Quartz 2D is a two-dimensional drawing engine accessible in the iOS environment and from all Mac OS X application environments outside of the kernel. You can use the Quartz 2D application programming interface (API) to gain access to features such as path-based drawing, painting with transparency, shading, drawing shadows, transparency layers, color management, anti-aliased rendering, PDF document generation, and PDF metadata access. Whenever possible, Quartz 2D leverages the power of the graphics hardware.
In Mac OS X, Quartz 2D can work with all other graphics and imaging technologies—Core Image, Core Video, OpenGL, and QuickTime. It's possible to create an image in Quartz from a QuickTime graphics importer, using the QuickTime function GraphicsImportCreateCGImage
. See QuickTime Framework Reference for details. Moving Data Between Quartz 2D and Core Image in Mac OS X describes how you can provide images to Core Image, which is a framework that supports image processing.
Under Windows: Run the downloaded installation program, and follow the instructions from the installation wizard. Under Mac OS X: Under Mac OS X 10.4 to 10.8, download this installer (19.5 MB). In both cases, double-click on the downloaded file and run Sweet Home 3D application found in the opened folder. If the system refuses to launch Sweet Home 3D for security reasons, click on its. A/UX; Classic Mac OS. System 1; System 6; System 7; Mac OS 8; Mac OS 9; MkLinux; Outliners. Acta (software) MORE (application) Screen savers. After Dark; Utilities.
Similarly, in iOS, Quartz 2D works with all available graphics and animation technologies, such as Core Animation, OpenGL ES, and the UIKit classes.
The Page
Quartz 2D uses the painter's model for its imaging. In the painter's model, each successive drawing operation applies a layer of 'paint' to an output 'canvas,' often called a page. The paint on the page can be modified by overlaying more paint through additional drawing operations. An object drawn on the page cannot be modified except by overlaying more paint. This model allows you to construct extremely sophisticated images from a small number of powerful primitives.
Figure 1-1 shows how the painter's model works. To get the image in the top part of the figure, the shape on the left was drawn first followed by the solid shape. The solid shape overlays the first shape, obscuring all but the perimeter of the first shape. The shapes are drawn in the opposite order in the bottom of the figure, with the solid shape drawn first. As you can see, in the painter's model the drawing order is important.
The page may be a real sheet of paper (if the output device is a printer); it may be a virtual sheet of paper (if the output device is a PDF file); it may even be a bitmap image. The exact nature of the page depends on the particular graphics context you use.
Drawing Destinations: The Graphics Context
A graphics context is an opaque data type (CGContextRef
) that encapsulates the information Quartz uses to draw images to an output device, such as a PDF file, a bitmap, or a window on a display. The information inside a graphics context includes graphics drawing parameters and a device-specific representation of the paint on the page. All objects in Quartz are drawn to, or contained by, a graphics context.
You can think of a graphics context as a drawing destination, as shown in Figure 1-2. When you draw with Quartz, all device-specific characteristics are contained within the specific type of graphics context you use. In other words, you can draw the same image to a different device simply by providing a different graphics context to the same sequence of Quartz drawing routines. You do not need to perform any device-specific calculations; Quartz does it for you.
These graphics contexts are available to your application:
A bitmap graphics context allows you to paint RGB colors, CMYK colors, or grayscale into a bitmap. A bitmap is a rectangular array (or raster) of pixels, each pixel representing a point in an image. Bitmap images are also called sampled images. See Creating a Bitmap Graphics Context.
A PDF graphics context allows you to create a PDF file. In a PDF file, your drawing is preserved as a sequence of commands. There are some significant differences between PDF files and bitmaps:
PDF files, unlike bitmaps, may contain more than one page.
When you draw a page from a PDF file on a different device, the resulting image is optimized for the display characteristics of that device.
PDF files are resolution independent by nature—the size at which they are drawn can be increased or decreased infinitely without sacrificing image detail. The user-perceived quality of a bitmap image is tied to the resolution at which the bitmap is intended to be viewed.
See Creating a PDF Graphics Context.
A window graphics context is a graphics context that you can use to draw into a window. Note that because Quartz 2D is a graphics engine and not a window management system, you use one of the application frameworks to obtain a graphics context for a window. See Creating a Window Graphics Context in Mac OS X for details.
A layer context (
CGLayerRef
) is an offscreen drawing destination associated with another graphics context. It is designed for optimal performance when drawing the layer to the graphics context that created it. A layer context can be a much better choice for offscreen drawing than a bitmap graphics context. See Core Graphics Layer Drawing.When you want to print in Mac OS X, you send your content to a PostScript graphics context that is managed by the printing framework. See Obtaining a Graphics Context for Printing for more information.
Quartz 2D Opaque Data Types
The Quartz 2D API defines a variety of opaque data types in addition to graphics contexts. Because the API is part of the Core Graphics framework, the data types and the routines that operate on them use the CG prefix.
