June 93 - GRAPHICAL TRUFFLES
FOUR COMMON GRAPHICS ANSWERS
QuickDraw regions were almost lost when Bill Atkinson crashed his car and nearly killed himself.
Considering that Steve Wozniak also crashed his airplane, crashing must be a hallmark of Apple
genius. I'm no Macintosh wizard, though I did crash my car once. To aid and abet other non-
wizards, I'll divulge four cool answers that apply to nearly any QuickDraw question:
- Check the graphics state.
- Check the QuickDraw version.
- Do it off-screen.
- Use the bottlenecks.
They may not answer your questions completely, but they'll probably get you partway there.
CHECK THE GRAPHICS STATE
Whenever you call a QuickDraw routine, its behavior depends heavily on the state of the machine at
the time of the call: things like the pen size, transfer mode, and color environment all affect the
drawing. Most of the state information QuickDraw depends on can be found in two handy locations
-- the current grafPort and the current GDevice.
The grafPort maintains state information for the pen, the text, and the bitmap (or pixel map) to draw
into. The GDevice defines the color environment, among other things. This information is accessed
by many QuickDraw routines. For example, the LineTo routine draws a line from the current pen
location to the point you pass to the routine, using the current pen size, pattern, and transfer mode;
all these values are fields of the current grafPort. Because most QuickDraw routines use these
"implied" parameters, you can't fully understand the behavior of a QuickDraw routine without
knowing about them.
The current grafPort also defines where your drawing will occur. Even though you call a routine, it
may not draw, because QuickDraw applies a rectangle -- the portRect -- and two regions -- the
visRgn and clipRgn -- to your drawing. No drawing will occur outside the intersection of these
areas. QuickDraw places control of the clipRgn in your hands, first initializing it to be wide open (a
rectangular region that covers the entire QuickDraw coordinate space). If your grafPort is in a
window, control of the visRgn is placed in the hands of the Window Manager. (A region is a truly
marvelous concept, a compact description of strange shapes that can be extended and changed
dynamically. It's a good thing Bill Atkinson survived his crash.)
Let's try applying this first answer to a common QuickDraw question: Why can't you nest calls to
OpenPicture? Well, as you may know, when you call OpenPicture to begin saving picture data, a
handle is created to store the picture information until the corresponding ClosePicture call. This
handle is kept in the picSave field of the current grafPort. If you nest a second OpenPicture call,
where in the grafPort will you store the newly created handle? Answer: There is no place, so you
can't nest OpenPicture calls. Because so many other Managers rely on QuickDraw, this answer will help with questions about
other Managers as a bonus.
CHECK THE QUICKDRAW VERSION
There are currently seven versions of QuickDraw.
You can find out which version is available using Gestalt, and that's usually the most important thing
for your code to know about. But many developers also want to know which machine and system
software combinations produce which versions of QuickDraw. For example, some developers code
for 32-Bit QuickDraw and want to inform their users of the minimum Macintosh machine
requirement. The ROM version, extensions, and system software all combine to affect which version
of QuickDraw is available.
ROM versions of QuickDraw can be neatly categorized into three classes of machines: black and
white, Color QuickDraw, and "ci class." The original Macintosh and the Macintosh 512K, Plus,
Portable, SE, and PowerBook 100 are examples of the black-and-white class. The Macintosh II, IIx,
IIcx, and SE/30 fall into the Color QuickDraw (256K ROM) class. The Macintosh IIci, IIsi, LC II,
IIfx, and later models belong to the ci class (>256K ROM).
Black-and-white class. There are only two common versions of QuickDraw on black-and-white
machines today: original black-and-white QuickDraw and System 7 black-and-white QuickDraw.
(The uncommon ones are present only with pre-Macintosh Plus ROMs or system versions earlier
than 4.2.) When System 7 is installed on a machine of this class, it installs some new routines so that
a few Color QuickDraw routines can be used (you get 1-bit GWorlds, you can correctly display
pictures containing direct-color information, you can create version 2 pictures, and so on).
Black-and-white QuickDraw is documented inInside MacintoshVolumes I and IV. For a
comprehensive list of the routines that System 7 adds to black-and-white QuickDraw, see
"QuickDraw's CopyBits Procedure: Better Than Ever in System 7.0" in develop Issue 6.
