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From: jackiw@cs.swarthmore.edu (Nick Jackiw)
Newsgroups: comp.sys.mac.programmer
Subject: Re: CalcMask
Message-ID: <49QP9FC@cs.swarthmore.edu>
Date: 31 Aug 90 17:26:21 GMT
References: <1990Aug31.154627.14859@midway.uchicago.edu>
Reply-To: jackiw@cs.swarthmore.edu (Nick Jackiw)
Organization: Visual Geometry Project, Swarthmore College, PA
Lines: 49

gft_james@gsbacd.uchicago.edu writes:
> 
> PROCEDURE CalcMask (srcPtr,dstPtr: Ptr; srcRow, dstRow, height,
>                     words: INTEGER);
> 
> This sounds like exactly what I need, but I can't for the life of me figger out
> [what the arguments should be]

"The SeedFill+CalcMask procedures operate on a portion of a bitmap. In both
routines, srcPtr and dstPtr point to [the bits themselves, not the bitmap.
e. g. srcPtr:=yourBitMap.baseAddr]. SrcRow and dstRow specify the row
width in bytes (i. e. the rowBytes field of the BitMap record) ... .
Height and words determine the number of bits to be filled or calculated;
words is the width of the rectangle in words and height is the height
off the rectangle in pixels." [IV-24]

Thus, in two equi-sized and bounded bitmaps, aBits and bBits, to calculate
in bBits an image of the portion of aBits stored in aRect, do:

const
 pixPerByte=8; {Assume B&W}

var aRect:Rect; aBits, bBits:BitMap;
    srcPtr,dstPtr:ptr;
    offset:longint;

begin
{Assume aBits, aRect, and bBits are all appropriately initialized}
{aRect must delimit an area which begins and ends on word boundaries}
{in the bitmaps.}

 {The bits we want to mask begin somewhere at or past aBits.baseaddr.}
 offset:=aBits.rowBytes*(aRect.top-aBits.bounds.top);  {Move some rows down}
 offset:=offset+(aRect.left-aBits.bounds.left) div pixPerByte; {Move over}
 
 CalcMask(ptr(ord(aBits.baseAddr)+offset),
          ptr(ord(bBits.baseAddr)+offset),
          aBits.rowBytes,bBits.rowBytes,
          (aRect.bottom-aRect.top),
          (aRect.right-aRect.left) div (2*pixPerByte));
 end;

Hint: Without Inside Mac IV, life itself would be impossible.

-- 
+-------------------+-jackiw@cs.swarthmore.edu / !rutgers!bpa!swatsun!jackiw-+
|  nicholas jackiw  | jackiw%campus.swarthmore.edu@swarthmr.bitnet           |
+-------------------+-VGP/MathDept/Swarthmore College, Swarthmore, PA 19081--+
"Ah...I've got this CHRONIC pain."                             _True Believer_