QuickDraw
Encyclopedia
QuickDraw is the 2D graphics
library and associated Application Programming Interface (API)
which is a core part of the classic Apple Macintosh operating system
. It was initially written by Bill Atkinson
and Andy Hertzfeld
. QuickDraw still exists as part of the libraries of Mac OS X
, but has been largely superseded by the more modern Quartz
graphics system. In Mac OS X v10.4
, QuickDraw has been officially deprecated
. In Mac OS X v10.5
applications using QuickDraw cannot make use of the added 64-bit support.
's LisaGraph of the early 1980s and was designed to fit well with the Pascal-based interfaces and development environments of the early Apple
systems. In addition, QuickDraw is a raster graphics
system, which defines the pixel
as its basic unit of graphical information. This is in contrast to vector graphics
systems, where graphics primitives are defined in mathematical terms and rasterized as required to the display resolution. A raster system requires much less processing power however, and was the prevailing paradigm at the time that QuickDraw was developed.
QuickDraw defines a key data structure, the graphics port, or GrafPort. This is a logical drawing area where graphics can be drawn. The most obvious on-screen "object" corresponding to a GrafPort is a window
, but the entire desktop view can be a GrafPort, and off-screen ports can also exist.
The GrafPort defines a coordinate system
. In QuickDraw, this has a resolution of 16 bits, giving 65,536 unique vertical and horizontal locations. These are numbered from -32,767 on the extreme left (or top), to +32,768 on the extreme right (or bottom). A window is usually set up so that the top, left corner of its content area is located at 0,0 in the associated GrafPort . A window's content area does not include the window's frame, drop shadow
or title bar (if any).
QuickDraw coordinates refer to the infinitely thin lines between pixel
locations. An actual pixel is drawn in the space to the immediate right and below the coordinate. This makes it easier for programmers to avoid graphical glitches caused by off-by-one error
s.
On the Macintosh, pixels are square and a GrafPort has a default resolution of 72 pixels per inch, chosen to match conventions established by the printing industry of having 72 points
to the inch.
QuickDraw also contains a number of scaling and mapping functions.
QuickDraw maintains a number of global variable
s per process, chief among these being the current port. This originally simplified the API, since all operations pertain to "the current port", but as the OS has developed, this use of global state has also made QuickDraw much harder to integrate with modern design approaches such as multi-threading
, pre-emptive multitasking and so on. To address these problems, the Carbon
API
(a bridge between Mac OS 9 and OS X) adds additional parameters to some of the routines, allowing for the (opaque) storage of thread information and a new (non-polled) event structure.
Each of these objects (except text) may be drawn using a "pen", which can have any rectangular dimensions, pattern or color. Note that, because the pen is rectangular and axis-aligned, diagonal lines will end up thicker than horizontal or vertical ones. Shapes may be drawn filled or framed, using any pattern or color. A filled Arc forms a wedge. Text may be drawn in any installed font, in a variety of stylistic variations, and at any size and color. Text is scaled in a variety of ways depending on how it is stored - TrueType
fonts will scale smoothly to any size, whereas bitmap fonts do not usually scale well.
An important feature of QuickDraw was support for transfer modes, which governed how a destination pixel value was related to its previous value and the color of the object being drawn.
The set of attributes of the pen and text drawing are associated with the GrafPort.
Regions are a key data structure in QuickDraw. They define an arbitrary set of pixels, rather like a bitmap, but in a compressed form which can be very rapidly manipulated in complex ways. Regions can be combined (union), subtracted (difference), and XORed to form other Regions. They can be used within a GrafPort for clipping
, or drawn filled or framed like any other shape. A series of framed shapes and connected lines may be combined into a Region. A Region need not consist of a contiguous set of pixels - disconnected regions are possible and common. Although regions could allow powerful graphic manipulations they are limited by the current implementation that restricts the maximum region data storage size to a sixteen bit value and so are not practical as a general-purpose drawing composition tool and practical use at high resolution is also restricted. Regions underpin the rest of QuickDraw, permitting clipping to arbitrary shapes, essential for the implementation of multiple overlapping windows. Invented by Bill Atkinson, Regions were patented as a separate invention by Apple.http://patft1.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%25%2FPTO%25%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F4622545
A region is specified (after initial creation) by an opening of the region, drawing various QuickDraw shapes, and closing the region. Hidden routines construct the region as the QuickDraw commands are executed. Bitmaps may also be converted to regions, and bitmaps may be made from regions by "painting" or "filling" the region into a graphics port.
