Add HACKING info

diff --git a/HACKING b/HACKING
index 6fdb36dc3f975f1227f2458a35df82a653a586df..59902651f921356c83bedf0cf41ba2f354f2d82d 100644 (file)
--- a/HACKING
+++ b/HACKING
@@ -21,3 +21,10 @@ object-oriented language.
 
 "xmpp" and "ympp" are really misnomers, as they only represent the Meters Per Pixel in UTM mode. Otherwise they are an artificial
 zooming system. In expedia mode it represents the "Alti", in Google mode it represents 2^(scale), e.g. 2^0 = 1, 2^8 = 256.
+
+---
+Implementing a MapSource
+
+VikMapSource is the "interface", the really base class of the MapSource tree.
+In order to implement a MapSource, you have to prefer to derive from VikMapSourceDefault, a less abstract class, adding a property based implementation for some aspects of the VikMapSource interface.
+Then, you have to provide implementation for coord_to_mapcoord, mapcoord_to_center_coord and download methods.