WM_HSCROLL
The
WM_HSCROLL message is sent to a window when a scroll event occurs in the window s standard horizontal scroll bar. This message is also
sent to the owner of a horizontal scroll bar control when a scroll event occurs
in the control.
WM_HSCROLL
nScrollCode = (int) LOWORD(wParam); // scroll bar value
nPos = (short int) HIWORD(wParam); // scroll box position
hwndScrollBar = (HWND) lParam; // handle of scroll bar
Parameters
nScrollCode
Value of the
low-order word of wParam. Specifies a scroll bar value that indicates
the user s scrolling request. This parameter can be one of the
following values:
|
Value |
Meaning |
|
SB_BOTTOM |
Scrolls to
the lower right. |
|
SB_ENDSCROLL |
Ends scroll. |
|
SB_LINELEFT |
Scrolls
left by one unit. |
|
SB_LINERIGHT |
Scrolls
right by one unit. |
|
SB_PAGELEFT |
Scrolls
left by the width of the window. |
|
SB_PAGERIGHT |
Scrolls
right by the width of the window. |
|
SB_THUMBPOSITION |
Scrolls to
the absolute position. The current position is specified by the nPos
parameter. |
|
SB_THUMBTRACK |
Drags
scroll box to the specified position. The current position is specified by
the nPos parameter. |
|
SB_TOP |
Scrolls to
the upper left. |
nPos
Value of the
high-order word of wParam. Specifies the current position of the scroll
box if the nScrollCode parameter is SB_THUMBPOSITION or SB_THUMBTRACK;
otherwise, nPos is not used.
hwndScrollBar
Value of lParam.
Identifies the control if WM_HSCROLL is sent by a scroll bar control. If WM_HSCROLL
is sent by a window s standard scroll bar, hwndScrollBar is not
used.
Return Values
If an
application processes this message, it should return zero.
Remarks
The
SB_THUMBTRACK notification message is typically used by applications that
provide feedback as the user drags the scroll box.
If an
application scrolls the content of the window, it must also reset the position
of the scroll box by using the SetScrollPos function.
Note that the
WM_HSCROLL message carries only 16 bits of scroll box position data. Thus,
applications that rely solely on WM_HSCROLL (and WM_VSCROLL) for scroll
position data have a practical maximum position value of 65,535.
However, because
the SetScrollPos, SetScrollRange, GetScrollPos, and GetScrollRange
functions support 32-bit scroll bar position data, there is a way to circumvent
the 16-bit barrier of the WM_HSCROLL and WM_VSCROLL messages. See GetScrollPos
for a description of the technique and its limits.
See Also