if you can get dynamic text(text that changes values "dynamically," ie. in real time, good place to look would be to search the files for something that comes up when you press the f3 key) to come up on screen, you could simply register the mob's position. It's x and z, in minecraft, though. Y is up/down. Notch set it that way. Just use a list that finds all entities that are instances of entitymob in a certain radius of the player, and have that dynamic text I mentioned earlier, display entitymob.posX and entitymob.posZ in that text. Shouldn't be too hard, if you run that through the onTickInGame boolean, out of your main mod file.
I believe there is an easier way to do this than that, as I've worked with RSPS clients before and they use a simple method to get the x and y of a model on the screen and then use that to draw things such as HP bars.
Anyone got any ideas?
How to get the 2D position? I don't know, but I'm sure it involves a lot of math and digging into the rendering code or the graphics library.
This is what I mean:
EDIT: Your post just showed up.
I believe there is an easier way to do this than that, as I've worked with RSPS clients before and they use a simple method to get the x and y of a model on the screen and then use that to draw things such as HP bars.