Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!batcomputer!eacj
From: eacj@batcomputer.tn.cornell.edu (Julian Vrieslander)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Stupid QuickDraw question
Message-ID: <7439@batcomputer.tn.cornell.edu>
Date: 21 Feb 89 05:03:59 GMT
References: <71976CXT105@PSUVM>
Reply-To: eacj@tcgould.tn.cornell.edu (Julian Vrieslander)
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 51

In article <71976CXT105@PSUVM> CXT105@PSUVM.BITNET (Christopher Tate) writes:
>What is the best way to plot a single point in a given GrafPort (window, screen
>or other)?

As mentioned in earlier postings, the fastest way to draw points is to set
the appropriate bits in the bit image, bypassing Quickdraw completely.
But writing directly into the screen's bitMap (screenBits) is strongly
discouraged by the Apple compatibility police, and for good reason.  You
have to do your own clipping if the destination window is not completely
visible, and you have to know the details of how the bits in memory are
mapped into pixels (may have color or grayscale, etc.).  Drawing into an
offscale bitMap and CopyBits-ing into the window makes life somewhat
easier, but adds a delay.  Another, simpler approach that gives a moderate
speed gain is calling the traps directly.  In LightspeedC this looks as
follows:

#include <pascal.h>
#include <OSUtil.h>

/* Quickdraw trap numbers */
#define LINE_TRAP 0x92
#define MOVETO_TRAP 0x93
...

DrawSomePointsFast()
   {	
   register short x,y;
   long MoveToProc,LineProc;
	
   /* 
   Get addresses of QuickDraw traps; calling them directly saves time.
   */
   LineProc = NGetTrapAddress(LINE_TRAP,ToolTrap);
   MoveToProc = NGetTrapAddress(MOVETO_TRAP,ToolTrap);

   /* This is a loop where a lot of points get drawn */   
   for(...)
      {
      ...
      CallPascal(x,y,MoveToProc);
      CallPascal(0,0,LineProc);
      }
   }

This technique might be discussed in one of the Mac Tech Notes (but I don't have
them with me).
-- 
Julian Vrieslander 
Neurobiology & Behavior, W250 Mudd Hall, Cornell University, Ithaca NY 14853    
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