- When using OpenGL on Mac OS X, there are two things to keep in mind: One, you have to link the OpenGL framework. Outside of Xcode, you can pass the -framework flag to the linker: $ gcc -framework OpenGL -o myopenglprogram myopenglprogram.c (Note that this flag only works on OS X.).
- It seems that most of the answers aren't aware of why this question is being asked. Apple’s OpenGL drivers have been basically ignored for five years. They are languishing on an ancient version—4.1—with a few extensions from 4.2 available.
- This is one of the most popular Doom source ports. It is available for DOS, Windows, Linux and Mac OS X, and should build on any POSIX platform which supports SDL. It enhances Doom with things like TCP/IP networking, OpenGL renderer, Heretic support and much more.
- Currently, Mac OS X 10.5 “Leopard” uses the older, more limited OpenGL 2.1 standard, though it’s expected that Mac OS X 10.6 “Snow Leopard,” which comes out in September, will use OpenGL.
Important:OpenGL was deprecated in macOS 10.14. To create high-performance code on GPUs, use the Metal framework instead. See Metal.
You can tell that Apple has an implementation of OpenGL on its platform by looking at the user interface for many of the applications that are installed with OS X. The reflections built into iChat (Figure 1-1) provide one of the more notable examples. The responsiveness of the windows, the instant results of applying an effect in iPhoto, and many other operations in OS X are due to the use of OpenGL. OpenGL is available to all Macintosh applications.
OpenGL for OS X is implemented as a set of frameworks that contain the OpenGL runtime engine and its drawing software. These frameworks use platform-neutral virtual resources to free your programming as much as possible from the underlying graphics hardware. OS X provides a set of application programming interfaces (APIs) that Cocoa applications can use to support OpenGL drawing.
This chapter provides an overview of OpenGL and the interfaces your application uses on the Mac platform to tap into it.
Hardware-accelerated OpenGL window and desktop rendering, limited to using OpenGL for texture composition, has been in use in Mac OS X, in a technology called Quartz Extreme, since Mac OS X v10.2. Quartz 2D Extreme is an enhancement of this feature and more directly comparable to Xgl.
To understand how OpenGL fits into OS X and your application, you should first understand how OpenGL is designed.
OpenGL Implements a Client-Server Model
OpenGL uses a client-server model, as shown in Figure 1-2. When your application calls an OpenGL function, it talks to an OpenGL client. The client delivers drawing commands to an OpenGL server. The nature of the client, the server, and the communication path between them is specific to each implementation of OpenGL. For example, the server and clients could be on different computers, or they could be different processes on the same computer.
A client-server model allows the graphics workload to be divided between the client and the server. For example, all Macintosh computers ship with dedicated graphics hardware that is optimized to perform graphics calculations in parallel. Figure 1-3 shows a common arrangement of CPUs and GPUs. With this hardware configuration, the OpenGL client executes on the CPU and the server executes on the GPU.
OpenGL Commands Can Be Executed Asynchronously
A benefit of the OpenGL client-server model is that the client can return control to the application before the command has finished executing. An OpenGL client may also buffer or delay execution of OpenGL commands. If OpenGL required all commands to complete before returning control to the application, then either the CPU or the GPU would be idle waiting for the other to provide it data, resulting in reduced performance.
Some OpenGL commands implicitly or explicitly require the client to wait until some or all previously submitted commands have completed. OpenGL applications should be designed to reduce the frequency of client-server synchronizations. See OpenGL Application Design Strategies for more information on how to design your OpenGL application.
OpenGL Commands Are Executed In Order
OpenGL guarantees that commands are executed in the order they are received by OpenGL.
OpenGL Copies Client Data at Call-Time
When an application calls an OpenGL function, the OpenGL client copies any data provided in the parameters before returning control to the application. For example, if a parameter points at an array of vertex data stored in application memory, OpenGL must copy that data before returning. Therefore, an application is free to change memory it owns regardless of calls it makes to OpenGL.
The data that the client copies is often reformatted before it is transmitted to the server. Copying, modifying, and transmitting parameters to the server adds overhead to calling OpenGL. Applications should be designed to minimize copy overhead.
OpenGL Relies on Platform-Specific Libraries For Critical Functionality
OpenGL provides a rich set of cross-platform drawing commands, but does not define functions to interact with an operating system’s graphics subsystem. Instead, OpenGL expects each implementation to define an interface to create rendering contexts and associate them with the graphics subsystem. A rendering context holds all of the data stored in the OpenGL state machine. Allowing multiple contexts allows the state in one machine to be changed by an application without affecting other contexts.
