TweetFollow Us on Twitter

April 91 - TAspectPicture

TAspectPicture

James Plamondon

The Bed of Procrustes

Greek mythology contains the tale of Procrustes, a wealthy man of Eleusis who was in the habit of taking in travelers for the night. After treating such a traveler to a sumptuous dinner, Procrustes would take him to a room in which there was an iron bed, exactly the right size for a man of average height. Procrustes would then bid his guest to lay down on the bed. If the guest was of average height, then all was well; his sleep would be comfortable and uninterrupted; in the morning he would go on his way.

However, if the guest was shorter than average, Procrustes would place him upon a rack, stretching him out until he was tall enough to fit the bed. Likewise, if the guest were taller than average, Procrustes would decapitate him, to ensure that he, too, fit the bed. The tale of Procrustes was all the more terrible to the ancient Greeks, because of the high value they placed on hospitality.

MacApp often reminds me of Procrustes and his iron bed: so long as one is writing an "average" application-one that uses documents, views, and controls in the manner foreseen by MacApp's designers-all is well. Otherwise, you may have to decapitate your feature list, or extend the MacApp source code, to fit MacApp's iron bed. This limitation is all the more terrible to us, because of the high value object programmers place on code reusability and extensibility.

TAspectPicture

Recently, I found myself strapped to the iron bed when I least expected it. I wanted to do something that appeared to be simple: display a picture in a button-like control. No problem, right? TPicture, in MacApp's UDialog unit, does just that-so I used it. Unfortunately, TPicture (like old Procrustes) distorts its picture as necessary to make it fit in its extent. I needed to maintain the picture's original aspect ratio.

Well, TPicture was still close; surely, I'd just have to override a single routine to get the behavior I wanted. So I looked at the TPicture.Draw() source, and was quite discouraged to see that it called ControlArea() to get the rectangle in which to draw the picture. I had expected to find a routine called something like GetPictureArea(), which would be easy to override. Overriding ControlArea() would have undesirable side-effects. Darn.

OK, no problem; I'd just override Draw(). Whoops! I couldn't do that-calling INHERITED Draw() would then call TPicture.Draw(), drawing the picture twice (differently each time). If I didn't call INHERITED Draw(), my control would not be properly adorned, since adornment is performed by the version of Draw() that is inherited by TPicture. Object Pascal-the language I was using-does not allow me to call a grandparent's version of Draw(), only that of the parent class. Procrustes' iron bed was beckoning.

Well, if there's one thing I've learned in object programming, it's never to write any code you don't have to. If I couldn't inherit the solution to my problem, maybe I could get someone to give it to me. So I described my problem to MacApp.Tech$ as a contest, in which the person supplying the best solution would win. I got a number of excellent responses.

Knepper's solution

Chris Knepper submitted an entry which I classify as an "elegant kludge." This apparent oxymoron describes a solution which relies on the implementation, rather than the interface, of a method (thus, it's a kludge), but which does so in a clever way. Here it is:
PROCEDURE TAspectPicture.Draw(area: Rect); OVERRIDE;
VAR
    saveDataHandle: PicHandle;
BEGIN
    { 1st. draw the picture "correctly" }
    …fill in this blank…

        { 2nd. (the hard part!) call INHERITED Draw }
    { without having TPicture.Draw do anything }
    saveDataHandle := fDataHandle;
    fDataHandle := NIL;
        INHERITED Draw(area);
    fDataHandle := saveDataHandle;
END;  { Draw }

Since TPicture.Draw() just calls INHERITED Draw() if fDataHandle is NIL, this OVERRIDE of TAspectPicture does the trick. TControl.Draw() gets called, the adornments get drawn, and everybody's happy-assuming that the "fill in the blank" part draws the picture in the right place, with the correct aspect ratio.

Eastman's solution

Gordon Eastman's entry was also a kludge, and if it was somewhat less elegant, it was downright cunning. His approach relies on the inner workings of Object Pascal and the MPW Linker. Here it is:
PROCEDURE TControl_Draw(area: Rect; me: TControl); EXTERNAL;
PROCEDURE TAspectPicture.Draw(area: Rect); OVERRIDE;
BEGIN
    { draw picture with correct aspect ratio, then… }
    TControl_Draw(area, SELF);
END;  { Draw }

To quote Eastman's description of his solution, "This is a slime dog trick that relies on how the MPW Pascal compiler and linker work. The linker sees TControl.Draw as TControl_Draw. The compiler generates an extra SELF parameter for methods." I beg to differ; this solution is an affront to slime dogs everywhere. But it works (this week, anyway).

Berdahl's solution

Eric Berdahl found the whole contest laughable, I think; to his mind, it was a undeniable demonstration of the superiority of C++ over Object Pascal. Just to rub it in, he submitted an entry showing how easy it is to implement TAspectPicture in C++, which allows calls to ancestral methods via its scope resolution operator. Here's his solution:
TAspectPicture::Draw(Rect* area) {
//  Compute the rect, then draw the pict, then…
//  Skip TPicture::Draw and go directly to TControl::Draw
TControl::Draw(area);
}  // Draw

The solution does indeed prove C++'s superiority (in this specific ability, at least). It's worth noting again, though, that this whole problem stems from a flaw in the design of the class, not of the language-if MacApp's TPicture class had a GetPictRect() method, there would have been no problem. Good languages are a poor substitute for good design.

