TweetFollow Us on Twitter

Technical Questions
Volume Number:1
Issue Number:11
Column Tag:Ask Prof. Mac

Technical Questions Answered

By Steve Brecher, Software Supply, MacTutor Contributing Editor

[Prof. Mac is dedicated to helping you solve your Macintosh Programming problems. Each month Prof. Mac will research out your problem and print the best possible solution in MacTutor. Don't waste time in frustration! Send your technical questions to Prof. Mac and let him research your problem for you. Write to Prof. Mac, care of this Journal. -Ed.]

Coordinate Systems

Q. Moving a window by using MoveWindow(..., <portRect.left+offset>, <portRect.top+offset>, ...) doesn't work. What do I need to do?

A. The coordinates you pass to MoveWindow must be global coordinates, so transform them with calls to LocalToGlobal first. The distinction between local and global coordinates can be confusing (it was to me, anyway), so let's discuss coordinate systems.

A coordinate system is an abstraction. I visualize it as an infinitely large sheet of graph paper with one intersection of grid lines designated 0,0. By assigning one grid intersection (0,0 or any other ) to a specific bit in memory, we thereby are able to refer to pixels (memory bits) in terms of coordinates rather than in terms of RAM addresses. This is very convenient when thinking about graphics.

The QuickDraw bitmap is what associates a particlar coordinate system (graph paper) with a particular set of memory locations.

Think of the sheet of graph paper thumbtacked to a bit in memory. The thumbtack goes through the graph paper at the intersection designated by the top, left coordinates of the bitmap's bounds rectangle; this can be any intersection at all -- it needn't be 0,0. The tack's point sticks into memory at the location designated by the bitmap's baseAddr.

A point expressed in local coordinates is merely one that has been thus assigned to a pixel as specified by the relevant grafPort's bitmap. Each and every coordinate found in a grafPort (in the sense of a field in a Pascal record) is, by definition, local to that grafPort.

When we wish to compare the locations with respect to memory (screen) of points in two different grafPorts, we must adjust their coordinate systems so that the same intersection on each port's graph paper is assigned ("thumbtacked") to the same pixel. The convention for doing this is to "move" each graph paper so that its 0,0 coordinate is at the lowest-addressed pixel. Note that this method of inter-port comparison works only if both lowest-addressed pixels (baseAddr's) are the same! This implied requirement -- satisfied, of course, if both baseAddr's are equal to screenBase -- is usually taken for granted in IM discussions.

A local coordinate is an expression of vertical and horizontal distance from the 0,0 intersection on the particular piece of graph paper associated with a grafPort. A global coordinate is an expression of vertical and horizontal distance from the baseAddr pixel. If (and only if) two ports have the same baseAddr, then global coordinates from each may be compared and yield a valid graphics relationship.

While the QuickDraw chapter of Inside Macintosh says (of two ports being compared) "using the same bit image (such as the screen)", the rest of IM when using the term "global" takes for granted that the screen is in fact the common bit image for both ports.

When IM says a document being drawn "sticks to the coordinate system," I mentally translate that to "sticks to the graph paper"; similarly, I mentally translate "sticks to the screen" to "sticks to memory."

Of course, the memory locations designated by a bitmap do not have to coincide with the memory from which the screen is displayed. Drawing merely affects the memory designated by the bitmap; if that memory is (all or partially) in the screen buffer, then the screen display will be affected.

QuickDraw Regions Limitation

Q. L. Tannenbaum of Long Beach, CA, submitted some MacFORTH code that illustrates a problem with QuickDraw's handling of complex regions. His program created 17 vertically-oriented rectangles while defining a region. Subsequently FrameRgn didn't seem to work correctly. He wants to know if the problem is in his code or in QuickDraw.

A. By doing some experiments ,and with the help of MacsBug, I analyzed the problem as follows.

There is a problem in QuickDraw's handling of regions containing more than 12 vertical (higher than wide) rectangles. FrameRgn of a region containing more than 12 vertical rectangles will paint them instead of frame them, and rectangles after the 12th (from left to right) will be enlarged horizonally.

If there are more than 24 such Rectangles, FrameRgn will crash with an address error.

The problem seems to be due to the way region information is stored, in conjunction with the fact that some routines (e.g., FrameRgn, possibly as a part of code common to other routines) allocate a fixed amount of space on the stack which is not large enough to accommodate a chunk of information recorded for the region.

For (at least) multiple rectangles, region information is stored in chunks consisting of pairs of arrays of coordinates in the form

  top[i]         left[1] right[1] left[2] right[2] ... left[n] right[n]
  bottom[i]    left[1] right[1] left[2] right[2] ... left[n] right[n] 

where i ranges over 1 to the number of horizontal lines on which the rectangle corners lie, from top to bottom of the grafPort's portrect. Each array is terminated with a $7FFF marker.

For horizontally-oriented rectangles, n=1, and each array contains exactly 3 coordinates. For vertically-oriented rectangles, n is equal to the number of rectangles, and each array is therefore potentially large. QuickDraw appears to do a Link A6,#-562, and part of the stack frame thus allocated appears to be filled with a chunk of coordinates via autoincremented A2 as the destination address of a move loop. If the chunk is too large, stack frame underflow will result.

