TweetFollow Us on Twitter

Using Windows
Volume Number:1
Issue Number:4
Column Tag:C Workshop

Using Windows

By Robert B. Denny

Layers and Interfaces

One of the most important things to come out of the computer world in the seventies is the concept of layered architecture. Layering provides us with a clean way to deal with the complexities of modern operating system and communications architectures. One of the most visible instances of layering is the ISO Open Systems Architecture which is widely used and quoted in standards for networks.

I consider layering to be a survival skill for software developers. Take time to consider the Macintosh from bottom to top. At the bottom, we have solid-state physics which attempts to explain the behavior of what might be particles or waves. At the top (user’s view) we have dragging, clicking, icons, windows, etc. Both the physics and the user concepts are abstract ideas. How many layers can you conceive of in a Macintosh?

Let’s formalize this a bit. A layer is a structured set of related things that together provide a set of tools or services for implementing other things. An interface is a set of means for accessing the services provided by a layer. Finally a given layer might make use of the services provided by a “lower” layer in implementing it’s own services. It is this latter notion that makes layers have ranking.

How does all of this help us deal with complex systems? By restricting our thinking to the layer we are working on, we avoid cluttering our mind with unnecessary details. This kind of thinking comes naturally, but we can reinforce it by being aware of it’s importance.

Most of the developers I have talked with share the feeling that the Mac is a difficult system to learn. Inside Macintosh is a wealth of information, but it has little overall structure. There is a section called Inside Macintosh: A Road Map which does discuss the overall architecture, but this thread is not carried elsewhere, and one tends to “dive in” to a particular area of interest.

Here is my personal view of the Macintosh operating system as a set of layers. Below these layers are the low-level stuff I seldom deal with and above these layers are the programs I write. The boxes show the sections of the Mac system that I frequently encounter when developing user-oriented applications.

Data-Driven Software

Another key concept needeed for Macintosh programming is that of data or table-driven software. This is another common technique that grew out of the seventies, when system complexity took a quantum jump.

A data-driven routine consists of a combination of code and data, split up so that variations are possible with no changes to the code. This technique is usually employed where there are a variety of related objects that need some sort of service or management that can be done with a common “engine” in code.

This is sort of a gray area; you might say that all routines are sensitive to data, or they wouldn’t be useful. True, but a routine that stores no data of it’s own is special. It is usually called with a reference to a data structure which contains the state and attributes of the particular object that the routine is to work on. The data structure could even contain a reference to one or more “action routines” which are unique to the object in question. Examining the contents of such data structures can often provide great insight into the sublties of the routine or service.

Most of the “managers” in the Macintosh interface use this technique. The data structures are referred to as “records” from the Pascal terminology. In C, they can be implemented as struct’s.

The Window Manager

From the user’s viewpoint, a window is an object on the desktop that provides some sort of user interface. There is a whole set of guidelines describing how windows should look and behave. Window appearance and behavior is the essence of the Macintosh.

From the developer’s viewpoint, a window is a structured set of regions in a port under the control of the Window Manager. The Window Manager provides a layered interface to window services on the Macintosh, using QuickDraw to draw the pictures that create the abstract notion of windows on the screen.

Besides handling the windows themselves, the Window Manager handles shuffling, dragging and re-sizing of overlapping windows, generating events for owning applications to update window contents as required. This powerful and complex layer of the Mac architecture has a surprisingly simple interface.

The Window Manager uses a data structure, called a window record, to keep track of each window. It contains the currrent attributes and state of the corresponding window. The window records are kept on a linked list whose order corresponds to the planar ordering of the window images on the screen, as shown in figure 2.

If you haven’t looked over the section on the Window Manager in Inside Macintosh, now would be a good time to do so. In particular, study the section describing the window record and each of it’s fields. We’ll look at some of the more important fields here, but we can’t cover them all. In C, the window record can be represented as follows:


#define boolean char
struct WindowRec
 grafPort port;
 short  windowKind;
 Handle windowDefProc;
 Handle dataHandle;
 Handle titleHandle;
 short  titleWidth;
 Handle controlList;
 struct WindowRec *nextWindow;
 long   refCon;

Note that the first thing in the window record is a GrafPort structure. This is the data structure used by QuickDraw for manipulating “ports” in general. Of course, a window is a port, so it follows that the window’s data would include (nested within) a GrafPort.

Before we dig any deeper into the window record, lets look at how it relates to other important data structures. Pointers and handles are represented alike in the interest of simplicity in Fig. 3.


Looking at figure 3, observe the linkage of the region structs. The visRgn and clipRgn are hooked to the GrafPort, while the strucRgn, contRgn and updateRgn are hooked to the WindowRecord. The latter three regions are used only in the context of a window. If you are unclear about the role of regions, refer to Chris Derossi’s Pascal Procedures in MacTutor, Vol.1, No.3, February, 1985.

Note also that the ControlRecord for each control that is associated with the window is hooked to a linked list, and has a “back-link” pointing back to the owning window’s WindowRecord. This implies that the Window Manager uses information about the controls, and that the Control Manager uses information about the owning window and it’s port. For example, the Window Manager function drawControls() traces down the linked list of ControlRecords, drawing each control in turn.

