1 files changed, 33 insertions, 4 deletions

diff --git a/drawinglayer/inc/drawinglayer/primitive2d/alphaprimitive2d.hxx b/drawinglayer/inc/drawinglayer/primitive2d/alphaprimitive2d.hxx
index af82017f0d..89cbc8e076 100644
--- a/drawinglayer/inc/drawinglayer/primitive2d/alphaprimitive2d.hxx
+++ b/drawinglayer/inc/drawinglayer/primitive2d/alphaprimitive2d.hxx
@@ -44,23 +44,52 @@ namespace drawinglayer
 {
     namespace primitive2d
     {
+        /** AlphaPrimitive2D class
+
+            This is the basic primitive for applying freely defined transparence
+            to freely defined content. The basic idea is to associate a content
+            which is defined as a sequence of primitives and hold as child content
+            in the GroupPrimitive2D with an alpha channel also defined as a sequence 
+            of primitives and hold in the Alpha member.
+
+            The basic definition is to use the Alpha content as Alpha-Mask by
+            interpreting the Alpha-content not as RGB, but as Luminance alpha mask
+            using the common RGB_to_luminance definition as e.g. used by VCL.
+
+            The defining geometry is the Range of the child primitive sequence,
+            this means the renderers will/shall use this geometric information for
+            rendering, not the alpha one. The alpha one should/will be clipped 
+            accordingly.
+         */
         class AlphaPrimitive2D : public GroupPrimitive2D
         {
         private:
-            Primitive2DSequence						maAlpha; // transparence sequence
+            /// The Alpha-Mask who's RGB-Values are interpreted as Luminance
+            Primitive2DSequence						maAlpha;
 
         public:
+            /** constructor
+
+                @param rChildren
+                The content which is defined to have a transparency. The
+                range of this primitive is defined by this content
+
+                @param rAlpha
+                The definition of the Alpha-channel for this primitive. It
+                will be interpreted as mask by interpreting as gray values
+                using the common RGB_to_luminance definitions
+             */
             AlphaPrimitive2D(
                 const Primitive2DSequence& rChildren, 
                 const Primitive2DSequence& rAlpha);
 
-            // get data
+            /// data read access
             const Primitive2DSequence& getAlpha() const { return maAlpha; }
 
-            // compare operator
+            /// compare operator
             virtual bool operator==(const BasePrimitive2D& rPrimitive) const;
 
-            // provide unique ID
+            /// provide unique ID
             DeclPrimitrive2DIDBlock()
         };
     } // end of namespace primitive2d