TweetFollow Us on Twitter

December 94 - GRAPHICAL TRUFFLES

GRAPHICAL TRUFFLES

A Space-Saving PICT Trick

GUILLERMO A. ORTIZ AND DAVE JOHNSON

[IMAGE Dave_Guillermo.gif]

On the Macintosh, the standard file format for storing images is the PICT format. When pixel maps are stored in PICTs, the color table is always included. If you have a large number of PICTs that all use the same color table, however, it's redundant to have a separate copy of the color table in each PICT. It would be better to strip the color tables out of the PICTs themselves, store only one copy of the color table on disk, and use that color table for all the PICTs. This column describes a simple way to do that.

OF COLOR TABLES AND PICTS
One of the really neat features of the Macintosh and QuickDraw is that the process to store a pixel image in a picture is really simple. The code can be as simple as opening a picture to start PICT recording, doing a CopyBits of a PixMap onto itself, and closing the picture; QuickDraw does the rest.

newPict = OpenPicture(&offRect);
CopyBits(srcPix, srcPix, &offRect, &offRect, 
	srcCopy, nil);
ClosePicture();

Here I use OpenPicture for simplicity, but as pointed out in Inside Macintosh: Imaging With QuickDraw , you should really use OpenCPicture, especially if you want to specify a resolution other than 72 dpi. *

This code works great, but there's a catch: every time you do this, the whole PixMap -- including its color table -- is recorded into the picture. For a PixMap that's 8 bits deep (256 colors), the color table takes a little over 2K. This may not be that big a deal for one or two pictures, but what if you're pressing a CD withthousands of pictures that use the same color table? Suddenly all those embedded color tables add up to a significant chunk of space. For pictures delivered on floppy disks, space may be at even more of a premium, and those extra few kilobytes might matter. Also note that if you create PICTs with multiple calls to CopyBits, a color table is stored witheach PixMap in the picture, making the problem even worse.

LEARNING TO SHARE
More often than not, a series of PICT files will all use the same color table (usually the default color table). In these cases it would be much more economical if we could somehow store only one copy of the color table, and then share it amongall the pictures. As it turns out, doing that is pretty easy. The solution has two parts: first, we need to be able to create PICTs that don't include a color table, and later we need to be able to draw those same PICTs using the appropriate color table, stored separately from the picture.

JUST SAY NIL
The first part of the solution is easy. In a PixMap, the pmTable field contains a handle to a color table. When recording a picture, QuickDraw simply stores the color table specified by the pmTable field into the PICT. But if pmTable is nil, there's no color table to put in the picture, so its size ends up smaller. Only one extra line of code is needed to do this:

// Set PixMap color table handle to nil.
(*srcPix)->pmTable = nil;

Naturally, you'll need to save the color table handle beforehand, and afterward restore it before disposing of the PixMap, so that QuickDraw can dispose of all the pieces correctly. But even more important, you'll use the color table handle to create a 'clut' resource that you can save and that can later be used to draw the PICT with its correct colors. The sample program named CLUTLess, included on this issue's CD, contains the complete code to do this.

In reality, QuickDraw adds more than just a nil color table handle to the picture when the code described above is executed. The reason for this is that some applications assume that PixMaps in a picture always have a color table, and they would die horrible deaths if QuickDraw didn't somehow protect them from themselves. To avoid this problem, QuickDraw stores a color table "stub" into the PICT that it recognizes as such when playing back the picture.

If you simply call DrawPicture to display the "clutless" picture you've made, QuickDraw will see the color table stub and create a color table for the picture on the fly. This color table is a color ramp between the current port's foreground color and its background color -- in most cases this means that you get a grayscale image. (If the foreground color and background color are not black and white, respectively, you'll get a "colorized" image.) Figure 1, which appears along with Figure 2 on the inside back cover of this issue ofdevelop , shows an example of a once-colorful picture drawn this way.

GET IT TOGETHER
To display the image in its original colors, you need to somehow get the saved color table back into the PICT before drawing. You can do this by replacing the QuickDraw low-level routine that's called when a PixMap opcode is found in a picture. This replacement low-level routine will simply add the color table to the PixMap and then let QuickDraw continue on its merry way, doing all the real work of drawing, but with the correct color table in place. Replacing a low-level routine is a standard technique:

void SetNewBitsProc (WindowPtr aWindow, CQDProcs *theProcs)
{
	// Load structure with the standard routines.
	SetStdCProcs(theProcs); 
	// Change the one we want to override.
	theProcs->bitsProc = NewQDBitsProc(AddClutProc);
	// Set our window's port to use them.
	aWindow->grafProcs = theProcs;
}

