Fix Eevee blackbody wrong with non-default scene linear color space

* Port over new code tables from Cycles
* Convert Rec.709 to scene linear for lookup table.
* Move code for wavelength and blackbody to IMB so they can access the
  required transforms, which are not in blenlib.
* Remove clamping from blackbody shader to bypass the texture read.
  Since it's variable now easiest to just always read from the texture
  than pass additional parameters.
* Fold XYZ to RGB conversion into the wavelength table.

Ref T68926

2 files changed, 4 insertions, 20 deletions

diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_blackbody.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_blackbody.glsl
index d0111aa3839..e257483f364 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_blackbody.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_blackbody.glsl
@@ -1,13 +1,5 @@
 void node_blackbody(float temperature, sampler1DArray spectrummap, float layer, out vec4 color)
 {
-  if (temperature >= 12000.0) {
-    color = vec4(0.826270103, 0.994478524, 1.56626022, 1.0);
-  }
-  else if (temperature < 965.0) {
-    color = vec4(4.70366907, 0.0, 0.0, 1.0);
-  }
-  else {
-    float t = (temperature - 965.0) / (12000.0 - 965.0);
-    color = vec4(texture(spectrummap, vec2(t, layer)).rgb, 1.0);
-  }
+  float t = (temperature - 800.0) / (12000.0 - 800.0);
+  color = vec4(texture(spectrummap, vec2(t, layer)).rgb, 1.0);
 }
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_wavelength.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_wavelength.glsl
index 2c5d38eabbe..48d627dcd0b 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_wavelength.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_wavelength.glsl
@@ -1,15 +1,7 @@
-void node_wavelength(float wavelength,
-                     sampler1DArray spectrummap,
-                     float layer,
-                     vec3 xyz_to_r,
-                     vec3 xyz_to_g,
-                     vec3 xyz_to_b,
-                     out vec4 color)
+void node_wavelength(float wavelength, sampler1DArray spectrummap, float layer, out vec4 color)
 {
-  mat3 xyz_to_rgb = mat3(xyz_to_r, xyz_to_g, xyz_to_b);
   float t = (wavelength - 380.0) / (780.0 - 380.0);
-  vec3 xyz = texture(spectrummap, vec2(t, layer)).rgb;
-  vec3 rgb = xyz * xyz_to_rgb;
+  vec3 rgb = texture(spectrummap, vec2(t, layer)).rgb;
   rgb *= 1.0 / 2.52; /* Empirical scale from lg to make all comps <= 1. */
   color = vec4(clamp(rgb, 0.0, 1.0), 1.0);
 }