Cycles / Wavelength to RGB node:

* Added a node to convert wavelength (in nanometers, from 380nm to 780nm) to RGB values. This can be useful to match real world colors easier.

* Code cleanup:
** Moved color functions (xyz and hsv) into dedicated utility files.
** Remove svm_lerp(), use interp() instead. 

Documentation:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/More#Wavelength

Example render:
http://www.pasteall.org/pic/show.php?id=53202

This is part of my GSoC 2013. (revisions 57322, 57326, 57335 and 57367 from soc-2013-dingto). 

6 files changed, 112 insertions, 108 deletions

diff --git a/intern/cycles/kernel/svm/svm.h b/intern/cycles/kernel/svm/svm.h
index cfb930d92e8..7f0bb3163a1 100644
--- a/intern/cycles/kernel/svm/svm.h
+++ b/intern/cycles/kernel/svm/svm.h
@@ -152,6 +152,7 @@ CCL_NAMESPACE_END
 #include "svm_displace.h"
 #include "svm_fresnel.h"
 #include "svm_wireframe.h"
+#include "svm_wavelength.h"
 #include "svm_camera.h"
 #include "svm_geometry.h"
 #include "svm_hsv.h"
@@ -362,6 +363,9 @@ __device_noinline void svm_eval_nodes(KernelGlobals *kg, ShaderData *sd, ShaderT
 				svm_node_wireframe(kg, sd, stack, node.y, node.z, node.w);
 				break;
 #ifdef __EXTRA_NODES__
+			case NODE_WAVELENGTH:
+				svm_node_wavelength(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_hsv.h b/intern/cycles/kernel/svm/svm_hsv.h
index 348f13f59f2..6e6a9dff159 100644
--- a/intern/cycles/kernel/svm/svm_hsv.h
+++ b/intern/cycles/kernel/svm/svm_hsv.h
@@ -21,80 +21,6 @@
 
 CCL_NAMESPACE_BEGIN
 
-__device float3 rgb_to_hsv(float3 rgb)
-{
-	float cmax, cmin, h, s, v, cdelta;
-	float3 c;
-
-	cmax = fmaxf(rgb.x, fmaxf(rgb.y, rgb.z));
-	cmin = min(rgb.x, min(rgb.y, rgb.z));
-	cdelta = cmax - cmin;
-
-	v = cmax;
-
-	if(cmax != 0.0f) {
-		s = cdelta/cmax;
-	}
-	else {
-		s = 0.0f;
-		h = 0.0f;
-	}
-
-	if(s == 0.0f) {
-		h = 0.0f;
-	}
-	else {
-		float3 cmax3 = make_float3(cmax, cmax, cmax);
-		c = (cmax3 - rgb)/cdelta;
-
-		if(rgb.x == cmax) h = c.z - c.y;
-		else if(rgb.y == cmax) h = 2.0f + c.x -  c.z;
-		else h = 4.0f + c.y - c.x;
-
-		h /= 6.0f;
-
-		if(h < 0.0f)
-			h += 1.0f;
-	}
-
-	return make_float3(h, s, v);
-}
-
-__device float3 hsv_to_rgb(float3 hsv)
-{
-	float i, f, p, q, t, h, s, v;
-	float3 rgb;
-
-	h = hsv.x;
-	s = hsv.y;
-	v = hsv.z;
-
-	if(s == 0.0f) {
-		rgb = make_float3(v, v, v);
-	}
-	else {
-		if(h == 1.0f)
-			h = 0.0f;
-		
-		h *= 6.0f;
-		i = floorf(h);
-		f = h - i;
-		rgb = make_float3(f, f, f);
-		p = v*(1.0f-s);
-		q = v*(1.0f-(s*f));
-		t = v*(1.0f-(s*(1.0f-f)));
-		
-		if(i == 0.0f) rgb = make_float3(v, t, p);
-		else if(i == 1.0f) rgb = make_float3(q, v, p);
-		else if(i == 2.0f) rgb = make_float3(p, v, t);
-		else if(i == 3.0f) rgb = make_float3(p, q, v);
-		else if(i == 4.0f) rgb = make_float3(t, p, v);
-		else rgb = make_float3(v, p, q);
-	}
-
-	return rgb;
-}
-
 __device void svm_node_hsv(KernelGlobals *kg, ShaderData *sd, float *stack, uint in_color_offset, uint fac_offset, uint out_color_offset, int *offset)
 {
 	/* read extra data */
diff --git a/intern/cycles/kernel/svm/svm_mix.h b/intern/cycles/kernel/svm/svm_mix.h
index 888e4d9645e..d6a306af64d 100644
--- a/intern/cycles/kernel/svm/svm_mix.h
+++ b/intern/cycles/kernel/svm/svm_mix.h
@@ -16,28 +16,21 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
-#include "svm_hsv.h"
-
 CCL_NAMESPACE_BEGIN
 
-__device float3 svm_lerp(const float3 a, const float3 b, float t)
-{
-	return (a * (1.0f - t) + b * t);
-}
-
 __device float3 svm_mix_blend(float t, float3 col1, float3 col2)
 {
-	return svm_lerp(col1, col2, t);
+	return interp(col1, col2, t);
 }
 
 __device float3 svm_mix_add(float t, float3 col1, float3 col2)
 {
-	return svm_lerp(col1, col1 + col2, t);
+	return interp(col1, col1 + col2, t);
 }
 
 __device float3 svm_mix_mul(float t, float3 col1, float3 col2)
 {
-	return svm_lerp(col1, col1 * col2, t);
+	return interp(col1, col1 * col2, t);
 }
 
