Draw Bitmap on the screen (no deformation)

I have a CFbsBitmap called aImage.

I want to draw it on the screen.

I use this code:

CWindowGc& gc = SystemGc();
// Update the screen
gc.Activate(Window());
TRect drawRect(Rect());
gc.Clear(drawRect);

gc.DrawBitmap(drawRect, aImage);

This function, DrawBitmap, scales the bitmap in order to fit inside the TRect called drawRect. Is it possible to make it fit but without changing the aspect ratio? I mean, if the Rect is 320x240 and the original image is 3200x480, I would like to have a result of 320x48 on the screen (the same ratio) and not a 320x240 deformed one.

Any Idea is welcome.