Why don't you use the good old grid + A* pathfinding?

It is a pretty simple approach, limit the amount of paths calculated and you should have an OK FPS rate.

If you need better approachs you will have to look for a better graph representation for A* than a grid.

I suggest reading:

http://theory.stanford.edu/~amitp/GameProgramming/ (A LOT of information on A*)

http://theory.stanford.edu/~amitp/GameProgramming/MapRepresentations.html (Map representation only)

i'm not that good to make grid movement smooth . i compare AOE to starcraft, i think both use grid map, but starcraft has micro skill, AOE not. smooth unit movement is important for micro.

Alright so you have three major steps to use navmeshes.

i searched and found people talking about navigation mesh, but i don't understand why there are so many nodes that doesn't belong to any obstacle. i think a shortest path never travel through them. why are they there?

yeah, starcraft 2 is my goal, i'm talking about it's terrain and moving system. i'm already have a set of 2D assets that can form the game. but building assets can't fit in grid. i mean it's shape isn't square or rectangle or diamond, so i think of 'polygon' solution above. but it's seem unofficial and no one do it. i feel a little awkward

yeah my problem seem solved, thank you all for the support.