Our replacement routine first saves the contents of the PixMap's pmTable field so that it can later restore this value before returning. It then puts a handle to the appropriate color table in the pmTable field and calls StdBits to let QuickDraw do the hard work of drawing. Finally, it restores the saved pmTable value in the PixMap. (Note that to be completely bulletproof you might want this routine to check to see if the imageactually needs a color table -- that is, check to make sureit's an indexed image, not direct. In our sample code weknow this routine won't get called with a direct PixMap.)

pascal void AddClutProc (BitMap *src, Rect *srcR, 
					Rect *dstR, short mode, RgnHandle msk) 
{
	CTabHandle	saveCTH;

	// Save color table handle. 
	saveCTH = ((PixMapPtr) src)->pmTable;
	// Put 'clut' resource.
	((PixMapPtr) src)->pmTable = gSharedClut;
	// Let QuickDraw do the work.
	StdBits(src, srcR, dstR, mode, msk); 
	// Restore saved handle and return.
	((PixMapPtr) src)->pmTable = saveCTH;
}

Once the new QDProcs are in place, you can simply call DrawPicture and the correct color table will be inserted on the fly. Figure 2 shows the same PICT as in Figure 1, drawn with the correct color table this time.

BUT WHAT IF . . .
The sample code illustrates the case in which the pictures are being created from PixMaps directly and the color tables are being removed as it happens. But what if the images already exist, and they need to be "postprocessed" in order to strip out the color tables? Using techniques similar to those described above, it's not hard; see this issue's CD for an example.

Another common case might be this: you have a large number of pictures that among them share just a few color tables. To deal with this, you could use a PicComment to store a number in the PICT that will indicate which of the color tables to use for that PICT.

IS IT FOR YOU?
These techniques are probably useful only if you plan to deliver a lot of images that all use the same color table (most likely on a CD). Stripping out the color tables may help you cram more images onto your distribution media or fit a few more images in memory, perhaps allowing for faster redraw (for example, when a sequence of pictures is being used for animation).

Remember that the images thus created will be seen as grayscale (or colorized) images in any application that's not aware it needs to load a separate color table from a resource. But if you find yourself jumping through flaming hoops to try to cram just a few more PICTs on your disk, this may be just the trick you need.


GUILLERMO A. ORTIZ of Apple's Developer Technical Support group left on sabbatical just after completing the first draft of this column, but before he had a chance to write a bio. He left his office chanting his favorite mind-soothing mantra, "Nothing compensates like cash."*

DAVE JOHNSON watched in astonishment recently as a large hawk or falcon of some kind (he's not much of an ornithologist) devoured a freshly killed dove just outside his living room window in San Francisco. Whoa. *

Thanks to Cameron Esfahani, Josh Horwich, and Don Moccia for reviewing this column. *

 
AAPL
$101.63
Apple Inc.
-0.03
MSFT
$46.24
Microsoft Corpora
-0.46
GOOG
$573.10
Google Inc.
-2.52

MacTech Search:
Community Search:

Software Updates via MacUpdate

OS X Yosemite 10.10 DP8 - Developer Prev...
Note: This is a Developer Preview. You must be a registered Apple Mac Developer to download this update. You can also sign up for the free OS X Beta Program to download and preview public beta... Read more
FotoMagico 4.5 - Powerful slideshow crea...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Screenshot Path 1.2.1 - Change the defau...
Screenshot Path lets you change the folder where OS X saves screenshots. Screenshots are saved by default to the user’s desktop. This is handy for the occasional screenshot but those looking to take... Read more
Fantastical 1.3.16 - Create calendar eve...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
GIMP 2.8.14 - Powerful, free image editi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
HoudahSpot 3.9.3 - Advanced front-end fo...
HoudahSpot is an advanced file search tool built upon MacOS X Spotlight. Spotlight unleashed Create detailed queries to locate the exact file you need Narrow down searches. Zero in on files Save... Read more
djay 4.2.3 - Transform your Mac into a f...
djay transforms your Mac into a full-fledged DJ system, allowing you to mix your iTunes music library on a hyper-realistic turntable interface. Perform live, record mixes on-the-go, or enable... Read more
iDefrag 2.2.8 - Disk defragmentation and...
iDefrag helps defragment and optimize your disk for improved performance. Features include: Supports HFS and HFS+ (Mac OS Extended). Supports case sensitive and journaled filesystems. Supports... Read more
Bookends 12.2.3 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Access the power of Bookends directly from Mellel, Nisus Writer Pro, or MS Word (... Read more
Copy 1.47.0410 - Cloud storage and file...
Note: You must first sign up to use Copy (get a 5GB sign-up bonus through our 'Download' link above). Copy lets you sync, protect, and share. Everywhere. Want to bring some files home? No problem!... Read more

