8.7 Transferring Images between Client and Server
Xlib provides functions that you can use to transfer images between a client and the server.
Because the server may require diverse data formats,
Xlib provides an image object that fully describes the data in memory
and that provides for basic operations on that data.
You should reference the data
through the image object rather than referencing the data directly.
However, some implementations of the Xlib library may efficiently deal with
frequently used data formats by replacing
functions in the procedure vector with special case functions.
Supported operations include destroying the image, getting a pixel,
storing a pixel, extracting a subimage of an image, and adding a constant
to an image (see section "
Manipulating Images").
All the image manipulation functions discussed in this section make use of
the
XImage
structure,
which describes an image as it exists in the client's memory.
typedef struct _XImage {
int width, height; /* size of image */
int xoffset; /* number of pixels offset in X direction */
int format; /* XYBitmap, XYPixmap, ZPixmap */
char *data; /* pointer to image data */
int byte_order; /* data byte order, LSBFirst, MSBFirst */
int bitmap_unit; /* quant. of scanline 8, 16, 32 */
int bitmap_bit_order; /* LSBFirst, MSBFirst */
int bitmap_pad; /* 8, 16, 32 either XY or ZPixmap */
int depth; /* depth of image */
int bytes_per_line; /* accelerator to next scanline */
int bits_per_pixel; /* bits per pixel (ZPixmap) */
unsigned long red_mask; /* bits in z arrangement */
unsigned long green_mask;
unsigned long blue_mask;
XPointer obdata; /* hook for the object routines to hang on */
struct funcs { /* image manipulation routines */
struct _XImage *(*create_image)();
int (*destroy_image)();
unsigned long (*get_pixel)();
int (*put_pixel)();
struct _XImage *(*sub_image)();
int (*add_pixel)();
} f;
} XImage;
To initialize the image manipulation routines of an image structure, use
XInitImage().
To combine an image with a rectangle of a drawable on the display,
use
XPutImage().
To return the contents of a rectangle in a given drawable on the display,
use
XGetImage().
To copy the contents of a rectangle on the display
to a location within a preexisting image structure, use
XGetSubImage().
Christophe Tronche, [email protected]