The internal structure of a region, other than the storage length and its bounding rectangle, is opaque - there are no Apple-published documents available, though the mechanism is outlined in the patent. Regions are implemented using both vertical and horizontal compression
. A region is stored as a series of horizontal scan lines ("rasters
"), each of which contains a vertical coordinate followed by a list of horizontal inversion coordinates. Each inversion point can be thought of as toggling inclusion in the region for all the points after it: the first point turns the region on, the second turns it off, and so on. Further compression is achieved by storing each line differentially: each line contains only the differences from the previous line rather than a full set of inversion points. Finally, identical adjacent scan lines are efficiently encoded by simply skipping them. In this way, a commonly used region, the rounded corner rectangle, is efficiently encoded, and complex operations such as region composition and image clipping may be done without requiring either extensive processor cycles or large amounts of memory. (The original systems executing QuickDraw code used processors operating at 8 megahertz clock rates and systems had but 128 kilobytes of writable memory.)
Because regions are bound to a specific orientation, a ninety degree rotation of a region would require both detailed reverse engineering
of the structure and extensive coding. A general rotation is impractical when compared to rotating the original source boundary description and simply creating a new region. However, the API includes conversion routines to and from BitMaps. (Bitmaps may also be rotated using well known methods, but with various degrees of image degradation depending upon angle chosen, the storage and processor cycles available to the operation, and the complexity of the algorithm.)
Apple has recently (in the Carbon API
) defined regions as an opaque structure under some program compilation options.
format.
An entire BitMap (or PixMap, when referring to color images) may be copied from one GrafPort to another, with scaling and clipping. Known as blitting
, or CopyBits, after the name of the function, this operation is the basis for most animation and sprite-like effects on the Mac.
QuickDraw provides a similar blitting function which is designed to implement scrolling within a GrafPort - the image in the port can be shifted to a new location without scaling (but with clipping if desired).
Each graphics primitive operation is vectored through the StdProcs, a series of function pointer
s stored in the GrafPort. This limited polymorphism
permits individual operations to be overridden or replaced by custom functions, allowing printer
drivers to intercept graphics commands and translate them to suitable printer operations. In this way, QuickDraw can be rendered using PostScript
, a fact that enabled the Macintosh to practically invent desktop publishing
.
Similar to a subclass
, the Window data structure began with the associated GrafPort, thus basically making windows exchangeable with any GrafPort. While convenient, this could be a source of programming errors.
development. For the Macintosh it was initially simplified, but then later extended. Originally, QuickDraw GrafPorts only supported a bit depth of 1, that is one bit per pixel, or black and white. This suited the built-in screen of the early Macintosh, with its fixed size of 512×342 pixels. Limited color was supported using a crude planar model, allowing QuickDraw to drive some types of dot-matrix printer that used multi-colored ribbons, but very few applications supported this feature.
In 1987, the Macintosh II
was developed and launched, which was designed as a more conventional three-box design - CPU
, monitor
and keyboard
all separate. Because the monitor was separate, and larger than the original Mac, the video
architecture had to necessarily change. In addition, the Mac II took the Macintosh from black-and-white to full color. Apple also decided at this time to support a seamless desktop spanning multiple monitors, an industry first. Thus Color QuickDraw, a significant extension of the original QuickDraw, was created. The original architecture lacked much provision for expandability, but using a series of hacks, the Apple developers managed to make the addition of color and the new video architecture virtually seamless to both developers and end users.
Color QuickDraw introduced new data structures, including GDevices to represent each attached video card/monitor, and a new color GrafPort (CGrafPort) structure to handle color, as well as PixMaps instead of BitMaps for multiple bits-per-pixel images. One of the hacks for compatibility used here was that the new structure was exactly the same size as the old one, with most data members in the same place, but with additional handles and pointers to color structures in place of the BitMap fields. The upper two bits of the rowBytes field were pressed into use as flags to distinguish a GrafPort from a CGrafPort (they were always zero on old-style GrafPorts because a BitMap could never feasibly be so wide as to ever set these bits). The use of these two high bits would come back to haunt QuickDraw later, as it forced a maximum row width of just 4,096 on 32-bit PixMaps, which became problematic for high-resolution graphics work. Later development (Carbon) eliminated this limitation but was not fully backward compatible. A Palette Manager was also added in Color QuickDraw which managed the arbitration of colors on indexed video devices. Most graphics primitives operations remained either unchanged (but would operate in color), or else new color versions of the black and white APIs were added.
