TweetFollow Us on Twitter

Window Barrier
Volume Number:4
Issue Number:1
Column Tag:ABC's of C

Breaking the Four Window Barrier

By William Rausch, Kennewick, WA

It seems that every good Macintosh example program (of a text editor, graphics program, or whatever) is hung up on the idea of four windows. Of course, those that aren’t such good example programs only use one window! This limit always seems to be a result of the unnecessary use of global data structures.

Most multi-window Macintosh example programs contain some lines that look like:

WindowPtr some_windows[how_many];
data_structure some_data[how_many];

where how_many is defined to be four. The programmer will claim that it is easy to change this number to be as large as necessary, and the application can be easily recompiled. That is fine for the programmer, but what about the end user. He is stuck with whatever number the programmer happens to choose. If the programmer happens to choose a number of windows and data structures that perfectly fits a 512K Macintosh, then the user is probably not able to take advantage of the extra memory of a Macintosh Plus, much less a Macintosh with even more memory.

In actuality, it is not necessary to predefine any number of windows, or the data structures that are associated with them. Since the Macintosh has an operating system that knows all about windows and how to keep track of them, it makes little sense for the application programmer to duplicate this effort.

The window data structure contains a 32-bit field called refCon which Inside Macintosh describes as “the window’s reference value field, which the application may store into and access for any purpose”. One such purpose, which is mentioned but not demonstrated in many books on Macintosh programming, is to store a handle to some application specific data structure which contains the information that is pertinent to that window.

Since every event given to an application by the Event Manager will contain a pointer to the window concerned, there is no need for the application to keep an array of WindowPtrs; and since each window contains a refCon field, there is no need to keep an array of data structures. Instead, allocate the necessary space for the data structure at the time the new window is created, and put its handle in the refCon field of the window’s data structure. Then, whenever an event is processed, just pass the WindowPtr along to the functions which are going to process the event. These functions then can get access to the data structure when they need it.

The code fragments which follow demonstrate the concepts described:

enum window_type
  {
  type_a,
  type_b,
  type_c
  };

typedef union
  {
  struct
    {
    ...         /* type_a window data */
    } a;
  struct
    {
    ...         /* type_b window data */
    } b;
  struct
    {
    ...         /* type_c window data */
    } c;
  } content,*content_ptr,**content_hndl;

typedef struct 
  {
  enum window_type xxx;   /* optional, appl. specific */
  content_hndl yyy;   /* could include union directly */
  ...
  } window_data, *data_ptr, **data_hndl;

...

make_window(type)
enum window_type type;
  {
  WindowRecord *a_window;
  data_hndl a_data;
  content_hndl a_content;
  ...

  a_window = 
    (WindowRecord *)NewWindow(...);
  a_data = 
    (data_hndl)NewHandle(sizeof(w_data));
  a_content = (content_hndl)NewHandle
                       (sizeof(content));
  (**a_data).xxx = type;
  (**a_data).yyy = a_content;
  a_window->refCon = (long)a_data;
  ...
  }

...

event_loop()
  {
  EventRecord the_event;
  WindowPtr which_window;
  int window_code;
  ...

  while (TRUE)
    {
    if (GetNextEvent(everyEvent, 
                     &the_event))
      {
      switch (the_event.what)
        {
        case mouseDown:
        window_code = FindWindow
                      (the_event.where, 
                       &which_window);
        switch (window_code)
          {
          case inSysWindow:
          SystemClick(&the_event,
                      which_window);
          break;
          
          case inContent:
          process_window(which_window);
          break;

          ...
          }
        break;

        ...
        }
      }
    else
      {
      }
    }
  }

...

process_window(the_window)
WindowRecord *the_window;
  {
  data_hndl the_data;
  ...

  the_data = 
      (data_hndl)(the_window->refCon);
  switch ((**the_data).xxx)
    {
    case type_a:
    process_a_window(the_window);
    break;

    case type_b:
    process_b_window(the_window);
    break;

    case type_c:
    process_c_window(the_window);
    break;
    }
  ...
  }

This general technique may, in some very particular cases, slow things down a little. Generally, this won’t be the case because most applications spend a majority of their time processing NULL events. If you wanted to speed things up a little bit and still maintain the dynamic allocation capabilities of this programming approach, use just one globally declared WindowPtr and one data_handle and just update them to always point at the window/data_structure that the current event refers to. Then you wouldn’t have to pass the event’s WindowPtr to the called function(s).

Of course, most applications need to be able to find all of their windows at times, e.g., when Quitting the application so that changes can be saved, or when updating the windows. At those times, it is still possible to avoid using a global array merely by calling FrontWindow() and following the linked list of pointers stored in the nextWindow field of the window’s data structure.

This approach to creating windows in an application, which I call “fire and forget” (and which could be considered as a small first step towards object oriented programming), will allow your application to create as many new windows (and their associated data structures) as the user desires. It is also a convenient way of manipulating different types of windows in a single application. (It is very easy, for example, to imagine MacDraw and MacWrite in a single application!) Of course, your application has to check available memory each time it tries to create a new window/data structure to make sure there is enough available, but that is a small price to pay for the increased utility the user can get from having a program that “grows” with his hardware.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Adobe InDesign CC 2018 13.0.0.125 - Prof...
InDesign CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous InDesign customer). Adobe InDesign CC 2018 is part of Creative Cloud.... Read more
Adobe Illustrator CC 2018 22.0.0 - Profe...
Illustrator CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Illustrator customer). Adobe Illustrator CC 2018 is the industry... Read more
Adobe After Effects CC 2018 15.0 - Creat...
After Effects CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous After Effects customer). The new, more connected After Effects CC... Read more
Adobe Premiere Pro CC 2018 12.0.0 - Digi...
Premiere Pro CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Premiere Pro customer). Adobe Premiere Pro CC 2018 lets you edit... Read more
Adobe Dreamweaver CC 2018 18.0.0.10136 -...
Dreamweaver CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Dreamweaver customer). Adobe Dreamweaver CC 2018 allows you to... Read more
Adobe Lightroom 20170919-1412-ccb76bd] -...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
Adobe Photoshop CC 2018 19.0.0 - Profess...
Photoshop CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Photoshop customer). Adobe Photoshop CC 2018, the industry standard... Read more
Adobe Muse CC 2017 2018.0.0 - Design and...
Muse CC 2018 is available as part of Adobe Creative Cloud for as little as $14.99/month (or $9.99/month if you're a previous Muse customer). Adobe Muse 2018 enables designers to create websites as... Read more
Adobe Animate CC 2017 18.0.0.107 - Anima...
Animate CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Flash Professional customer). Animate CC 2018 (was Flash CC) lets you... Read more
Hopper Disassembler 4.3.0- - Binary disa...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more

