2.2.1. Display Macros

Applications should not directly modify any part of the Display and Screen structures. The members should be considered read-only, although they may change as the result of other operations on the display.

The following lists the C language macros, their corresponding function equivalents that are for other language bindings, and what data they both can return.

AllPlanes

AllPlanes

unsigned long XAllPlanes() 

Both return a value with all bits set to 1 suitable for use in a plane argument to a procedure.

BlackPixel, WhitePixel

Both BlackPixel() and WhitePixel() can be used in implementing a monochrome application. These pixel values are for permanently allocated entries in the default colormap. The actual RGB (red, green, and blue) values are settable on some screens and, in any case, may not actually be black or white. The names are intended to convey the expected relative intensity of the colors.

BlackPixel(display, screen_number)

unsigned long XBlackPixel(display, screen_number)
      Display *display;
      int screen_number;

Both return the black pixel value for the specified screen.

WhitePixel(display, screen_number)

unsigned long XWhitePixel(display, screen_number)
      Display *display;
      int screen_number;

Both return the white pixel value for the specified screen.

ConnectionNumber

ConnectionNumber(display)

int XConnectionNumber(display)
      Display *display;

DefaultColormap(display, screen_number)

Colormap XDefaultColormap(display, screen_number)
      Display *display;
      int screen_number;

Both return the default colormap ID for allocation on the specified screen. Most routine allocations of color should be made out of this colormap.

DefaultDepth

DefaultDepth(display, screen_number)

int XDefaultDepth(display, screen_number)
      Display *display;
      int screen_number;

XListDepths

int *XListDepths(display, screen_number, count_return)
      Display *display;
      int screen_number;
      int *count_return;

The XListDepths() function returns the array of depths that are available on the specified screen. If the specified screen_number is valid and sufficient memory for the array can be allocated, XListDepths() sets count_return to the number of available depths. Otherwise, it does not set count_return and returns NULL. To release the memory allocated for the array of depths, use XFree().

DefaultGC

DefaultGC(display, screen_number)

GC XDefaultGC(display, screen_number)
      Display *display;
      int screen_number;

Both return the default graphics context for the root window of the specified screen. This GC is created for the convenience of simple applications and contains the default GC components with the foreground and background pixel values initialized to the black and white pixels for the screen, respectively. You can modify its contents freely because it is not used in any Xlib function. This GC should never be freed.

DefaultRootWindow

DefaultRootWindow(display)

Window XDefaultRootWindow(display)
      Display *display;

Both return the root window for the default screen.

DefaultScreenOfDisplay

DefaultScreenOfDisplay(display)

Screen *XDefaultScreenOfDisplay(display)
      Display *display;

Both return a pointer to the default screen.

ScreensOfDisplay

ScreenOfDisplay(display, screen_number)

Screen *XScreenOfDisplay(display, screen_number)
      Display *display;
      int screen_number;

Both return a pointer to the indicated screen.

DefaultScreen

DefaultScreen(display)

int XDefaultScreen(display)
      Display *display;

Both return the default screen number referenced by the XOpenDisplay() function. This macro or function should be used to retrieve the screen number in applications that will use only a single screen.

DefaultVisual

DefaultVisual(display, screen_number)

Visual *XDefaultVisual(display, screen_number)
      Display *display;
      int screen_number;

Both return the default visual type for the specified screen. For further information about visual types, see section 3.1.

DisplayCells

DisplayCells(display, screen_number)

int XDisplayCells(display, screen_number)
      Display *display;
      int screen_number;

Both return the number of entries in the default colormap.

DisplayPlanes

DisplayPlanes(display, screen_number)

int XDisplayPlanes(display, screen_number)
      Display *display;
      int screen_number;

Both return the depth of the root window of the specified screen. For an explanation of depth, see the glossary.

DisplayString

DisplayString(display)

char *XDisplayString(display)
      Display *display;

Both return the string that was passed to XOpenDisplay() when the current display was opened. On POSIX-conformant systems, if the passed string was NULL, these return the value of the DISPLAY environment variable when the current display was opened. These are useful to applications that invoke the fork system call and want to open a new connection to the same display from the child process as well as for printing error messages.

XExtendedMaxRequestSize

long XExtendedMaxRequestSize(display)
	Display *display;

The XExtendedMaxRequestSize() function returns zero if the specified display does not support an extended-length protocol encoding; otherwise, it returns the maximum request size (in 4-byte units) supported by the server using the extended-length encoding. The Xlib functions XDrawLines(), XDrawArcs(), XFillPolygon(), XChangeProperty(), XSetClipRectangles(), and XSetRegion() will use the extended-length encoding as necessary, if supported by the server. Use of the extended-length encoding in other Xlib functions (for example, XDrawPoints(), XDrawRectangles(), XDrawSegments(), XFillArcs(), XFillRectangles(), XPutImage()) is permitted but not required; an Xlib implementation may choose to split the data across multiple smaller requests instead.

XMaxRequestSize

long XMaxRequestSize(display)
	Display *display;

The XMaxRequestSize() function returns the maximum request size (in 4-byte units) supported by the server without using an extended-length protocol encoding. Single protocol requests to the server can be no larger than this size unless an extended-length protocol encoding is supported by the server. The protocol guarantees the size to be no smaller than 4096 units (16384 bytes). Xlib automatically breaks data up into multiple protocol requests as necessary for the following functions: XDrawPoints(), XDrawRectangles(), XDrawSegments(), XFillArcs(), XFillRectangles(), and XPutImage().

LastKnownRequestProcessed

LastKnownRequestProcessed(display)

unsigned long XLastKnownRequestProcessed(display)
     Display *display;

Both extract the full serial number of the last request known by Xlib to have been processed by the X server. Xlib automatically sets this number when replies, events, and errors are received.

NextRequest

NextRequest(display)

unsigned long XNextRequest(display)
     Display *display;

Both extract the full serial number that is to be used for the next request. Serial numbers are maintained separately for each display connection.

ProtocolVersion

ProtocolVersion(display)

int XProtocolVersion(display)
      Display *display;

Both return the major version number (11) of the X protocol associated with the connected display.

ProtocolRevision

ProtocolRevision(display)

int XProtocolRevision(display)
      Display *display;

Both return the minor protocol revision number of the X server.

QLength

QLength(display)

int XQLength(display)
      Display *display;

Both return the length of the event queue for the connected display. Note that there may be more events that have not been read into the queue yet (see XEventsQueued()).

RootWindow

RootWindow(display, screen_number)

Window XRootWindow(display, screen_number)
      Display *display;
      int screen_number;

Both return the root window. These are useful with functions that need a drawable of a particular screen and for creating top-level windows.

ScreenCount

ScreenCount(display)

int XScreenCount(display)
      Display *display;

Both return the number of available screens.

ServerVendor

ServerVendor(display)

char *XServerVendor(display)
      Display *display;

Both return a pointer to a null-terminated string that provides some identification of the owner of the X server implementation. If the data returned by the server is in the Latin Portable Character Encoding, then the string is in the Host Portable Character Encoding. Otherwise, the contents of the string are implementation dependent.

VendorRelease

VendorRelease(display)

int XVendorRelease(display)
      Display *display;

Both return a number related to a vendor's release of the X server.

Next: Image Format Functions and Macros