Initially, Color QuickDraw was only capable of operating with 1, 2, 4 and 8-bit video cards, which were all that was available at the time. Soon after however, 24-bit video cards appeared (so-called true color), and QuickDraw was updated again to support up to 32 bits per pixel (in reality, 24 bits, with 8 unused) of color data ("32-Bit QuickDraw"). The architecture always allowed for this however, so no new APIs were necessary. The color data structures themselves allowed a color depth of 1, 2, 4, 8, 15 and 24 bits, yielding 1, 4, 16, 256, 32,768 and 16,777,216 colors respectively, or 4, 16 and 256 scales of grey. QuickDraw took care of managing the resampling of colors to the available color depths of the actual video hardware, or transfer between offscreen image buffers, including optionally dither
ing images down to a lower depth to improve image quality. A set of color sampling utilities were also added so that programmers could generate optimal color palettes for use with indexed video devices.
The architecture of QuickDraw had always allowed the creation of GrafPorts and their associated BitMaps or PixMaps "offscreen", where graphics could be composed in memory without it being visible immediately on the screen. Pixels could be transferred between these offscreen ports and the screen using the QuickDraw blitting function CopyBits. Such offscreen compositing is the workhorse for games and graphics-intensive applications. However, until the advent of 32-Bit QuickDraw, such offscreen worlds had to be created and set up by hand by the programmer within his application, and involving as it did three or more separate and fairly complex data structures (CGrafPort, PixMap and GDevice, and for indexed devices, the color look-up table and its inverse), could be error prone. With 32-Bit QuickDraw, OS support for handling this was added, with the "Offscreen Graphics World" or GWorld. The video buffer (PixMap) of a GWorld could be stored in main memory, or when available in unused parts of video ram where copying to the screen could be optimized for speed by avoiding the need to transfer a large amount of pixel data across the main memory bus.
With the advent of QuickTime
, QuickDraw gained the ability to deal with compressed raster data, such as JPEG
. The QuickTime Image Compression Manager integrated closely with QuickDraw: in particular, image decompression calls were full-fledged QuickDraw drawing calls, and if a picture was being recorded, the compressed data would be saved as part of the picture, for display when the picture was later drawn. The Image Compression Manager also added integration with ColorSync
color matching.
After this, apart from back-end changes to optimize for new processor architectures (PowerPC
), QuickDraw remained largely unchanged throughout the rest of the life of the classic Mac OS. QuickDraw GX
and QuickDraw 3D
shared the QuickDraw name and were able to interoperate with QuickDraw PixMap and picture data structures, but were otherwise completely separate in functionality.
With Mac OS X, QuickDraw became part of the Carbon API
. With the release of Mac OS X 10.4, QuickDraw was officially deprecated.
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
library and associated Application Programming Interface (API)
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
which is a core part of the classic Apple Macintosh operating system
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
. It was initially written by Bill Atkinson
Bill Atkinson
Bill Atkinson is an American computer engineer and photographer. Atkinson worked at Apple Computer from 1978 to 1990. He received his undergraduate degree from the University of California, San Diego, where Apple Macintosh developer Jef Raskin was one of his professors...
and Andy Hertzfeld
Andy Hertzfeld
Andy Hertzfeld is a computer scientist who was a member of the original Apple Macintosh development team during the 1980s. After buying an Apple II in January 1978, he went to work for Apple Computer from August 1979 until March 1984, where he was a designer for the Macintosh system software...
. QuickDraw still exists as part of the libraries of Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, but has been largely superseded by the more modern Quartz
Quartz (graphics layer)
Quartz specifically refers to a pair of Mac OS X technologies, each part of the Core Graphics framework: Quartz 2D and Quartz Compositor. It includes both a 2D renderer in Core Graphics and the composition engine that sends instructions to the graphics card...
graphics system. In Mac OS X v10.4
Mac OS X v10.4
Mac OS X v10.4 Tiger is the fifth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Tiger was released to the public on 29 April 2005 for US$129.95 as the successor to Mac OS X Panther , which had been released 18 months earlier...
