EDIT
Nice tip from @Bradley Uffner ! (unfortunately he deleted his answer)
There is a tutorial here on how to achieve such effect :
http://alastaira.wordpress.com/2013/11/01/hand-drawn-shaders-and-creating-tonal-art-maps/
Another thing I've found recently which might interests you :
http://blogs.msdn.com/b/hemipteran/archive/2014/03/26/generating-noise-for-applications.aspx
I've didn't read well the title of your question, Windows Forms do not support shaders at all.
Be more specific about the meaning of a crayon shader
Regarding using shaders in WPF, you cannot apply them at a line-level but on a Control
level instead.
This the class representing a shader in WPF:
http://msdn.microsoft.com/en-us/library/system.windows.media.effects.effect(v=vs.110).aspx
What I suggest
- use an Image and set its Source property to use a
WriteableBitmap
- use the excellent WriteableBitmapEx library to easily draw on it, basically it's the
WriteableBitmap
in WPF but with many extension methods for drawing lines, circles, rectangles etc ... - then apply your shader to the Effect property of
Image
For developing your shader
Use Shazzam, it allows you to develop an HLSL shader for WPF in a cool interface, preview it instantly and it will generate the Effect
class ready to paste on your project.
There might be a couple of interesting shader for you in DOSBox SVN-Daum
Here's an example of the cartoon shader :
Obviously there will be quite some work as copy-pasting the shader to Shazzam won't work right away but you'll know what are the maths behind achieving the effect.
Mark the answer as accepted if you are satisfied with it :D if not edit your question and add more details.