Proportional scaling

[Simon Lord]

I have an abject on my card which can be scaled at runtime, the next 
step is to get this object to scale proportionally using it's current H 
x W as the aspect ratio when the shiftKey is down.

So if the object is currently shaped like a rectangle, when I hold the 
shiftKey down and continue dragging the object will maintain the same 
aspect ratio at the time I held the shiftKey down.

Unfortunately I'm at a lose at to where to even start the math on this.

Sincerely,
Simon