WINCAP: Captures Screens Using DIB API

WINCAP demonstrates how to capture, save, and print the
 entire screen, portions of the screen, or specific
windows. The program also defines routines that accomplish
common device-independent bitmap (DIB) functions; these
routines form the DIB application programming interface
(API). WINCAP uses the DIB API functions for most of the
screen capture, printing, and saving work. See the
DIBAPI.TXT file for a description of the DIB API
functions.

WINCAP illustrates the following techniques:

>  Capturing the screen (or a specific window) into a DIB

>  Capturing the screen to a device-dependent bitmap (DDB)

>  Printing a DIB using banding

>  Loading and saving a DIB to a disk file (.BMP file)

>  Converting between DIBs and DDBs

>  Displaying the captured screen DDB

All of these techniques call the DIB API. WINCAP includes
the source code for these functions. You can call these
functions easily from a different application by simply
compiling the enclosed DIBAPI.DLL, and linking with the
DIBAPI.LIB import library.

The preferred way to capture a screen in Microsoft(R)
Windows(TM) is to copy the screen pixels into a DIB, and
then to use this DIB in subsequent operations (for
example, to save the bitmap to a file or print the
bitmap).

If you do not use a DIB in the intermediate step, the
results of the screen print may be less than desirable. If
you use a DIB to hold the screen image, device-dependent
information is removed from the bitmap. This simplifies
the process of displaying the image on devices with
different display capabilities. For instance, capturing a
screen from a 24-bit display adapter and printing it on a
1-bit (monochrome) printer can produce exceptional results
if DIBs are used. Additionally, many printer drivers
implement gray-scale dithering; the output on these
printers is also excellent when DIBs are used.

NOTE:  Because bitmaps are device-dependent, you should
avoid the BitBlt function when printing bitmaps. The type
of bitmaps that the BitBlt function requires are normally
in the format of the display driver rather than the
printer driver. Depending on the drivers involved, the
results of using BitBlt to print a bitmap can vary from
extremely poor output quality to no output at all.

Although all printer drivers are able to BitBlt a
monochrome bitmap to the printer, this technique generally
produces poor results because the printer cannot apply
gray-scaling to the image.
 
This technique of using a DIB to convert a bitmap between
display devices with different capabilities can also be
used to convert bitmaps while preserving the original
color information (for example, loading a 256-color bitmap
from a .BMP file and printing it to a 3-color printer or
displaying it on a 24-bit display).

The file DIBAPI.TXT contains more information on function
parameters and usage. A Windows Help file for the DIB APIs
is also included.

WINCAP was built and tested under Microsoft Windows
version 3.1.


