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In the X Window System, OpenGL rendering is made available as an extension to longer using them for example, when the program is iconi ed. To create a.
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An exception is a pixel buffer pbuffer , which is a GLX drawable but cannot be used for X rendering. Think of a context as a complete description of how to draw what the drawing commands specify. Only one rendering context can be bound to at most one window or pixmap in a given thread.

If a context is bound, it is considered the current context. OpenGL routines do not specify a drawable or rendering context as parameters. Instead, they implicitly affect the current bound drawable using the current rendering context of the calling thread.

Handling Window and Input Events

Resources, in X, are data structures maintained by the server rather than by client programs. Colormaps as well as windows, pixmaps, and fonts are implemented as resources. Rather than keeping information about a window in the client program and sending an entire window data structure from client to server, for instance, window data is stored in the server and given a unique integer ID called an XID. To manipulate or query the window data, the client sends the window's ID number; the server can then perform any requested operation on that window.

This reduces network traffic. Because pixmaps and windows are resources, they are part of the X server and can be shared by different processes or threads. OpenGL contexts are also resources. A colormap maps pixel values from the framebuffer to intensities on the screen. Each pixel value indexes into the colormap to produce intensities of red, green, and blue for display.

Depending on hardware limitations, one or more colormaps may be installed at one time so that windows associated with those maps display with the correct colors. If there is only one colormap, two windows that load colormaps with different values look correct only when they have their particular colormap installed. The X window manager takes care of colormap installation and tries to make sure that the X client with input focus has its colormaps installed.

On all systems, the colormap is a limited resource.

3D Graphics and Animation Programming Tutorial in C/Linux #10 - Vertex shader, add vertices colors

Every X window needs a colormap. In other cases, you may need to assign one. Colormaps are also discussed in detail in O'Reilly, Volume One. This section first describes programming with widgets and with the Xt X Toolkit library, then briefly mentions some other toolkits that facilitate integrating OpenGL with the X Window System. A widget is a piece of a user interface.

It usually makes sense to use one of the standard widget sets.

X Window System

A widget set provides a collection of user interface elements. A widget set may contain, for example, a simple window with scrollbars, a simple dialog with buttons, and so on. A standard widget set allows you to easily provide a common look and feel for your applications. If you use IRIS IM, your application follows the same conventions as other applications on the desktop and becomes easier to learn and to use. This simplicity does not come free; an application that has minimal user interactions incurs a performance penalty over the same application written in Xlib. Widgets are built using Xt, the X Toolkit Intrinsics, a library of routines for creating and using widgets.

OpenGL - Wikipedia

Xt uses a callback-driven programming model. It provides tools for common tasks like input handling and animation and frees you from having to handle a lot of the details of Xlib programming. Note that in most but not all cases, using Xlib is necessary only for colormap manipulation, fonts, and 2D rendering.

The program itself is followed by a brief explanation of the steps involved and a more detailed exploration of the steps to follow during integration and setup of your own program. Figure Display From simplest. Except for window creation and event handling, these steps are actually independent of whether the program uses Xt and Motif or Xlib. XtOpenApplication actually opens the display and performs some additional setup:. See the glXQueryExtension man page for more information. If glXQueryExtension succeeds, use glXQueryVersion to find which version of GLX is being used; an older version of the extension may not be able to do everything your version can do.

The following pseudo code demonstrates checking for the version number:. GLX 1.

In addition to providing a few new functions and a mechanism for using extensions introduced in GLX 1. A visual determines how pixel values are mapped to the screen. To find a visual with the attributes you want, call glXChooseVisual with the desired parameters. The following is the function's format:.

The first two parameters specify the display and screen. Typically, you specify the default screen that is returned by the DefaultScreen macro. The third parameter is a list of the attributes you want your visual to have, specified as an array of integers with the special value None as the final element in the array. Attributes can specify the following:.

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In Example , the only attribute specified is an RGB display:. It is guaranteed to have Boolean attributes matching those specified and integer attributes with values at least as large as those specified.

For detailed information, see the glXChooseVisual man page. The framebuffer capabilities and other attributes of a window are determined statically by the visual used to create it.

For example, to change a window from single-buffer to double-buffer, you have to switch to a different window created with a different visual. Creating a rendering context is the application's responsibility. Therefore, before you can draw anything, you must create a rendering context for OpenGL using glXCreateContext , which has the following function format:.

Direct or indirect rendering. For best performance, always request direct rendering.

An Introduction to OpenGL Programming

The OpenGL implementation automatically switches to indirect rendering when direct rendering is not possible for example, when rendering remotely. After picking a visual and creating a context, you need to create a drawable window or pixmap that uses the chosen visual. If you are working with Xlib, bind the context to the window by calling glXMakeCurrent.

Example is a complete Xlib program and illustrates how the function is used. The call fails if the context and the drawable are mismatched—that is, if they were created with different visuals. A window can become visible only if it is mapped and all its parent windows are mapped. Note that mapping the window is not directly related to binding it to an OpenGL rendering context, but both need to happen if you want to display an OpenGL application. Mapping the window or realizing the widget is not synchronous with the call that performs the action.

When a window is mapped, the window manager makes it visible if no other actions are specified to happen before. For example, some window managers display just an outline of the window instead of the window itself, letting the user position the window. When the user clicks, the window becomes visible.

If a window is mapped but is not yet visible, you may already have set OpenGL state; for example, you may load textures or set colors, but rendering to the window is discarded this includes rendering to a back buffer if you are doing double-buffering. You need to get an Expose event—if using Xlib—or the expose callback before the window is guaranteed to be visible on the screen. Translate This Website. International Translation Network. First Name:. Send Message. As spoken natural language dialog systems technology continues to make great strides, numerous issues regarding dialog processing still need to be res A broad-ranging survey of our current understanding of visual languages and their theoretical foundations.

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