Latest Forum Discussions

See All

The Sleeping Prince Review
The Sleeping Prince Review By Jennifer Allen on September 15th, 2014 Our Rating: :: RESTRICTIVE KINGDOM SAVINGUniversal App - Designed for iPhone and iPad The Sleeping Prince looks and feels great to play, but its lack of peril and... | Read more »
It Came From Canada: Terra Battle
In some way or another, most Japanese RPGs owe something to Final Fantasy. But with Terra Battle, the now-common mix of Western medieval fantasy with Eastern anime aesthetic feels earned. After all, its developer, Mistwalker, was founded by the... | Read more »
Five Nights at Freddy’s Review
Five Nights at Freddy’s Review By Rob Thomas on September 15th, 2014 Our Rating: :: FIVE FRIGHTS AT FREDDY'SUniversal App - Designed for iPhone and iPad Can you survive five nights as the new night watchman of Freddy Fazbear’s... | Read more »
Phantom Rift Review
Phantom Rift Review By Nadia Oxford on September 15th, 2014 Our Rating: :: FRIENDLY PHANTOMUniversal App - Designed for iPhone and iPad Despite a snag here and there, Phantom Rift is a well-crafted and imaginative adventure RPG.   | Read more »
Phantom Rift – Tips, Tricks, Strategies,...
Hello, Wanderers: | Read more »
Meet the Newest Character for Temple Run...
Meet the Newest Character for Temple Run 2, from National Geographic Kids’ Action-Adventure Book Posted by Jessica Fisher on September 15th, 2014 [ | Read more »
Battle Riders Review
Battle Riders Review By Jordan Minor on September 15th, 2014 Our Rating: :: UNTWISTED METALUniversal App - Designed for iPhone and iPad BattleRiders has cool car combat, but it could be crazier.   | Read more »
Rapture - World Conquest (Games)
Rapture - World Conquest 1.0.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.0 (iTunes) Description: The End is coming! Bombard the globe with devastating miracles and decimate the enemy civilizations. Guide your... | Read more »
Toonia Jelly: Music Review
Toonia Jelly: Music Review By Amy Solomon on September 15th, 2014 Our Rating: :: CUTE MUSICAL EXPLORATIONUniversal App - Designed for iPhone and iPad Toonia Jelly: Music is a charming exploratory app for young children with a... | Read more »
CounterSpy Review
CounterSpy Review By Lee Hamlet on September 15th, 2014 Our Rating: :: AN EXCELLENT PORTUniversal App - Designed for iPhone and iPad Shaken or stirred, CounterSpy is simply the best stealth action game to sneak its way onto the App... | Read more »

Price Scanner via MacPrices.net

10% off iPhone 6 and 6 Plus Otterbox cases
Get 10% off on popular Otterbox iPhone 6 and iPhone 6 Plus cases at MacMall through September 19th. Use code OTTERBOX10 to see the discount. Read more
15-inch MacBook Pros on sale for up to $125 o...
Amazon has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP including free shipping: - 15″ 2.2GHz Retina MacBook Pro: $1899.99 save $100 - 15″ 2.5GHz Retina MacBook Pro: $2374... Read more
27-inch 3.2GHz iMac on sale for $1698, $101 o...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
More To Making A Larger iPad Than Expanded Sc...
CNET’s Ross Rubin has posted a thoughtful analysis of prospects for a larger display iPad Pro, noting that Microsoft and Samsung currently have the large-display touchscreen tablet category to... Read more
SwiftKey Keyboard Finally Coming To iPhone An...
At the TechCrunch Disrupt event in San Francisco, Swiftkey unveiled the first details about SwiftKey Keyboard for iPhone, iPad & iPod touch. SwiftKey’s philosophy is that you should be able to... Read more
Save $75 on the 16GB iPad mini with Retina Di...
Best Buy has the 16GB iPad mini with Retina Display on sale for $324.99 on their online store for a limited time. Their price is $75 off MSRP, and it’s the lowest price available for this mini.... Read more
21-inch 1.4GHz iMac on sale for $979, $120 of...
B&H Photo has the new 21″ 1.4GHz iMac on sale for $979.99 including free shipping plus NY sales tax only. Their price is $120 off MSRP. B&H will also include free copies of Parallels Desktop... Read more
Apple restocks refurbished 21-inch 1.4GHz iMa...
The Apple Store has restocked Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
13-inch 2.6GHz/256GB Retina MacBook Pro on sa...
Adorama has the 13″ 2.6GHz/256GB Retina MacBook Pro on sale for $1379 including free shipping plus NY & NJ sales tax only. Their price is $120 off MSRP, and it’s the lowest price available for... Read more
Macally iPhone 6 Cases
Macally has introduced a Line of Snap-On Shell Cases, Frame Bumper Cases and a Rugged Protective Case for iPhone 6 with 4.7inch Screen, such as the SNAP case in a variety of brilliant metallic... 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
*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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.