08e41e78e5 100644
--- a/intern/cycles/kernel/svm/svm.h
+++ b/intern/cycles/kernel/svm/svm.h
@@ -146,6 +146,7 @@ CCL_NAMESPACE_END
 
 #include "svm_attribute.h"
 #include "svm_gradient.h"
+#include "svm_blackbody.h"
 #include "svm_closure.h"
 #include "svm_noisetex.h"
 #include "svm_convert.h"
@@ -366,6 +367,9 @@ __device_noinline void svm_eval_nodes(KernelGlobals *kg, ShaderData *sd, ShaderT
 			case NODE_WAVELENGTH:
 				svm_node_wavelength(sd, stack, node.y, node.z);
 				break;
+			case NODE_BLACKBODY:
+				svm_node_blackbody(kg, sd, stack, node.y, node.z);
+				break;
 			case NODE_SET_DISPLACEMENT:
 				svm_node_set_displacement(sd, stack, node.y);
 				break;
diff --git a/intern/cycles/kernel/svm/svm_blackbody.h b/intern/cycles/kernel/svm/svm_blackbody.h
new file mode 100644
index 00000000000..cc0a3630494
--- /dev/null
+++ b/intern/cycles/kernel/svm/svm_blackbody.h
@@ -0,0 +1,108 @@
+/*
+ * 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.
+ */
+
+CCL_NAMESPACE_BEGIN
+
+/* Blackbody Node */
+
+__device void svm_node_blackbody(KernelGlobals *kg, ShaderData *sd, float *stack, uint temperature_offset, uint col_offset)
+{
+	/* Output */
+	float3 color_rgb;
+
+	/* Input */
+	float temperature = stack_load_float(stack, temperature_offset);
+
+	/* ToDo: Use a lookup table to speed this up and outsource it from the kernel */
+	float X = 0, Y = 0, Z = 0;
+
+	const float cie_colour_match[81][3] = {
+		{0.0014,0.0000,0.0065}, {0.0022,0.0001,0.0105}, {0.0042,0.0001,0.0201},
+		{0.0076,0.0002,0.0362}, {0.0143,0.0004,0.0679}, {0.0232,0.0006,0.1102},
+		{0.0435,0.0012,0.2074}, {0.0776,0.0022,0.3713}, {0.1344,0.0040,0.6456},
+		{0.2148,0.0073,1.0391}, {0.2839,0.0116,1.3856}, {0.3285,0.0168,1.6230},
+		{0.3483,0.0230,1.7471}, {0.3481,0.0298,1.7826}, {0.3362,0.0380,1.7721},
+		{0.3187,0.0480,1.7441}, {0.2908,0.0600,1.6692}, {0.2511,0.0739,1.5281},
+		{0.1954,0.0910,1.2876}, {0.1421,0.1126,1.0419}, {0.0956,0.1390,0.8130},
+		{0.0580,0.1693,0.6162}, {0.0320,0.2080,0.4652}, {0.0147,0.2586,0.3533},
+		{0.0049,0.3230,0.2720}, {0.0024,0.4073,0.2123}, {0.0093,0.5030,0.1582},
+		{0.0291,0.6082,0.1117}, {0.0633,0.7100,0.0782}, {0.1096,0.7932,0.0573},
+		{0.1655,0.8620,0.0422}, {0.2257,0.9149,0.0298}, {0.2904,0.9540,0.0203},
+		{0.3597,0.9803,0.0134}, {0.4334,0.9950,0.0087}, {0.5121,1.0000,0.0057},
+		{0.5945,0.9950,0.0039}, {0.6784,0.9786,0.0027}, {0.7621,0.9520,0.0021},
+		{0.8425,0.9154,0.0018}, {0.9163,0.8700,0.0017}, {0.9786,0.8163,0.0014},
+		{1.0263,0.7570,0.0011}, {1.0567,0.6949,0.0010}, {1.0622,0.6310,0.0008},
+		{1.0456,0.5668,0.0006}, {1.0026,0.5030,0.0003}, {0.9384,0.4412,0.0002},
+		{0.8544,0.3810,0.0002}, {0.7514,0.3210,0.0001}, {0.6424,0.2650,0.0000},
+		{0.5419,0.2170,0.0000}, {0.4479,0.1750,0.0000}, {0.3608,0.1382,0.0000},
+		{0.2835,0.1070,0.0000}, {0.2187,0.0816,0.0000}, {0.1649,0.0610,0.0000},
+		{0.1212,0.0446,0.0000}, {0.0874,0.0320,0.0000}, {0.0636,0.0232,0.0000},
+		{0.0468,0.0170,0.0000}, {0.0329,0.0119,0.0000}, {0.0227,0.0082,0.0000},
+		{0.0158,0.0057,0.0000}, {0.0114,0.0041,0.0000}, {0.0081,0.0029,0.0000},
+		{0.0058,0.0021,0.0000}, {0.0041,0.0015,0.0000}, {0.0029,0.0010,0.0000},
+		{0.0020,0.0007,0.0000}, {0.0014,0.0005,0.0000}, {0.0010,0.0004,0.0000},
+		{0.0007,0.0002,0.0000}, {0.0005,0.0002,0.0000}, {0.0003,0.0001,0.0000},
+		{0.0002,0.0001,0.0000}, {0.0002,0.0001,0.0000}, {0.0001,0.0000,0.0000},
+		{0.0001,0.0000,0.0000}, {0.0001,0.0000,0.0000}, {0.0000,0.0000,0.0000}
+	};
+
+	const float c1 = 3.74183e-16; // 2*pi*h*c^2, W*m^2
+	const float c2 = 1.4388e-2;   // h*c/k, m*K, h is Planck's const, k is Boltzmann's
+	const float dlambda = 5.0f * 1e-9;  // in meters
+
+	for (int i = 0; i < 81; ++i) {
+		float lambda = 380.0f + 5.0f * i;
+		float wlm = lambda * 1e-9;   // 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 = (c1 * powf(wlm, -5.0)) / (expf(c2 / (wlm * temperature)) -1.0f);
+		float Me = spec_intens * dlambda;
+
+		X += Me * cie_colour_match[i][0];
+		Y += Me * cie_colour_match[i][1];
+		Z += Me * cie_colour_match[i][2];
+	}
+
+	/* Convert to RGB */
+	color_rgb = xyz_to_rgb(X, Y, Z);
+
+	/* Clamp to zero if values are smaller */
+	color_rgb = max(color_rgb, make_float3(0.0f, 0.0f, 0.0f));
+
+	/* Scale color by luminance */
+	color_rgb /= Y;
+
+	if (stack_valid(col_offset))
+		stack_store_float3(stack, col_offset, color_rgb);
+}
+
+CCL_NAMESPACE_END
diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index d7a98bfba90..cd893652dac 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -2988,14 +2988,12 @@ BlackbodyNode::BlackbodyNode()
 
 void BlackbodyNode::compile(SVMCompiler& compiler)
 {
-/*
-	ShaderInput *temperature in = input("Temperature");
+	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);
-*/
 }
 
 void BlackbodyNode::compile(OSLCompiler& compiler)