ICEY (Games)
ICEY 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ICEY is a 2D side-scrolling action game. As you follow the narrator's omnipresent voice, you will see through ICEY's eyes and learn the... | Read more »
The best new games we played this week -...
We've made it, folks. Another weekend is upon us. It's time to sit back and relax with the best new releases of the week. Puzzles, strategy RPGs, and arcade games abound this week. There's a lot of quality stuff to unpack this week, so let's hop... | Read more »
Wheels of Aurelia (Games)
Wheels of Aurelia 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: | Read more »
Halcyon 6: Starbase Commander guide - ti...
Halcyon 6 is a well-loved indie RPG with stellar tactical combat and some pretty good writing, too. It's now landed on the App Store, so mobile fans, if you're itching for a good intergalactic adventure, here's your game. Being a strategy RPG, the... | Read more »
Game of Thrones: Conquest guide - how to...
Fans of base building games might be excited to know that yet another entry in the genre has materialized - Game of Thrones: Conquest. Yes, you can now join the many kingdoms of the famed book series, or create your own, as you try to conquer... | Read more »
Halcyon 6: Starbase Commander (Games)
Halcyon 6: Starbase Commander 1.4.2.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.4.2.0 (iTunes) Description: An epic space strategy RPG with base building, deep tactical combat, crew management, alien diplomacy,... | Read more »
Legacy of Discord celebrates its 1 year...
It’s been a thrilling first year for fans of Legacy of Discord, the stunning PvP dungeon-crawling ARPG from YOOZOO Games, and now it’s time to celebrate the game’s first anniversary. The developers are amping up the festivities with some exciting... | Read more »
3 reasons to play Thunder Armada - the n...
The bygone days of the Battleship board game might have past, but naval combat simulators still find an audience on mobile. Thunder Armada is Chinese developer Chyogames latest entry into the genre, drawing inspiration from the explosive exchanges... | Read more »
Experience a full 3D fantasy MMORPG, as...
Those hoping to sink their teeth into a meaty hack and slash RPG that encourages you to fight with others might want to check out EZFun’s new Eternity Guardians. Available to download for iOS and Android, Eternity Guardians is an MMORPG that lets... | Read more »
Warhammer Quest 2 (Games)
Warhammer Quest 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon adventures in the Warhammer World are back! | Read more »

Price Scanner via MacPrices.net

9″ iPads on sale for $30 off, starting at $29...
MacMall has 9″ iPads on sale for $30 off including free shipping: – 9″ 32GB iPad: $299 – 9″ 128GB iPad: $399 Read more
Apple restocks full line of refurbished 13″ M...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
13″ 3.1GHz/256GB MacBook Pro on sale for $167...
Amazon has the 2017 13″ 3.1GHz/256GB Space Gray MacBook Pro on sale today for $121 off MSRP including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1678 $121 off MSRP Keep an... Read more
13″ MacBook Pros on sale for up to $120 off M...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for up to $120 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
15″ MacBook Pros on sale for up to $200 off M...
B&H Photo has 15″ MacBook Pros on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2249, $150... Read more
Roundup of Apple Certified Refurbished iMacs,...
Apple has a full line of Certified Refurbished 2017 21″ and 27″ iMacs available starting at $1019 and ranging up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free... Read more
Sale! 27″ 3.8GHz 5K iMac for $2098, save $201...
Amazon has the 27″ 3.8GHz 5K iMac (MNED2LL/A) on sale today for $2098 including free shipping. Their price is $201 off MSRP, and it’s the lowest price available for this model (Apple’s $1949... Read more
Sale! 10″ Apple WiFi iPad Pros for up to $100...
B&H Photo has 10.5″ WiFi iPad Pros in stock today and on sale for $50-$100 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB iPad Pro: $... Read more
Apple iMacs on sale for up to $130 off MSRP w...
B&H Photo has 21-inch and 27-inch iMacs in stock and on sale for up to $130 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2179 $... Read more
2017 3.5GHz 6-Core Mac Pro on sale for $2799,...
B&H Photo has the 2017 3.5GHz 6-Core Mac Pro (MD878LL/A) on sale today for $2799 including free shipping plus NY & NJ sales tax only . Their price is $200 off MSRP. Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Commerce Engineer, *Apple* Media Products -...
Commerce Engineer, Apple Media Products (New York City) Job Number: 113028813New York City, New York, United StatesPosted: Sep. 20, 2017Weekly Hours: 40.00 Job Read more
US- *Apple* Store Leader Program - Apple (Un...
US- Apple Store Leader Program Job Number: VariousUnited StatesPosted: Oct. 19, 2017Retail Store Job Summary Learn and grow as you explore the art of leadership at Read more
Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Retail - Multiple Positions - Farmin...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.