Geometry Nodes: add support for blackbody shader node

This adds the existing Blackbody shader node to geometry nodes, with the
same functionality.

Pull Request: https://projects.blender.org/blender/blender/pulls/114768

scripts/startup/bl_ui/node_add_menu_geometry.py

@@ -33,6 +33,7 @@ class NODE_MT_geometry_node_GEO_COLOR(Menu):
 
     def draw(self, _context):
         layout = self.layout
+        node_add_menu.add_node_type(layout, "ShaderNodeBlackbody")
         node_add_menu.add_node_type(layout, "ShaderNodeValToRGB")
         node_add_menu.add_node_type(layout, "ShaderNodeRGBCurve")
         layout.separator()

source/blender/imbuf/IMB_colormanagement.h

@@ -534,10 +534,12 @@ enum {
 /** \name Rendering Tables
  * \{ */
 
+void IMB_colormanagement_blackbody_temperature_to_rgb(float r_dest[4], float value);
 void IMB_colormanagement_blackbody_temperature_to_rgb_table(float *r_table,
                                                             int width,
                                                             float min,
                                                             float max);
+void IMB_colormanagement_wavelength_to_rgb(float r_dest[4], float value);
 void IMB_colormanagement_wavelength_to_rgb_table(float *r_table, int width);
 
 /** \} */

source/blender/imbuf/intern/colormanagement.cc

@@ -4340,6 +4340,19 @@ static void blackbody_temperature_to_rec709(float rec709[3], float t)
   }
 }
 
+void IMB_colormanagement_blackbody_temperature_to_rgb(float r_dest[4], float value)
+{
+  float rec709[3];
+  blackbody_temperature_to_rec709(rec709, value);
+
+  float rgb[3];
+  IMB_colormanagement_rec709_to_scene_linear(rgb, rec709);
+  clamp_v3(rgb, 0.0f, FLT_MAX);
+
+  copy_v3_v3(r_dest, rgb);
+  r_dest[3] = 1.0f;
+}
+
 void IMB_colormanagement_blackbody_temperature_to_rgb_table(float *r_table,
                                                             const int width,
                                                             const float min,
@@ -4347,16 +4360,7 @@ void IMB_colormanagement_blackbody_temperature_to_rgb_table(float *r_table,
 {
   for (int i = 0; i < width; i++) {
     float temperature = min + (max - min) / float(width) * float(i);
-
-    float rec709[3];
-    blackbody_temperature_to_rec709(rec709, temperature);
-
-    float rgb[3];
-    IMB_colormanagement_rec709_to_scene_linear(rgb, rec709);
-    clamp_v3(rgb, 0.0f, FLT_MAX);
-
-    copy_v3_v3(&r_table[i * 4], rgb);
-    r_table[i * 4 + 3] = 0.0f;
+    IMB_colormanagement_blackbody_temperature_to_rgb(&r_table[i * 4], temperature);
   }
 }
 
@@ -4420,20 +4424,24 @@ static void wavelength_to_xyz(float xyz[3], float lambda_nm)
   }
 }
 
+void IMB_colormanagement_wavelength_to_rgb(float r_dest[4], float value)
+{
+  float xyz[3];
+  wavelength_to_xyz(xyz, value);
+
+  float rgb[3];
+  IMB_colormanagement_xyz_to_scene_linear(rgb, xyz);
+  clamp_v3(rgb, 0.0f, FLT_MAX);
+
+  copy_v3_v3(r_dest, rgb);
+  r_dest[3] = 1.0f;
+}
+
 void IMB_colormanagement_wavelength_to_rgb_table(float *r_table, const int width)
 {
   for (int i = 0; i < width; i++) {
-    float temperature = 380 + 400 / float(width) * float(i);
-
-    float xyz[3];
-    wavelength_to_xyz(xyz, temperature);
-
-    float rgb[3];
-    IMB_colormanagement_xyz_to_scene_linear(rgb, xyz);
-    clamp_v3(rgb, 0.0f, FLT_MAX);
-
-    copy_v3_v3(&r_table[i * 4], rgb);
-    r_table[i * 4 + 3] = 0.0f;
+    float wavelength = 380 + 400 / float(width) * float(i);
+    IMB_colormanagement_wavelength_to_rgb(&r_table[i * 4], wavelength);
   }
 }
 

source/blender/nodes/shader/nodes/node_shader_blackbody.cc

@@ -2,14 +2,19 @@
  *
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include "FN_multi_function_builder.hh"
+#include "NOD_multi_function.hh"
 #include "node_shader_util.hh"
+#include "node_util.hh"
 
+#include "BLI_color.hh"
 #include "IMB_colormanagement.h"
 
 namespace blender::nodes::node_shader_blackbody_cc {
 
 static void node_declare(NodeDeclarationBuilder &b)
 {
+  b.is_function_node();
   b.add_input<decl::Float>("Temperature").default_value(1500.0f).min(800.0f).max(12000.0f);
   b.add_output<decl::Color>("Color");
 }
@@ -31,6 +36,16 @@ static int node_shader_gpu_blackbody(GPUMaterial *mat,
   return GPU_stack_link(mat, node, "node_blackbody", in, out, ramp_texture, GPU_constant(&layer));
 }
 
+static void sh_node_blackbody_build_multi_function(nodes::NodeMultiFunctionBuilder &builder)
+{
+  static auto fn = mf::build::SI1_SO<float, ColorGeometry4f>("Blackbody", [](float temperature) {
+    float color[4];
+    IMB_colormanagement_blackbody_temperature_to_rgb(color, temperature);
+    return ColorGeometry4f(color);
+  });
+  builder.set_matching_fn(fn);
+}
+
 NODE_SHADER_MATERIALX_BEGIN
 #ifdef WITH_MATERIALX
 {
@@ -57,10 +72,11 @@ void register_node_type_sh_blackbody()
 
   static bNodeType ntype;
 
-  sh_node_type_base(&ntype, SH_NODE_BLACKBODY, "Blackbody", NODE_CLASS_CONVERTER);
+  sh_fn_node_type_base(&ntype, SH_NODE_BLACKBODY, "Blackbody", NODE_CLASS_CONVERTER);
   ntype.declare = file_ns::node_declare;
   blender::bke::node_type_size_preset(&ntype, blender::bke::eNodeSizePreset::MIDDLE);
   ntype.gpu_fn = file_ns::node_shader_gpu_blackbody;
+  ntype.build_multi_function = file_ns::sh_node_blackbody_build_multi_function;
   ntype.materialx_fn = file_ns::node_shader_materialx;
 
   nodeRegisterType(&ntype);