, QuickDraw has been officially deprecated
Deprecation
In the process of authoring computer software, its standards or documentation, deprecation is a status applied to software features to indicate that they should be avoided, typically because they have been superseded...
. In Mac OS X v10.5
Mac OS X v10.5
Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...
applications using QuickDraw cannot make use of the added 64-bit support.
Principles of QuickDraw
QuickDraw was grounded in the Apple LisaApple Lisa
The Apple Lisa—also known as the Lisa—is a :personal computer designed by Apple Computer, Inc. during the early 1980s....
's LisaGraph of the early 1980s and was designed to fit well with the Pascal-based interfaces and development environments of the early Apple
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
systems. In addition, QuickDraw is a raster graphics
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...
system, which defines the pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
as its basic unit of graphical information. This is in contrast to vector graphics
Vector graphics
Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
systems, where graphics primitives are defined in mathematical terms and rasterized as required to the display resolution. A raster system requires much less processing power however, and was the prevailing paradigm at the time that QuickDraw was developed.
QuickDraw defines a key data structure, the graphics port, or GrafPort. This is a logical drawing area where graphics can be drawn. The most obvious on-screen "object" corresponding to a GrafPort is a window
Window (computing)
In computing, a window is a visual area containing some kind of user interface. It usually has a rectangular shape that can overlap with the area of other windows...
, but the entire desktop view can be a GrafPort, and off-screen ports can also exist.
The GrafPort defines a coordinate system
Coordinate system
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...
. In QuickDraw, this has a resolution of 16 bits, giving 65,536 unique vertical and horizontal locations. These are numbered from -32,767 on the extreme left (or top), to +32,768 on the extreme right (or bottom). A window is usually set up so that the top, left corner of its content area is located at 0,0 in the associated GrafPort . A window's content area does not include the window's frame, drop shadow
Drop shadow
In computer graphics, a drop shadow is a visual effect consisting of drawing that looks like the shadow of an object, giving the impression that the object is raised above the objects behind it. The drop shadow is often used for elements of a graphical user interface such as windows or menus, and...
or title bar (if any).
QuickDraw coordinates refer to the infinitely thin lines between pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
locations. An actual pixel is drawn in the space to the immediate right and below the coordinate. This makes it easier for programmers to avoid graphical glitches caused by off-by-one error
Off-by-one error
An off-by-one error is a logical error involving the discrete equivalent of a boundary condition. It often occurs in computer programming when an iterative loop iterates one time too many or too few...
s.
On the Macintosh, pixels are square and a GrafPort has a default resolution of 72 pixels per inch, chosen to match conventions established by the printing industry of having 72 points
Point (typography)
In typography, a point is the smallest unit of measure, being a subdivision of the larger pica. It is commonly abbreviated as pt. The point has long been the usual unit for measuring font size and leading and other minute items on a printed page....
to the inch.
QuickDraw also contains a number of scaling and mapping functions.
QuickDraw maintains a number of global variable
Global variable
In computer programming, a global variable is a variable that is accessible in every scope . Interaction mechanisms with global variables are called global environment mechanisms...
s per process, chief among these being the current port. This originally simplified the API, since all operations pertain to "the current port", but as the OS has developed, this use of global state has also made QuickDraw much harder to integrate with modern design approaches such as multi-threading
Thread (computer science)
In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...
, pre-emptive multitasking and so on. To address these problems, the Carbon
Carbon (API)
Carbon is one of Apple Inc.'s procedural application programming interfaces for the Macintosh operating system. It provides C programming language access to Macintosh system services...
API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
(a bridge between Mac OS 9 and OS X) adds additional parameters to some of the routines, allowing for the (opaque) storage of thread information and a new (non-polled) event structure.
Graphics primitives
Everything seen on a classic Mac OS screen is drawn by QuickDraw, but the library itself is quite low level. The primitive objects it can draw are:- Lines
- Rectangles
- Rounded (and oval) cornered rectangles
- Ovals (including circles)
- Arcs (and wedges), both circular and oval
- Polygons (arbitrary closed shapes built from a list of points joined by lines)
- Regions (arbitrary sets of pixels—see below)
- BitmapBitmapIn computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to...
s and Pixmaps - Text
Each of these objects (except text) may be drawn using a "pen", which can have any rectangular dimensions, pattern or color. Note that, because the pen is rectangular and axis-aligned, diagonal lines will end up thicker than horizontal or vertical ones. Shapes may be drawn filled or framed, using any pattern or color. A filled Arc forms a wedge. Text may be drawn in any installed font, in a variety of stylistic variations, and at any size and color. Text is scaled in a variety of ways depending on how it is stored - TrueType
TrueType
TrueType is an outline font standard originally developed by Apple Computer in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript...
fonts will scale smoothly to any size, whereas bitmap fonts do not usually scale well.
