XReadScreen(3)XReadScreen(3)NAMEXReadScreen - returns the displayed colors in a rectangle of the screen
SYNOPSIS
XImage XReadScreen (Display *display, Window w, int x, int y, unsigned
int width, unsigned int height, Bool includeCursor)
Arguments
display
Specifies the connection to the X server.
w Specifies the window from whose screen the data is read.
x, y Specify the X and Y coordinates of the upper-left corner of the
rectangle relative to the origin of the window w.
width, height
Specify the width and height of the rectangle.
includeCursor
Specifies whether the cursor image is to be included in the col‐
ors returned.
DESCRIPTION
This routine provides access to the colors displayed on the screen of
the given window. On some types of advanced display devices, the dis‐
played colors can be a composite of the data contained in several dif‐
ferent frame stores and these frame stores can be of different depth
and visual types.
In addition, there can be overlay/underlay window pairs in which part
of the underlay is visible beneath the overlay. Because the data
returned by XGetImage is undefined for portions of the rectangle that
have different depths, XGetImage is inadequate to return a picture of
the what user is actually seeing on the screen. In addition, XGetImage
cannot composite pixel information for an overlay/underlay window pair
because the pixel information lies in different drawables. XReadScreen
addresses these problems.
Rather than returning pixel information, XReadScreen returns color
information-the actual displayed colors visible on the screen. It
returns the color information from any window within the boundaries of
the specified rectangle. Unlike XGetImage, the returned contents of
visible regions of inferior or overlapping windows of a different depth
than the specified window's depth are not undefined. Instead, the
actual displayed colors for these windows is returned.
Note: The colors returned are the ones that would be displayed if an
unlimited number of hardware color LUTs were available on the screen.
Thus, the colors returned are the theoretical display colors. If col‐
ormap flashing is present on the screen because there aren't enough
hardware color LUTs to display all of the software colormaps simultane‐
ously, the returned colors may be different from the colors that are
actually displayed.
If w is an overlay window, the overlay color information is returned
everywhere there is opaque paint in the specified rectangle. The color
information of the underlay is returned everywhere there is transparent
paint in the overlay. In general, since this underlay can be an over‐
lay window containing transparent paint, the color information for a
coordinate (x, y) which contains transparent paint is the youngest non-
inferior that has opaque paint at (x, y).
The color data is returned as an XImage. The returned image has the
same width and height as the arguments specified. The format of the
image is ZPixmap. The depth of the image is 24 and the bits_per_pixel
is 32. The most significant 8 bits of color information for each color
channel (red, green blue) will be returned in the bit positions defined
by red_mask, green_mask, and blue_mask in the XImage. The values of
the following attributes of the XImage are server dependent:
byte_order, bitmap_unit, bitmap_bit_order, bitmap_pad, bytes_per_line,
red_mask, green_mask, blue_mask.
If includeCursor is True, the cursor image is included in the returned
colors. Otherwise, it is excluded.
Note that the borders of the argument window (and other windows) can be
included and read with this request.
If a problem occurs, XReadScreen returns NULL.
11 July 1995 XReadScreen(3)