The missing solution

No one submitted a solution that I was expecting: changing the MacApp source code to add the method GetPictRect() to TPicture, and modifying TPicture.Draw() to call it. I think of the MacApp source as being like putty-if I don't like it, I change it. So long as I mark my changes well, it's not too hard to move them to the next version of MacApp.

Of course, I always notify the MacApp wizards of my changes, in the hope that they may be incorporated directly into MacApp in the future (thus relieving me of the burden of maintaining my changes with each new MacApp release).

I carefully worded my contest rules to allow this solution. Perhaps everyone else worships the MacApp source as an immutable deity; if so, burn me for a heretic.

Cheung's solution(s!)

Tseung Cheung supplied not just one, but two solutions. The first overrode ControlArea(), since that's the routine called by TPicture.Draw() to calculate the rect in which to draw the control's picture. While it works, this solution has a number of side effects (since ControlArea() is used in a lot of other places).

The second solution used the trick described under Knepper's Solution, above, to bypass TPicture.Draw() by setting fDataHandle to NIL before calling INHERITED Draw(), and then restoring it afterwards. It was the only submission which met all of the contest's "victory conditions," and so it is the winner-and a pretty good one at that. Here it is:

{  CenterRectInRect(): Centre the inner rect within the
outer rect, either horizontally, or vertically, or both }
PROCEDURE CenterRectInRect(VAR inner: Rect; outer: Rect;
                                        horiz, vert: Boolean);
VAR
    innerSize, outerSize:   Point;
BEGIN
    WITH outer DO
        SetPt(outerSize, right - left, bottom - top);

        WITH inner DO
BEGIN
            SetPt(innerSize, right - left, bottom - top);
            IF horiz THEN
                left := outer.left+(outerSize.h-innerSize.h) DIV 2;
            IF vert THEN
                top := outer.top+(outerSize.v-innerSize.v) DIV 2;
            right := left + innerSize.h;
            bottom := top + innerSize.v;
        END;  { with }
END;  { CenterRectInRect}
TYPE
TAspectPicture = OBJECT(TPicture)
    PROCEDURE Draw(area: Rect); OVERRIDE;
END;  { TAspectPicture  }

{   Draw():  Modified from TPicture.Draw to grab the actual
    picture frame, and then centre this frame within the
    TPicture area before drawing it. }
PROCEDURE TAspectPicture.Draw(area: Rect); OVERRIDE;
VAR
    oldState:   SignedByte;
    cntlFrame,
    myPicFrame: Rect;
    saveDataHandle: picHandle;
BEGIN
    IF fDataHandle <> NIL THEN
        BEGIN
            IF fRsrcID <> kNoResource THEN
                LoadResource(Handle(fDataHandle));

                IF fDataHandle^ <> NIL THEN
                BEGIN   { If there's room for the picture… }
                    ControlArea(cntlFrame);
                    myPicFrame := fDataHandle^^.picFrame;
                    CenterRectInRect(myPicFrame, cntlFrame,                                                     TRUE, TRUE);
                    oldState :=                                                             GetHandleBits(Handle(fDataHandle));
                    HNoPurge(Handle(fDataHandle));
                    PenNormal;
                    DrawPicture(fDataHandle, myPicFrame);
                    SetHandleBits(Handle(fDataHandle),                                                          oldState);
                END;  { then }
        END;  { then }

        saveDataHandle := fDataHandle;
    fDataHandle := NIL;
    INHERITED Draw(area);
    fDataHandle := saveDataHandle;
END;  { Draw }

And the moral of this story is…

A number of lessons can be drawn from this example.

First, it would have been better had MacApp's TPicture class contained a GetPictRect() method, which was called by TPicture.Draw() as ControlArea() is now. TPicture.GetPictRect() could have called ControlArea(), so the added method would not have changed the functionality of the code at all.

This is just one example of a problem that runs throughout MacApp: its methods do too much. The MacApp wizards know this, and will admit to feeling deeply ashamed of themselves for it (or will with enough beer in them). They, too, are imperfect people, who write imperfect code-but there are only so many hours in a man-month, and even wizards need sleep.

Second, a sufficiently powerful language can hide a multitude of sins. C++'s scope resolution operator does not remove the problem, but it makes dealing with it much easier. A powerful language can never make up for a bad design, but MacApp cannot reasonably be expected to reach perfection anytime soon, whereas I'm supposed to have shipped yesterday. MacApp 3.0's being in C++ sounds better and better each day (but perhaps I'm having ear trouble).

Third, this example shows that in MacApp development, you can do just about anything, one way or another-or another, or another, or another.

