Restrict picking to non-transparent parts

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@32503 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
YANPE
(related to #4175)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@32504 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e