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These APIs don't create OpenGL content, they manage content, direct it to a drawing destination, and control various aspects of the rendering operation.

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. 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. 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. 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.

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. X11 for OS X is available as an optional installation.

It's not shown in Figure This document does not show how to use these libraries. 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. 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. 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. 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.

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. 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. 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. 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.

The logical flow of data from an application through OpenGL to a drawable object is shown in Figure 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. 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. 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 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 The green rectangles are drawn to point out each virtual screen. Issue 1 arrived on March 3, Full archives and easy navigation for your pleasure.

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These infrequent sponsored emails help us to provide our Xpresso newsletter for free. Your application must handle these changes and adjust how it uses OpenGL. 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.

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. Higher resolution textures, detailed models, and more complex lighting and shading algorithms can improve image quality.

Critical Mac terminology is defined in that chapter as well as in the Glossary. 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.

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. Rost, is an excellent guide for those who want to write programs that compute surface properties also known as shaders.