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                        Using the Mouse and Keyboard
 
An application that uses the mouse and keyboard for input must respond to
activation, mouse, and keyboard events. The following sections describe how
to handle these three related topics.
 
Responding to Activation Events
 
A client window receives a WM_ACTIVATE message when its parent frame window
is being activated or deactivated. The activation or deactivation message is
usually accompanied by messages to set or lose the keyboard focus.
Therefore, applications should not use the WM_ACTIVATE message to change the
keyboard focus.
 
The low word of the first message parameter is TRUE if the window is
activated, and FALSE if the window is deactivated.
 
One use for the WM_ACTIVATE message is to toggle the state of an
application's private variable that tells whether a window is active or not,
as shown in the following code fragment:
 
case WM_ACTIVATE:
     fActivated = (BOOL) mp1;
     return(0L);
 
It is important to know the activation state of a window in order to
correctly handle mouse-button clicks.
 
Responding to Mouse Messages
 
Mouse messages occur when a user presses or releases one of the mouse
buttons (a click) and when the mouse is moved. All mouse messages contain
the x- and y-coordinates of the mouse-pointer hot spot (relative to the
window coordinates of the window receiving the message) at the time the
event occurs.
 
The system sends a WM_HITTEST message to the window that is about to receive
a mouse message. The window can determine if it should actually receive the
mouse message or not. The default processing of this message in the
WinDefWindowProc function is to return HT_NORMAL if the window is enabled
and HT_ERROR if the window is disabled. If the return value is HT_ERROR, the
system does not send the mouse message to the window. Most applications pass
WM_HITTEST messages on to the WinDefWindowProc function by default so
disabled windows do not receive mouse messages. Windows that specifically
respond to WM_HITTEST messages can change this default behavior.
 
Because windows process WM_HITTEST and mouse messages, an application can
ignore hit-test code in a mouse message unless the application returns
special values for hit-test code. One possible use for hit-test code is to
react differently to a mouse click in a disabled window.
 
The contents of the mouse-message arguments (mp1 and mp2) are listed below:
 
♦  The x-position is in low word of mp1.
 
♦  The y-position is in high word of mp1.
 
♦  The hit-test code is in low word of mp2.
 
Responding to Button Clicks
 
Applications typically respond to mouse button-down events differently
depending on whether the window is currently active. The first button-down
event in an inactive window should activate a window. A subsequent
button-down event in an active window produces an application-specific
action.
 
Typically, an application processes mouse clicks in the client window of a
standard frame window. Because the activated/deactivated status of a window
is a frame-window characteristic, the system does not provide an easy way to
determine if the client window is active. That is, the window handle
returned by the WinQueryActiveWindow function is the active frame-window
handle rather than the client window owned by the frame.
 
The following are two typical methods for determining if a client is an
active frame window:
 
♦  Call the WinQueryActiveWindow function and compare the window handle it
   returns with the frame window that contains the client window, as shown
   in the following code fragment:
 
      fActivated = (WinQueryWindow(hwndClient, QW_PARENT, FALSE) ==
          WinQueryActiveWindow(HWND_DESKTOP, FALSE))
 
♦  Maintain a private variable for the client window that is set and cleared
   when processing WM_ACTIVATE messages. Each time the frame window is
   activated, the client window receives a WM_ACTIVATE message with the low
   word of the first parameter equal to TRUE. When the frame window is
   deactivated, the client window receives a WM_ACTIVATE message with a
   FALSE activation indicator. The following code fragment shows how to use
   activation messages to toggle a private-status variable:
 
      case WM_ACTIVATE:
           fActivated = (BOOL) mp1;
           return (0L);
 
Depending on the method used to determine if a client window is active, a
mouse button-down message is passed to the WinDefWindowProc function if the
window is not active at the time of the message. The default processing
activates the window and its frame.
 
A common problem for an application processing WM_BUTTON1DOWN or similar
messages is the failure to activate or set the window focus. If the window
processes character messages, the window procedure should call the
WinSetFocus function to make sure the window receives the input focus and is
activated. If the window does not need the keyboard focus, an application
should call the WinSetActiveWindow function.
 
