I've been trying to emulate the look of SCORE (don't ask why, I just like it) and the hardest thing has been getting the signature look of its slurs & ties.
I've attached an example of how my current efforts look (work in progress - has a few mistakes). I use the Scorlatti font and a TON of tweaks to get something that looks like SCORE.
I think such a tweak will go pretty deep so if any experts here are willing to help that would be great. I hope it doesn't have to involve any C++ to achieve this.
Abraham Lee created this code "flat-ties-and-slurs" for me years ago but it has some major limitations and still doesn't look like what I'm after.
So I had to use something else. And that something else is the shapeII code from OpenLilyLib. I meticulously reshape every single tie and slur to get a satisfactory shape but this takes a lot of time and I wish I had a code that does some of the work for me.
There is a very pleasant almost flat but not completely flat part in the middle portion of the bezier curve.
Here are some references (I can get more if needed)
flat-ties-and-slurs.ly
SCORElily example.pdf