calculation of srcwidth and dstwidth for wrastop()

[Ted A. Campbell]

I am writing an application utilizing tam() and wrastop()
routines for graphics output. The work has gone well, 
except that at certain points I need to save screen 
images to memory, and blit images from memory to the
display, etc. The wrastop() routines allow this, but 
the calculation of the srcwidth and dstwidth parameters
remains a great mystery to me. Why, if the rectangle
width is specified later, do these parameters need to
be given. I have tried several methods of calculation:
none seems to work all of the time. If anyone has had
experience in the mysteries of wrastop() and can open 
this mystery to me, I shall be most appreciative.

Thanks very much.

Ted A. Campbell
tcamp at uncecs.edu