From ec4b18cd30935a01669b7179d3d16ff22406a59e Mon Sep 17 00:00:00 2001
From: PaddleStroke <pierrelouis.boyer@gmail.com>
Date: Tue, 23 Sep 2025 00:47:12 +0200
Subject: [PATCH] Link: make OverrideMaterial use the per-face override.
 (#23544)

* Link: make OverrideMaterial use the per-face override.

* Fix small issue on per face transparency

* update names

* Update ViewProviderExt.cpp
---
 src/Gui/ViewProviderLink.cpp         | 59 +++++++++++++++++++++++-----
 src/Mod/Part/Gui/ViewProviderExt.cpp | 21 ++++++----
 2 files changed, 62 insertions(+), 18 deletions(-)

diff --git a/src/Gui/ViewProviderLink.cpp b/src/Gui/ViewProviderLink.cpp
index 2adc25e259..e6d7384b1a 100644
--- a/src/Gui/ViewProviderLink.cpp
+++ b/src/Gui/ViewProviderLink.cpp
@@ -2079,18 +2079,57 @@ void ViewProviderLink::checkIcon(const App::LinkBaseExtension *ext) {
     }
 }
 
-void ViewProviderLink::applyMaterial() {
-    if(OverrideMaterial.getValue())
-        linkView->setMaterial(-1,&ShapeMaterial.getValue());
+void ViewProviderLink::applyMaterial()
+{
+    if (OverrideMaterial.getValue()) {
+        // Dispatch a generic Coin3D action to the linked object's scene graph.
+        // If the linked object is a Part shape, its SoBrepFaceSet node will
+        // handle this action and apply the color to all its faces.
+        // This is decoupled and respects the core/module architecture.
+
+        // 1. Get the material from our property.
+        const auto& material = ShapeMaterial.getValue();
+
+        // 2. Prepare the color for the rendering action. The action's ultimate
+        // consumer (SoBrepFaceSet) expects a Base::Color where .a is transparency,
+        // so we must perform the conversion here at the boundary.
+        Base::Color renderColor = material.diffuseColor;
+        renderColor.a = 1.0f - material.transparency;
+
+        // 3. Create a map with the "Face" wildcard to signify "all faces".
+        std::map<std::string, Base::Color> colorMap;
+        colorMap["Face"] = renderColor;
+
+        // 4. Create and dispatch the action. We use a secondary context action,
+        // which is the established mechanism for this kind of override.
+        SoSelectionElementAction action(SoSelectionElementAction::Color,
+                                        true);  // true for secondary
+        action.swapColors(colorMap);
+        linkView->getLinkRoot()->doAction(&action);
+
+        // 5. Ensure the old global override mechanism is not used.
+        linkView->setMaterial(-1, nullptr);
+    }
     else {
-        for(int i=0;i<linkView->getSize();++i) {
-            if(MaterialList.getSize()>i &&
-               OverrideMaterialList.getSize()>i && OverrideMaterialList[i])
-                linkView->setMaterial(i,&MaterialList[i]);
-            else
-                linkView->setMaterial(i,nullptr);
+        // OVERRIDE IS DISABLED:
+        // We must clear the per-face override we just applied.
+
+        // 1. Dispatch an empty Color action to clear the secondary context.
+        SoSelectionElementAction action(SoSelectionElementAction::Color, true);
+        linkView->getLinkRoot()->doAction(&action);
+
+        // 2. Re-apply any other material settings (e.g., for array elements,
+        // or clear the old global override if it was set).
+        linkView->setMaterial(-1, nullptr);
+        for (int i = 0; i < linkView->getSize(); ++i) {
+            if (MaterialList.getSize() > i && OverrideMaterialList.getSize() > i
+                && OverrideMaterialList[i]) {
+                linkView->setMaterial(i, &MaterialList[i]);
+            }
+            else {
+                linkView->setMaterial(i, nullptr);
+            }
         }
-        linkView->setMaterial(-1,nullptr);
     }
 }
 
diff --git a/src/Mod/Part/Gui/ViewProviderExt.cpp b/src/Mod/Part/Gui/ViewProviderExt.cpp
index c2c326b808..23a79fb659 100644
--- a/src/Mod/Part/Gui/ViewProviderExt.cpp
+++ b/src/Mod/Part/Gui/ViewProviderExt.cpp
@@ -686,17 +686,19 @@ std::map<std::string,Base::Color> ViewProviderPartExt::getElementColors(const ch
             auto color = ShapeAppearance.getDiffuseColor();
             color.setTransparency(Base::fromPercent(Transparency.getValue()));
             bool singleColor = true;
-            for(int i=0;i<size;++i) {
-                if (ShapeAppearance.getDiffuseColor(i) != color) {
-                    ret[std::string(element, 4) + std::to_string(i + 1)] =
-                        ShapeAppearance.getDiffuseColor(i);
+            for (int i = 0; i < size; ++i) {
+                Base::Color faceColor = ShapeAppearance.getDiffuseColor(i);
+                faceColor.setTransparency(ShapeAppearance.getTransparency(i));
+                if (faceColor != color) {
+                    ret[std::string(element, 4) + std::to_string(i + 1)] = faceColor;
                 }
-                singleColor = singleColor
-                    && ShapeAppearance.getDiffuseColor(0) == ShapeAppearance.getDiffuseColor(i);
+                Base::Color firstFaceColor = ShapeAppearance.getDiffuseColor(0);
+                firstFaceColor.setTransparency(ShapeAppearance.getTransparency(0));
+                singleColor = singleColor && (faceColor == firstFaceColor);
             }
-            if(size && singleColor) {
+            if (size > 0 && singleColor) {
                 color = ShapeAppearance.getDiffuseColor(0);
-                color.setTransparency(Base::fromPercent(0.0F));
+                color.setTransparency(ShapeAppearance.getTransparency(0));
                 ret.clear();
             }
             ret["Face"] = color;
@@ -1403,3 +1405,6 @@ void ViewProviderPartExt::handleChangedPropertyName(Base::XMLReader& reader,
         Gui::ViewProviderGeometryObject::handleChangedPropertyName(reader, TypeName, PropName);
     }
 }
+
+
+