Responding to Mouse Movement
 
The system sends mouse-move messages to the window under the mouse pointer
or the current mouse-capture window, if any, whenever the mouse pointer
moves. This is useful for tracking the mouse pointer and changing its shape
based on its location in a window. For example, the mouse pointer changes
shape when it passes over the size border of a standard frame window.
 
All standard control windows use mouse-move messages to set the
mouse-pointer shape. If your application handles WM_MOUSEMOVE messages in
some situations but not others, unused messages should be passed to the
WinDefWindowProc function to change the shape of the mouse pointer.
 
Changing the Mouse Capture
 
Mouse messages are usually routed to the window under the mouse pointer.
Applications can call the WinSetCapture function to process all mouse
messages by a specified window. This is particularly useful when an
application is tracking the mouse pointer after a button-down message.
 
For example, in a paint application that uses a button-down message to start
a drawing operation, the application tracks the mouse using mouse-move
messages until a button-up message is received. If a user drags the mouse
pointer outside the window and releases the button, the button-up message
will not go to the original window unless the application has called the
WinSetCapture function for that window.
 
Some applications must receive a button-up message to match a button-down
message. When processing a button-down message, these applications call the
WinSetCapture function to set the capture to their own window, and then they
call the WinSetCapture function with a NULL window handle to release the
mouse capture when processing a matching button-up message.
 
Keyboard Messages
 
All keyboard messages come to a window as WM_CHAR messages. The system reads
the keyboard and collects keyboard events in the system queue. It then
routes these messages to the appropriate windows depending on the current
keyboard-focus window at the time the message is sent. WM_CHAR messages are
sent to the window that has the keyboard focus. If no window has the
keyboard focus, then WM_CHAR messages are posted to the active frame-window
queue. The following are two typical situations where applications receive
WM_CHAR messages:
 
♦  An application has a client window or custom control window, each of
   which can have the keyboard focus. If a window procedure for the client
   or control window does not process characters, it should pass them to its
   owner window, which can be accomplished by passing them through to the
   WinDefWindowProc function. This is especially true for dialog-control
   items, as this is how the TAB and direction-key control processing is
   implemented in the user interface.
 
♦  An application window owns a control window that handles some, but not
   all WM_CHAR messages. This is common in dialog windows. If a control
   window that has the focus in a dialog window cannot process a WM_CHAR
   message, it can call the WinDefWindowProc function to send the message to
   its owner, which is usually a dialog-frame window. The application dialog
   procedure then receives the WM_CHAR message. This is also the case when
   an application client window owns a control window.
 
Responding to Keyboard Messages
 
A WM_CHAR message may represent a key-down or key-up transition. It may
contain a character code, a virtual-key code, or a scan code. This message
also contains information about the state of the SHIFT, CONTROL, and ALT
keys.
 
Each time a user presses a key, at least two WM_CHAR messages are generated:
one when the key is pressed down, and one when the key is released. If the
key is held down long enough to trigger the keyboard repeat, multiple
WM_CHAR key-down messages are generated.
 
If the keyboard repeats faster than the application can retrieve the events
from the event queue, the system combines repeating character events into
one WM_CHAR event representing multiple-key events for the same key.
WM_CHAR messages contain a count byte indicating the number of keystrokes
represented by the message. Generally, this byte is set to 1, but it should
be checked every time a WM_CHAR message is processed to avoid missing
keystrokes.
 
A control may ignore the repeat count; for example, it may ignore the count
on ARROW keys. If the system is slow, it may be more aesthetic to have a
cursor move slowly than to see it jump 40 characters.
 
Applications decode WM_CHAR messages by examing individual bits in the flag
word contained in the low word of the first argument passed with every
WM_CHAR message. These bits may be set in various combinations. For example,
a WM_CHAR message can have the KC_KEYDOWN, KC_CHAR, KC_SCANCODE, and
KC_SHIFT attribute bits all set at the same time.
 