Associating OpenGL with the graphic subsystem usually means allowing OpenGL content to be rendered to a specific window. When content is associated with a window, the implementation creates whatever resources are required to allow OpenGL to render and display images.
OpenGL in OS X
OpenGL in OS X implements the OpenGL client-server model using a common OpenGL framework and plug-in drivers. The framework and driver combine to implement the client portion of OpenGL, as shown in Figure 1-4. Dedicated graphics hardware provides the server. Although this is the common scenario, Apple also provides a software renderer implemented entirely on the CPU.
OS X supports a display space that can include multiple dissimilar displays, each driven by different graphics cards with different capabilities. In addition, multiple OpenGL renderers can drive each graphics card. To accommodate this versatility, OpenGL for OS X is segmented into well-defined layers: a window system layer, a framework layer, and a driver layer, as shown in Figure 1-5. This segmentation allows for plug-in interfaces to both the window system layer and the framework layer. Plug-in interfaces offer flexibility in software and hardware configuration without violating the OpenGL standard.
The window system layer is an OS X–specific layer that your application uses to create OpenGL rendering contexts and associate them with the OS X windowing system. The
NSOpenGL classes and Core OpenGL (CGL) API also provide some additional controls for how OpenGL operates on that context. See OpenGL APIs Specific to OS X for more information. Finally, this layer also includes the OpenGL libraries—GL, GLU, and GLUT. (See Apple-Implemented OpenGL Libraries for details.)
The common OpenGL framework layer is the software interface to the graphics hardware. This layer contains Apple's implementation of the OpenGL specification.
The driver layer contains the optional GLD plug-in interface and one or more GLD plug-in drivers, which may have different software and hardware support capabilities. The GLD plug-in interface supports third-party plug-in drivers, allowing third-party hardware vendors to provide drivers optimized to take best advantage of their graphics hardware.
Accessing OpenGL Within Your Application
The programming interfaces that your application calls fall into two categories—those specific to the Macintosh platform and those defined by the OpenGL Working Group. The Apple-specific programming interfaces are what Cocoa applications use to communicate with the OS X windowing system. These APIs don't create OpenGL content, they manage content, direct it to a drawing destination, and control various aspects of the rendering operation. Your application calls the OpenGL APIs to create content. OpenGL routines accept vertex, pixel, and texture data and assemble the data to create an image. The final image resides in a framebuffer, which is presented to the user through the windowing-system specific API.
OpenGL APIs Specific to OS X
OS X offers two easy-to-use APIs that are specific to the Macintosh platform: the
NSOpenGL classes and the CGL API. Throughout this document, these APIs are referred to as the Apple-specific OpenGL APIs.
Cocoa provides many classes specifically for OpenGL:
NSOpenGLContextclass implements a standard OpenGL rendering context.
NSOpenGLPixelFormatclass is used by an application to specify the parameters used to create the OpenGL context.
NSOpenGLViewclass is a subclass of
NSOpenGLPixelFormatto display OpenGL content in a view. Applications that subclass
NSOpenGLViewdo not need to directly subclass
NSOpenGLContext. Applications that need customization or flexibility, can subclass
NSOpenGLLayerclass allows your application to integrate OpenGL drawing with Core Animation.
NSOpenGLPixelBufferclass provides hardware-accelerated offscreen drawing.
The Core OpenGL API (CGL) resides in the OpenGL framework and is used to implement the
NSOpenGL classes. CGL offers the most direct access to system functionality and provides the highest level of graphics performance and control for drawing to the full screen. CGL Reference provides a complete description of this API.
Apple-Implemented OpenGL Libraries
OS X also provides the full suite of graphics libraries that are part of every implementation of OpenGL: GL, GLU, GLUT, and GLX. Two of these—GL and GLU—provide low-level drawing support. The other two—GLUT and GLX—support drawing to the screen.
Your application typically interfaces directly with the core OpenGL library (GL), the OpenGL Utility library (GLU), and the OpenGL Utility Toolkit (GLUT). The GL library provides a low-level modular API that allows you to define graphical objects. It supports the core functions defined by the OpenGL specification. It provides support for two fundamental types of graphics primitives: objects defined by sets of vertices, such as line segments and simple polygons, and objects that are pixel-based images, such as filled rectangles and bitmaps. The GL API does not handle complex custom graphical objects; your application must decompose them into simpler geometries.
