Cygwin/X Contributor's Guide
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# Glossary

# B

Bitmap (Win32)

  Windows pixel map.

Bitmap (X)

  X pixel map with bit depth equal to one. X pixel maps of bit depth not equal to one are called pixmaps.

# C

Color Framebuffer Layer
(CFB)

  Deprecated X Server layer providing implementations of the X graphics functions to draw on an antiquated framebuffer device. CFB is optimized to minimize CPU instructions at the expense of additional memory accesses; this does not work well on modern machines because memory access is the system performance bottle neck. CFB can only be initialized to draw on one depth of framebuffer per instantiation; this was done to eliminate CPU instructions that checked the current framebuffer depth, thus saving processing time on early machines.

Colormap
(cmap)

  X Server colormap. Contains a table translating index values to red, green, blue 3-tuples that will be displayed on the screen when a given index value is contained in a bitmap.

# D

Device Dependent X Layer
(DDX)

  X Server layer that depends on the hardware; but not the operating system.

Device Independent X Layer
(DIX)

  X Server layer that does not depend on the hardware layer, nor the operating system.

# F

Framebuffer Layer
(FB)

  X Server layer providing implementations of the X graphics functions to draw on a modern framebuffer device. FB is optimized to minimize memory accesses at the expense of additional CPU instructions; this works well on modern machines because memory access is the system performance bottle neck.

# G

Graphics Context
(GC)

  X Server graphics context. Stores information describing a graphics operation to perform, such as the foreground and background colors, fill style, stipple, and tile.

git
(git)

  git is an open source distributed version control system. More information can be found at the git project homepage.

# M

Machine Independent Layer
(MI)

  X Server layer providing user input and graphics display functions that are independent of the machine used by the DDX layer. The MI drawing functions depend on only three DDX functions: `FillSpans`, `GetSpans`, and `SetSpans`.

# O

Offscreen Framebuffer

  Essentially a bitmap, in the Windows sense, of size and color format that can be displayed on the screen. An offscreen framebuffer may be identical in size and color format to the primary framebuffer, but this is not always required.

OS Layer
(OS)

  X Server layer that depends on the operating system; but not the hardware.

# P

Pixmap

  X pixel map with bit depth not equal to one. X pixel maps of bit depth one are called bitmaps.

Primary Framebuffer

  The block of memory, essentially a bitmap, that describes what is currently being displayed on the screen. Any updates to the primary framebuffer will be displayed on the screen after the next screen refresh.

Privates

  Additional information associated with internal X Server structures, such as colormaps, GCs, pixmaps, or screens.

# S

Screen

  X Server screen. A screen usually corresponds to a display device; however, Cygwin/X's X Server corresponds each screen to one Windows window. A single instance of the Cygwin/X X Server may have several screens.

Shadow

  X Server shadow layer that allows FB to draw to an offscreen framebuffer and occasionally call a DDX function that transfers the updated regions to the screen.

# X

X Display Manager
(XDM)

  An X Display Manager presents a graphical login screen to X users. Often an XDM will allow the user to select a desktop environment or window manager to be for their login session. Some X Display Managers are xdm, gdm (Gnome Display Manager), and kdm (KDE Display Manager).

X Display Manager Control Protocol
(XDMCP)

  XDMCP allows XDM to process logins for users remote to the machine that XDM is running on; login sessions will be run on the machine running XDM. For example, at a university you may use XDMCP to login to an X session running on an engineering department computer from your dorm room.

  See Also: X Display Manager.

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