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 */