TweetFollow Us on Twitter

MacPaint files
Volume Number:1
Issue Number:7
Column Tag:C Workshop

MacPaint file format

By Keith McGreggor

The MacPaint file format is rapidly becoming the standard for transferring graphic information from one application to another. This article will explain that format and show you how to transfer your own images into MacPaint files.

A Little Bit of QuickDraw

The Macintosh’s screen is a bit image. That is, what appears on the screen is actually a collection of consecutive bits in memory that the hardware in the Mac interprets as screen dots (or pixels). If the value of one of these bits is 1, then the pixel corresponding to it will be black. If the bit is 0, then the pixel will be white.

Figure #1. Bits represent pixels

The Mac screen is 512 pixels wide by 342 pixels tall. The bit image in memory takes up 175,104 bits (or 21,888 bytes with 8 bits per byte). We can consider the screen bit image as being 342 rows with 64 bytes per row. Due to the 68000 microprocessor in the Macintosh, every bit image must have an even number of bytes per row, and the rows must begin and end on word boundaries.

In C, the easiest way to define a bit image is with an array of characters. For example, if we wanted to define the Macintosh screen’s bit image, the definition would be:

Figure #2. C definition of a bit image

Bit images are manipulated by Quick- Draw through the use of bitmaps. A bit- map is a structure which points to a bit image and associates a coordinate system with it. The definition of a bitmap is:

Figure #3. C definition of a bitmap

The baseAddr field points to the first byte (character) in the bit image. The rowBytes field contains the number of bytes per row in the bit image. The rectangle bounds provides the coordinate system for the bits. The top left corner of the rectangle is aligned with the first bit of the bit image.

Since we can treat bit images in C as arrays of characters, we don’t always have to display them immediately. You can easily create a picture in a bit image off-screen, and later in your program “stamp” it onto the Mac’s screen.

The Macintosh’s ROM contains several QuickDraw calls that allow you to manipulate bitmaps (on- or off-screen). We’ll look at two of these later in the program.

MacPaint images are kept in the data fork of a MacPaint file. The file is essentially a 512 byte header followed by a bit image that is 576 pixels wide by 720 pixels tall (or 72 bytes by 720 rows).

Figure #4. The MacPaint File Format

The 512 bytes of header contain version information, pattern definitions, and an unused area for future expansion. If you change the contents of this section with care, you can set up your own patterns. If the version number is zero, the default patterns are used. If the number is not zero, then the patterns in the header are used.

Fig.#5.The Paint File Header Format

The MacPaint file bit image is considerably larger than the Macintosh screen’s bit image. In fact, if you were to store a bit image 72 bytes by 720 rows directly onto disk, each MacPaint file would take a minimum of 52K bytes! To make these files smaller, each row of pixels has been compressed using the PackBits routine in the Macintosh ROM. Using PackBits, the typical MacPaint file compresses down to around 10K bytes.

Dipping in the Bit Bucket

To make your program transfer an image into a MacPaint file, you need only to copy the bitmap containing the image into the compressed MacPaint file format. To be able to do this, you need to use two ROM routines, CopyBits and PackBits.

CopyBits transfers the contents of one bitmap into another. If you want, you can specify a mask region in the destination bitmap to prevent CopyBits from destroying the entire image. CopyBits will shrink or expand the contents of the source bitmap to fit the destination bitmap’s rectangle. To call CopyBits from C, use this format:

Figure #6. Calling CopyBits from C

where “copymode” is one of the source transfer modes:

Figure #7. Source Transfer Modes

PackBits compacts a string of bytes by compressing runs of equal bytes. You call PackBits from C like so:

Figure #8. Calling PackBits from C

where “numbytes” is the number of bytes pointed to by “srcPtr.”

Initially, “dstPtr” should point to the first destination byte. The PackBits routine will move “dstPtr” to point to the next available byte. To find out how much space the original bytes were compacted into, you need to subtract the original location of “dstPtr” from its current location.

Fig. #9 How PackBits moves “dstPtr”

About the Program

This program will demonstrate how to “cut” a part of an image into a MacPaint file. It is written for the Consulair Mac C system and Toolkit. You’ll probably need to change things a bit to make it work with other versions of C.

