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Appendix A. X11 APIs for OpenGL Configuration

Appendix A. X11 APIs for OpenGL Configuration

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• 256MB RAM

• 200MB of available hard disk space

• A built-in display or a display connected to an Apple-supplied video card

When the installation is complete, X11 is launched using the /Applications/

Utilities/X11.app application. In the Application menu, you’ll find the familiar “xterm” application. Xterm will set up the X11 execution environment

for you and makes it easy to launch your X11 applications. If you need more

information on configuring your X11 environment, see Apple’s comprehensive

guide on its website [9].

Like most X11 distributions, the X11 install comes with the Athena and Xt widget sets. If your application uses another widget set (most commercial applications do), you’ll have to do a bit more installation work to configure your Mac.

One of these widget sets, Motif, is quite popular in the commercial X software

world. Motif is a layer above raw X11 that provides a variety of higher-level,

object-oriented (though not C++) rendering widgets. Many large-scale applications use Motif in the Unix world, and a compatible version of Motif for Mac

OS X, called OpenMotif, can be downloaded from the OpenMotif website [20].

This version of OpenMotif requires a complete compile process, however, so

you may prefer to use a precompiled version. IST makes a variety of packaged versions of OpenMotif for many platforms, including an installer .dmg

for OS X. Despite this not being an official Open Group version of OpenMotif,

installing from the disk image is considerably easier than building Motif from

scratch. IST’s version of this packaged OpenMotif can be downloaded from the

company’s website [17].



Building X11 Applications on OS X

Once the software is installed, building your X11 applications on OS X is similar

to building them on any other Unix platform. By definition, this means that your

X11 application builds will look different from standard native OS X application

builds. Specifically, you will be linking against libraries in /usr/lib rather

than specifying frameworks.

Following is a sample makefile from our x11 simple example for an

OpenMotif/OpenGL application on OS X (Tiger):

# Object files

CXXOBJS = main.o oglMotif.o

default: oglMotif

# Compile

$(CXXOBJS): %.o: %.c++



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g++ -g -Wall -I/usr/OpenMotif/include \

-I/usr/X11R6/include -c $< -o $@

# Link

oglMotif: $(CXXOBJS)

g++ -g -o $@ $(CXXOBJS) -L/usr/X11R6/lib \

-L/usr/OpenMotif/lib -lGL -lGLw -lXm -lXt -lX11

clean:

rm -f *.o oglMotif



Note the -I and -L options of the compile and link lines, respectively. They refer

to the default installation directories for both X11 and OpenMotif. Also note the

lack of any -framework options. You cannot mix and match references to the

Mac OS X OpenGL libraries for an X11 application.

As far as the build process goes, X11 on OS X is quite straightforward. It probably will not require many changes for the Mac when bringing applications from

other platforms running Unix.



X11 Color Models

X11 shows its age (or seniority, if you prefer) with the prevalence of color index

rendering. Two X11 color models use color index (or color mapped) rendering:

PseudoColor and DirectColor. PseudoColor is the more common of these two

and represents each pixel in the framebuffer as an index into a single colormap.

DirectColor, by contrast, has a separate color map for red, green, and blue. As

you would expect, each pixel in the framebuffer contains an index for each of

the three color maps.

If you wish to run an application that uses the PseudoColor model, you can

launch X11 in 256-color mode. To do so, select the output tab from the X11.app

preferences pane, and select “256 colors” from the Colors drop-down menu. You

must restart X11.app for this change to take effect.

The TrueColor color model stores a maximum of four color component intensity

values in the framebuffer—one each for red, green, blue, and alpha. Modern

graphics applications typically use this color model.

By default, X11.app is configured to take the color setting from the display. The

display setting is typically millions for 24-bit color. This setting is appropriate

for TrueColor X11 applications.



X11 Color Models



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Appendix B



Glossary



API Acronym for application programming interface. An API is a set of functions, classes, and tokens used to define a particular set of software tools.

OpenGL is an API for graphics.

ARB See OpenGL Architecture Review Board.

Context sharing Reusing resources from one OpenGL context in another

OpenGL context.

Deferred validation The caching or postponement of data or state changes in

OpenGL until these changes are required at drawing time.

Direct memory access A hardware-to-hardware fetching of data. In the context of graphics, it usually entails the GPU fetching data from a region of

specially mapped or reserved host system memory.

Display capture To take over a particular display as part of a full-screen application.

Fragment A collection of all framebuffer state information for a single pixel.

A fragment may have some or all of color, alpha, depth, stencil, and other related data. The data associated with a fragment is defined when the drawable

or surface for the framebuffer containing this fragment is constructed.

