drawing irruglar shape with rounded corners

[mlecho]

hi, i have been tasked to create a rollover state that has dynamic irregular shapes that surround the movieclip target. The target is always a rectangle (thank god) and the shapes will look roughly like:


I think i will have to draw this old school without using the easy predfined shape classes. I first thought about doing two rounded rectangles to fake it, but the line cross over (pointing green arrow) will overlap. Anyone have ideas on how to approach this? If i go with the drawing api, is there a formula to working out the rounded curveTo angles on the corners to always be the same radius?

[neznein9]

Supposing you want 10pt curves on everything, you stop your lineTo 10px short and then use curveTo around the actual corner, landing 10px into the next line. Then the actual "corner" where the two straightaways would converge is your anchor point in the curve.

[mlecho]

that graph just answered all my questions! Thanks for the direction