The program opens a single window and draws a few inverted rectangles in it. Then, a gray flashing rectangle will appear and follow the position of the cursor. Use the mouse to position this rectangle where you want, and then press the mouse button. The image inside the rectangle will be cut from the screen (using CopyBits) and transferred into a MacPaint file called “DummyFileName” (using repeated calls to PackBits).

The key routine, MakePaintFile, takes as input a C string containing a filename, and a pointer to a bitmap of arbitrary size. It then creates that file (if possible) on the active disk drive, sets the file signature and type to a MacPaint file type, and compresses that bitmap into the file using PackBits. If the bitmap is smaller than 576 by 720 (as will usually be the case), the bitmap is padded with white space. If the bitmap is larger than 576 by 720, the bitmap is clipped to 576 by 720.

/*
 * MakePaint.h
 *        a C routine to create a MacPaint file
 *        from a given bitmap
 *
 * (c) 1985 by Keith McGreggor for MacTutor
 *       
 */

#define WRITEONLY 7

MakePaintFile( myfilename, mybitmap )
char myfilename[63];
struct ABitMap *mybitmap;
{
 char dstbuf[511],srcbuf[511];
 char *srcPtr;
 char *dstPtr;
 char *mypointer;
 short i,j,dstBytes;
 FILE myfile;
 short t,b,vsize,hsize;
 
// attempt to create the file
 
 myfile = creat( myfilename, WRITEONLY );
 if (myfile != 0) {

// turn the file into a MacPaint file
// and write out a 512 byte header
// full of zeros (we’re not using any of
// our own patterns)

    SetFileSignature(myfilename,’MPNT’); 
    SetFileType(myfilename,’PNTG’);
    for (i = 0; i < 512; i++) fputc(0,myfile);

// figure out how big the bitmap is and set up
// a general pointer to the bit image

    mypointer = mybitmap->baseAddr;
    hsize = mybitmap->rowBytes;
    vsize = (mybitmap->bounds.bottom)
                        - (mybitmap->bounds.top);

// now, write out 720 rows of bytes

    for (j = 1; j <= 720; j++) {

// reinitialize source and destination pointers

 srcPtr = &srcbuf[0];
 dstPtr = &dstbuf[0];

// copy the next row of bytes into srcbuf[],
// clipping or expanding where necessary

 for (i = 0; i < 72; i++) {
        if ((i < hsize) && (j <= vsize)) {
      srcbuf[i] = *mypointer;
           mypointer++;
           }
            else srcbuf[i] = 0;  // 8 white bits
 }

// compress srcbuf[] into dstbuf[]

 #PackBits(&srcPtr,&dstPtr,72);

// figure out how much compression occurred 
// and write those bytes out to the file

 dstBytes= (short)(dstPtr-&dstbuf[0]);
 for (i = 0; i < dstBytes; i++)
                   fputc(dstbuf[i],myfile);
    }

// all 720 lines have been written, so
// close up everything and return

    close(myfile);
 }
}




 /*    CutToPaint.C
  *      A sample program to illustrate
  *      the use of PackBits and CopyBits
  *
  * (c) 1985 by Keith McGreggor for MacTutor
  */
  #Options -N
  #include “Stdio.h”
  #include “MacCdefs.h”
  #include “Window.h”
  #define TRUE 0xFF
  _#define BUTTONNOTPRESSED !#Button()
  #define GRAY &(QD->gray)
  
  // allocate the application’s window
  
  WindowPtr mywindow;
  Rect mywindowrect = { 40, 5, 300, 507 };
  
  // allocate the tracking variables
  
  Rect trackingrect{0,0,100,100};
  short globx,globy,incx,incy;
  
  // allocate a bitmap and bit image to
  // hold the cut bits
  
  struct ABitMap{
   char *baseAddr;
 short  rowbytes;
 Rect bounds;
 };
 
  struct ABitMap targetmap;
  char theactualbits[14][100];
  
  #include “MakePaint.h”
  /* ------------------------------------*/
  // draw some inverted rectangles
  // just to have something to “cut”
  
