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From: jmunkki@kampi.hut.fi (Juri Munkki)
Newsgroups: comp.sys.mac,comp.sys.mac.programmer
Subject: Re: Quickdraw efficiency question
Message-ID: <23543@santra.UUCP>
Date: 11 Jul 89 11:42:50 GMT
References: <1681@neoucom.UUCP>
Sender: news@santra.UUCP
Reply-To: jmunkki@kampi.hut.fi (Juri Munkki)
Organization: Helsinki University of Technology, Finland
Lines: 40

In article <1681@neoucom.UUCP> sam@neoucom.UUCP (Scott A. Mason) writes:
>Question:
>
>Which would be faster when drawing multiple characters to a window?
>
>  1) repeated calls to DrawChar
>  2) building a string and calling DrawString.
>
>Intuitively, I would think that DrawString would be faster, but then again,
>doesn't DrawString make repeated calls to DrawChar?  BTW, I want to do this
>for a terminal emulation program, and want maximum screen drawing speed.

The answer is that calling DrawString is several times faster than calling
DrawChar (six times faster when I tested this on a Mac+). There are several
reasons for this. For every call to a text drawing routine, QuickDraw and
the Font Manager will have to figure out where the font is (maybe even call
the resource manager to read the font from a file).

Finally, when the font is ready, QuickDraw starts drawing the actual text.
The text is drawn one scan-line at a time. In addition to drawing the
characters, the clipping regions have to be accumulated. When you call
DrawChar, the regions are created for every character. When you call
DrawText or DrawString, the regions are interpreted only once.

Disclaimer: This article is based on educated guesses. I might be wrong.

Maybe you should get the communications manager from Apple. They should
know how to write a fast terminal. This would save you the trouble of
writing YATE (Yet Another Terminal Emulator).

A good VT100 emulator takes about 20 pages of C source code. Add another
10-15 pages for a scrollback buffer and copy/paste support. Add another
10 pages for a decent user interface with file save and maybe a dialog
to change the terminal settings. (The pages are in Courier-7 and about
25% of the lines are comments.)

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|     Juri Munkki jmunkki@hut.fi  jmunkki@fingate.bitnet        I Want   Ne   |
|     Helsinki University of Technology Computing Centre        My Own   XT   |
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