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:

C STRUCT FOR WINDOW RECORDS

#define boolean char
struct WindowRec
 {
 grafPort port;
 short  windowKind;
 booleanvisible;
 booleanhilited;
 booleangoAwayFlag;
 booleanspareFlag;
 RgnHandlestrucRgn;
 RgnHandlecontRgn;
 RgnHandleupdateRgn;
 Handle windowDefProc;
 Handle dataHandle;
 Handle titleHandle;
 short  titleWidth;
 Handle controlList;
 struct WindowRec *nextWindow;
 PicHandlewindowPic;
 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.

PORTS, REGIONS AND WINDOWS

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
 */
vs_rect.top = 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
 */
hs_rect.top = pr->bottom - 15;
hs_rect.left = pr->left - 1;
hs_rect.bottom = pr->bottom + 1;
hs_rect.right = pr->right - 14;

Afterword

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

OmniGraffle Pro 6.1.4 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniGraffle 6.1.4 - Create diagrams, flo...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
MegaSeg 5.9.5 - Professional MP3 DJ appl...
MegaSeg is a complete solution for pro audio/video DJ mixing, radio automation, and music scheduling with rock-solid performance and an easy-to-use design. Mix with visual waveforms and Magic... Read more
MarsEdit 3.6.8 - Quick and convenient bl...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more
BBEdit 11.0.3 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
Microsoft Office Preview 15.8 - Popular...
Welcome to the new and modern Microsoft Office for Mac. You will receive regular updates automatically until the official release in the second half of 2015. With the redesigned Ribbon and your... Read more
Yosemite Cache Cleaner 9.0.5 - Clear cac...
Yosemite Cache Cleaner is an award-winning general purpose tool for OS X. YCC makes system maintenance simple with an easy point-and-click interface to many OS X functions. Novice and expert users... Read more
ExpanDrive 4.3.2 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
RapidWeaver 6.0.8 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Artlantis Studio 5.1.2.7 - 3D rendering...
Artlantis Studio is a unique and ideal tool for performing very high resolution rendering easily and in real time. The new FastRadiosity engine now lets you compute images in radiosity-even in... Read more

Bored? MyLeisure FreeTime Maximizer Will...
Bored? MyLeisure FreeTime Maximizer Will Take Care of That! Posted by Jessica Fisher on March 5th, 2015 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
New Publisher Allstar Games Heads West w...
Allstar Games has announced its first mobile title designed for western audiences, Allstar Heroes. The game will be a massive online battle arena (MOBA) that offers dozens of heroes for you to collect and pit against your opponents. As each hero has... | Read more »
RAD Boarding Review
RAD Boarding Review By Jennifer Allen on March 5th, 2015 Our Rating: :: NEARLY RADUniversal App - Designed for iPhone and iPad RAD Boarding isn’t quite one of the greats, but it has potential.   | Read more »
Presenting the International Mobile Gami...
11th Annual International Mobile Gaming Awards ceremony, hosted by actress Allison Haislip, gathered mobile game developers and publishers from around the world. They chose 13 winners out of the 93 nominations. British studio USTWO won the the Grand... | Read more »
AG Drive Review
AG Drive Review By Tre Lawrence on March 5th, 2015 Our Rating: :: FUTURISTIC STREET RACING.Universal App - Designed for iPhone and iPad Futuristic racing… interstellar style.   | Read more »
GDC 2015 – Nightmare Guardians is an Int...
GDC 2015 – Nightmare Guardians is an Interesting Hybrid of MOBA and Lane Defense Posted by Rob Rich on March 5th, 2015 [ permalink ] I have to say that lane defense (i.e. | Read more »
Overkill 3 Review
Overkill 3 Review By Tre Lawrence on March 5th, 2015 Our Rating: :: WHO'S NEXT?Universal App - Designed for iPhone and iPad Cover system gameplay in the third-person.   Developer: Craneballs Price: Free Version Reviewed: 1.1.6... | Read more »
Warner Bros. Interactive Entertainment A...
Warner Bros. has some exciting games coming down the pipe! | Read more »
GDC 2015 – Star Trek Timelines will Prob...
GDC 2015 – Star Trek Timelines will Probably Make Your Inner Trekkie Squeal With Glee Posted by Rob Rich on March 4th, 2015 [ permalink ] Any popular fictional universe has its fair share of fan fiction – where belo | Read more »
Protect Yourself from an Onslaught of Ca...
Surprise Attack Games has announced a Cat-astrophic new physics puzzler called Fort Meow! In the game, a young girl named Nia finds her grandfather’s journal which triggers an all mighty feline attack! Why do the cats want the journal? Who knows,... | Read more »

Price Scanner via MacPrices.net

Apple restocks refurbished 15-inch Retina Mac...
The Apple Store has restocked Apple Certified Refurbished 2014 15″ Retina MacBook Pros, available for up to $400 off the cost of new models. An Apple one-year warranty is included with each model,... Read more
Roundup of MacBook Air sale prices, models up...
B&H Photo has MacBook Airs on sale for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $799 100 off MSRP - 11″ 256GB MacBook Air: $999 $100... Read more
New Firstrade Mobile App Enables On-The-Go Tr...
Firstrade Securities Inc. has announced its new mobile app, which gives investors immediate access to the company’s trading platform on all mobile devices. The app was developed in-house and was... Read more
Sonnet Introduces USB 3.0 + eSATA Thunderbolt...
Sonnet has announced the launch of its new USB 3.0 + eSATA Thunderbolt Adapter for easy connectivity to USB 3.0 devices and eSATA storage, and USB 3.0 + Gigabit Ethernet Thunderbolt Adapter for easy... Read more
Apple restocks refurbished 27-inch 5K iMacs f...
The Apple Store has restocked Apple Certified Refurbished 27″ 3.5GHz 5K iMacs for $2119 including free shipping. Their price is $380 off the cost of new models, and it’s the lowest price available... Read more
Free Clean Reader Mobile App Hides Swear Word...
The new Clean Reader app, now available in the Apple App Store and Google Play, delivers the opportunity of reading any book without being exposed to profanity. By selecting how clean they want their... Read more
Kinsa Launches “Groups” App to Monitor Illnes...
Kinsa, makers of the first FDA approved app-enabled smartphone thermometer thst won the 2013 Cleveland Clinic Medical Innovation Grand Prize and recently appeared in Apple’s “Parenthood” TV... Read more
iPad: A More Positive Outlook – The ‘Book Mys...
It’s good to hear someone saying positive things about the iPad. I’ve been trying to bend my mind around how Apple’s tablet could have gone from zero to bestselling personal computing device on the... Read more
Mac Pros on sale for up to $279 off MSRP
Amazon has Mac Pros in stock and on sale for up to $279 off MSRP. Shipping is free: - 4-Core Mac Pro: $2725.87, $273 off MSRP (9%) - 6-Core Mac Pro: $3719.99, $279 off MSRP (7%) Read more
Sale! 13-inch Retina MacBook Pros for up to $...
B&H Photo has 13″ Retina MacBook Pros on sale for up to $205 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1219.99 save $80 - 13″ 2.... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
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
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Position Opening at *Apple* - Apple (United...
…Summary** As a Specialist, you help create the energy and excitement around Apple products, providing the right solutions and getting products into customers' hands. You Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.