The GLU library combines functions from the GL library to support more advanced graphics features. It runs on all conforming implementations of OpenGL. GLU is capable of creating and handling complex polygons (including quartic equations), processing nonuniform rational b-spline curves (NURBs), scaling images, and decomposing a surface to a series of polygons (tessellation).
The GLUT library provides a cross-platform API for performing operations associated with the user windowing environment—displaying and redrawing content, handling events, and so on. It is implemented on most UNIX, Linux, and Windows platforms. Code that you write with GLUT can be reused across multiple platforms. However, such code is constrained by a generic set of user interface elements and event-handling options. This document does not show how to use GLUT. The GLUTBasics sample project shows you how to get started with GLUT.
GLX is an OpenGL extension that supports using OpenGL within a window provided by the X Window system. X11 for OS X is available as an optional installation. (It's not shown in Figure 1-6.) See OpenGL Programming for the X Window System, published by Addison Wesley for more information.
This document does not show how to use these libraries. For detailed information, either go to the OpenGL Foundation website http://www.opengl.org or see the most recent version of 'The Red book'—OpenGL Programming Guide, published by Addison Wesley.
There are a number of terms that you’ll want to understand so that you can write code effectively using OpenGL: renderer, renderer attributes, buffer attributes, pixel format objects, rendering contexts, drawable objects, and virtual screens. As an OpenGL programmer, some of these may seem familiar to you. However, understanding the Apple-specific nuances of these terms will help you get the most out of OpenGL on the Macintosh platform.
A renderer is the combination of the hardware and software that OpenGL uses to execute OpenGL commands. The characteristics of the final image depend on the capabilities of the graphics hardware associated with the renderer and the device used to display the image. OS X supports graphics accelerator cards with varying capabilities, as well as a software renderer. It is possible for multiple renderers, each with different capabilities or features, to drive a single set of graphics hardware. To learn how to determine the exact features of a renderer, see Determining the OpenGL Capabilities Supported by the Renderer.
Renderer and Buffer Attributes
Your application uses renderer and buffer attributes to communicate renderer and buffer requirements to OpenGL. The Apple implementation of OpenGL dynamically selects the best renderer for the current rendering task and does so transparently to your application. If your application has very specific rendering requirements and wants to control renderer selection, it can do so by supplying the appropriate renderer attributes. Buffer attributes describe such things as color and depth buffer sizes, and whether the data is stereoscopic or monoscopic.
Renderer and buffer attributes are represented by constants defined in the Apple-specific OpenGL APIs. OpenGL uses the attributes you supply to perform the setup work needed prior to drawing content. Drawing to a Window or View provides a simple example that shows how to use renderer and buffer attributes. Choosing Renderer and Buffer Attributes explains how to choose renderer and buffer attributes to achieve specific rendering goals.
Pixel Format Objects
A pixel format describes the format for pixel data storage in memory. The description includes the number and order of components as well as their names (typically red, blue, green and alpha). It also includes other information, such as whether a pixel contains stencil and depth values. A pixel format object is an opaque data structure that holds a pixel format along with a list of renderers and display devices that satisfy the requirements specified by an application.
Each of the Apple-specific OpenGL APIs defines a pixel format data type and accessor routines that you can use to obtain the information referenced by this object. See Virtual Screens for more information on renderer and display devices.
OpenGL profiles are new in OS X 10.7. An OpenGL profile is a renderer attribute used to request a specific version of the OpenGL specification. When your application provides an OpenGL profile as part of its renderer attributes, it only receives renderers that provide the complete feature set promised by that profile. The render can implement a different version of the OpenGL so long as the version it supplies to your application provides the same functionality that your application requested.
Opengl 4 Mac Os X
A rendering context, or simply context, contains OpenGL state information and objects for your application. State variables include such things as drawing color, the viewing and projection transformations, lighting characteristics, and material properties. State variables are set per context. When your application creates OpenGL objects (for example, textures), these are also associated with the rendering context.
Although your application can maintain more than one context, only one context can be the current context in a thread. The current context is the rendering context that receives OpenGL commands issued by your application.
A drawable object refers to an object allocated by the windowing system that can serve as an OpenGL framebuffer. A drawable object is the destination for OpenGL drawing operations. The behavior of drawable objects is not part of the OpenGL specification, but is defined by the OS X windowing system.