Fourth, and finally, I offered to split the payment for this article with the winner of the contest because I knew that FrameWorks didn't pay anything for its articles. Ha, ha, funny me. A new editor took over FrameWorks, changed the policy-and now I have to fork over some real money to the winner. I out-foxed myself. There's got to be a lesson in here somewhere.

Procrustes revisited

The fact that we were able to get the TAspectPicture class to work-eventually-suggests that the analogy between MacApp and the iron bed of Procrustes is unfair. But I think not; I think it's fair to say that, even after racking our brains, the solutions we came up with were quite a stretch-and that's what Procrustes' iron bed was all about. n
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Pinegrow 4 - Mockup and design webpages...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
iExplorer 4.1.11 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Evernote 6.13.1 - Create searchable note...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
Myriad 4.2.1 - Audio batch processor.
Myriad is, simply put, one of the best audio batch processors. Totally redesigned, it looks beautiful and delivers incredible performance. Let Myriad do the heavy lifting while you get back to doing... Read more
Garmin Express 5.8.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Arq 5.10 - Online backup to Google Drive...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more
Garmin Express 5.8.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Myriad 4.2.1 - Audio batch processor.
Myriad is, simply put, one of the best audio batch processors. Totally redesigned, it looks beautiful and delivers incredible performance. Let Myriad do the heavy lifting while you get back to doing... Read more
Arq 5.10 - Online backup to Google Drive...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more
Evernote 6.13.1 - Create searchable note...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more

Latest Forum Discussions

See All

warbot.io wants you for the robot wars
Fans of epic gundam-style battles will find a lot to love in warbot.io, the first game for up and coming developer Wondersquad. The game saw a lot of success when it first launched for browsers and Facebook, and now even more people are getting the... | Read more »
Uncover alien mysteries in cross-genre s...
If the Alien franchise taught us anything, it’s that landing on a strange planet at the behest of a faceless corporation is probably asking for trouble. And Eldritch Game’s Deliria doesn’t prove otherwise. In 2107, Dimension LG7 is rich with... | Read more »
The best mobile games to play during dre...
| Read more »
The mobile gamer's guide to Black F...
We're starting to catch wind of some exciting deals in the mobile gaming space for Black Friday. There are big discounts on mobile phones and accessories cropping up already, so you might want to get a move on things ahead of the big day. It's... | Read more »
The best pre-Black Friday deals - Novemb...
Black Friday will soon be upon us, but online retailers are already getting a headstart on the steep discounts. Don't wait until Friday—you'll find some pretty good deals all over the internet without waiting in lines or competing with other... | Read more »
Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »
A Boy and His Blob (Games)
A Boy and His Blob 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Lowest Black Friday prices on Apple MacBooks:...
Save $150-$420 on the purchase of a MacBook Pro, MacBook, or MacBook Air this Black Friday and Holiday weekend with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices... Read more
Black Friday: Apple Watch Series 1 for $70 of...
Macy’s has discounted Series 1 Apple Watches by $70 on their online store as part of their Black Friday sale: – 38mm Series 1 Apple Watch: $179, $70 off – 42mm Series 1 Apple Watch: $209, $70 off... Read more
Apple offers 2016 13-inch MacBook Airs, certi...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Black Friday sale: Mac minis for $100 off MSR...
B&H Photo has Mac minis on sale for up to $100 off MSRP as part of their Black Friday sale, each including free shipping plus NY & NJ sales tax only: – 1.4GHz Mac mini: $399 $100 off MSRP – 2... Read more
Use your Apple Education discount to save up...
Purchase a new Mac using Apple’s Education discount, and take up to $300 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Adorama posts Black Friday deals on Apple Mac...
Adorama has posted Black Friday sale prices on many Macs, with MacBooks and iMacs available for up to $200 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: MacBook Pros... Read more
Save up to $300 on 15″ 2.2GHz MacBook Pros
B&H Photo has the 15″ 2.2GHz MacBook Pro available for $200 off MSRP including free shipping plus NY & NJ sales tax only: – 15″ 2.2GHz MacBook Pro (MJLQ2LL/A): $1799 $200 off MSRP Amazon.com... Read more
Save up to $180 with Apple Certified Refurbis...
Apple has Certified Refurbished 2017 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.8GHz/8GB/128GB MacBook Air (... Read more
Black Friday deals on Apple Macs now live at...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP for Black Friday week. Shipping is free. Note that stock of some Macs may come and go during the week, so... Read more
Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more

Jobs Board

*Apple* Professional Learning Specialist - A...
# Apple Professional Learning Specialist Job Number: 112953711 Houston, Texas, United States Posted: 07-Sep-2017 Weekly Hours: 40.00 **Job Summary** The Apple 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
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* Pro/Consumer Apps Support Engineer -...
…exemplify AppleCare's expert technical support paired with exceptional customer service for Apple 's software apps. This person is a problem solver, who understands Read more
Partner Marketing Manager, *Apple* Pay - Ap...
Job Summary The Apple Pay partner marketing team is looking for a Marketing Manager to develop and drive US programs. The right candidate will be passionate about Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.