Name

Syntax

#include <X11/Xlib.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <X11/extensions/XShm.h>

Bool    XShmQueryExtension(
    Display *display);

Bool XShmQueryVersion(
    Display *display;
    int *major, *minor;
    Bool *pixmaps);

Status XShmPixmapFormat(
    Display *display);

Status XShmAttach(
    Display *display;
    XShmSegmentInfo *shminfo);

Status XShmDetach(
    Display *display;
    XShmSegmentInfo *shminfo);

XImage *XShmCreateImage (
    Display *display;
    Visual *visual;
    unsigned int depth;
    int format;
    char *data;
    XShmSegmentInfo *shminfo;
    unsigned int width, height);

Status XShmPutImage(
    Display *display;
    Drawable d;
    GC gc;
    XImage *image;
    int src_x, src_y, dest_x, dest_y;
    unsigned int width, height;
    bool send_event);

Status XShmGetImage (
    Display *display;
    Drawable d;
    XImage *image;
    int x, y;
    unsigned long plane_mask);

Pixmap XShmCreatePixmap(
        Display *display;
        Drawable d;
        char *data;
    XShmSegmentInfo *shminfo;
    unsigned int width, height, depth);

Status XShmGetEventBase(
    Display *display);

Structures

Events:
typedef struct {
    int type;               /* of event */
    unsigned long serial;   /* # of last request processed by server*/
    Bool send_event;        /* true if this came from a SendEvent request*/
    Display *display;       /* Display the event was read from */
    Drawable drawable;      /* drawable of request */
    int major_code;         /* ShmReqCode */
    int minor_code;         /* X_ShmPutImage */
    ShmSeg shmseg;          /* the ShmSeg used in the request*/
    unsigned long offset;   /* the offset into ShmSeg used in the request*/
} XShmCompletionEvent;
a structure of type XShmSegmentInfo :
typedef struct {
    ShmSeg shmseg;      /* resource id */
    int shmid;          /* kernel id */
    char *shmaddr;      /* address in client */
    Bool readOnly;      /* how the server should attach it */
} XShmSegmentInfo;

Description
XShmQueryExtension   checks to see if the shared memory extensions
are available for the specified display. 
XShmQueryVersion   returns the
version numbers of the extension implementation. Shared memory pixmaps are
supported if the pixmaps argument returns true. 
XShmAttach   tells the server
to attach to your shared memory segment. If all goes well, you will get
a non-zero status, back and your XImage is ready for use. 
XShmDetach   tells
the server to detach from your shared memory segment. 
XShmPutImage   combines
an image in memory with a shape of the specified drawable. If XYBitmap format
is used, the depth must be one, or a “BadMatch” error results. The foreground
pixel in the GC defines the source for the one bits in the image, and the
background pixel defines the source for the zero bits. For XYPixmap and
ZPixmap, the depth must match the depth of the drawable, or a “BadMatch”
error results. 
XShmGetImage   reads image data into a shared memory XImage
where display is the display of interest, drawable is the source drawable,
image is the destination XImage, x and y are offsets within the drawable,
and plane_mask defines which planes are to be read. 
XShmCreateImage   allocates
the memory needed for an XImage structure for the specified display but
does not allocate space for the image itself. 
XShmPixmapFormat   gets the
format for the server. If your application can deal with the server pixmap
data format, a shared memory segment and shminfo structure are created.

XShmCreatePixmap   points to a pixmap which you can manipulate in all of
the usual ways, with the added bonus of being able to edit its contents
directly through the shared memory segment. 
XShmGetEventBase   gets the
completion event value. 

See AlsoMIT-SHM - The MIT Shared Memory Extension