Path: utzoo!utgpu!attcan!uunet!yale!husc6!huma1!fry
From: fry@huma1.HARVARD.EDU (David Fry)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Help with setting pixel color
Message-ID: <5057@husc6.harvard.edu>
Date: 2 Aug 88 12:46:41 GMT
References: <77900003@peterson> <1668@microsoft.UUCP>
Sender: news@husc6.harvard.edu
Reply-To: fry@huma1.UUCP (David Fry)
Organization: Harvard Math Department
Lines: 44

In article <1668@microsoft.UUCP> t-benw@microsoft.UUCP (Benjamin Waldman) writes:
>In article <77900003@peterson> peterson@peterson.applicon.UUCP writes:
>>
>>I would like to be able to set a pixel to a color using the color index
>>number rather than RGB (as in SetPixel(RGB Color)).
>>
>>I can use SetPixel, but it is much too slow for filling a window with
>>pixels (as in a grey scale picture).  Maybe I am missing "the" way to
>>draw an image into a window.  Can anyone help? I am new to color quickdraw!
>
>Have you read the Palette Manager manual?
>If you want to draw an image with certain colors, create a palette with
>those colors, and them use PmForeColor to set the color (you'll be setting
>a number corresponding to the palette position of your RGB color), and then
>use LineTo or something (this is also neat if you have run length encoded
>image data - if you have 10 pixels with the same value, do 1 PmForeColor,
>and then a Line to 10 pixels down the line).
>
>Unfortunately, I have no sample code, but good luck anyway.

This is certainly the "standard" way of drawing pixel data,
but it is mind-numbingly slow.  Much faster, and quite
adequate, is to create an offscreen PixMap, stuff the pixel
values into data structure, and then CopyBits that onto the
screen.  It's about 2000% faster, if not more.

First determine the color you want the pixel to be, say
MyColor, and then do a Color2Index() call to the index of that
color (or the closest) on the current color table.  Put that
value in the PixMap structure.  If you have an 8-bit image,
say, with only 256 colors, you can call the 256
Color2Index()'s at the beginning of the loop and you need only
move memory, which is very fast, with no toolbox calls, which
is relatively slow.   

If you're squeamish about offscreen PixMaps, and most people
seem to be, I recommend Knaster's "Macintosh Programming
Secrets," which has an extremely lucid account, with sample
code.

David Fry				fry@huma1.harvard.EDU
Department of Mathematics		fry@huma1.bitnet
Harvard University			...!harvard!huma1!fry
Cambridge, MA  02138