Eevee Wavelength Node Support

This patch adds wavelength node support to Eevee, similar to how
Eevee Blackbody node works, thus it is a little off from Cycles.

Reviewed By: #eevee_viewport, fclem, brecht
Differential Revision: https://developer.blender.org/D11326

1 files changed, 72 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/math_color.c b/source/blender/blenlib/intern/math_color.c
index 8fd2802a547..d5c63573c7a 100644
--- a/source/blender/blenlib/intern/math_color.c
+++ b/source/blender/blenlib/intern/math_color.c
@@ -713,3 +713,75 @@ void blackbody_temperature_to_rgb_table(float *r_table, int width, float min, fl
     r_table[i * 4 + 3] = 0.0f;
   }
 }
+
+/* ****************************** wavelength ******************************** */
+/* Wavelength to RGB. */
+
+/* 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 */
+
+static 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}};
+
+static void wavelength_to_xyz(float xyz[3], float lambda_nm)
+{
+  float ii = (lambda_nm - 380.0f) * (1.0f / 5.0f); /* Scaled 0..80. */
+  int i = (int)ii;
+
+  if (i < 0 || i >= 80) {
+    xyz[0] = 0.0f;
+    xyz[1] = 0.0f;
+    xyz[2] = 0.0f;
+  }
+  else {
+    ii -= i;
+    const float *c = cie_colour_match[i];
+    xyz[0] = c[0] + ii * (c[3] - c[0]);
+    xyz[1] = c[1] + ii * (c[4] - c[1]);
+    xyz[2] = c[2] + ii * (c[5] - c[2]);
+  }
+}
+
+void wavelength_to_xyz_table(float *r_table, int width)
+{
+  for (int i = 0; i < width; i++) {
+    float temperature = 380 + 400 / (float)width * (float)i;
+
+    float rgb[3];
+    wavelength_to_xyz(rgb, temperature);
+
+    copy_v3_v3(&r_table[i * 4], rgb);
+    r_table[i * 4 + 3] = 0.0f;
+  }
+}