A drawable object can be any of the following: a Cocoa view, offscreen memory, a full-screen graphics device, or a pixel buffer.
Note: A pixel buffer (pbuffer) is an OpenGL buffer designed for hardware-accelerated offscreen drawing and as a source for texturing. An application can render an image into a pixel buffer and then use the pixel buffer as a texture for other OpenGL commands. Although pixel buffers are supported on Apple’s implementation of OpenGL, Apple recommends you use framebuffer objects instead. See Drawing Offscreen for more information on offscreen rendering.
Before OpenGL can draw to a drawable object, the object must be attached to a rendering context. The characteristics of the drawable object narrow the selection of hardware and software specified by the rendering context. Apple’s OpenGL automatically allocates buffers, creates surfaces, and specifies which renderer is the current renderer.
The logical flow of data from an application through OpenGL to a drawable object is shown in Figure 1-7. The application issues OpenGL commands that are sent to the current rendering context. The current context, which contains state information, constrains how the commands are interpreted by the appropriate renderer. The renderer converts the OpenGL primitives to an image in the framebuffer. (See also Running an OpenGL Program in OS X .)
The characteristics and quality of the OpenGL content that the user sees depend on both the renderer and the physical display used to view the content. The combination of renderer and physical display is called a virtual screen. This important concept has implications for any OpenGL application running on OS X.
A simple system, with one graphics card and one physical display, typically has two virtual screens. One virtual screen consists of a hardware-based renderer and the physical display and the other virtual screen consists of a software-based renderer and the physical display. OS X provides a software-based renderer as a fallback. It's possible for your application to decline the use of this fallback. You'll see how in Choosing Renderer and Buffer Attributes.
The green rectangle around the OpenGL image in Figure 1-8 surrounds a virtual screen for a system with one graphics card and one display. Note that a virtual screen is not the physical display, which is why the green rectangle is drawn around the application window that shows the OpenGL content. In this case, it is the renderer provided by the graphics card combined with the characteristics of the display.
Because a virtual screen is not simply the physical display, a system with one display can use more than one virtual screen at a time, as shown in Figure 1-9. The green rectangles are drawn to point out each virtual screen. Imagine that the virtual screen on the right side uses a software-only renderer and that the one on the left uses a hardware-dependent renderer. Although this is a contrived example, it illustrates the point.
It's also possible to have a virtual screen that can represent more than one physical display. The green rectangle in Figure 1-10 is drawn around a virtual screen that spans two physical displays. In this case, the same graphics hardware drives a pair of identical displays. A mirrored display also has a single virtual screen associated with multiple physical displays.
The concept of a virtual screen is particularly important when the user drags an image from one physical screen to another. When this happens, the virtual screen may change, and with it, a number of attributes of the imaging process, such as the current renderer, may change. With the dual-headed graphics card shown in Figure 1-10, dragging between displays preserves the same virtual screen. However, Figure 1-11 shows the case for which two displays represent two unique virtual screens. Not only are the two graphics cards different, but it's possible that the renderer, buffer attributes, and pixel characteristics are different. A change in any of these three items can result in a change in the virtual screen.
When the user drags an image from one display to another, and the virtual screen is the same for both displays, the image quality should appear similar. However, for the case shown in Figure 1-11, the image quality can be quite different.
OpenGL for OS X transparently manages rendering across multiple monitors. A user can drag a window from one monitor to another, even though their display capabilities may be different or they may be driven by dissimilar graphics cards with dissimilar resolutions and color depths.
OpenGL dynamically switches renderers when the virtual screen that contains the majority of the pixels in an OpenGL window changes. When a window is split between multiple virtual screens, the framebuffer is rasterized entirely by the renderer driving the screen that contains the largest segment of the window. The regions of the window on the other virtual screens are drawn by copying the rasterized image. When the entire OpenGL drawable object is displayed on one virtual screen, there is no performance impact from multiple monitor support.
Applications need to track virtual screen changes and, if appropriate, update the current application state to reflect changes in renderer capabilities. See Working with Rendering Contexts.
An offline renderer is one that is not currently associated with a display. For example, a graphics processor might be powered down to conserve power, or there might not be a display hooked up to the graphics card. Offline renderers are not normally visible to your application, but your application can enable them by adding the appropriate renderer attribute. Taking advantage of offline renderers is useful because it gives the user a seamless experience when they plug in or remove displays.
