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                              About the Mouse
 
This topic describes the mouse functions. These functions give programs
direct access to the system mouse or other pointing device. Programs can
read individual mouse events (mouse motions and button presses) and carry
out actions based on those events.
 
In addition to using the keyboard for program input, you can use the mouse.
To use the mouse, you must first open it by using the MouOpen function (MS
OS/2 does not provide a default handle for the mouse as it does for the
keyboard and screen) and then draw the mouse pointer by using the
MouDrawPtr function. Once you have opened the mouse, you can read events
from the mouse-event queue by using the MouReadEventQue function. An event
defines the position of the mouse and the state of the mouse buttons. The
system copies an event to the queue whenever the user moves the mouse or
presses or releases a mouse button.
 
MS OS/2 specifies the position of the mouse either in screen coordinates or
as the number of mickeys relative to the last position. Screen coordinates
are relative to the upper-left corner of the screen. The x-axis values
increase to the right; the y-axis values increase downward. The screen units
are either character cells or pels, depending on the screen mode (character
cells for text mode, pels for graphics mode). The position never exceeds the
width or height of the screen.
 
A mickey is the mouse unit of motion. If the mouse position is specified in
mickeys, it represents the direction and distance the mouse has moved from
its last position. A program can determine how many centimeters the mouse
has moved by using the MouGetNumMickeys function to retrieve the
mickey-to-centimeter ratio. A position in mickeys is a signed value. If the
x-coordinate is negative, the mouse moved to the left; if positive, it moved
to the right. If the y-coordinate is negative, the mouse moved up; if
positive, it moved down.
 
MS OS/2 reports only the mouse events that are defined in the mouse-event
mask. A program can set or retrieve the event mask by using the
MouSetEventMask or MouGetEventMask function, determine how many mouse events
are in the queue by using the MouGetNumQueEl function, or flush any existing
events from the queue by using the MouFlushQue function.
 
MS OS/2 cannot draw the mouse pointer unless a pointer driver has been
specified in a device command in the config.sys file or a pointer-driver
name is explicitly given when the mouse is opened. The pointer driver
supplied with MS OS/2 is named pointdd.sys.
 
A program can change the shape of the mouse-pointer. Typically, the program
first retrieves the current shape by using the MouGetPtrShape function and
then modifies that shape before setting it by using the MouSetPtrShape
function. The mouse-pointer shape consists of two masks: an AND mask and an
XOR mask. MS OS/2 first combines the AND mask with the contents of the
screen at the current position by using the bitwise AND operator. It then
combines the result with the XOR mask by using the bitwise XOR operator. The
format of the masks depends on the screen mode: character-and-attribute
pairs for text mode and bitmaps for graphics mode.
 
If a program needs to temporarily hide the mouse pointer, the MouRemovePtr
function removes the mouse pointer from all or a portion of the screen.
 
MS OS/2 automatically updates the mouse-pointer position as the mouse moves,
but only if the amount of motion is greater than or equal to the scaling
factor. The scaling factor, set by using the MouSetScaleFact function,
defines the number of mickeys the mouse must move before the mouse pointer
moves one screen unit. For example, in text mode, the horizontal and
vertical scaling factors are usually the same as the width and height of a
character cell. This means that the mouse moves one character cell at a
time, rather than moving within a cell.
 
A program can move the mouse pointer by using the MouSetPtrPos function or
retrieve the current pointer position by using the MouGetPtrPos function.
 
Other mouse functions carry out special tasks for adapting the mouse for
real-mode operation and for modifying the operation of one or more of the
mouse functions.
 
As with files in the file system, the mouse is a shared resource, available
to every program in the current screen group. If two or more programs open
and use the mouse, what one does affects the other. For this reason, you
should close the mouse when you no longer need it.
 
 
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