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:
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 |
| Black-and-white class | Pre-7.0 | gestaltOriginalQD |
| 7.0 and later | gestaltOriginalQD | |
| and | ||
| gestaltSystemVersio | ||
| n = $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 12.
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 discussion above).
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 QuickDraw's functionality.
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 cGrafPort.
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.
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. *