The various “boolean” fields in the WindowRecord indicate the current state of the window’s visibility, highlighting (see below) and whether it has a “go-away” box. CAUTION: the Window Manager uses 255 as TRUE and 0 as FALSE. Typically C defines TRUE as 1. You should test these flags for “not FALSE”, rather than explicitly TRUE.

The three RgnHandles point to Rgn structs which describe important parts of the window’s port. We’ll cover these later in the section on anatomy and next month’s column on window dynamics.

The windowDefProc field is a handle that points to a vectored set of routines that give the window it’s look. Associated with this is the dataHandle field, which points to private data used by the DefProc. “DefProc” is short for Definition Procedure, really a set of routines that perform the following:

Window Definition Procedure Tasks

• Draw window frame

• Return region where mouse was clicked

• Calculate structure & content regions

• Draw “grow” image of the window

• Draw a “size box” in the content region

Note that the Window Manager has no idea what the window actually looks like. The appearance is completely governed by the DefProc, which is described by a handle in the WindowRecord. The six standard DefProcs handle windows of the types shown below in figure 5 with the symbolic value for the definition ID you pass to the Window Manager when creating the window.

Note that the documentProc flavor has the outlines for scroll bars. Scrollers are controls, not part of the basic window’s definition. These are the standard window types. You could write a DefProc package for a custom window type. The hooks for this are described in Inside Macintosh in the Window Manager section.

The titleHandle field points to the window’s title string and the titleWidth field contains the width of the title in pixels. ControlList is the listhead for the linked list of ControRecords for the controls associated with this window.

NextWindow is a pointer to the next window on the window list. As we stated earlier, the “next” window is the one behind this window. If this is the back-most window, NextWindow is NULL.

WindowPic is a handle to a QuickDraw picture for the window, or NULL if the application is responsible for updating the window. This implies that the window manager will automatically update a window if it’s contents are a QuickDraw Picture without generating update events.

Finally, there is a “hack” in the definitions used in Inside Macintosh. A WindowPtr is defined as a pointer to a grafPort, rather than a pointer to a WindowRecord. The name for the later is WindowPeek. It seems that the most frequent use of WindowRecord information involves the data contained in the embedded grafPort. Keep this quirk in mind.

Anatomy of a Document Window

The six standard window types are shown in figure 5. Of the six, the documentProc type is the most complex. In this section we’ll look at the window as a set of regions. Viewing the window this way is essential when writing programs which manipulate them, particularly the routines that handle activation and updating of the window. A document window with scroll bars is shown in figure 6.

All windows have a structure region and a content region. The structure region covers the entire window, frame and all. The content region is the area inside the frame. These regions change only when the window is moved or re-sized.

The frame may include go-away and drag regions. The content region may include a grow region.These are not really regions in the formal sense, as defined by QuickDraw. The DefProc is responsible for handling these regions, not QuickDraw. The scroll bars are handled by the Control Manager, not the Window Manager.

The WindowRecord contains a handle to another region, the Update Region. This region describes the portion of the content region that needs updating, redrawing, after some change. We’ll deal with this in next month’s column on window dynamics.

One of the fine points not made clear in Inside Macintosh is the relationship between the “grow image”, the grow region and the scroll bars usually present in a document window. The grow image is the line-tracing of the window that appears when you click in the grow region.

The Control Manager can build scroll bars of any dimension. The convention is that scroll bars are 16 pixels wide. This matches the width of the “scroller” areas that appear in the grow image, and the width and height of the grow icon. These areas are fixed, set by the documentProc DefProc. Here is a fat-bits view of the lower right corner of the document window shown above (see fig. 7). Note that the scroll bar edges overlap the grow icon and the window frame by one pixel. The following fragment of C code computes the boundsRects for the scrollers, given the portRect for the window. Get the portRect from the grafPort that is embedded in the WindowRecord:

 struct rect/* Define a “rect” */
 short  top;
 short  left;
 short  bottom;
 short  right;

struct grafPort *wp; /* Window Pointer */
struct rect *pr; /* -> portRect */
struct rect vs_rect; /* Vert. scroller */ 
struct rect hs_rect; /* Hor. scroller */

pr = &(wp->portRect);

 * Compute bounds rect for vertical scroll
 */ = pr->top - 1;
vs_rect.left = pr->right - 15;
vs_rect.bottom = pr->bottom - 14;
vs_rect.right - pr->right + 1;
 * Compute bounds rect for horiz. scroll
 */ = pr->bottom - 15;
hs_rect.left = pr->left - 1;
hs_rect.bottom = pr->bottom + 1;
hs_rect.right = pr->right - 14;


Next month we’ll deal with window dynamics, dragging, growing, updating and activating. This is an area of Mac programming that seems complex on the surface. If you have tried your hand at window-oriented programs, you probably had many surprises and mysteries and you may have developed a few OPT’s (old programmer’s tales). One of my most memorable surprises was discovering what happens if you omit the beginUpdate() and endUpdate() calls when handling an update event.