Quartz 2D creates objects from opaque data types that your application operates on to achieve a particular drawing output. Figure 1-3 shows the sorts of results you can achieve when you apply drawing operations to three of the objects provided by Quartz 2D. For example:
You can rotate and display a PDF page by creating a PDF page object, applying a rotation operation to the graphics context, and asking Quartz 2D to draw the page to a graphics context.
You can draw a pattern by creating a pattern object, defining the shape that makes up the pattern, and setting up Quartz 2D to use the pattern as paint when it draws to a graphics context.
You can fill an area with an axial or radial shading by creating a shading object, providing a function that determines the color at each point in the shading, and then asking Quartz 2D to use the shading as a fill color.
The opaque data types available in Quartz 2D include the following:
CGPathRef
, used for vector graphics to create paths that you fill or stroke. See Paths.CGImageRef
, used to represent bitmap images and bitmap image masks based on sample data that you supply. See Bitmap Images and Image Masks.CGLayerRef
, used to represent a drawing layer that can be used for repeated drawing (such as for backgrounds or patterns) and for offscreen drawing. See Core Graphics Layer DrawingCGPatternRef
, used for repeated drawing. See Patterns.CGShadingRef
andCGGradientRef
, used to paint gradients. See Gradients.CGFunctionRef
, used to define callback functions that take an arbitrary number of floating-point arguments. You use this data type when you create gradients for a shading. See Gradients.CGColorRef
andCGColorSpaceRef
, used to inform Quartz how to interpret color. See Color and Color Spaces.CGImageSourceRef
andCGImageDestinationRef
, which you use to move data into and out of Quartz. See Data Management in Quartz 2D and Image I/O Programming Guide.CGFontRef
, used to draw text. See Text.CGPDFDictionaryRef
,CGPDFObjectRef
,CGPDFPageRef
,CGPDFStream
,CGPDFStringRef
, andCGPDFArrayRef
, which provide access to PDF metadata. See PDF Document Creation, Viewing, and Transforming.CGPDFScannerRef
andCGPDFContentStreamRef
, which parse PDF metadata. See PDF Document Parsing.CGPSConverterRef
, used to convert PostScript to PDF. It is not available in iOS. See PostScript Conversion.
Graphics States
Quartz modifies the results of drawing operations according to the parameters in the current graphics state. The graphics state contains parameters that would otherwise be taken as arguments to drawing routines. Routines that draw to a graphics context consult the graphics state to determine how to render their results. For example, when you call a function to set the fill color, you are modifying a value stored in the current graphics state. Other commonly used elements of the current graphics state include the line width, the current position, and the text font size.
The graphics context contains a stack of graphics states. When Quartz creates a graphics context, the stack is empty. When you save the graphics state, Quartz pushes a copy of the current graphics state onto the stack. When you restore the graphics state, Quartz pops the graphics state off the top of the stack. The popped state becomes the current graphics state.
To save the current graphics state, use the function CGContextSaveGState
to push a copy of the current graphics state onto the stack. To restore a previously saved graphics state, use the function CGContextRestoreGState
Papa panda adventure run mac os. to replace the current graphics state with the graphics state that's on top of the stack.
Note that not all aspects of the current drawing environment are elements of the graphics state. For example, the current path is not considered part of the graphics state and is therefore not saved when you call the function CGContextSaveGState
. The graphics state parameters that are saved when you call this function are listed in Table 1-1.
Parameters | Discussed in this chapter |
---|---|
Current transformation matrix (CTM) | |
Clipping area | |
Line: width, join, cap, dash, miter limit | |
Accuracy of curve estimation (flatness) | |
Anti-aliasing setting | |
Color: fill and stroke settings | |
Alpha value (transparency) | |
Rendering intent | |
Color space: fill and stroke settings | |
Text: font, font size, character spacing, text drawing mode | |
Blend mode | Paths and Bitmap Images and Image Masks |
Quartz 2D Coordinate Systems
A coordinate system, shown in Figure 1-4, defines the range of locations used to express the location and sizes of objects to be drawn on the page. You specify the location and size of graphics in the user-space coordinate system, or, more simply, the user space. Coordinates are defined as floating-point values.
Because different devices have different underlying imaging capabilities, the locations and sizes of graphics must be defined in a device-independent manner. For example, a screen display device might be capable of displaying no more than 96 pixels per inch, while a printer might be capable of displaying 300 pixels per inch. If you define the coordinate system at the device level (in this example, either 96 pixels or 300 pixels), objects drawn in that space cannot be reproduced on other devices without visible distortion. They will appear too large or too small.
