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Finding out about the display

Some simple routines can be used to discover general characteristics of the display. These shall be described in some detail as an introduction to some X concepts.

int DefaultScreen(display)  /* This returns the default screen number; the only */
                             /* one you're likely to use */

int ScreenCount(display)    /* This returns the number of possible screens */ 

int  DefaultDepth()         /* A graphics display can be thought of as overlying  
                              bitplanes where only one bit per plane affects the 
                              color of a pixel. This routine returns the number  
                              of planes used */

unsigned long AllPlanes()   /* The bits in the returned long
                             represent the planes used */

int DisplayPlanes(display, screen_number) /* returns the number of possible planes*/

Colormap DefaultColormap(display, screen_number) /* Information on the current 
                       colors is stored in a table called a colormap */

int DisplayCells(display, screen_number) /* returns number of entries in the  
                                          default colormap */

unsigned long BlackPixel(display, screen_number) /* There are permanently */
unsigned long WhitePixel(display, screen_number) /* allocated entries in  
    the default colormap for black and white. These routines return 
    longs that are used to reference these colors */

GC DefaultGC(display, screen_number)  /* Graphics commands get details about
    the current  foreground color, etc, from a Graphics Context structure.
    This  routine returns the default one */

Window DefaultRootWindow(display)     /* This returns the initial window that
                                       covers the screen */

Visual *DefaultVisual(display,screen_number) /* So that various kinds of hardware 
    can be supported `invisibly', some  hardware-specific information
    is stored in the visual structure*/

int DisplayHeight(display,screen_number)    /* height of display in pixels */

int DisplayWidth(display,screen_number)     /* width of display in pixels */

Tim Love
Mon Mar 11 17:03:18 GMT 1996