Adding --surface-color in conversion settings to force the use of surface color instead of diffuse color. Issue #5075

src/ifcgeom/ConversionSettings.h

@@ -331,6 +331,13 @@ namespace ifcopenshell {
 				static constexpr bool defaultvalue = false;
 			};
 
+			struct SurfaceColour : public SettingBase<SurfaceColour, bool> {
+                static constexpr const char* const name = "surface-colour";
+                static constexpr const char* const description =
+                    "Prioritizes the surface color instead of using diffuse.";
+                static constexpr bool defaultvalue = false;
+            };
+
 			enum PiecewiseStepMethod  {
 				MAXSTEPSIZE,
 				MINSTEPS };

src/ifcgeom/mapping/mapping.cpp

@@ -565,10 +565,14 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcStyledItem* inst) {
         return surface_style;
     }
 
+     surface_style->use_surface_color = settings_.get<settings::SurfaceColour>().get();
+
     static taxonomy::colour white = taxonomy::colour(1., 1., 1.);
     double rgb[3];
     if (process_colour(shading->SurfaceColour(), rgb)) {
-        surface_style->diffuse.components() << rgb[0], rgb[1], rgb[2];
+        surface_style->surface.components() << rgb[0], rgb[1], rgb[2];
+    } else {
+		surface_style->surface = white;
     }
 
     if (auto rendering_style = shading->as<IfcSchema::IfcSurfaceStyleRendering>()) {

src/ifcgeom/taxonomy.h

@@ -305,8 +305,10 @@ typedef item const* ptr;
 
 				std::string name;
 				colour diffuse;
+				colour surface;
 				colour specular;
 				double specularity, transparency;
+				bool use_surface_color;
 
 				void print(std::ostream& o, int indent = 0) const;
 
@@ -321,8 +323,15 @@ typedef item const* ptr;
 				// @todo equality implementation based on values?
 				bool operator==(const style& other) const { return instance == other.instance; }
 
-				style() : specularity(std::numeric_limits<double>::quiet_NaN()), transparency(std::numeric_limits<double>::quiet_NaN()) {}
-				style(const std::string& name) : name(name), specularity(std::numeric_limits<double>::quiet_NaN()), transparency(std::numeric_limits<double>::quiet_NaN()) {}
+				style() : specularity(std::numeric_limits<double>::quiet_NaN()), transparency(std::numeric_limits<double>::quiet_NaN()), use_surface_color(false) {}
+				style(const std::string& name) : name(name), specularity(std::numeric_limits<double>::quiet_NaN()), transparency(std::numeric_limits<double>::quiet_NaN()), use_surface_color(false) {}
+
+				colour get_color() const {
+                    if (use_surface_color && surface) {
+                        return surface;
+					}
+					return diffuse;
+				}
 
 				bool has_specularity() const {
 					return !std::isnan(specularity);

src/serializers/GltfSerializer.cpp

@@ -97,9 +97,9 @@ int GltfSerializer::writeMaterial(const ifcopenshell::geometry::taxonomy::style:
 
 	std::array<double, 4> base;
 	base.fill(1.0);
-	if (style->diffuse) {
+	if (style->get_color()) {
 		for (int i = 0; i < 3; ++i) {
-			base[i] = style->diffuse.ccomponents()(i);
+			base[i] = style->get_color().ccomponents()(i);
 		}
 	}
 	if (style->transparency == style->transparency) {