  DrawSomeStuff()
  {
  Rect temprect;
  short i;
  
  #MoveTo(10,240);
  #DrawString(“\020Press the button!”);
  for (i=0;i<200;i += 10) {
   #SetRect(&temprect,i+20,i+20,i+100,i+40);
 #InvertRect(&temprect);
 }
  }
  
  /*------------------------------------*/
  // Open a window for drawing
  // and do general housekeeping
  
  InitializeOurSystem()
  {
  #InitDialogs(0);
  mywindow = (WindowPtr)#NewWindow(0,  &mywindowrect,”\021A Window for 
bits”,  TRUE,0,-1,TRUE,0);
  #SetPort(mywindow);
  DrawSomeStuff();
  #FlushEvents(-1,0);
  #InitCursor();
  #PenSize(2,2);   // set up pen for
  #PenMode(patXor);  // drawing the
  #PenPat(GRAY);   // ghost rectange
  }

  /*------------------------------------*/
  // Draw the ghost rectangle
  
  DrawCurrentPosition()
  {
  #FrameRect(&trackingrect);
  }

  /*--------------------------------------*/
  // Find out where the mouse is and
  // update global variables
  
  GetNewMouse()
  {
  Point mypoint;
  
  #GetMouse(&mypoint);
  #GlobalToLocal(&mypoint);
  incx = mypoint.h-globx;
  incy = mypoint.v-globy;
  globx = mypoint.h;
  globy = mypoint.v;
  }

  /*------------------------------------*/
  // move the ghost rectange to track
  // the motion of the mouse
  
  UpdatePostion()
  {
  #OffsetRect(&trackingrect,incx,incy);
  }
  
  /*------------------------------------*/
  // First, move around a ghost rectange
  // until the button is pressed.
  // Then, create a bitmap and copy
  // whatever is inside the rectange to
  // the bitmap.
  
  CutARectangle()
  {
  globx = 0;
  globy = 0;
  while (BUTTONNOTPRESSED) {
   DrawCurrentPosition();
 GetNewMouse();
 DrawCurrentPosition();
 UpdatePosition();
  }
  #FlushEvents(-1,0);
  #LocalToGlobal(&trackingrect.topleft);
  #LocalToGlobal(&trackingrect.botRight);
  targetmap.baseAddr = &theactualbits[0][0];
  targetmap.rowBytes = 14;
  targetmap.bounds.left = 0;
  targetmap.bounds.top = 0;
  targetmap.bounds.right = trackingrect.right-trackingrect.left;
  targetmap.bounds.bottom = trackingrect.bottom-   trackingrect.top;
  
  // mywindow -> portBits is the Macintosh screen bit image
  
  #CopyBits(&(mywindow->portBits), &targetmap,
   &trackingrect,
 &(targetmap.bounds),
 srcCopy,
 0);
  }
  
  /*------------------------------------*/
  // call makepaintfile to save the
  // bitmap away as a macpaint file
  // named “dummyfilename”
  // (note: see MakePaint.h listing)
  
