Part: add missing API ViewProviderPartExt::getElementColors()

This API is defined in Gui::ViewProvider to allow color override in
Link. In particular, the implementation in PartGui::ViewProviderPartExt
allows override for various part shapes.

src/Mod/Part/Gui/ViewProviderExt.cpp

@@ -97,6 +97,8 @@
 # include <QMenu>
 #endif
 
+#include <boost/algorithm/string/predicate.hpp>
+
 /// Here the FreeCAD includes sorted by Base,App,Gui......
 #include <Base/Console.h>
 #include <Base/Parameter.h>
@@ -745,6 +747,91 @@ void ViewProviderPartExt::setHighlightedFaces(const std::vector<App::Material>&
     }
 }
 
+std::map<std::string,App::Color> ViewProviderPartExt::getElementColors(const char *element) const {
+    std::map<std::string,App::Color> ret;
+
+    if(!element || !element[0]) {
+        auto color = ShapeColor.getValue();
+        color.a = Transparency.getValue()/100.0f;
+        ret["Face"] = color;
+        ret["Edge"] = LineColor.getValue();
+        ret["Vertex"] = PointColor.getValue();
+        return ret;
+    }
+
+    if(boost::starts_with(element,"Face")) {
+        auto size = DiffuseColor.getSize();
+        if(element[4]=='*') {
+            auto color = ShapeColor.getValue();
+            color.a = Transparency.getValue()/100.0f;
+            bool singleColor = true;
+            for(int i=0;i<size;++i) {
+                if(DiffuseColor[i]!=color)
+                    ret[std::string(element,4)+std::to_string(i+1)] = DiffuseColor[i];
+                singleColor = singleColor && DiffuseColor[0]==DiffuseColor[i];
+            }
+            if(size && singleColor) {
+                color = DiffuseColor[0];
+                ret.clear();
+            }
+            ret["Face"] = color;
+        }else{
+            int idx = atoi(element+4);
+            if(idx>0 && idx<=size)
+                ret[element] = DiffuseColor[idx-1];
+            else
+                ret[element] = ShapeColor.getValue();
+            if(size==1)
+                ret[element].a = Transparency.getValue()/100.0f;
+        }
+    } else if (boost::starts_with(element,"Edge")) {
+        auto size = LineColorArray.getSize();
+        if(element[4]=='*') {
+            auto color = LineColor.getValue();
+            bool singleColor = true;
+            for(int i=0;i<size;++i) {
+                if(LineColorArray[i]!=color)
+                    ret[std::string(element,4)+std::to_string(i+1)] = LineColorArray[i];
+                singleColor = singleColor && LineColorArray[0]==LineColorArray[i];
+            }
+            if(singleColor && size) {
+                color = LineColorArray[0];
+                ret.clear();
+            }
+            ret["Edge"] = color;
+        }else{
+            int idx = atoi(element+4);
+            if(idx>0 && idx<=size)
+                ret[element] = LineColorArray[idx-1];
+            else
+                ret[element] = LineColor.getValue();
+        }
+    } else if (boost::starts_with(element,"Vertex")) {
+        auto size = PointColorArray.getSize();
+        if(element[5]=='*') {
+            auto color = PointColor.getValue();
+            bool singleColor = true;
+            for(int i=0;i<size;++i) {
+                if(PointColorArray[i]!=color)
+                    ret[std::string(element,5)+std::to_string(i+1)] = PointColorArray[i];
+                singleColor = singleColor && PointColorArray[0]==PointColorArray[i];
+            }
+            if(singleColor && size) {
+                color = PointColorArray[0];
+                ret.clear();
+            }
+            ret["Vertex"] = color;
+        }else{
+            int idx = atoi(element+5);
+            if(idx>0 && idx<=size)
+                ret[element] = PointColorArray[idx-1];
+            else
+                ret[element] = PointColor.getValue();
+        }
+    }
+    return ret;
+}
+
 void ViewProviderPartExt::unsetHighlightedFaces()
 {
     DiffuseColor.touch();

src/Mod/Part/Gui/ViewProviderExt.h

@@ -129,6 +129,12 @@ class PartGuiExport ViewProviderPartExt : public Gui::ViewProviderGeometryObject
     void unsetHighlightedPoints();
     //@}
 
+    /** @name Color mangement methods 
+     */
+    //@{
+    virtual std::map<std::string,App::Color> getElementColors(const char *element=0) const override;
+    //@}
+
     virtual bool isUpdateForced() const override {
         return forceUpdateCount>0;
     }