Core: Convert transparency to alpha (#24891)

* Core: Convert transparency to alpha

Create new `Base::getVersion()` function for extracting a program
version enumeration given a version string.

Convert transparency to alpha value for old project files.

* Base/App: Address review comments

---------

Co-authored-by: wmayer <wmayer@freecad.org>

src/App/PropertyStandard.cpp

@@ -35,6 +35,7 @@
 #include <Base/Console.h>
 #include <Base/Exception.h>
 #include <Base/Interpreter.h>
+#include <Base/ProgramVersion.h>
 #include <Base/Reader.h>
 #include <Base/Writer.h>
 #include <Base/Quantity.h>
@@ -2226,6 +2227,25 @@ unsigned int PropertyBoolList::getMemSize() const
 // PropertyColor
 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
+namespace
+{
+/// The definition of "alpha" was corrected in FreeCAD 1.1 -- returns true if the reader is working
+/// on a file that pre-dates that correction.
+bool readerRequiresAlphaConversion(const Base::XMLReader &reader)
+{
+    return Base::getVersion(reader.ProgramVersion) < Base::Version::v1_1;
+}
+
+/// Given a material, invert the alpha channel of all of its colors.
+void convertAlphaInMaterial(App::Material& material)
+{
+    material.ambientColor.a = 1.0F - material.ambientColor.a;
+    material.diffuseColor.a = 1.0F - material.diffuseColor.a;
+    material.specularColor.a = 1.0F - material.specularColor.a;
+    material.emissiveColor.a = 1.0F - material.emissiveColor.a;
+}
+}
+
 TYPESYSTEM_SOURCE(App::PropertyColor, App::Property)
 
 //**************************************************************************
@@ -2367,6 +2387,12 @@ void PropertyColor::Restore(Base::XMLReader& reader)
     reader.readElement("PropertyColor");
     // get the value of my Attribute
     unsigned long rgba = reader.getAttribute<unsigned long>("value");
+    if (readerRequiresAlphaConversion(reader)) {
+        // Convert transparency / alpha value
+        constexpr unsigned long alphaMax = 0xff;
+        unsigned long alpha = alphaMax - (rgba & alphaMax);
+        rgba = rgba - (rgba & alphaMax) + alpha;
+    }
     setValue(rgba);
 }
 
@@ -2448,6 +2474,8 @@ void PropertyColorList::Restore(Base::XMLReader& reader)
             // initiate a file read
             reader.addFile(file.c_str(), this);
         }
+
+        requiresAlphaConversion = readerRequiresAlphaConversion(reader);
     }
 }
 
@@ -2472,6 +2500,11 @@ void PropertyColorList::RestoreDocFile(Base::Reader& reader)
         str >> value;
         it.setPackedValue(value);
     }
+    if (requiresAlphaConversion) {
+        for (auto& it : values) {
+            it.a = 1.0F - it.a;
+        }
+    }
     setValues(values);
 }
 
@@ -2702,6 +2735,9 @@ void PropertyMaterial::Restore(Base::XMLReader& reader)
     _cMat.emissiveColor.setPackedValue(reader.getAttribute<unsigned long>("emissiveColor"));
     _cMat.shininess = (float)reader.getAttribute<double>("shininess");
     _cMat.transparency = (float)reader.getAttribute<double>("transparency");
+    if (readerRequiresAlphaConversion(reader)) {
+        convertAlphaInMaterial(_cMat);
+    }
     if (reader.hasAttribute("image")) {
         _cMat.image = reader.getAttribute<const char*>("image");
     }
@@ -3247,6 +3283,8 @@ void PropertyMaterialList::Restore(Base::XMLReader& reader)
             // initiate a file read
             reader.addFile(file.c_str(), this);
         }
+
+        requiresAlphaConversion = readerRequiresAlphaConversion(reader);
     }
 }
 
@@ -3330,6 +3368,7 @@ void PropertyMaterialList::RestoreDocFileV0(uint32_t count, Base::Reader& reader
         str >> valueF;
         it.transparency = valueF;
     }
+    convertAlpha(values);
     setValues(values);
 }
 
@@ -3360,9 +3399,17 @@ void PropertyMaterialList::RestoreDocFileV3(Base::Reader& reader)
         readString(str, it.imagePath);
         readString(str, it.uuid);
     }
+    convertAlpha(values);
     setValues(values);
 }
 
+void PropertyMaterialList::convertAlpha(std::vector<App::Material>& materials) const
+{
+    if (requiresAlphaConversion) {
+        std::ranges::for_each(materials, convertAlphaInMaterial);
+    }
+}
+
 void PropertyMaterialList::readString(Base::InputStream& str, std::string& value)
 {
     uint32_t uCt {};