ThatOpen · cvillagrasa · Jul 11, 2026
diff --git a/src/cpp/web-ifc/geometry/IfcGeometryLoader.cpp b/src/cpp/web-ifc/geometry/IfcGeometryLoader.cpp
@@ -1026,6 +1026,7 @@ namespace webifc::geometry
       return {};
     }
     case schema::IFCSURFACESTYLERENDERING:
+    case schema::IFCSURFACESTYLESHADING:
     {
       _loader.MoveToArgumentOffset(expressID, 0);
       auto outputColor = GetColor(_loader.GetRefArgument());
@@ -1039,11 +1040,6 @@ namespace webifc::geometry
 
       return outputColor;
     }
-    case schema::IFCSURFACESTYLESHADING:
-    {
-      _loader.MoveToArgumentOffset(expressID, 0);
-      return GetColor(_loader.GetRefArgument());
-    }
     case schema::IFCSTYLEDREPRESENTATION:
     {
       _loader.MoveToArgumentOffset(expressID, 3);

diff --git a/tests/functional/ShadingTransparency.spec.ts b/tests/functional/ShadingTransparency.spec.ts
@@ -0,0 +1,144 @@
+import * as WebIFC from '../../dist/web-ifc-api-node.js';
+import {IFCBUILDINGELEMENTPROXY} from '../../dist/web-ifc-api-node.js';
+
+import type {IfcAPI} from '../../dist/web-ifc-api-node.js';
+
+const SHADING_TRANSPARENCY_IFC4 = `ISO-10303-21;
+HEADER;
+FILE_DESCRIPTION(('ViewDefinition [CoordinationView]'),'2;1');
+FILE_NAME('','',(''),(''),'','','');
+FILE_SCHEMA(('IFC4'));
+ENDSEC;
+DATA;
+#1=IFCCARTESIANPOINT((0.,0.,0.));
+#2=IFCDIRECTION((0.,0.,1.));
+#3=IFCDIRECTION((1.,0.,0.));
+#4=IFCAXIS2PLACEMENT3D(#1,#2,#3);
+#5=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.0000000000000001E-05,#4,$);
+#6=IFCSIUNIT(*,.LENGTHUNIT.,$,.METRE.);
+#7=IFCUNITASSIGNMENT((#6));
+#8=IFCPROJECT('1x7xm5lGf9o8yVrMp7_oY3',$,'Shading transparency repro',$,$,$,$,(#5),#7);
+#9=IFCAXIS2PLACEMENT3D(#1,$,$);
+#10=IFCLOCALPLACEMENT($,#9);
+#11=IFCSITE('2zqnrS0557_gMa3Jzg7KCA',$,'Site',$,$,#10,$,$,.ELEMENT.,$,$,$,$,$);
+#12=IFCRELAGGREGATES('3bVA_CHvz6GQIw9DLQws4X',$,$,$,#8,(#11));
+#13=IFCCOLOURRGB($,1.,0.,0.);
+#14=IFCSURFACESTYLESHADING(#13,0.80000000000000004);
+#15=IFCSURFACESTYLE('shading with transparency',.BOTH.,(#14));
+#16=IFCSURFACESTYLERENDERING(#13,0.80000000000000004,$,$,$,$,$,$,.NOTDEFINED.);
+#17=IFCSURFACESTYLE('rendering with transparency',.BOTH.,(#16));
+#18=IFCRECTANGLEPROFILEDEF(.AREA.,$,$,1.,1.);
+#19=IFCDIRECTION((0.,0.,1.));
+#20=IFCEXTRUDEDAREASOLID(#18,$,#19,1.);
+#21=IFCSTYLEDITEM(#20,(#15),$);
+#22=IFCSHAPEREPRESENTATION(#5,'Body','SweptSolid',(#20));
+#23=IFCPRODUCTDEFINITIONSHAPE($,$,(#22));
+#24=IFCCARTESIANPOINT((0.,0.,0.));
+#25=IFCAXIS2PLACEMENT3D(#24,$,$);
+#26=IFCLOCALPLACEMENT(#10,#25);
+#27=IFCBUILDINGELEMENTPROXY('1$N9WPo3bE6wRF4P$YuzAX',$,'shading box',$,$,#26,#23,$,$);
+#28=IFCRECTANGLEPROFILEDEF(.AREA.,$,$,1.,1.);
+#29=IFCDIRECTION((0.,0.,1.));
+#30=IFCEXTRUDEDAREASOLID(#28,$,#29,1.);
+#31=IFCSTYLEDITEM(#30,(#17),$);
+#32=IFCSHAPEREPRESENTATION(#5,'Body','SweptSolid',(#30));
+#33=IFCPRODUCTDEFINITIONSHAPE($,$,(#32));
+#34=IFCCARTESIANPOINT((3.,0.,0.));
+#35=IFCAXIS2PLACEMENT3D(#34,$,$);
+#36=IFCLOCALPLACEMENT(#10,#35);
+#37=IFCBUILDINGELEMENTPROXY('0wKFqjAy15eQieFk7gc1RM',$,'rendering box',$,$,#36,#33,$,$);
+#38=IFCRELCONTAINEDINSPATIALSTRUCTURE('1EGVveoy18y8ZUzzCxJAQ7',$,$,$,(#27,#37),#11);
+ENDSEC;
+END-ISO-10303-21;
+`;
+
+const SHADING_IFC2X3 = `ISO-10303-21;
+HEADER;
+FILE_DESCRIPTION(('ViewDefinition [CoordinationView]'),'2;1');
+FILE_NAME('','',(''),(''),'','','');