The mp1 and mp2 parameters that are part of the message contain different
information depending on the nature of the keyboard event, as follows:
 
♦  The flag word is in low word of mp1.
 
♦  The repeat key count is in low byte of high word of mp1.
 
♦  The scan code is in high byte of high word of mp1.
 
♦  The char code is in low word of mp2.
 
♦  The virtual key code is in high word of mp2.
 
An application window procedure should return TRUE if it processes a
particular WM_CHAR message, or FALSE otherwise. Typically, applications
respond to key-down events and ignore key-up events.
 
The following sections describe the different types of WM_CHAR messages.
Generally, decoding these messages consists of layers of conditional
statements to eliminate and discriminate the different combinations of
attributes that can occur in a keyboard message.
 
Key-Down or Key-Up Events
 
Generally, the first attribute that an application checks in a WM_CHAR
message is the key-down or key-up events. The distinction between a key-down
and a key-up event is found by examining the KC_KEYUP bit of the low word of
the first message parameter. If this flag bit is set, then the message is
from a key-up event. If the bit is clear, then the message is from a
key-down event. The following code fragment shows how to decode a message
for this information:
 
case WM_CHAR:
    fs = SHORT1FROMMP(mp1);
 
    if ((fs & KC_KEYUP))
 
        /* this is a key-up event   */
 
    else
 
        /* this is a key-down event */
 
    return TRUE;
 
Repeat-Count Events
 
Applications should always check the key repeat-count part of a WM_CHAR
message to see if the message represents more than one keystroke. The count
is greater than one if the keyboard is sending characters to the system
queue faster than the application can retrieve them. If the system queue
fills up, the system combines consecutive keyboard events for each key in a
single WM_CHAR message with the repeat count set to the number of combined
events. The repeat count is in the low byte of the high word of the first
message parameter.
 
Character Codes
 
The most typical use of WM_CHAR messages is to extract a character code from
the message and display the character on the screen. When the KC_CHAR bit is
set in the WM_CHAR message, the low word of the second message parameter
contains a character code based on the current code page. Generally, this
value is a glyph code (typically an ASCII code) for the character for the
key that was pressed.
 
The following code fragment shows how to respond to a character message:
 
    fs = SHORT1FROMMP(mp1);
 
    if (fs & KC_CHAR) {
 
        /* CHAR is in SHORT1FROMMP(mp2) */
 
        /* handle the key character */
 
        return(TRUE);
}
 
Note that if the KC_CHAR bit is not set, the SHORT1FROMMP(mp2) parameter may
still contain useful information. If either the ALT or CTRL key, or both,
are down, the KC_CHAR bit will not be set when the user presses another key.
For example, when the A key is pressed while the ALT key is down, the low
word of mp2 will contain a 0x0041, the KC_ALT bit will be set, and the
KC_CHAR bit will be clear. If the translation does not generate any valid
characters, the char field is set to zero.
 
Virtual-Key Codes
 
WM_CHAR messages often contain virtual-key codes that correspond to various
function keys and ARROW keys on a typical keyboard. These keys do not
correspond to any particular glyph code but are used to initiate operations.
When the KC_VIRTUALKEY bit is set in flag word of a WM_CHAR message, the
high word of the second message parameter contains a virtual-key code for
the key.
 
Note that some keys, such as the ENTER key, have both a valid character code
and a virtual-key code. WM_CHAR messages for these keys will contain
character codes for newline characters (ASCII 11) and virtual-key codes
(VK_ENTER).
 