An important feature of QuickDraw was support for transfer modes, which governed how a destination pixel value was related to its previous value and the color of the object being drawn.
The set of attributes of the pen and text drawing are associated with the GrafPort.
Regions are a key data structure in QuickDraw. They define an arbitrary set of pixels, rather like a bitmap, but in a compressed form which can be very rapidly manipulated in complex ways. Regions can be combined (union), subtracted (difference), and XORed to form other Regions. They can be used within a GrafPort for clipping
Clipping
-Words:* Clipping , the cutting-out of articles from a paper publication* Clipping , shortening the articulation of a speech sound, usually a vowel* Clipping , the formation of a new word by shortening it, e.g...
, or drawn filled or framed like any other shape. A series of framed shapes and connected lines may be combined into a Region. A Region need not consist of a contiguous set of pixels - disconnected regions are possible and common. Although regions could allow powerful graphic manipulations they are limited by the current implementation that restricts the maximum region data storage size to a sixteen bit value and so are not practical as a general-purpose drawing composition tool and practical use at high resolution is also restricted. Regions underpin the rest of QuickDraw, permitting clipping to arbitrary shapes, essential for the implementation of multiple overlapping windows. Invented by Bill Atkinson, Regions were patented as a separate invention by Apple.http://patft1.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%25%2FPTO%25%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F4622545
A region is specified (after initial creation) by an opening of the region, drawing various QuickDraw shapes, and closing the region. Hidden routines construct the region as the QuickDraw commands are executed. Bitmaps may also be converted to regions, and bitmaps may be made from regions by "painting" or "filling" the region into a graphics port.
The internal structure of a region, other than the storage length and its bounding rectangle, is opaque - there are no Apple-published documents available, though the mechanism is outlined in the patent. Regions are implemented using both vertical and horizontal compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
. A region is stored as a series of horizontal scan lines ("rasters
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...
"), each of which contains a vertical coordinate followed by a list of horizontal inversion coordinates. Each inversion point can be thought of as toggling inclusion in the region for all the points after it: the first point turns the region on, the second turns it off, and so on. Further compression is achieved by storing each line differentially: each line contains only the differences from the previous line rather than a full set of inversion points. Finally, identical adjacent scan lines are efficiently encoded by simply skipping them. In this way, a commonly used region, the rounded corner rectangle, is efficiently encoded, and complex operations such as region composition and image clipping may be done without requiring either extensive processor cycles or large amounts of memory. (The original systems executing QuickDraw code used processors operating at 8 megahertz clock rates and systems had but 128 kilobytes of writable memory.)
Because regions are bound to a specific orientation, a ninety degree rotation of a region would require both detailed reverse engineering
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
of the structure and extensive coding. A general rotation is impractical when compared to rotating the original source boundary description and simply creating a new region. However, the API includes conversion routines to and from BitMaps. (Bitmaps may also be rotated using well known methods, but with various degrees of image degradation depending upon angle chosen, the storage and processor cycles available to the operation, and the complexity of the algorithm.)
Apple has recently (in the Carbon API
Carbon (API)
Carbon is one of Apple Inc.'s procedural application programming interfaces for the Macintosh operating system. It provides C programming language access to Macintosh system services...
) defined regions as an opaque structure under some program compilation options.
Higher level operations
Any series of graphics calls to QuickDraw can be recorded in a structure called a Picture. This can then be saved in memory and "played back" at any time, reproducing the graphics sequence. At playback time the picture may be placed at new coordinates or scaled. A picture can be saved to disk in which form it defines the Apple PICTPICT
PICT is a graphics file format introduced on the original Apple Macintosh computer as its standard metafile format. It allows the interchange of graphics , and some limited text support, between Mac applications, and was the native graphics format of QuickDraw.The original version, PICT 1, was...
format.
