This function specifically supports rudimentary screen dumps.
XImage *XGetImage(display, d, x, y, width, height, plane_mask, format)
        Display *display;
        Drawable d;
        int x, y;
        unsigned int width, height;
        unsigned long plane_mask;
        int format;


display Specifies the connection to the X server.
d Specifies the drawable.
Specify the x and y coordinates, which are relative to the origin of the drawable and define the upper-left corner of the rectangle.
Specify the width and height of the subimage, which define the dimensions of the rectangle.
plane_mask Specifies the plane mask.
format Specifies the format for the image. You can pass XYPixmap or ZPixmap .


The XGetImage() function returns a pointer to an XImage structure. This structure provides you with the contents of the specified rectangle of the drawable in the format you specify. If the format argument is XYPixmap , the image contains only the bit planes you passed to the plane_mask argument. If the plane_mask argument only requests a subset of the planes of the display, the depth of the returned image will be the number of planes requested. If the format argument is ZPixmap , XGetImage() returns as zero the bits in all planes not specified in the plane_mask argument. The function performs no range checking on the values in plane_mask and ignores extraneous bits.

XGetImage() returns the depth of the image to the depth member of the XImage structure. The depth of the image is as specified when the drawable was created, except when getting a subset of the planes in XYPixmap format, when the depth is given by the number of bits set to 1 in plane_mask.

If the drawable is a pixmap, the given rectangle must be wholly contained within the pixmap, or a BadMatch error results. If the drawable is a window, the window must be viewable, and it must be the case that if there were no inferiors or overlapping windows, the specified rectangle of the window would be fully visible on the screen and wholly contained within the outside edges of the window, or a BadMatch error results. Note that the borders of the window can be included and read with this request. If the window has backing-store, the backing-store contents are returned for regions of the window that are obscured by noninferior windows. If the window does not have backing-store, the returned contents of such obscured regions are undefined. The returned contents of visible regions of inferiors of a different depth than the specified window's depth are also undefined. The pointer cursor image is not included in the returned contents. If a problem occurs, XGetImage() returns NULL.

XGetImage() can generate BadDrawable , BadMatch , and BadValue errors.


BadDrawable A value for a Drawable argument does not name a defined Window or Pixmap.
BadMatch An InputOnly window is used as a Drawable.
BadMatch Some argument or pair of arguments has the correct type and range but fails to match in some other way required by the request.
BadValue Some numeric value falls outside the range of values accepted by the request. Unless a specific range is specified for an argument, the full range defined by the argument's type is accepted. Any argument defined as a set of alternatives can generate this error.

See also

XAddPixel(), XCreateImage(), XDestroyImage(), XGetPixel(), XInitImage(), XPutImage(), XPutPixel(), XGetSubImage(), "Transferring Images between Client and Server".
Christophe Tronche, ch@tronche.com