The following code fragment shows how to decode a WM_CHAR message containing
a valid virtual-key code:
 
fs = SHORT1FROMMP(mp1);
 
if (fs & KC_VIRTUALKEY) {
 
    /* virtual key is in SHORT2FROMMP(mp2) */
 
    switch (SHORT2FROMMP(mp2)) {
        case VK_TAB:
 
            /* handle the TAB key   */
 
            return (TRUE);
 
        case VK_LEFT:
 
            /* handle the LEFT ARROW key  */
 
            return (TRUE);
 
        case VK_UP:
 
            /* handle the UP key    */
 
            return (TRUE);
 
        case VK_RIGHT:
 
            /* handle the RIGHT ARROW key */
 
            return (TRUE);
 
        case VK_DOWN:
 
            /* handle the DOWN ARROW key  */
 
        return (TRUE);
 
            /* etc...               */
 
        default:
            return (FALSE);
    }
}
 
Scan Codes
 
A third possible value in a WM_CHAR message is the scan code for the key
pressed. The scan code represents the value generated by the keyboard
hardware when a key is pressed. An application can use the scan code to
identify the physical key pressed, as opposed to the character code
represented by the same key. The byte-length value for the scan code is in
the high byte of the high word of the first message parameter.
 
All WM_CHAR messages that are generated by the keyboard have valid scan
codes. WM_CHAR messages that are posted by other applications may or may not
have valid scan codes. The following code fragment shows how to extract a
scan code from a WM_CHAR message:
 
fs = SHORT1FROMMP(mp1);
 
if (fs & KC_SCANCODE) {
 
    /* scan code is in (UCHAR) CHAR4FROMMP(mp1)) */
 
    return (TRUE);
}
 
Accelerator-Table Entries
 
The system checks all incoming keyboard messages to see if they match any
existing accelerator-table entries, either in the system queue or in the
application-message queue. The translation first checks the accelerator
table associated with the active frame window, and if no match is found, it
uses the accelerator table associated with the message queues. If the
keyboard event corresponds to an accelerator-table entry, the WM_CHAR
message changes to a WM_COMMAND, WM_SYSCOMMAND, or WM_HELP message,
depending on the attributes of the accelerator table. The original WM_CHAR
message is not processed by the application.
 
Accelerator tables should be used to implement keyboard shortcuts in
applications rather than translating command keystrokes. For example, if an
application uses the F2 key to save a document, a keyboard accelerator entry
for the F2 virtual key should be created so that it generates a WM_COMMAND
message rather than a WM_CHAR message.
 
Changing the Keyboard Focus
 
Applications can change the keyboard focus window by calling the
WinSetFocus function for the new focus window.
 
The WinSetFocus function causes the following events to occur:
 
♦  If a window currently has the keyboard focus, the window receives a
   WM_SETFOCUS message indicating that the window has lost the focus.
 
♦  If a window currently has the keyboard focus, the window receives a
   WM_SETSELECTION message indicating that the window should remove the
   highlight from the current selection.
 
♦  If changing the keyboard focus causes a change in the active window, and
   if there is a currently active window, the system sends a WM_ACTIVATE
   message to the active window, indicating that the window is no longer
   active.
 
♦  If a new application is being made the active application, the system
   sends a WM_ACTIVATE message to the current active application, indicating
   that the window is no longer active.
 
♦  A new active window, a new focus window, and the active application are
   established.
 
♦  If a new application is being made the active application, the system
   sends a WM_ACTIVATE message to the new application, indicating that the
   application has become active.
 
♦  If the active window is changing, the system sends a WM_ACTIVATE message
   to the new main window, indicating that this main window is now active.
 
♦  The system sends the new focus window a WM_SETSELECTION message,
   indicating that the focus window should select the current selection.
 
♦  The system sends the new focus window a WM_SETFOCUS message, indicating
   that the focus window is now active.
 
Using the WinQueryActiveWindow or WinQueryFocus function while processing
the WinSetFocus function causes the previous active and focus windows to be
returned until new active and focus windows are established. In other words,
even though WM_SETFOCUS and WM_ACTIVATE messages with the fFocus parameter
equal to FALSE may have been sent to the previous windows, those windows are
considered active and have the focus until the system establishes new active
and focus windows.
 
If the application calls WinSetFocus while processing a WM_ACTIVATE message,
the system does not send a WM_SETFOCUS message (with fFocus set to FALSE),
because no window has the focus.
 
 
                                      ♦