For more information about configuring a context to see offline renderers, see Choosing Renderer and Buffer Attributes. To enable your application to switch to a renderer when a display is attached, see Update the Rendering Context When the Renderer or Geometry Changes.
Running an OpenGL Program in OS X
Figure 1-12 shows the flow of data in an OpenGL program, regardless of the platform that the program runs on.
Per-vertex operations include such things as applying transformation matrices to add perspective or to clip, and applying lighting effects. Per-pixel operations include such things as color conversion and applying blur and distortion effects. Pixels destined for textures are sent to texture assembly, where OpenGL stores textures until it needs to apply them onto an object.
OpenGL rasterizes the processed vertex and pixel data, meaning that the data are converged to create fragments. A fragment encapsulates all the values for a pixel, including color, depth, and sometimes texture values. These values are used during antialiasing and any other calculations needed to fill shapes and to connect vertices.
Per-fragment operations include applying environment effects, depth and stencil testing, and performing other operations such as blending and dithering. Some operations—such as hidden-surface removal—end the processing of a fragment. OpenGL draws fully processed fragments into the appropriate location in the framebuffer.
The dashed arrows in Figure 1-12 indicate reading pixel data back from the framebuffer. They represent operations performed by OpenGL functions such as
So far you've seen how OpenGL operates on any platform. But how do Cocoa applications provide data to the OpenGL for processing? A Mac application must perform these tasks:
Set up a list of buffer and renderer attributes that define the sort of drawing you want to perform. (See Renderer and Buffer Attributes.)
Request the system to create a pixel format object that contains a pixel format that meets the constraints of the buffer and render attributes and a list of all suitable combinations of displays and renderers. (See Pixel Format Objects and Virtual Screens.)
Create a rendering context to hold state information that controls such things as drawing color, view and projection matrices, characteristics of light, and conventions used to pack pixels. When you set up this context, you must provide a pixel format object because the rendering context needs to know the set of virtual screens that can be used for drawing. (See Rendering Contexts.)
Bind a drawable object to the rendering context. The drawable object is what captures the OpenGL drawing sent to that rendering context. (See Drawable Objects.)
Make the rendering context the current context. OpenGL automatically targets the current context. Although your application might have several rendering contexts set up, only the current one is the active one for drawing purposes.
Issue OpenGL drawing commands.
Flush the contents of the rendering context. This causes previously submitted commands to be rendered to the drawable object and displays them to the user.
The tasks described in the first five bullet items are platform-specific. Drawing to a Window or View provides simple examples of how to perform them. As you read other parts of this document, you'll see there are a number of other tasks that, although not mandatory for drawing, are really quite necessary for any application that wants to use OpenGL to perform complex 3D drawing efficiently on a wide variety of Macintosh systems.
Making Great OpenGL Applications on the Macintosh
OpenGL lets you create applications with outstanding graphics performance as well as a great user experience—but neither of these things come for free. Your application performs best when it works with OpenGL rather than against it. With that in mind, here are guidelines you should follow to create high-performance, future-looking OpenGL applications:
Ensure your application runs successfully with offline renderers and multiple graphics cards.
Apple ships many sophisticated hardware configurations. Your application should handle renderer changes seamlessly. You should test your application on a Mac with multiple graphics processors and include tests for attaching and removing displays. For more information on how to implement hot plugging correctly, see Working with Rendering Contexts
Avoid finishing and flushing operations.
Pay particular attention to OpenGL functions that force previously submitted commands to complete. Synchronizing the graphics hardware to the CPU may result in dramatically lower performance. Performance is covered in detail in OpenGL Application Design Strategies.
Use multithreading to improve the performance of your OpenGL application.
Many Macs support multiple simultaneous threads of execution. Your application should take advantage of concurrency. Well-behaved applications can take advantage of concurrency in just a few line of code. See Concurrency and OpenGL.
Use buffer objects to manage your data.
Vertex buffer objects (VBOs) allow OpenGL to manage your application’s vertex data. Using vertex buffer objects gives OpenGL more opportunities to cache vertex data in a format that is friendly to the graphics hardware, improving application performance. For more information see Best Practices for Working with Vertex Data.
Similarly, pixel buffer objects (PBOs) should be used to manage your image data. See Best Practices for Working with Texture Data
Use framebuffer objects (FBOs) when you need to render to offscreen memory.
Framebuffer objects allow your application to create offscreen rendering targets without many of the limitations of platform-dependent interfaces. See Rendering to a Framebuffer Object.
