Silverlight comes with a shrunk down version of the CLR
called the CoreCLR and also comes with a reduced version of
the core class libraries.
Silverlight uses a subset of the 2.0 API and removes a lot
of stuff that would only be used on a desktop or a server and
removes overloads that people are not likely going to use and
according to some blog posts even things like
System.Collections will be removed giving preference to the
generics-based API in System.Collections.Generic.
Nice graphic showing my Inkscape skills:
To support this "thin" profile in Moonlight we
had a couple of choices.
We really did not want to branch our source code and chop
code left and right until we removed all the extra baggage.
We also did not want to use compilation defines because that
would get ugly very fast.
Instead what we did was
productize Linker tool that
was developed as part of the Google Summer of Code last year.
The Linker could take an assembly and a description of the
desired API entry points and produce a new assembly that only
contains the requested entry points plus any of its
dependencies. Although the Linker from last year was able to
do some basic linking, but as with all software projects, the
devil is on the details. JB
has been working on productizing the tool ever since he joined
Novell back in May.
The idea was that we would feed the linker a superset of
our 2.0 library (2.0 plus the handful of Silverlight-esque
APIs) plus a linker description file, and it would produce the
resulting Silverlight compatible assembly.
The above approach allowed us to minimize the number of
ifdefs that were required in the source code. In addition
to the linking stage we also needed a way of inject a number
of security attributes (again to avoid having a mess of ifdefs
So JB created new specialized tool that allows us to add,
remove and validate assemblies. We call this the Tuner.
Both the linker and the tuner are based on Cecil a library
for handling CIL files.
The tuner can do most of the heavy lifting, but there are a
couple of areas that still required human intervention:
- In a handful of cases abstract methods are no
longer exposed in Silverlight, we had to work around
this directly (XmlReader).
- In a few cases there are some interfaces and class
hierarchy changes required, those also had to be done
Finally, since our C# compiler depends very strongly on its
mscorlib (the reason we have 3 compilers today, one for each
profile is linked precisely to this dependency on mscorlib) we
had to add special support to the VM to allow the compiler to
call into methods that we had hidden as part of the tuning
This afternoon for the first time JB was able to build the
2.1 profile from the start up to the Silverlight support
libraries and the Silverlight plugin with the tuned
Although we have been debugging Moonlight with 2.0
assemblies for the past few months due to some of the API
changes some applications like the SimpleXPSViewer did not
There is still some work left to do as you can see from the
warnings generated by the tuner, but we are getting there.
With the 2.1 profile in place it is now possible for people
on Linux and MacOS to develop Silverlight applications without
The bad news is that the 2.1 profile will not be available
in Mono's 1.2.5 release as we branched that release a few
weeks ago. So developers interested in doing Silverlight
development on Linux or MacOS will have to wait until our
1.2.6 release in a couple of months.
In the meantime Ankit has added support
for compiling existing Silverlight VS Solutions as well as
generating Unix makefiles from the VS solution file. You must
be using an SVN release of MonoDevelop (sadly, 0.15
wont do it). for this to work though:
bash$ mdtool generate-makefiles SilverlightAirlines.sln --simple-makefiles
Creating configure script
Adding variables to top-level Makefile
Makefiles were successfully generated.
The default is to generate auto-tools based makefiles. It
is recommended that people with acid reflux, ulcers or other
delicate stomach conditions use the --simple-makefiles
option. --simple-makefiles produces a configure and Makefile
script that are essentially the labor of love.
If we can sort out the license for the Silverlight.js
template, we should also be able to ship MonoDevelop templates
for creating Silverlight content.