Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!microsoft!glenns
From: glenns@microsoft.UUCP (Glenn Steffler)
Newsgroups: comp.sys.amiga
Subject: Re: Non-distruction graphics
Summary: easy, use XOR
Keywords: video blitter
Message-ID: <1011@microsoft.UUCP>
Date: 26 Nov 88 12:31:16 GMT
References: <6287@dayton.UUCP>
Reply-To: glenns@microsoft.UUCP (Glenn Steffler)
Followup-To: comp.sys.amiga
Distribution: na
Organization: Microsoft Corp., Redmond WA
Lines: 33

In article <6287@dayton.UUCP> joe@dayton.UUCP (Joseph P. Larson) writes:
[ wants to draw lines, and then restore old stuff ]
>What I need instead of draw and erase (erase is basically redraw old
>line with background color) is draw and recover old.  The best method
>I have discovered for this would be to write a DrawXOR routine to replace
>my use of Draw().  It would XOR the bits in the line with what they are
>now instead.  Then to erase I can XOR them again.  But this sounds rather
>slow.

Are you writing a home brew draw?  The Exec draws plenty fast for me...
Besides, I seem to have read that the blitter has built in XOR capacity.
This then could not be any slower than normal drawing. 

Albeit, the blitter would have to do a READ and a WRITE to XOR, but it's
quick at them type things, it was made for it.

>So -- anyone got a better solution?  Maybe I should add another bit plane
>and just fiddle with the bits in that plane?  Ick.

TALK ABOUT SLOW!!  UGGG!! Another plane ?  

>Maybe I have to manipulate everything myself instead of calling Intuition
>text and draw routines?

Wha???  Are you drawing to the window while you are also drawing your lines?
If so, then yes, this could be tricky.  Otherwise, save hastle and use Intu.

>          When you fall on your head do you land on your feet?

I generally spew blood all over, gag on my spit and die.

--
Buggs  - Bill the cat for V.P. -- Opps, make that Zippy the Quale for V.P. !