Generate objects before binding them.
Earlier version of OpenGL allowed your applications to create its own object names before binding them. However, you should avoid this. Always use the OpenGL API to generate object names.
Migrate your OpenGL Applications to OpenGL 3.2
The OpenGL 3.2 Core profile provides a clean break from earlier versions of OpenGL in favor of a simpler shader-based pipeline. For better compatibility with future hardware and OS X releases, migrate your applications away from legacy versions of OpenGL. Many of the recommendations listed above are required when your application uses OpenGL 3.2.
Harness the power of Apple’s development tools.
Apple provides many tools that help create OpenGL applications and analyze and tune their performance. Learning how to use these tools helps you create fast, reliable applications. Tuning Your OpenGL Application describes many of these tools.
Important:OpenGL was deprecated in macOS 10.14. To create high-performance code on GPUs, use the Metal framework instead. See Metal.
Important OpenGL was deprecated in macOS 10.14. To create high-performance code on GPUs, use the Metal framework instead. See Metal.
OpenGL is an open, cross-platform graphics standard with broad industry support. OpenGL greatly eases the task of writing real-time 2D or 3D graphics applications by providing a mature, well-documented graphics processing pipeline that supports the abstraction of current and future hardware accelerators.
At a Glance
OpenGL is an excellent choice for graphics development on the Macintosh platform because it offers the following advantages:
Reliable Implementation. The OpenGL client-server model abstracts hardware details and guarantees consistent presentation on any compliant hardware and software configuration. Every implementation of OpenGL adheres to the OpenGL specification and must pass a set of conformance tests.
Performance. Applications can harness the considerable power of the graphics hardware to improve rendering speeds and quality.
Industry acceptance. The specification for OpenGL is controlled by the Khronos Group, an industry consortium whose members include many of the major companies in the computer graphics industry, including Apple. In addition to OpenGL for OS X, there are OpenGL implementations for Windows, Linux, Irix, Solaris, and many game consoles.
OpenGL Is a C-based, Platform-Neutral API
Because OpenGL is a C-based API, it is extremely portable and widely supported. As a C API, it integrates seamlessly with Objective-C based Cocoa applications. OpenGL provides functions your application uses to generate 2D or 3D images. Your application presents the rendered images to the screen or copies them back to its own memory.
The OpenGL specification does not provide a windowing layer of its own. It relies on functions defined by OS X to integrate OpenGL drawing with the windowing system. Your application creates an OS X OpenGL rendering context and attaches a rendering target to it (known as a drawable object). The rendering context manages OpenGL state changes and objects created by calls to the OpenGL API. The drawable object is the final destination for OpenGL drawing commands and is typically associated with a Cocoa window or view.
Different Rendering Destinations Require Different Setup Commands
Depending on whether your application intends to draw OpenGL content to a window, to draw to the entire screen, or to perform offscreen image processing, it takes different steps to create the rendering context and associate it with a drawable object.
Relevant Chapters:Drawing to a Window or View, Drawing to the Full Screen and Drawing Offscreen
OpenGL on Macs Exists in a Heterogenous Environment
Macs support different types of graphics processors, each with different rendering capabilities, supporting versions of OpenGL from 1.x through OpenGL 3.2. When creating a rendering context, your application can accept a broad range of renderers or it can restrict itself to devices with specific capabilities. Once you have a context, you can configure how that context executes OpenGL commands.
OpenGL on the Mac is not only a heterogenous environment, but it is also a dynamic environment. Users can add or remove displays, or take a laptop running on battery power and plug it into a wall. When the graphics environment on the Mac changes, the renderer associated with the context may change. Your application must handle these changes and adjust how it uses OpenGL.
Relevant Chapters:Choosing Renderer and Buffer Attributes, Working with Rendering Contexts, and Determining the OpenGL Capabilities Supported by the Renderer
OpenGL Helps Applications Harness the Power of Graphics Processors
Graphics processors are massively parallelized devices optimized for graphics operations. To access that computing power adds additional overhead because data must move from your application to the GPU over slower internal buses. Accessing the same data simultaneously from both your application and OpenGL is usually restricted. To get great performance in your application, you must carefully design your application to feed data and commands to OpenGL so that the graphics hardware runs in parallel with your application. A poorly tuned application may stall either on the CPU or the GPU waiting for the other to finish processing.
