Fix color handling (#1843)

* Fix color handling

* Use sRGB in tests

* Explicit test for STEP color handling

Author: adam-urbanczyk

cadquery/occ_impl/assembly.py

@@ -20,7 +20,11 @@
 from OCP.TDataStd import TDataStd_Name
 from OCP.TDF import TDF_Label
 from OCP.TopLoc import TopLoc_Location
-from OCP.Quantity import Quantity_ColorRGBA
+from OCP.Quantity import (
+    Quantity_ColorRGBA,
+    Quantity_Color,
+    Quantity_TOC_sRGB,
+)
 from OCP.BRepAlgoAPI import BRepAlgoAPI_Fuse
 from OCP.TopTools import TopTools_ListOfShape
 from OCP.BOPAlgo import BOPAlgo_GlueEnum, BOPAlgo_MakeConnected
@@ -92,12 +96,16 @@ def __init__(self, *args, **kwargs):
                 raise ValueError(f"Unknown color name: {args[0]}")
         elif len(args) == 3:
             r, g, b = args
-            self.wrapped = Quantity_ColorRGBA(r, g, b, 1)
+            self.wrapped = Quantity_ColorRGBA(
+                Quantity_Color(r, g, b, Quantity_TOC_sRGB), 1
+            )
             if kwargs.get("a"):
                 self.wrapped.SetAlpha(kwargs.get("a"))
         elif len(args) == 4:
             r, g, b, a = args
-            self.wrapped = Quantity_ColorRGBA(r, g, b, a)
+            self.wrapped = Quantity_ColorRGBA(
+                Quantity_Color(r, g, b, Quantity_TOC_sRGB), a
+            )
         else:
             raise ValueError(f"Unsupported arguments: {args}, {kwargs}")
 
@@ -114,9 +122,9 @@ def toTuple(self) -> Tuple[float, float, float, float]:
         Convert Color to RGB tuple.
         """
         a = self.wrapped.Alpha()
-        rgb = self.wrapped.GetRGB()
+        rgb = self.wrapped.GetRGB().Values(Quantity_TOC_sRGB)
 
-        return (rgb.Red(), rgb.Green(), rgb.Blue(), a)
+        return (*rgb, a)
 
     def __getstate__(self) -> Tuple[float, float, float, float]:
 

tests/test_assembly.py

@@ -34,7 +34,7 @@
 from OCP.STEPCAFControl import STEPCAFControl_Reader
 from OCP.IFSelect import IFSelect_RetDone
 from OCP.TDF import TDF_ChildIterator
-from OCP.Quantity import Quantity_ColorRGBA, Quantity_TOC_RGB
+from OCP.Quantity import Quantity_ColorRGBA, Quantity_TOC_sRGB
 from OCP.TopAbs import TopAbs_ShapeEnum
 
 
@@ -427,7 +427,7 @@ def get_doc_nodes(doc, leaf=False):
                         child, XCAFDoc_ColorType.XCAFDoc_ColorSurf, color_subshape
                     ):
                         face_color = (
-                            *color_subshape.GetRGB().Values(Quantity_TOC_RGB),
+                            *color_subshape.GetRGB().Values(Quantity_TOC_sRGB),
                             color_subshape.Alpha(),
                         )
 
@@ -442,7 +442,7 @@ def get_doc_nodes(doc, leaf=False):
                     ):
                         color_subshapes_set.add(
                             (
-                                *color_subshape.GetRGB().Values(Quantity_TOC_RGB),
+                                *color_subshape.GetRGB().Values(Quantity_TOC_sRGB),
                                 color_subshape.Alpha(),
                             )
                         )
@@ -454,9 +454,9 @@ def get_doc_nodes(doc, leaf=False):
             {
                 "path": PurePath(node.Id.ToCString()),
                 "name": TCollection_ExtendedString(name_att.Get()).ToExtString(),
-                "color": (*color.GetRGB().Values(Quantity_TOC_RGB), color.Alpha()),
+                "color": (*color.GetRGB().Values(Quantity_TOC_sRGB), color.Alpha()),
                 "color_shape": (
-                    *color_shape.GetRGB().Values(Quantity_TOC_RGB),
+                    *color_shape.GetRGB().Values(Quantity_TOC_sRGB),
                     color_shape.Alpha(),
                 ),
                 "color_subshapes": color_subshapes,
@@ -1972,3 +1972,31 @@ def test_remove_without_parent():
 
     assert len(assy.children) == 1
     assert len(assy.objects) == 1
+
+
+def test_step_color(tmp_path_factory):
+    """
+    Checks color handling for STEP export.
+    """
+
+    # Use a temporary directory
+    tmpdir = tmp_path_factory.mktemp("out")
+    step_color_path = os.path.join(tmpdir, "step_color.step")
+
+    # Create a simple assembly with color
+    assy = cq.Assembly()
+    assy.add(cq.Workplane().box(10, 10, 10), color=cq.Color(0.47, 0.253, 0.18, 1.0))
+
+    success = exportStepMeta(assy, step_color_path)
+    assert success
+
+    # Read the file as a string and check for the correct colors
+    with open(step_color_path, "r") as f:
+        step_content = f.readlines()
+
+        # Step through and try to find the COLOUR line
+        for line in step_content:
+            if "COLOUR_RGB(''," in line:
+                assert "0.47" in line
+                assert "0.25" in line
+                assert "0.18" in line