How to run opengl on mac
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: 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.
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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.
Using OpenGL in Mac OS X
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 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 , dragging between displays preserves the same virtual screen. However, Figure 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 , the image quality can be quite different. 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.
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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.
Figure 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 indicate reading pixel data back from the framebuffer.
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. 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.
Using OpenGL in Mac OS X
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. 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. 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. 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. 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. 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.
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. Your application creates an OS X OpenGL rendering context and attaches a rendering target to it known as a drawable object. The drawable object is the final destination for OpenGL drawing commands and is typically associated with a Cocoa window or view.
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. Macs support different types of graphics processors, each with different rendering capabilities, supporting versions of OpenGL from 1.
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. 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.