When you are ready to optimize your application’s performance, Apple provides both general-purpose and OpenGL-specific profiling tools that make it easy to learn where your application spends its time.
Relevant Chapters:Optimizing OpenGL for High Resolution, OpenGL on the Mac Platform,OpenGL Application Design Strategies, Best Practices for Working with Vertex Data, Best Practices for Working with Texture Data, Customizing the OpenGL Pipeline with Shaders, and Tuning Your OpenGL Application
Concurrency in OpenGL Applications Requires Additional Effort
Opengl Driver For Mac Os X
Many Macs ship with multiple processors or multiple cores, and future hardware is expected to add more of each. Designing applications to take advantage of multiprocessing is critical. OpenGL places additional restrictions on multithreaded applications. If you intend to add concurrency to an OpenGL application, you must ensure that the application does not access the same context from two different threads at the same time.
Performance Tuning Allows Your Application to Provide an Exceptional User Experience
Once you’ve improved the performance of your OpenGL application and taken advantage of concurrency, put some of the freed processing power to work for you. Higher resolution textures, detailed models, and more complex lighting and shading algorithms can improve image quality. Full-scene antialiasing on modern graphics hardware can eliminate many of the “jaggies” common on lower resolution images.
Relevant Chapters:Customizing the OpenGL Pipeline with Shaders,Techniques for Scene Antialiasing
How to Use This Document
If you have never programmed in OpenGL on the Mac, you should read this book in its entirety, starting with OpenGL on the Mac Platform. Critical Mac terminology is defined in that chapter as well as in the Glossary.
If you already have an OpenGL application running on the Mac, but have not yet updated it for OS X v10.7, read Choosing Renderer and Buffer Attributes to learn how to choose an OpenGL profile for your application.
To find out how to update an existing OpenGL app for high resolution, see Optimizing OpenGL for High Resolution.
Once you have OpenGL content in your application, read OpenGL Application Design Strategies to learn fundamental patterns for implementing high-performance OpenGL applications, and the chapters that follow to learn how to apply those patterns to specific OpenGL problems.
Important: Although this guide describes how to create rendering contexts that support OpenGL 3.2, most code examples and discussion in the rest of the book describe the earlier legacy versions of OpenGL. See Updating an Application to Support the OpenGL 3.2 Core Specification for more information on migrating your application to OpenGL 3.2.
This guide assumes that you have some experience with OpenGL programming, but want to learn how to apply that knowledge to create software for the Mac. Although this guide provides advice on optimizing OpenGL code, it does not provide entry-level information on how to use the OpenGL API. If you are unfamiliar with OpenGL, you should read OpenGL on the Mac Platform to get an overview of OpenGL on the Mac platform, and then read the following OpenGL programming guide and reference documents:
OpenGL Programming Guide, by Dave Shreiner and the Khronos OpenGL Working Group; otherwise known as 'The Red book.”
OpenGL Shading Language, by Randi J. Rost, is an excellent guide for those who want to write programs that compute surface properties (also known as shaders).
OpenGL Reference Pages.
Before reading this document, you should be familiar with Cocoa windows and views as introduced in Window Programming Guide and View Programming Guide.
Keep these reference documents handy as you develop your OpenGL program for OS X:
NSOpenGLView Class Reference, NSOpenGLContext Class Reference, NSOpenGLPixelBuffer Class Reference, and NSOpenGLPixelFormat Class Reference provide a complete description of the classes and methods needed to integrate OpenGL content into a Cocoa application.
CGL Reference describes low-level functions that can be used to create full-screen OpenGL applications.
OpenGL Extensions Guide provides information about OpenGL extensions supported in OS X.
The OpenGL Foundation website, http://www.opengl.org, provides information on OpenGL commands, the Khronos OpenGL Working Group, logo requirements, OpenGL news, and many other topics. It's a site that you'll want to visit regularly. Among the many resources it provides, the following are important reference documents for OpenGL developers:
OpenGL Specification provides detailed information on how an OpenGL implementation is expected to handle each OpenGL command.
OpenGL Reference describes the main OpenGL library.
OpenGL GLU Reference describes the OpenGL Utility Library, which contains convenience functions implemented on top of the OpenGL API.
OpenGL GLUT Reference describes the OpenGL Utility Toolkit, a cross-platform windowing API.
OpenGL API Code and Tutorial Listings provides code examples for fundamental tasks, such as modeling and texture mapping, as well as for advanced techniques, such as high dynamic range rendering (HDRR).