Color QuickDraw class. This class of machines has 8-bit Color QuickDraw built into ROM, so it will
always be there regardless of the system version. When these machines are running system versions
earlier than System 7, they can be extended to handle direct color through the use of the 32-Bit
QuickDraw INIT. Finally, if they're running System 7, System 7 Color QuickDraw is available.
Inside MacintoshVolume V describes 8-bit Color QuickDraw. For documentation on the various 32-
Bit QuickDraw versions, including System 7 Color QuickDraw, the best place to look is Inside
Macintosh Volume VI. If you really need to know the differences in capabilities among the versions,
32-Bit QuickDraw v. 1.0 is covered in "Realistic Color for Real-World Applications" in develop Issue
1, and the features added in 32-Bit QuickDraw v. 1.2 are documented in the Tech Note "32-Bit
QuickDraw: Version 1.2 Features."
ci class. This class of machines has only three possible QuickDraw versions. The least common
version, 32-Bit QuickDraw v. 1.01, is found on a IIci running system software version 6.0.4. The
other machines in this class that can run System 6 need at least version 6.0.5, which will patch in 32-
Bit QuickDraw v. 1.2. Finally, System 7 provides its own version of Color QuickDraw.
Again, for documentation on the various 32-Bit QuickDraw versions, including System 7 Color
QuickDraw, seeInside MacintoshVolume VI.
In the GestaltEqu.h header file, you'll find Gestalt values for six QuickDraw versions:
gestaltOriginalQD =0x000,// 1-bit QD
gestalt8BitQD = 0x100,// 8-bit color QD
gestalt32BitQD = 0x200,// 32-bit v1.0
gestalt32BitQD11 =0x210,// 32-bit v1.1
gestalt32BitQD12 =0x220,// 32-bit v1.2
gestalt32BitQD13 =0x230,// 32-bit v1.3
One of these -- gestalt32BitQD11 -- will never be returned, so this list accounts for only five of the
total of seven versions. The sixth is 32-Bit QuickDraw
v. 1.01, mentioned above, which returns the Gestalt value 0x201 but doesn't have a gestalt constant
defined for it. The seventh is System 7 with a black-and-white machine: You'll need to check for
both black-and-white QuickDraw (gestaltOriginalQD) and System 7 (gestaltSystemVersion greater
than or equal to $0700). If both are true, you're running System 7 black-and-white QuickDraw.
That's the only way to tell.
Table 1 shows all the possible combinations, in one handy location.
Table 1Possible Combinations of ROM Versions and System Software Versions
|ROM Class||System Version||Gestalt Value
|7.0 and later||gestaltOriginalQD and gestaltSystemVersion = $0700 or greater
|Color QuickDraw class||Pre-7.0, no INITs||gestalt8BitQD
|6.0.3 or 6.0.4, and||gestalt32BitQD
|32-Bit QuickDraw INIT v. 1.0||
|System 6 from 6.0.5 on, and||gestalt32BitQD12
|32-Bit QuickDraw INIT v. 1.2||
|7.0 and later||gestalt32BitQD13
|ci class||6.0.4||gestalt32BitQD + 1
|System 6 from 6.0.5 on||gestalt32BitQD12
|7.0 and later||gestalt32BitQD13
Exactly which permutations you need to code for depends entirely on what you're doing, but
typically the major divisions are color versus black-and-white, direct color versus indexed color, and
GWorlds versus no GWorlds. Whenever possible, of course, you should make decisions in your code
based on the QuickDraw version rather than on the specific machine configuration.
DO IT OFF-SCREEN
Off-screen environments give you explicit and total control over an image. Since the image and its
associated data structures are no longer tied to a physical device, many of the complexities and
limitations of QuickDraw are reduced, and your hands -- previously tied tightly behind your back --
are now freed. You'll typically manipulate your image off-screen and then use CopyBits to move the
image to the screen. The FX snippet on this issue's CD provides a robust demonstration of some
snazzy CopyBits effects, and there's a nice overview of how to perform animation using off-screen
graphics environments in the Graphical Truffles column ("Animation at a Glance") in develop Issue
Using CopyBits and off-screen environments for speed is covered eloquently in Konstantin Othmer
and Mike Reed's article "Drawing in GWorlds for Speed and Versatility" in develop Issue 10, so I
won't dwell on it here. Also, the Tech Note "Principia Offscreen Graphics Environments" gives
details for creating off-screen environments on machines without 32-Bit QuickDraw (see the
The point is this: when faced with a question in the "How do I . . ." category, try this answer on for
size first. That may be as far as you need to go.