  SaveItAway()
  {
  MakePaintFile(“DummyFileName”,&targetmap);
  }
  
  /*----------------------------------*/
  // Our main program
  
  main()
  {
   InitializeOurSystem();
 CutARectangle();
 SaveItAway();
 #ExitToShell();
  }
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Six fantastic ways to spend National Vid...
As if anyone needed an excuse to play games today, I am about to give you one: it is National Video Games Day. A day for us to play games, like we no doubt do every day. Let’s not look a gift horse in the mouth. Instead, feast your eyes on this... | Read more »
Old School RuneScape players turn out in...
The sheer leap in technological advancements in our lifetime has been mind-blowing. We went from Commodore 64s to VR glasses in what feels like a heartbeat, but more importantly, the internet. It can be a dark mess, but it also brought hundreds of... | Read more »
Today's Best Mobile Game Discounts...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Nintendo and The Pokémon Company's...
Unless you have been living under a rock, you know that Nintendo has been locked in an epic battle with Pocketpair, creator of the obvious Pokémon rip-off Palworld. Nintendo often resorts to legal retaliation at the drop of a hat, but it seems this... | Read more »
Apple exclusive mobile games don’t make...
If you are a gamer on phones, no doubt you have been as distressed as I am on one huge sticking point: exclusivity. For years, Xbox and PlayStation have done battle, and before this was the Sega Genesis and the Nintendo NES. On console, it makes... | Read more »
Regionally exclusive events make no sens...
Last week, over on our sister site AppSpy, I babbled excitedly about the Pokémon GO Safari Days event. You can get nine Eevees with an explorer hat per day. Or, can you? Specifically, you, reader. Do you have the time or funds to possibly fly for... | Read more »
As Jon Bellamy defends his choice to can...
Back in March, Jagex announced the appointment of a new CEO, Jon Bellamy. Mr Bellamy then decided to almost immediately paint a huge target on his back by cancelling the Runescapes Pride event. This led to widespread condemnation about his perceived... | Read more »
Marvel Contest of Champions adds two mor...
When I saw the latest two Marvel Contest of Champions characters, I scoffed. Mr Knight and Silver Samurai, thought I, they are running out of good choices. Then I realised no, I was being far too cynical. This is one of the things that games do best... | Read more »
Grass is green, and water is wet: Pokémo...
It must be a day that ends in Y, because Pokémon Trading Card Game Pocket has kicked off its Zoroark Drop Event. Here you can get a promo version of another card, and look forward to the next Wonder Pick Event and the next Mass Outbreak that will be... | Read more »
Enter the Gungeon review
It took me a minute to get around to reviewing this game for a couple of very good reasons. The first is that Enter the Gungeon's style of roguelike bullet-hell action is teetering on the edge of being straight-up malicious, which made getting... | Read more »

Price Scanner via MacPrices.net

Take $150 off every Apple 11-inch M3 iPad Air
Amazon is offering a $150 discount on 11-inch M3 WiFi iPad Airs right now. Shipping is free: – 11″ 128GB M3 WiFi iPad Air: $449, $150 off – 11″ 256GB M3 WiFi iPad Air: $549, $150 off – 11″ 512GB M3... Read more
Apple iPad minis back on sale for $100 off MS...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
Apple’s 16-inch M4 Max MacBook Pros are on sa...
Amazon has 16-inch M4 Max MacBook Pros (Silver and Black colors) on sale for up to $410 off Apple’s MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather than a third-party... Read more
Red Pocket Mobile is offering a $150 rebate o...
Red Pocket Mobile has new Apple iPhone 17’s on sale for $150 off MSRP when you switch and open up a new line of service. Red Pocket Mobile is a nationwide MVNO using all the major wireless carrier... Read more
Switch to Verizon, and get any iPhone 16 for...
With yesterday’s introduction of the new iPhone 17 models, Verizon responded by running “on us” promos across much of the iPhone 16 lineup: iPhone 16 and 16 Plus show as $0/mo for 36 months with bill... Read more
Here is a summary of the new features in Appl...
Apple’s September 2025 event introduced major updates across its most popular product lines, focusing on health, performance, and design breakthroughs. The AirPods Pro 3 now feature best-in-class... Read more
Apple’s Smartphone Lineup Could Use A Touch o...
COMMENTARY – Whatever happened to the old adage, “less is more”? Apple’s smartphone lineup. — which is due for its annual refresh either this month or next (possibly at an Apple Event on September 9... Read more
Take $50 off every 11th-generation A16 WiFi i...
Amazon has Apple’s 11th-generation A16 WiFi iPads in stock on sale for $50 off MSRP right now. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-generation 256GB... Read more
Sunday Sale: 14-inch M4 MacBook Pros for up t...
Don’t pay full price! Amazon has Apple’s 14-inch M4 MacBook Pros (Silver and Black colors) on sale for up to $220 off MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather... Read more
Mac mini with M4 Pro CPU back on sale for $12...
B&H Photo has Apple’s Mac mini with the M4 Pro CPU back on sale for $1259, $140 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – Mac mini M4 Pro CPU (24GB/512GB): $1259, $... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.