Quartz accomplishes device independence with a separate coordinate system—user space—mapping it to the coordinate system of the output device—device space—using the current transformation matrix, or CTM. A matrix is a mathematical construct used to efficiently describe a set of related equations. The current transformation matrix is a particular type of matrix called an affine transform, which maps points from one coordinate space to another by applying translation, rotation, and scaling operations (calculations that move, rotate, and resize a coordinate system).
The current transformation matrix has a secondary purpose: It allows you to transform how objects are drawn. For example, to draw a box rotated by 45 degrees, you rotate the coordinate system of the page (the CTM) before you draw the box. Quartz draws to the output device using the rotated coordinate system.
A point in user space is represented by a coordinate pair (x,y), where x represents the location along the horizontal axis (left and right) and y represents the vertical axis (up and down). The origin of the user coordinate space is the point (0,0). The origin is located at the lower-left corner of the page, as shown in Figure 1-4. In the default coordinate system for Quartz, the x-axis increases as it moves from the left toward the right of the page. The y-axis increases in value as it moves from the bottom toward the top of the page. Antibody (crazyrems) mac os.
Some technologies set up their graphics contexts using a different default coordinate system than the one used by Quartz. Relative to Quartz, such a coordinate system is a modified coordinate system and must be compensated for when performing some Quartz drawing operations. The most common modified coordinate system places the origin in the upper-left corner of the context and changes the y-axis to point towards the bottom of the page. A few places where you might see this specific coordinate system used are the following:
In Mac OS X, a subclass of
NSView
that overrides itsisFlipped
method to returnYES
.In iOS, a drawing context returned by an
UIView
.In iOS, a drawing context created by calling the
UIGraphicsBeginImageContextWithOptions
function.
The reason UIKit returns Quartz drawing contexts with modified coordinate systems is that UIKit uses a different default coordinate convention; it applies the transform to Quartz contexts it creates so that they match its conventions. If your application wants to use the same drawing routines to draw to both a UIView
object and a PDF graphics context (which is created by Quartz and uses the default coordinate system), you need to apply a transform so that the PDF graphics context receives the same modified coordinate system. To do this, apply a transform that translates the origin to the upper-left corner of the PDF context and scales the y-coordinate by -1
.
Using a scaling transform to negate the y-coordinate alters some conventions in Quartz drawing. For example, if you call CGContextDrawImage
to draw an image into the context, the image is modified by the transform when it is drawn into the destination. Similarly, path drawing routines accept parameters that specify whether an arc is drawn in a clockwise or counterclockwise direction in the default coordinate system. If a coordinate system is modified, the result is also modified, as if the image were reflected in a mirror. In Figure 1-5, passing the same parameters into Quartz results in a clockwise arc in the default coordinate system and a counterclockwise arc after the y-coordinate is negated by the transform.
It is up to your application to adjust any Quartz calls it makes to a context that has a transform applied to it. For example, if you want an image or PDF to draw correctly into a graphics context, your application may need to temporarily adjust the CTM of the graphics context. In iOS, if you use a UIImage
object to wrap a CGImage
object you create, you do not need to modify the CTM. The UIImage
object automatically compensates for the modified coordinate system applied by UIKit.
Important: The above discussion is essential to understand if you plan to write applications that directly target Quartz on iOS, but it is not sufficient. On iOS 3.2 and later, when UIKit creates a drawing context for your application, it also makes additional changes to the context to match the default UIKIt conventions. In particular, patterns and shadows, which are not affected by the CTM, are adjusted separately so that their conventions match UIKit's coordinate system. In this case, there is no equivalent mechanism to the CTM that your application can use to change a context created by Quartz to match the behavior for a context provided by UIKit; your application must recognize the what kind of context it is drawing into and adjust its behavior to match the expectations of the context.
Memory Management: Object Ownership
Quartz uses the Core Foundation memory management model, in which objects are reference counted. When created, Core Foundation objects start out with a reference count of 1. You can increment the reference count by calling a function to retain the object, and decrement the reference count by calling a function to release the object. When the reference count is decremented to 0, the object is freed. This model allows objects to safely share references to other objects.
There are a few simple rules to keep in mind:
If you create or copy an object, you own it, and therefore you must release it. That is, in general, if you obtain an object from a function with the words 'Create' or 'Copy' in its name, you must release the object when you're done with it. Otherwise, a memory leak results.
If you obtain an object from a function that does not contain the words 'Create' or 'Copy' in its name, you do not own a reference to the object, and you must not release it. The object will be released by its owner at some point in the future.
If you do not own an object and you need to keep it around, you must retain it and release it when you're done with it. You use the Quartz 2D functions specific to an object to retain and release that object. For example, if you receive a reference to a CGColorspace object, you use the functions
CGColorSpaceRetain
andCGColorSpaceRelease
to retain and release the object as needed. You can also use the Core Foundation functionsCFRetain
andCFRelease
, but you must be careful not to passNULL
to these functions.
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- By R. Scott Thompson
- Published Mar 10, 2006 by Addison-Wesley Professional.