An entire BitMap (or PixMap, when referring to color images) may be copied from one GrafPort to another, with scaling and clipping. Known as blitting
Bit blit
Bit BLIT is a computer graphics operation in which several bitmaps are combined into one using a raster operator....
, or CopyBits, after the name of the function, this operation is the basis for most animation and sprite-like effects on the Mac.
QuickDraw provides a similar blitting function which is designed to implement scrolling within a GrafPort - the image in the port can be shifted to a new location without scaling (but with clipping if desired).
Each graphics primitive operation is vectored through the StdProcs, a series of function pointer
Function pointer
A function pointer is a type of pointer in C, C++, D, and other C-like programming languages, and Fortran 2003. When dereferenced, a function pointer can be used to invoke a function and pass it arguments just like a normal function...
s stored in the GrafPort. This limited polymorphism
Polymorphism in object-oriented programming
Subtype polymorphism, almost universally called just polymorphism in the context of object-oriented programming, is the ability to create a variable, a function, or an object that has more than one form. The word derives from the Greek "πολυμορφισμός" meaning "having multiple forms"...
permits individual operations to be overridden or replaced by custom functions, allowing printer
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...
drivers to intercept graphics commands and translate them to suitable printer operations. In this way, QuickDraw can be rendered using PostScript
PostScript
PostScript is a dynamically typed concatenative programming language created by John Warnock and Charles Geschke in 1982. It is best known for its use as a page description language in the electronic and desktop publishing areas. Adobe PostScript 3 is also the worldwide printing and imaging...
, a fact that enabled the Macintosh to practically invent desktop publishing
Desktop publishing
Desktop publishing is the creation of documents using page layout software on a personal computer.The term has been used for publishing at all levels, from small-circulation documents such as local newsletters to books, magazines and newspapers...
.
Similar to a subclass
Inheritance (computer science)
In object-oriented programming , inheritance is a way to reuse code of existing objects, establish a subtype from an existing object, or both, depending upon programming language support...
, the Window data structure began with the associated GrafPort, thus basically making windows exchangeable with any GrafPort. While convenient, this could be a source of programming errors.
History
QuickDraw started life as LisaGraf, as part of the Apple LisaApple Lisa
The Apple Lisa—also known as the Lisa—is a :personal computer designed by Apple Computer, Inc. during the early 1980s....
development. For the Macintosh it was initially simplified, but then later extended. Originally, QuickDraw GrafPorts only supported a bit depth of 1, that is one bit per pixel, or black and white. This suited the built-in screen of the early Macintosh, with its fixed size of 512×342 pixels. Limited color was supported using a crude planar model, allowing QuickDraw to drive some types of dot-matrix printer that used multi-colored ribbons, but very few applications supported this feature.
In 1987, the Macintosh II
Macintosh II
The Apple Macintosh II was the first personal computer model of the Macintosh II series in the Apple Macintosh line and the first Macintosh to support a color display.- History :...
was developed and launched, which was designed as a more conventional three-box design - CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, monitor
Computer display
A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...
and keyboard
Computer keyboard
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
all separate. Because the monitor was separate, and larger than the original Mac, the video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
architecture had to necessarily change. In addition, the Mac II took the Macintosh from black-and-white to full color. Apple also decided at this time to support a seamless desktop spanning multiple monitors, an industry first. Thus Color QuickDraw, a significant extension of the original QuickDraw, was created. The original architecture lacked much provision for expandability, but using a series of hacks, the Apple developers managed to make the addition of color and the new video architecture virtually seamless to both developers and end users.
Color QuickDraw introduced new data structures, including GDevices to represent each attached video card/monitor, and a new color GrafPort (CGrafPort) structure to handle color, as well as PixMaps instead of BitMaps for multiple bits-per-pixel images. One of the hacks for compatibility used here was that the new structure was exactly the same size as the old one, with most data members in the same place, but with additional handles and pointers to color structures in place of the BitMap fields. The upper two bits of the rowBytes field were pressed into use as flags to distinguish a GrafPort from a CGrafPort (they were always zero on old-style GrafPorts because a BitMap could never feasibly be so wide as to ever set these bits). The use of these two high bits would come back to haunt QuickDraw later, as it forced a maximum row width of just 4,096 on 32-bit PixMaps, which became problematic for high-resolution graphics work. Later development (Carbon) eliminated this limitation but was not fully backward compatible. A Palette Manager was also added in Color QuickDraw which managed the arbitration of colors on indexed video devices. Most graphics primitives operations remained either unchanged (but would operate in color), or else new color versions of the black and white APIs were added.
