Here's a pretty standard shader effect with a demo CAPX program for you to try out. Yes, we know there is already an Outline effect, but we couldn't get that one to work properly.
SOBEL EDGE DETECTION SHADER:
For those who want a challenge, go ahead and modify our shader code to implement a edge detection line thickness effect as in the Outline effect. It would serve as a good tutorial base to work with. Open both Outline.fx and Edge.fx with a text editor and see what needs to be tweaked. Remember to edit Edge.xml to introduce the new line thickness parameter.