USE THE BOTTLENECKS
QuickDraw routines are easily customizable, which can be incredibly useful; however, this feature is
typically underused. (In fact, most of the Macintosh is customizable. There ought to be a whole
chapter in Inside Macintosh on customization; there are so many places in the OS that you can
intercept, you could probably patch out the whole OS if you were so inclined.) You can replace
QuickDraw's "guts" with viscera of your own design, completely (and reversibly) transforming
Here's one example of how this can be useful: Let's say we want to find out the exact colors used in a
picture that contains innumerable colors. We'll be drawing the picture to an 8-bit color monitor, and
we want to manually select the best 256 colors, replacing the default color table that DrawPicture
uses. There are two methods of getting the colors used in a PICT: use the System 7 Picture Utilities
Package, or do it yourself. The Picture Utilities Package is available only in System 7, so if we want
to run on earlier systems, our only choice is to do it ourselves. We do that by using the bottlenecks.
You can replace all the bottlenecks with no-ops except for a few carefully selected ones, then draw
the picture. Your replacement bottlenecks will be able to watch all the picture data go by and can
keep track, say, of the colors used in the picture. (Two sample programs on the CD,
CollectPictColors and GMundo, demonstrate this technique.) So, for instance, to draw our many-
colored picture with a custom-picked set of 256 colors, we actually have to draw the picture twice:
the first time, we replace the bottlenecks, allowing us to use -- collect, extract, or read -- the colors
in the picture. We can then set up the destination cGrafPort with the colors we want to show,
restore the bottlenecks, and draw the picture again, this time to actually image it into the destination
THAT'S IT FOR NOW When you're faced with a question about QuickDraw, try running through the answers in this
column first, to see if any of them fit. Is the state of the machine at the time of the call different than
you assumed? Did you check the QuickDraw features and version? Can you do it off-screen? Can
you intercept processing at the bottleneck level to customize QuickDraw's routines? It's likely that
one of these answers will help.
- "Graphical Truffles: Animation at a Glance" by Edgar Lee, develop Issue 12.
- "Drawing in GWorlds for Speed and Versatility" by Konstantin Othmer and Mike Reed, develop Issue 10.
- "QuickDraw's CopyBits Procedure: Better Than Ever in System 7.0" by Konstantin Othmer, develop Issue
- "Realistic Color for Real-World Applications" by Bruce Leak, develop Issue 1.
- Inside Macintosh Volume VI (Addison-Wesley, 1991), Chapter 17, "Color QuickDraw."
- Inside Macintosh Volume V (Addison-Wesley, 1988), Chapter 4, "Color QuickDraw."
- Inside Macintosh Volume IV (Addison-Wesley, 1986), Chapter 4, "QuickDraw."
- Inside Macintosh Volume I (Addison-Wesley, 1985), Chapter 6, "QuickDraw."
- Macintosh (Imaging) Technical Notes "Principia Offscreen Graphics Environments" (formerly #120) and
"32-Bit QuickDraw: Version 1.2 Features" (formerly #275).
BILL GUSCHWAN (AppleLink ANGUS) asked Howard Roark to dialog with him: "So, Angus, you ditched med school to
become a protector of the dogcow? I love you, man." Angus: "Well, Howard, as Tori Amos would say, 'Sometimes I hear
my voice and it's been here silent all these years.'" Howard: "You know, I ditched architecture school, not unlike David
Byrne. Speaking of Talking Heads, you got kicked out of one of his concerts because you wanted to dance." Angus:
"Words are very unnecessary, they can only do harm, so I dance." Howard: "Even your idol Wittgenstein went back to
school. What about you?" Angus: "As you know, Howard, even Atlas shrugged." *
Thanks to Edgar Lee, Konstantin Othmer, Brigham Stevens, Forrest Tanaka, and John Wang for reviewing this column. *