You can draw it directly with engine or with bitmaps.
Bitmap:
You need to cut a mask in photoshop which has the size and form of your "window".
Now, render a filled rectangle in the size of your rectangle bitmap (with mask) and then draw the mask OVER your filled rectangle. You will only see through the mask.

Engine:
The same can be done in pure engine drawing with some sinus/cosinus functions if youve got some skills in maths