Framebuffer A destination buffer to which the results of OpenGL rendering

are written.

Frame rate quantization A description of the artifact observed when analyzing the performance of double-buffered OpenGL windows, where the frame

rate moves between discrete states defined by integer divisors of the monitor refresh rate. For example, a 60Hz monitor refresh may cause a doublebuffered application to run at 60Hz, 30Hz, or 20Hz.

GLSL Acronym for OpenGL Shading Language.

GLX The OpenGL and X-Windows interface layer. The GLX specification

describes how OpenGL contexts and drawables interact with X-Windows

widgets and windows.



281



Immediate mode rendering Rendering with objects passed from the host to

the GPU on a per-frame basis. Compared to retained mode rendering, immediate mode rendering implies more function-calling overhead in each rendering frame in addition to more bus bandwidth used with each frame.

OpenGL Architecture Review Board The standards body that defines which

features, functionality, and APIs appear in core OpenGL versions, extensions,

and associated specifications.

OpenGL Shading Language The high-level shading language employed by

OpenGL.

Red Book The familiar name for the OpenGL programming guide.

Retained mode rendering Rendering with objects already cached on the

GPU. Typically glBind . . . Object calls invoke retained mode rendering.

Display lists are another form of this style of rendering.

Throughput The data transfer rate that an application achieves for a particular form of data over some data path. In graphics, throughput typically refers

to the rate at which data can be transferred from main memory to the graphics processor.

vbl-sync Vertical blanking synchronized is a configuration option of graphics

applications that ties the redrawing of the framebuffer to the refresh rate of

the display device.

Virtualized desktop A single, continuous desktop that may span multiple,

potentially heterogeneous graphics devices. Dragging windows among the

displays attached to these graphics devices is seamless and continuous.



282



Appendix B: Glossary



Appendix C



The Cocoa API for

OpenGL

Configuration in

Leopard,

Mac OS X 10.5



Cocoa, also known as AppKit, is the Objective-C API for writing modern Mac

OS X applications. Cocoa provides a high-level, object-oriented set of classes

and interfaces for the OpenGL subsystem and for user–interface interaction.

Cocoa is the modern successor to the NextStep API from NeXT Computer; the

company’s initials explain the “NS” prefix on all of the class definitions and data

types. Cocoa provides a more object-oriented API than any other option on the

Mac, which is useful for building UIs, handling events, and functioning as an

interface to OpenGL.

We presume you’re reading this appendix with a fundamental understanding of

the Objective-C language and basic Cocoa, so we won’t spend any time reviewing core Cocoa concepts like the Objective-C language, views, actions, outlets,

Interface Builder, and so on. We also assume you’ve already read one of the

many good books on these key background elements of Cocoa. If not, we’ve got

a reference or two for you in Appendix D. In the following sections, we’ll explore two ways of creating a Cocoa-based application: one that relies heavily on

Interface Builder and one that requires more code but yields a bit more flexibility and capability. We’ll also tackle some advanced OpenGL topics concerning

off-screen rendering, context sharing, and more.

This appendix is a repeat of the earlier chapter focused on Cocoa and OpenGL

but with a focus on Leopard. Though all the basic concepts from that chapter

still apply, Leopard does it a bit differently. Because of that, rather than trying

to integrate the two, we’ve broken them into two tracks. If you’re on Tiger or

earlier, read Chapter 8, but if you’re using Leopard, check out this appendix.



283



NSGL



AGL

CGL

CoreGraphics



Figure C-1 AppKit API and Framework in Overall OpenGL Infrastructure on

the Mac



Overview

The AppKit OpenGL API is part of the overall Apple OpenGL infrastructure.

It constitutes a layer above CGL but also has the ability to reach down into

both CGL and lower layers. Figure C-1 shows where the AppKit (also known as

Cocoa or NSGL) API and framework reside relative to other API layers.

The AppKit framework is typically found at /System/Library/Frameworks

but may also be in a path specific to your SDK installation. As with other

APIs, linking against AppKit requires specification of this framework path

(Table C-1).



NSOpenGLView

In this section, we will create an XCode project showing how to create a custom view to handle OpenGL rendering using a Cocoa UI element. This project

will be a foundation project that we will return to when we create other examples with increased functionality throughout this appendix. We’ll begin with the

overall project setup and creation—so launch XCode, and we’ll get started.

Create a new XCode project of type Cocoa Application. This action will create your project, set it to link properly against the Cocoa frameworks, and create

a sample main program from which we’ll begin. If you do not feel like walking

through the steps or would like to see the finished product first, check out the

sample code from our website (www.macopenglbook.com).

