So, um, it seemed kinda simple, so I decided to port the AdvanceMAME 2xScale filter to VergeC.
Download Link
Simple function, takes an image and returns a new scaled and enhanced version of it. Due to my initial misunderstanding of the code, what bug I made I then turned into a feature: you can enable interpolation as well as enhancement by setting the 'type' argument to 1.
The best enhancement is a modified 4x scale. Try scale2x with blurring on, and then scale2x again on the result, but with no blurring.
You can, of course, keep reapplying the filter to an image.
It will never be fast enough for real time use, but it could be used to pre-filter some graphics.
int oScale2x(int srcimg, int blur_type)
//Returns the handle to a new enhanced version of srcimg.
//If blur_type is set to 1, will interpolate as well as enhance the image.
Note that this isn't the same as 2xSAI, but in some ways it's just as cool, if not cooler.