 __device float3 svm_mix_screen(float t, float3 col1, float3 col2)
@@ -75,7 +68,7 @@ __device float3 svm_mix_overlay(float t, float3 col1, float3 col2)
 
 __device float3 svm_mix_sub(float t, float3 col1, float3 col2)
 {
-	return svm_lerp(col1, col1 - col2, t);
+	return interp(col1, col1 - col2, t);
 }
 
 __device float3 svm_mix_div(float t, float3 col1, float3 col2)
@@ -93,7 +86,7 @@ __device float3 svm_mix_div(float t, float3 col1, float3 col2)
 
 __device float3 svm_mix_diff(float t, float3 col1, float3 col2)
 {
-	return svm_lerp(col1, fabs(col1 - col2), t);
+	return interp(col1, fabs(col1 - col2), t);
 }
 
 __device float3 svm_mix_dark(float t, float3 col1, float3 col2)
@@ -191,7 +184,7 @@ __device float3 svm_mix_hue(float t, float3 col1, float3 col2)
 		hsv.x = hsv2.x;
 		float3 tmp = hsv_to_rgb(hsv); 
 
-		outcol = svm_lerp(outcol, tmp, t);
+		outcol = interp(outcol, tmp, t);
 	}
 
 	return outcol;
@@ -238,7 +231,7 @@ __device float3 svm_mix_color(float t, float3 col1, float3 col2)
 		hsv.y = hsv2.y;
 		float3 tmp = hsv_to_rgb(hsv); 
 
-		outcol = svm_lerp(outcol, tmp, t);
+		outcol = interp(outcol, tmp, t);
 	}
 
 	return outcol;
diff --git a/intern/cycles/kernel/svm/svm_sky.h b/intern/cycles/kernel/svm/svm_sky.h
index eaba4d18365..8b4e35816d0 100644
--- a/intern/cycles/kernel/svm/svm_sky.h
+++ b/intern/cycles/kernel/svm/svm_sky.h
@@ -18,26 +18,6 @@
 
 CCL_NAMESPACE_BEGIN
 
-__device float3 xyY_to_xyz(float x, float y, float Y)
-{
-	float X, Z;
-
-	if(y != 0.0f) X = (x / y) * Y;
-	else X = 0.0f;
-
-	if(y != 0.0f && Y != 0.0f) Z = (1.0f - x - y) / y * Y;
-	else Z = 0.0f;
-
-	return make_float3(X, Y, Z);
-}
-
-__device float3 xyz_to_rgb(float x, float y, float z)
-{
-	return make_float3(3.240479f * x + -1.537150f * y + -0.498535f * z,
-					  -0.969256f * x +  1.875991f * y +  0.041556f * z,
-					   0.055648f * x + -0.204043f * y +  1.057311f * z);
-}
-
 /*
  * "A Practical Analytic Model for Daylight"
  * A. J. Preetham, Peter Shirley, Brian Smits
diff --git a/intern/cycles/kernel/svm/svm_types.h b/intern/cycles/kernel/svm/svm_types.h
index af188477a73..e5b3e2b972f 100644
--- a/intern/cycles/kernel/svm/svm_types.h
+++ b/intern/cycles/kernel/svm/svm_types.h
@@ -52,6 +52,7 @@ typedef enum NodeType {
 	NODE_CONVERT,
 	NODE_FRESNEL,
 	NODE_WIREFRAME,
+	NODE_WAVELENGTH,
 	NODE_EMISSION_WEIGHT,
 	NODE_TEX_GRADIENT,
 	NODE_TEX_VORONOI,
diff --git a/intern/cycles/kernel/svm/svm_wavelength.h b/intern/cycles/kernel/svm/svm_wavelength.h
new file mode 100644
index 00000000000..f9dd24dacef
--- /dev/null
+++ b/intern/cycles/kernel/svm/svm_wavelength.h
@@ -0,0 +1,100 @@
+/*
+ * 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
+
+/* Wavelength to RGB */
+
+__device void svm_node_wavelength(ShaderData *sd, float *stack, uint wavelength, uint color_out)
+{	
+	// CIE colour matching functions xBar, yBar, and zBar for
+	//	 wavelengths from 380 through 780 nanometers, every 5
+	//	 nanometers.  For a wavelength lambda in this range:
+	//		  cie_colour_match[(lambda - 380) / 5][0] = xBar
+	//		  cie_colour_match[(lambda - 380) / 5][1] = yBar
+	//		  cie_colour_match[(lambda - 380) / 5][2] = zBar
+	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}
+	};
+
+	float lambda_nm = stack_load_float(stack, wavelength);
+	float ii = (lambda_nm-380.0f) * (1.0f/5.0f);  // scaled 0..80
+	int i = float_to_int(ii);
+	float3 color;
+	
+	if (i < 0 || i >= 80) {
+		color = make_float3(0.0f, 0.0f, 0.0f);
+	}
+	else {
+		ii -= i;
+		const float *c = cie_colour_match[i];
+		color = interp(make_float3(c[0], c[1], c[2]), make_float3(c[3], c[4], c[5]), ii);
+	}
+	
+	color = xyz_to_rgb(color.x, color.y, color.z);
+	color *= 1.0f/2.52f;	// Empirical scale from lg to make all comps <= 1
+	
+	/* Clamp to zero if values are smaller */
+	color = max(color, make_float3(0.0f, 0.0f, 0.0f));
+
+	if(stack_valid(color_out))
+		stack_store_float3(stack, color_out, color);
+}
+
+CCL_NAMESPACE_END
+