I submitted the above to Apple's Tech Support team, and Ginger Jernigan replied:

"It isn't a bug, it is a limitation in QuickDraw, which will be documented in the final version of Inside Macintosh. Your analysis of the situation was correct. We're working to fix it or at least alleviate the nasty problems that occur (like getting real syserrors from Quickdraw calls)."

Boldly Outlining Buttons

Q. Mike Scanlin asks: how do you get the thick border to outline a button in a dialog box for the button representing the default if the user hits Return (usually either "OK" or "Cancel")?

A. Usually such button highlighting appears in alert boxes. The Dialog Manager automatically highlights either item 1 or item 2 in an alert box. Whether item 1 or item 2 is highlighted depends on the value of a bit in the "stages" word for the current stage of the alert. (See Inside Macintosh, Dialog Manager, pp. 34-36.)

The stages word is located in the ALRT resource, and is divided into four 4-bit parts, each part governing one stage, or consecutive occurrence, of the alert. One bit in each part governs item highlighting; if the bit is clear, item 1 is highlighted, and if it's set, item 2 is highlighted.

Often item 1 is an "OK" button and item 2 is a "Cancel" button, and IM assumes this in its illustration. But in fact the Dialog Manager will highlight item 1 or item 2 regardless of what kind of item it is. This can somethimes be a problem. For example, if you have an alert with only a message (a statText item) and an "OK" button, you don't want any highlighting. But the Dialog Manager will relentlessly highlight either item 1 or item 2; if the statText is item 2 and the appropriate bit in the stages word is set, the text will have an ugly bold round-corner rectangle drawn around it. If the bit is clear, the "OK" button will be highlighted, which would be silly since it's the only enabled item.

The only way to handle such a situation is to add a dummy item to the alert's item list (such as a one-character statText item located outside of the alert's rectangle) and let that dummy item "take" the highlighting. In our example, the dummy item could be item 1, and the bits in the stages word would be clear so that item 1 is highlighted. To see an example of this technique, use ResEdit to examine the Finder's DITL 129 resource.

To highlight a button in a dialog that is not an alert, you can use a userItem. Usually a userItem just draws a non-standard item, such as a picture. In this case, we can employ a userItem to change the appearance of another item -- namely, of our button.

A userItem consists of a procedure, as documented in IM, Dialog Manager, p. 11. We will ignore the itemNo parameter, since the item that the userItem will be operating on is not the userItem itself, but the button we want to outline. The QuickDraw techniques for boldly outlining a button are shown on p. 13 of the Dialog Manager section:

PenSize(3,3);
InsetRect(displayRect,-4,-4);
FrameRoundRect(displayRect,16,16)

--where displayRect is the button's display rectangle; GetDItem can be used to obtain it.

Print Dialogs

Q. Paul Cozza of Long Beach, CA, asks: two undocumented Printing Manager routines -- PRSTLINIT and PRJOBINIT -- were mentioned on p. 32 of the First Draft (6/11/84) of Printing Manager section of Inside Macintosh. Apple promised documentation in a later release of the manual, but the routines have mysteriously disappeared altogether from the latest version (Second Draft, 3/27/85, distributed with the May 1985 Software Supplement). If these routines are now unavailable, what is the way to modify the print style and job dialogs?

A. My guess is that the routines succumbed to the generalization of printing procedures that was necessitated by the advent of the Laserwriter.

In the Imagewriter file (I'll let you know about the Laserwriter as soon as I can afford one!), the style dialog is the DLOG -8192 resource, and the job dialog is DLOG -8191. If you examine DITL (dialog item list) -8192, you'll see only placeholders where the paper sizes appear in the style dialog.

At least with respect to Imagewriter paper sizes, it is possible to make some changes. The PREC 3 resource in the Imagewriter file specifies the names of the papers as they will appear in the style dialog, and the sizes of the paper. The format of the PREC 3 resource is as follows:

n [1-word count] -- number of paper sizes;

n pairs of words -- vertical,horizontal paper size in 120ths of an inch;

n Pascal-format strings -- names of paper sizes;

1 word -- ? (probably flags for Orientation, Pagination, Reduction).

Up to six paper sizes can be accommodated by the style dialog box. The distributed Imagewriter file PREC 3 resource contains the specifications of five sizes (US Letter, A4 letter, US Legal, International Fanfold, Computer Paper).

As to other aspects of the dialogs I'm afraid you're on your own; I note the following warning in IM : "Your application should not change the data in the print record -- be sure to use only the standard dialogs for setting this information."

