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

1Password 6.6.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Safari Technology Preview 10.2 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
Eye Candy 7.2.0.50 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Microsoft Office 2016 15.31 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more
Spotify 1.0.49.125. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
QuickBooks 16.1.12.1564 R13 - Financial...
QuickBooks helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save. Built for... Read more
Dash 4.0.1 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
Tinderbox 7.0.0 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
Apple Remote Desktop Client 3.9 - Client...
Apple Remote Desktop Client is the best way to manage the Mac computers on your network. Distribute software, provide real-time online help to end users, create detailed software and hardware reports... Read more
Sparkle 2.1.1 - $79.99
Sparkle will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more

Tavern Guardians (Games)
Tavern Guardians 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Tavern Guardians is a Hack-and-Slash action game played in the style of a match-three. You can experience high pace action... | Read more »
Slay your way to glory in idle RPG Endle...
It’s a golden age for idle games on the mobile market, and those addictive little clickers have a new best friend. South Korean developer Ekkorr released Endless Frontier last year, and players have been idling away the hours in the company of its... | Read more »
Tiny Striker: World Football Guide - How...
| Read more »
Good news everyone! Futurama: Worlds of...
Futurama is finding a new home on mobile in TinyCo and Fox Interactive's new game, Futurama: Worlds of Tomorrow. They're really doing it up, bringing on board Futurama creator Matt Groening along with the original cast and writers. TinyCo wants... | Read more »
MUL.MASH.TAB.BA.GAL.GAL (Games)
MUL.MASH.TAB.BA.GAL.GAL 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ENDLESS UPGRADES. CONSTANT DANGER. ANCIENT WISDOM. BOUNCY BALLS. Launch Sale, 40% OFF for a very limited time!!! MUL.... | Read more »
Dungeon Rushers (Games)
Dungeon Rushers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon Rushers is a 2D tactical RPG combining dungeon crawler’s gameplay and turn based fights. Manage your team, loot dusty... | Read more »
Blasty Bubs is a colorful Pinball and Br...
QuickByte Games has another arcade treat in the works -- this time it's a mishmash of brick breaking and Pinball mechanics. It's called Blasty Bubs, and it's a top down brickbreaker that has you slinging balls around a board. [Read more] | Read more »
Corsola and Heracross are the new region...
Generation 2 finally launched in Pokémon GO, unleashing a brand new batch of Pokémon into the wild. Even before the update went live people were speculating on how to catch elusive Pokémon like the legendary "dogs", Unknown, and whether or not... | Read more »
The Warlock of Firetop Mountain (Games)
The Warlock of Firetop Mountain 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: An epic adventure through a mysterious mountain filled with monsters, magic and mayhem! “...it looks downright... | Read more »
Fantasy MMORPG MU Origin’s receives a hu...
Developer Webzen are looking to take their highly popular fantasy battler MU Origin to the next level this month, with its most ambitious overhaul yet. The latest update introduces the long sought after Server Arena, new treasure dungeons, and much... | Read more »

Price Scanner via MacPrices.net

Apple restocks refurbished 11-inch MacBook Ai...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models recently discontinued by Apple), available for up to $170 off original MSRP. An Apple one-year warranty is included with each... Read more
Apple Park Opens to Employees in April With T...
Apple has announced that Apple Park, the company’s new 175-acre campus, will be ready for employees to begin occupying in April. The process of moving more than 12,000 people will take over six... Read more
Manhattan Neighbors for Safer Telecommunicati...
A new education and advocacy group focused on cell phone and wireless risks, Manhattan Neighbors for Safer Telecommunications, launched today at http://www.ManhattanNeighbors.org. Manhattan... Read more
Portable Dual DisplayPort Monitor Dock Enable...
IOGEAR has announced the launch of its USB-C Dual DisplayPort Monitor Portable Dock (GUC3CMST). The dock enables users to easily connect two DisplayPort monitors to a USB-C or Thunderbolt 3 laptop to... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
Amazon.com has restocked the 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A) for $200 off MSRP including free shipping: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1099 $200 off MSRP This model tends to... Read more
Apple’s New iPad Ads Don’t Address Pro Users’...
Apple launched a new tranche of iPad Pro TV ads last week addressing actual queries and challenges from the Twitterverse, albeit using actors for the visuals. That’s great. As an iPad fan and heavy... Read more
Free Verbum Catholic Bible Study App For iOS
The Verbum mobile app runs on Logos’ powerful Bible software and is an advanced resource for mobile Catholic study. The Verbum app surrounds the Bible with the Tradition. Verbum comes with 15 free... Read more
27-inch Apple iMacs on sale for up to $200 of...
B&H Photo has 27″ Apple iMacs on sale for up to $200 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2099.99 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
Amazon has 2015 15″ 2.2GHz Retina MacBook Pros (MJLQ2LL/A) available for $1849.99 including free shipping. Apple charges $1999 for this model, so Amazon’s price is represents a $150 savings. Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 WiFis available for starting at $319 including free shipping. A standard Apple one-year warranty is included: - 16GB iPad Air 2 WiFi: $319 $60 off original... Read more

Jobs Board

Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.