Win32 console

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Windows PowerShell using the Win32 console window on Windows Vista.
GNU Midnight Commander using box drawing characters in the Win32 console.

Win32 console is a text user interface implementation within the system of Windows API, which runs console applications. A Win32 console has a screen buffer and an input buffer, and is available both as a window or in text mode screen, with switching back and forth available via Alt-Enter keys.

Win32 consoles are typically used for applications that do not need to display images but which might use color. Examples include command line interface tools; command line interpreters such as Windows Command Prompt, Windows PowerShell or Korn shell; file managers such as Far Manager and Midnight Commander; and editors such as the MS-DOS Editor.

Window and full screen modes[edit]

A Win32 console application may run in two modes.

One mode places the text in a window and uses an operating system's font rendering. In this mode, an application's interaction with user is controlled by the windowing system. This is analogous to X Window System applications such as xterm.

In a full screen mode Win32 console uses a hardware text mode and uploads a raster font to the video adapter. This is analogous to a text system console. Full screen uses Windows' built-in VGA driver, rather than any installed graphics drivers, unless another driver is VGA-compatible.[1] Therefore, it only supports VGA-compatible text modes, giving it a maximum character resolution of 80 columns by 28 rows.[2] This contrasts with comparable consoles in various other operating systems such as Linux, which are able to display higher resolutions through different drivers.

An application can be instantly switched between these two modes with Alt- Enter key combination. Text environments in Unix-like systems usually do not have such a feature.

Details[edit]

The input buffer is a queue where events are stored (from keyboard, mouse etc.). The output buffer is a rectangular grid where characters are stored, together with their attributes. A console window may have several output buffers, only one of which is active (i.e. displayed) for a given moment.

The console window may be displayed as a normal window on the desktop, or may be switched to full screen to use the actual hardware text mode, if a video driver permits a chosen screen size. Unfortunately, the display mode is locked in background intensity mode, thus blinking does not work. Also, the underscore attribute is not available.

Programs may access a Win32 console either via high-level functions (such as ReadConsole and WriteConsole) or via low-level functions (e.g. ReadConsoleInput and WriteConsoleOutput). These high-level functions are more limited than a Win32 GUI; for instance it is not possible for a program to change the color palette, nor is it possible to modify the font used by the console using these functions.[3]

Win32 console applications are often mistaken for MS-DOS applications, especially on Windows 9x and Windows Me. However, a Win32 Console application is, virtually, just a special form of a native Win32 application. Indeed, 32-bit Windows can run MS-DOS programs in Win32 console through the use of the NT Virtual DOS Machine (NTVDM).

In earlier versions of Windows, there was no native support for consoles. Since Windows 3.1 and earlier was merely a graphical interface for MS-DOS, most text applications that ran on earlier Windows versions were actually MS-DOS applications running in "DOS boxes". To simplify the task of porting applications to Windows, early versions of Visual C++ were supplied with QuickWin, a library that implemented basic console functionality inside a regular window (a similar library for Borland C++ was called EasyWin).

Implementations[edit]

Windows 9x and Me[edit]

Windows 95/98/Me support is relatively poor compared to Windows NT, because the console window runs in the system virtual DOS machine and so keyboard input to a Win32 console application had to be directed to it by conagent.exe running in a DOS VM that are also used for real DOS applications by hooking the keyboard interrupt. conagent.exe then calls Vcond (which is a VxD). Vcond then had to pass the keyboard input to the System VM, and then finally to the Win32 console application. Besides performance, another problem with this implementation is that drives that are local to a DOS VM are not visible to a Win32 console application. This can cause confusion.

Under Windows 95/98/Me, the screen buffer mirrors the structure of VGA text buffer, with two bytes per character cell: one byte for character code, one byte for attributes (the character must be in OEM character set, the attribute is with high-intensity background/no blinking). This speeds up operation considerably if the actual VGA text mode is used.

Windows NT and CE based[edit]

The Client/Server Runtime Subsystem is responsible for Win32 console windows on Windows NT based operating systems.[4]

Under Windows NT and CE based versions of Windows, the screen buffer uses four bytes per character cell: two bytes for character code, two bytes for attributes. The character is then encoded in a 16-bit subset of Unicode (UCS-2).[5] For backward compatibility, the console APIs exist in two versions: Unicode and non-Unicode. The non-Unicode versions of APIs can use code page switching to extend the range of displayed characters (but only if TrueType fonts are used for the console window, thereby extending the range of codes available). Even UTF-8 is available as "code page 65001".

See also[edit]

Notes[edit]

  1. ^ VGA-Compatible Video Miniport Drivers, 2012-10-16, retrieved 2012-11-14 
  2. ^ Julio Sanchez; Maria P. Canton (2003), "VGA Fundamentals, Part II: DOS Graphics", The PC Graphics Handbook (for C++ Programmers) (Book), CRC Press, p. 125, ISBN 0849316782 
  3. ^ A hack is available: SetConsolePalette
  4. ^ Microsoft Security Advisory (930181): Exploit Code Published Affecting Windows Client Server Run-Time Subsystem
  5. ^ "Console Reference". Microsoft. 2009. Retrieved 2010-01-01. 

External links[edit]