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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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All the grabber-block functions operate using a left-hand coordinate system
that is based on character cells in a manner similar to that used by the
BIOS. The coordinate system origin (0,0) is located in the upper-left corner
of the screen. Positive x direction is to the right and positive y direction
is downward. The coordinate space consists of the set of integers that range
from 0 to (icCharsX - 1) in the x direction and from 0 to (icCharsY - 1) in
the y direction. The quantities icCharsX and icCharsY are found in the
grabber's INFOCONTEXT structure, which may be obtained at any time by
calling the extended-grabber function GetInfo. Notice that points in this
space represent the upper-left corner of the character cells, not their
center.
 
As indicated by their names, block functions operate on blocks of character
cells. A block is fully specified by its origin (relative to the screen
origin) and its x and y extents in the GRABREQUEST structure. The extents
are unsigned one-based values. A block is the set of character cells in the
rectangle defined by the origin of the block and the x and y coordinates.
Specifying an extent of 0 on either axis has the same effect as specifying
an extent equal to the maximum screen extent on that axis. In other words,
the entire screen may be easily specified by setting:
 
grXorg = grYorg = grXext = grYext = 0
 
For graphics mode, the same cell-based convention applies so that Windows
need not discern differences between graphics and text screens. The size of
a character cell in graphics mode is the same size cell that the BIOS would
use to display text using Interrupt 10h functions.  The current grabbers do
not yet support the specification of arbitrary block regions in graphics
mode. An attempt to specify any other block in graphics mode will return the
ERR_UNSUPPORTED error value.
 
The ERR_BOUNDARY error value indicates blocks that violate screen
boundaries.
 
 
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