Open the Resources folder, and double-click on the MainMenu.nib icon. This

will open the NIB file for this project in Interface Builder. Now switch to Interface Builder.

Table C-1 AppKit Cocoa Headers, Frameworks, and Overview

Framework path

Build flag

Header



284



/System/Library/Frameworks/AppKit.framework

-framework AppKit

#include



Appendix C: The Cocoa API for OpenGL Configuration in Leopard



Figure C-2 Window and NIB Ready to be Edited in Leopard Interface Builder.



In the MainMenu.nib window, double-click on the Window icon, and you’ll

see the window that will be your application window open. Position and scale

it as you like, and you should end up with something like Figure C-2 when

finished.

Next bring up the Library and Inspector tools, both available in the Tools

menu. Navigate to the Inspector icon in the Library window and drag the

custom view out and into our window. Position and scale the view within the

window to suite your tastes. Finally, in the Inspector window, name your

class something sensible, like MyOpenGLView. Your results should look similar

to Figure C-3.

So what did we just do? We told Interface Builder that we wanted to create a

CustomView, arrange it in the window, and name it. We’re trying to get a custom

OpenGL view, specifically the NSOpenGLView class. It provides the integration

between OpenGL and Cocoa. By subclassing it, we become able to customize

many aspects of its behavior, including pixel format selection and context sharing. But we’re getting ahead of ourselves. First we’ve got to get MyOpenGLView

into a form where we can write some code.

We’ll now use Interface Builder to instantiate a default object when the NIB file

is loaded, bind it to our CustomView and create some sample code.

First, let’s create an instance of our class. Return to the Library window and

find the blue cube icon. This stands for an arbitrary object to be instantiated on



NSOpenGLView



285



Figure C-3 Selection, Layout, and Specialization of a CustomView in Interface

Builder



our behalf. Drag that out and into the MainMenu window. Select the blue cube,

and look in the Inspector window. Type in the Class entry the name of our

custom view, MyOpenGLView. This creates a custom object, of our custom view

type in the NIB, and will recreate that when the NIB gets instantiated at runtime.

You should see something like Figure C-4.

Now let’s create the actual headers and code. In Interface Builder go to the

File menu and choose Write Class Files. This will prompt you to create files for

both the header and the source for this view. Accept the defaults, placed within

your project directory. Finally, drag those files into your XCode project and

we’re set to start coding. The final step in this setup operation is to change the

CustomView to derive from NSOpenGLView, the base Cocoa View class for rendering OpenGL content. To do so, open the code you’ve just generated within

XCode, and change the MyOpenGLView.h header so your project and code look

like Figure C-5.

We could have handled all of this setup, configuration, and routing

programmatically—but this book isn’t about Cocoa plumbing, so we’ll stay

at this level for now. In a later section, we’ll explore Cocoa configuration of a



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Appendix C: The Cocoa API for OpenGL Configuration in Leopard



Figure C-4 Create and Bind an Instance of our CustomView



Figure C-5 Custom View Derivation and Project Files in XCode 3.0

NSOpenGLView



287



generic NSView, which allows us a bit more flexibility. For now, switch back to

XCode and we’ll dig into the code.

In XCode, open the file MyOpenGLView.m. We’ll now begin adding methods to

handle key elements of the OpenGL render cycle. We start by adding a method

to select pixel formats. This code performs pixel format selection in three steps:

1. A structure is created containing a list of pixel format configuration

parameters.

2. That structure is passed to an NSOpenGLPixelFormat constructor to create

a new pixel format object.

3. That pixel format object is passed on to the base NSOpenGLView method for

finishing the initialization of this view.

Either add the code yourself to your project or grab it from the sample code

provided in Example C-1. Compile and run the code, and you should have a

window!

Example C-1 Configuration of an OpenGL View in initWithFrame

#include

#include

#include

#import "MyOpenGLView.h"

@implementation MyOpenGLView

- (id) initWithFrame: (NSRect) frame

{

time = 0;

angle = 0;

GLuint attributes[] =

{

NSOpenGLPFAWindow,

// choose among pixelformats capable of rendering to windows

NSOpenGLPFAAccelerated,

// require hardware-accelerated pixelformat

NSOpenGLPFADoubleBuffer,

// require double-buffered pixelformat

NSOpenGLPFAColorSize, 24,

// require 24 bits for color-channels

NSOpenGLPFAAlphaSize, 8,

// require an 8-bit alpha channel

NSOpenGLPFADepthSize, 24,

// require a 24-bit depth buffer

NSOpenGLPFAMinimumPolicy,

// select a pixelformat which meets or exceeds these requirements

0

};



288



Appendix C: The Cocoa API for OpenGL Configuration in Leopard



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