+FILE_SCHEMA(('IFC2X3'));
+ENDSEC;
+DATA;
+#1=IFCCARTESIANPOINT((0.,0.,0.));
+#2=IFCDIRECTION((0.,0.,1.));
+#3=IFCDIRECTION((1.,0.,0.));
+#4=IFCAXIS2PLACEMENT3D(#1,#2,#3);
+#5=IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.0000000000000001E-05,#4,$);
+#6=IFCSIUNIT(*,.LENGTHUNIT.,$,.METRE.);
+#7=IFCUNITASSIGNMENT((#6));
+#8=IFCPERSON($,$,$,$,$,$,$,$);
+#9=IFCORGANIZATION($,'org',$,$,$);
+#10=IFCPERSONANDORGANIZATION(#8,#9,$);
+#11=IFCORGANIZATION($,'org',$,$,$);
+#12=IFCAPPLICATION(#11,'1','app','app');
+#13=IFCOWNERHISTORY(#10,#12,$,.ADDED.,$,$,$,0);
+#14=IFCPROJECT('1pHRBOsmT8txw9xBa7JqLd',#13,'IFC2X3 shading repro',$,$,$,$,(#5),#7);
+#15=IFCAXIS2PLACEMENT3D(#1,$,$);
+#16=IFCLOCALPLACEMENT($,#15);
+#17=IFCSITE('29FHeh_Yr3af5Ouh7msCzT',#13,'Site',$,$,#16,$,$,.ELEMENT.,$,$,$,$,$);
+#18=IFCRELAGGREGATES('0$9Z_B8ATFjPYckHxMI5Yk',#13,$,$,#14,(#17));
+#19=IFCCOLOURRGB($,0.,1.,0.);
+#20=IFCSURFACESTYLESHADING(#19);
+#21=IFCSURFACESTYLE('plain IFC2X3 shading',.BOTH.,(#20));
+#22=IFCCARTESIANPOINT((0.,0.));
+#23=IFCAXIS2PLACEMENT2D(#22,$);
+#24=IFCRECTANGLEPROFILEDEF(.AREA.,$,#23,1.,1.);
+#25=IFCAXIS2PLACEMENT3D(#1,$,$);
+#26=IFCDIRECTION((0.,0.,1.));
+#27=IFCEXTRUDEDAREASOLID(#24,#25,#26,1.);
+#28=IFCPRESENTATIONSTYLEASSIGNMENT((#21));
+#29=IFCSTYLEDITEM(#27,(#28),$);
+#30=IFCSHAPEREPRESENTATION(#5,'Body','SweptSolid',(#27));
+#31=IFCPRODUCTDEFINITIONSHAPE($,$,(#30));
+#32=IFCAXIS2PLACEMENT3D(#1,$,$);
+#33=IFCLOCALPLACEMENT(#16,#32);
+#34=IFCBUILDINGELEMENTPROXY('2RLsNYqGPD4wePf6E53no2',#13,'ifc2x3 shading box',$,$,#33,#31,$,$);
+#35=IFCRELCONTAINEDINSPATIALSTRUCTURE('2DCzxJhfT8GvuOYkp9pSos',#13,$,$,(#34),#17);
+ENDSEC;
+END-ISO-10303-21;
+`;
+
+let ifcApi: IfcAPI;
+
+function colorOf(modelID: number, nameFragment: string) {
+    const ids = ifcApi.GetLineIDsWithType(modelID, IFCBUILDINGELEMENTPROXY);
+    for (let i = 0; i < ids.size(); i++) {
+        const id = ids.get(i);
+        if (!ifcApi.GetLine(modelID, id).Name.value.includes(nameFragment)) continue;
+        return ifcApi.GetFlatMesh(modelID, id).geometries.get(0).color;
+    }
+    throw new Error(`no element matching "${nameFragment}"`);
+}
+
+function open(content: string): number {
+    return ifcApi.OpenModel(new TextEncoder().encode(content));
+}
+
+beforeAll(async () => {
+    ifcApi = new WebIFC.IfcAPI();
+    await ifcApi.Init();
+    ifcApi.SetLogLevel(WebIFC.LogLevel.LOG_LEVEL_OFF);
+});
+
+describe('IfcSurfaceStyleShading transparency', () => {
+    test('IFC4 plain Shading Transparency is applied to the mesh color alpha', () => {
+        const modelID = open(SHADING_TRANSPARENCY_IFC4);
+        const color = colorOf(modelID, 'shading box');
+        expect(color.w).toBeCloseTo(0.2, 5);
+        ifcApi.CloseModel(modelID);
+    });
+
+    test('IFC4 Rendering Transparency keeps working the same way', () => {
+        const modelID = open(SHADING_TRANSPARENCY_IFC4);
+        const color = colorOf(modelID, 'rendering box');
+        expect(color.w).toBeCloseTo(0.2, 5);
+        ifcApi.CloseModel(modelID);
+    });
+
+    test('IFC2X3 Shading (no Transparency attribute) stays opaque', () => {
+        const modelID = open(SHADING_IFC2X3);
+        const color = colorOf(modelID, 'ifc2x3 shading box');
+        expect(color.w).toBeCloseTo(1.0, 5);
+        ifcApi.CloseModel(modelID);
+    });
+});