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Description
- Copyright 2006
- Dimensions: 7' x 9-1/4'
- Pages: 352
- Edition: 1st
Cube Physics 2d Mac Os Catalina
- Book
- ISBN-10: 0-321-33663-1
- ISBN-13: 978-0-321-33663-7
Core Graphics is the new graphics framework for Mac OS X. Quartz, the 2D drawing system, and Core Image, which processes both video and still images, are the key new technologies in this framework and provide the tools Mac OS X developers need to create and draw graphics for their applications that target the design-savvy Mac consumer audience. With the evolution of Mac OS X, Apple is phasing out use of its previous graphics framework, QuickDraw, and encouraging all developers to begin using Core Graphics. The model for Quartz is completely unique and entirely different from QuickDraw creating a steep learning curve for all developers moving over. This book is in an introduction and guide to working with Core Graphics, specifically Quartz and Core Image. It carries the developer through the fundamental Quartz models and basic concepts such as drawing, coordinating system basics, virtual paint, and CGContext. Once the fundamentals are covered, author Scott Thompson delves into more advanced topics such as shading, patterns, and manipulating image effects. Practical code examples enhance the discussion and offer Mac developers the information they need to incorporate these powerful graphics into their own Mac OS X Applications.
Sample Content
Online Sample Chapter
Downloadable Sample Chapter
Download the Sample Chapter related to this title.
Table of Contents
Chapter 1: Getting Started 1
Chapter 3: Introduction to Quartz 2D 37
Chapter 5: Transformations 103
Chapter 7: Line Art–Drawing 163
Chapter 9: Importing and Exporting Images 211
Chapter 11: Drawing Text with Quartz 2D 249
Chapter 13: Shadings and Patterns 277
Index: 313
Preface
Untitled Document
Preface
The graphics systems available to Macintosh applications have evolved very quickly over the past few years. Prior to the introduction of Mac OS X, the primary focus of all Macintosh graphics was the QuickDraw graphics library. QuickDraw not only provided the tools that applications needed to draw into their windows, but it also played a role in managing the screen, handling events, and changing the cursor. As the demands placed on the graphics system increased, Apple discovered that a reliance on QuickDraw imparted some limitations to their capability to expand the graphics system. During the transition to Mac OS X, many of QuickDraw's responsibilities migrated to other portions of the system. To handle many of the drawing and screen management tasks, Apple introduced a new graphics system called Quartz. In programming circles, Quartz is also known as Core Graphics.
Quartz not only handles many of the responsibilities of QuickDraw, it is the platform on which many of the innovations in the Mac OS X graphics system are built. For example, Core Graphics has taken over the job of collecting the images of windows and combing them on the screen. In performing this task, it takes advantage of modern graphics hardware to improve performance and introduce features such as translucent windows to the system. The end result is a remarkably flexible graphics system. Quartz allows applications to seamlessly integrate technologies as diverse as the motion graphics of QuickTime and the 3D graphics of OpenGL onto the same screen or even into the same window.
With the introduction of Mac OS X 10.4, Tiger, Apple has deprecated QuickDraw—and that library will not evolve any farther. Applications that only rely on QuickDraw for drawing will not enjoy any innovations Apple makes in the graphics system. Even worse, in the future, applications that rely on QuickDraw may actually pay a performance penalty. Any program that wants to take full advantage of the graphics system on Mac OS X will have to replace their QuickDraw drawing code with a more modern alternative. Apple recommends that application developers replace their QuickDraw graphics code with similar code that uses Quartz 2D.
Quartz 2D is a part of the Core Graphics system. It is a modern graphics library based on the imaging model that Adobe created originally for PostScript printers and later as part of the PDF graphics file format. This is the same imaging model that graphics professionals have used for several years to create the artwork on everything from books and advertisements to application splash screens and on-line games.
The Quartz 2D drawing model allows you to create sophisticated graphics with a simple API. The Quartz 2D imaging model is quite different from the drawing models of other graphics libraries. Its library can draw to many kinds of graphics devices while maximizing the fidelity of the graphics on each device. As a result, developers familiar other graphics libraries such as QuickDraw, GDI from Microsoft Windows, or the graphics portions of X11's XLib face a learning curve when trying to work with the device and resolution independent drawing model in Quartz 2D.
2d Physics Engine
The objective of this book is to present a practical introduction to Quartz 2D. Its aim is to help all programmers understand the Quartz 2D imaging model and make effective use of the library from any application environment. Most importantly, the text compares and contrasts the Quartz 2D imaging model with the pixel-based graphics models of other libraries. While this will be of particular value to developers making the transition from QuickDraw or GDI to Quartz 2D, it also provides valuable insight into how to use Quartz 2D effectively. The hope is that this information will be invaluable to anyone trying to draw graphics using Quartz 2D.
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