There is an underlying consistency to window dynamics. It’s all there in Inside Macintosh, but in peices. Understanding window dynamics is essential if you are to get beyond trivial programs without unnecessary screen drawing or ugly hacks. See you then.


Community Search:
MacTech Search:

Software Updates via MacUpdate

Warhammer 40,000: Freeblade guide - How...
Warhammer 40,000: Freebladejust launched in the App Store and it lets you live your childhood dream of blowing up and slashing a bunch of enemies as a massive, hulking Space Marine. It's not easy being a Space Marine though - and particularly if... | Read more »
Gopogo guide - How to bounce like the be...
Nitrome just launched a new game and, as to be expected, it's a lot of addictive fun. It's called Gopogo, and it challenges you to hoparound a bunch of platforms, avoiding enemies and picking up shiny stuff. It's not easy though - just like the... | Read more »
Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »
Snowboard Party 2 (Games)
Snowboard Party 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Crowned the best snowboarding game available on the market, Snowboard Party is back to fulfill all your adrenaline needs in... | Read more »
One Button Travel (Games)
One Button Travel 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: “To cut a long story short, If you like interactive fiction, just go buy this one.” - “Oozes the polish that... | Read more »
Light Apprentice Volume 1 (Games)
Light Apprentice Volume 1 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Light Apprentice Volume 1 includes Chapters 1 to 4, all gathered in a new exclusive game. When life in the world of... | Read more »
The best games like Animal Crossing on m...
Animal Crossing amiibo Festival is out right now for the Wii U, reminding us of just how much fun that world can be. Or at least to go back and check in on our villages once in a while. [Read more] | Read more »

Price Scanner via

iMobie Releases its Ace iOS Cleaner PhoneClea...
iMobie Inc. has announced the new update of PhoneClean 4, its iOS cleaner designed to reclaim wasted space on iPhone/iPad for use and keep the device fast. Alongside, iMobie hosts a 3-day giveaway of... Read more
U.S. Cellular Offering iPad Pro
U.S. Cellular today announced that it is offering the new iPad Pro with Wi-Fi + Cellular, featuring a 12.9-inch Retina display with 5.6 million pixels — the most ever in an iOS device. U.S. Cellular... Read more
Newegg Canada Unveils Black Friday Deals for...
Newegg Canada is offering more than 1,000 deep discounts to Canadian customers this Black Friday, available now through Cyber Monday, with new deals posted throughout the week. “Black Friday is... Read more
Black Friday: Macs on sale for up to $500 off...
BLACK FRIDAY B&H Photo has all new Macs on sale for up to $500 off MSRP as part of their early Black Friday sale including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
Black Friday: Up to $125 off iPad Air 2s at B...
BLACK FRIDAY Walmart has the 16GB iPad Air 2 WiFi on sale for $100 off MSRP on their online store. Choose free shipping or free local store pickup (if available): - 16GB iPad Air 2 WiFi: $399, save $... Read more
Black Friday: iPad mini 4s on sale for $100 o...
BLACK FRIDAY Best Buy has iPad mini 4s on sale for $100 off MSRP on their online store for Black Friday. Choose free shipping or free local store pickup (if available): - 16GB iPad mini 4 WiFi: $299.... Read more
Black Friday: Apple Watch for up to $100 off...
BLACK FRIDAY Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday. Below is a roundup of the deals being offered by authorized Watch resellers:... Read more
Black Friday: Target offers 6th Generation iP...
BLACK FRIDAY Save $40 to $60 on a 6th generation iPod touch at Target with free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: -... Read more
Black Friday: Walmart and Target offer iPod n...
BLACK FRIDAY Walmart has the 16GB iPod nano (various colors) on sale for $119.20 on their online store for a limited time. That’s $30 off MSRP. Choose free shipping or free local store pickup (if... Read more
Black Friday deals on the Apple Watch and App...
Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday weekend. Below is a roundup of the deals being offered by authorized Watch resellers: Apple... Read more

Jobs Board

Storefront Operations Coordinator, *Apple* -...
# Storefront Operations Coordinator, Apple -Latin America Job Number: 43587750 Miami, Florida, United States Posted: Oct. 16, 2015 Weekly Hours: 40.00 **Job Summary** The Read more
*Apple* Enterprise / Government Professional...
# Apple Enterprise / Gove ment Professional Services Engineer Job Number: 42292976 Reston, Virginia, United States Posted: Aug. 18, 2015 Weekly Hours: 40.00 **Job Read more
iOS Wallet & *Apple* Pay Engineer - App...
# iOS Wallet & Apple Pay Engineer Job Number: 40586801 Santa Clara Valley, Califo ia, United States Posted: Nov. 16, 2015 Weekly Hours: 40.00 **Job Summary** The iOS Read more
Software Engineer, *Apple* Watch - Clock Fa...
# Software Engineer, Apple Watch - Clock Face Team Job Number: 44368761 Santa Clara Valley, Califo ia, United States Posted: Nov. 14, 2015 Weekly Hours: 40.00 **Job Read more
Administrative Assistant, *Apple* Online St...
# Administrative Assistant, Apple Online Store Job Number: 43992352 Santa Clara Valley, Califo ia, United States Posted: Nov. 9, 2015 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.