 
AAPL
$102.50
Apple Inc.
+0.25
MSFT
$45.43
Microsoft Corpora
+0.55
GOOG
$571.60
Google Inc.
+2.40

MacTech Search:
Community Search:

Software Updates via MacUpdate

VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
SlingPlayer Plugin 3.3.20.505 - Browser...
SlingPlayer is the screen interface software that works hand-in-hand with the hardware inside the Slingbox to make your TV viewing experience just like that at home. It features an array of... Read more
Get Lyrical 3.8 - Auto-magically adds ly...
Get Lyrical auto-magically add lyrics to songs in iTunes. You can choose either a selection of tracks, or the current track. Or turn on "Active Tagging" to get lyrics for songs as you play them.... Read more
Viber 4.2.2 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device,... Read more
Cocktail 7.6 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
LaunchBar 6.1 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
BBEdit 10.5.12 - Powerful text and HTML...
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

Latest Forum Discussions

See All

This Week at 148Apps: August 25-29, 2014
Shiny Happy App Reviews   | Read more »
Qube Kingdom – Tips, Tricks, Strategies,...
Qube Kingdom is a tower defense game from DeNA. You rally your troops – magicians, archers, knights, barbarians, and others – and fight against an evil menace looking to dominate your kingdom of tiny squares. Planning a war isn’t easy, so here are a... | Read more »
Qube Kingdom Review
Qube Kingdom Review By Nadia Oxford on August 29th, 2014 Our Rating: :: KIND OF A SQUARE KINGDOMUniversal App - Designed for iPhone and iPad Qube Kingdom has cute visuals, but it’s a pretty basic tower defense game at heart.   | Read more »
Fire in the Hole Review
Fire in the Hole Review By Rob Thomas on August 29th, 2014 Our Rating: :: WALK THE PLANKUniversal App - Designed for iPhone and iPad Seafoam’s Fire in the Hole looks like a bright, 8-bit throwback, but there’s not enough booty to... | Read more »
Alien Creeps TD is Now Available Worldwi...
Alien Creeps TD is Now Available Worldwide Posted by Ellis Spice on August 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Dodo Master Review
Dodo Master Review By Jordan Minor on August 29th, 2014 Our Rating: :: NEST EGGiPad Only App - Designed for the iPad Dodo Master is tough but fair, and that’s what makes it a joy to play.   | Read more »
Motorsport Manager Review
Motorsport Manager Review By Lee Hamlet on August 29th, 2014 Our Rating: :: MARVELOUS MANAGEMENTUniversal App - Designed for iPhone and iPad Despite its depth and sense of tactical freedom, Motorsport Manager is one of the most... | Read more »
Motorsport Manager – Beginner Tips, Tric...
The world of Motorsport management can be an unforgiving and merciless one, so to help with some of the stress that comes with running a successful race team, here are a few hints and tips to leave your opponents in the dust. | Read more »
CalPal Update Brings the App to 2.0, Add...
CalPal Update Brings the App to 2.0, Adds Lots of New Stuff Posted by Ellis Spice on August 29th, 2014 [ permalink ] | Read more »
Baseball Battle Review
Baseball Battle Review By Jennifer Allen on August 29th, 2014 Our Rating: :: SIMPLE HITTINGUniversal App - Designed for iPhone and iPad Simple and cute, Baseball Battle is a fairly fun baseball game for those looking for something... | Read more »

Price Scanner via MacPrices.net

Labor Day Weekend MacBook Pro sale; 15-inch m...
B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP. Shipping is free, and B&H charges NY sales tax only. They’ll also include free copies of Parallels Desktop... Read more
Labor Day Weekend iPad mini sale; $50 to $100...
Best Buy has the iPad mini with Retina Display (WiFi models) on sale for $50 off MSRP on their online store for Labor Day Weekend. Choose free shipping or free local store pick up. Price is for... Read more
13-inch 1.4GHz MacBook Air on sale for $899,...
Adorama has the new 2014 13″ 1.4GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY & NJ tax only. Their price is $100 off MSRP. Read more
It’s Official: Apple Issues Invitations To Se...
Apple has issued one of its characteristically cryptic press invitations for a special event to be held at the Flint Center for the Performing Arts in hometown Cupertino on Sept. 9, 2014 at 10:00 am... Read more
Tablet Shipments To See First On-year Decline...
TrendForce analyst Caroline Chen notes that when the iPad launched in 2010, it was an instant hit and spurred a tablet PC revolution, with tablets so popular that that notebook PC sales stagnated and... Read more
SOBERLINK Releases Apple iOS Compatible Handh...
Cypress, California based SOBERLINK, Inc., creator of the first handheld Breathalyzer designed to improve recovery outcomes, continues to show prominence in the mobile alcohol monitoring space with... Read more
New 21″ 1.4GHz iMac on sale again for $999, s...
Best Buy has the new 21″ 1.4GHz iMac on sale for $999.99 on their online store. Their price is $100 off MSRP. Choose free shipping or free local store pick up. Price is for online orders only, in-... Read more
Smartphone Outlook Remains Strong for 2014, U...
According to a new mobile phone forecast from the International Data Corporation (IDC) Worldwide Quarterly Mobile Phone Tracker, more than 1.25 billion smartphones will be shipped worldwide in 2014,... Read more
Save up to $60 with Apple refurbished iPod to...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Many, but not all... Read more
12-Inch MacBook Air Coming in 4Q14 or 2015 –...
Digitimes’ Aaron Lee and Joseph Tsai report that according to Taiwan-based upstream supply chain insiders, Apple plans to launch a thinner MacBook model either at year end 2014 or in 2015, and that... 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* 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* 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* 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
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.