Interpolating a rectangle [Resolved]

[SLH]

I have a rectangle defined by it's bottom left coordinates, and a width and height.

I have a destination rectangle, and i want to interpolate between the 2.

I've done this in a linear fasion by doing linear interpolation on the 4 values (x,y,w,h).

Unfortunately this is no good for what i want as the rectangle represents a 2D viewport.

If the destination rectangle is much smaller than the initial size (which is often is) then to start with the width/height changes by a small percentage, but by the end it's changing by a much larger percentage.
As a result the animation looks like it starts of slowly zooming in, gradually speeding up.

What i want is a smooth zooming in. I guess that would meen for each time step i want the rectangle to change by a constant percentage.

I've got no idea of the maths involved though, so any help would be much appreciated.