dnl Setting up library version
AGG_LIB_VERSION="2:4:0"
dnl current-´ / /
dnl revision--´ /
dnl age---´
dnl Update the version information only immediately before a public release of antigrain
dnl If the library source code has changed, increment revision (c:r:a becomes c:r+1:a).
dnl If any interfaces have been added, removed, or changed since the last update,
dnl increment current, and set revision to 0.
dnl If any interfaces have been added since the last public release, then increment age.
dnl If any interfaces have been removed since the last public release, then set age to 0.
These instructions match what I found on the web for Linux library ABI versions. Since I am changing the library source, adding an interface, but not removing any interfaces I should increment the current to 3, reset the revision to 0 and increment the age to 1 --> 3:0:1 (not 2:0:1 as I said before). So the soname will be libagg3.