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From: ujmurphy@KING.MCS.DREXEL.EDU (Jim Murphy)
Newsgroups: comp.sys.apple2
Subject: Re: QuickDraw II
Message-ID: <9105182249.AA19338@mcs.drexel.edu>
Date: 18 May 91 22:49:13 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 43

albert, myself, and Jawaid wrote:

> ujmurphy@KING.MCS.DREXEL.EDU (Jim Murphy) writes (in a bit of haste):
>
>>albert erroneously wrote:
>
>>> quickdraw does draw faster to off-screen grafports because it doesn't have
>>> to do the 2/4-bit conversion when drawing stuff on-screen (did i get this
>>> right dave?).
>
>>    Wrongo! When drawing to _any_ GrafPort (onscreen or otherwise), QuickDraw
>>II uses the portInfo record (LocInfo structure) of the GrafPort to determine
>>what kind of pixel map it is dealing with.
>
>  Right- but The original assertion stands, if it's reason doesn't.  QuickDraw
>II draws much faster to off-screen grafports because off-screen grafports are
>in fast RAM.
>
>--
>Jawaid Bazyar               |  "Twenty seven faces- with their eyes turned to
>Graduated!/Comp Engineering |    the sky. I have got a camera, and an airtight
>bazyar@cs.uiuc.edu          |     alibi.."
>   Apple II Forever!        |  I need a job... Be privileged to pay me! :-)

     Well, what I said still stands. The reason I responded in that manner is
that albert was having some serious conceptual problems with how QD II handles
offscreen GrafPorts in weeks past. I think he is still having problems with
QD II.

     It seems that everyone believes that by using offscreen GrafPorts, your
programs will magically run faster. This is not the case, even with the fact
that offscreen pixImages are in fast RAM. It's only a _perceived_ speedup.
Sure, the original draw to an offscreen pixImage would occur at the current
speed of the fast RAM. But the PPToPort that transfers the pixImage to screen
RAM is working with the slow $E1 bank (ok, sure, you can use fUseShadowing).
The whole purpose of offscreen GrafPorts is to hide the fact that a screen
update is a discontinuous series of lines/fills/paints. It is just a technique
to hide this fact from the user.

Jim Murphy                             "I know that you believe you understand
Internet:  ujmurphy@mcs.drexel.edu     what you think I said. But I am not sure
GEnie:     J.MURPHY7                   you realize that what you heard is not 
AOL:       Jim Murphy                  what I meant."