Initially, Color QuickDraw was only capable of operating with 1, 2, 4 and 8-bit video cards, which were all that was available at the time. Soon after however, 24-bit video cards appeared (so-called true color), and QuickDraw was updated again to support up to 32 bits per pixel (in reality, 24 bits, with 8 unused) of color data ("32-Bit QuickDraw"). The architecture always allowed for this however, so no new APIs were necessary. The color data structures themselves allowed a color depth of 1, 2, 4, 8, 15 and 24 bits, yielding 1, 4, 16, 256, 32,768 and 16,777,216 colors respectively, or 4, 16 and 256 scales of grey. QuickDraw took care of managing the resampling of colors to the available color depths of the actual video hardware, or transfer between offscreen image buffers, including optionally dither
Dither
Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images...
ing images down to a lower depth to improve image quality. A set of color sampling utilities were also added so that programmers could generate optimal color palettes for use with indexed video devices.
The architecture of QuickDraw had always allowed the creation of GrafPorts and their associated BitMaps or PixMaps "offscreen", where graphics could be composed in memory without it being visible immediately on the screen. Pixels could be transferred between these offscreen ports and the screen using the QuickDraw blitting function CopyBits. Such offscreen compositing is the workhorse for games and graphics-intensive applications. However, until the advent of 32-Bit QuickDraw, such offscreen worlds had to be created and set up by hand by the programmer within his application, and involving as it did three or more separate and fairly complex data structures (CGrafPort, PixMap and GDevice, and for indexed devices, the color look-up table and its inverse), could be error prone. With 32-Bit QuickDraw, OS support for handling this was added, with the "Offscreen Graphics World" or GWorld. The video buffer (PixMap) of a GWorld could be stored in main memory, or when available in unused parts of video ram where copying to the screen could be optimized for speed by avoiding the need to transfer a large amount of pixel data across the main memory bus.
With the advent of QuickTime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
, QuickDraw gained the ability to deal with compressed raster data, such as JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
. The QuickTime Image Compression Manager integrated closely with QuickDraw: in particular, image decompression calls were full-fledged QuickDraw drawing calls, and if a picture was being recorded, the compressed data would be saved as part of the picture, for display when the picture was later drawn. The Image Compression Manager also added integration with ColorSync
ColorSync
ColorSync is Apple Inc's color management API for the Mac OS and Mac OS X.-Version history:Apple developed the original 1.0 version of ColorSync as a Mac-only architecture, which made it into an operating system release in 1993. In the same year, Apple co-founded the International Color Consortium...
color matching.
After this, apart from back-end changes to optimize for new processor architectures (PowerPC
PowerPC
PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
), QuickDraw remained largely unchanged throughout the rest of the life of the classic Mac OS. QuickDraw GX
QuickDraw GX
QuickDraw GX was a replacement for the QuickDraw 2D graphics engine and Printing Manager inside the "classic" Mac OS. Its underlying drawing platform was a resolution-independent object oriented retained mode system, making it much easier for programmers to perform common tasks...
and QuickDraw 3D
QuickDraw 3D
QuickDraw 3D, or QD3D for short, is a 3D graphics API developed by Apple Inc. starting in 1995, originally for their Macintosh computers, but delivered as a cross-platform system....
shared the QuickDraw name and were able to interoperate with QuickDraw PixMap and picture data structures, but were otherwise completely separate in functionality.
With Mac OS X, QuickDraw became part of the Carbon API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
. With the release of Mac OS X 10.4, QuickDraw was officially deprecated.
External links
- Imaging with QuickDraw - original QuickDraw documentation from developer.apple.com
- QuickDraw Reference - modern QuickDraw documentation from developer.apple.com
- QuickDraw - list of QuickDraw resources from developer.apple.com
- Folklore.org: Macintosh Stories: Round Rects Are Everywhere!, May 1981, story about creating QuickDraw
- MacPaint and Quickdraw source code, Computer History MuseumComputer History MuseumThe Computer History Museum is a museum established in 1996 in Mountain View, California, USA. The Museum is dedicated to preserving and presenting the stories and artifacts of the information age, and exploring the computing revolution and its impact on our lives.-History:The museum's origins...