This message is sent when the user clicks the horizontal scroll bar.
| Parameter | Description |
| wParam | Contains a scroll-bar code that specifies the user's scrolling request. It can be any one of the following values: | |
| Parameter | Description |
| Value | Meaning | ||
| SB_BOTTOM | Scroll to lower right. | ||
| SB_ENDSCROLL | End scroll. | ||
| SB_LINEDOWN | Scroll one line down. | ||
| SB_LINEUP | Scroll one line up. | ||
| SB_PAGEDOWN | Scroll one page down. | ||
| SB_PAGEUP | Scroll one page up. | ||
| SB_THUMBPOSITION | Scroll to absolute position. The current position is provided in the low-order word of lParam. | ||
| SB_THUMBTRACK | Drag thumb to specified position. The current position is provided in the low-order word of lParam. | ||
| SB_TOP | Scroll to upper left. | ||
| lParam | Specifies the window handle of the control. If the message is sent by a scroll-bar control, the high-order word of the lParam parameter contains the window handle of the control. If the message is sent as a result of the user clicking a pop-up window's scroll bar, the high-order word is not used. | ||
The SB_THUMBTRACK message typically is used by applications that give some feedback while the thumb is being dragged.
If an application scrolls the document in the window, it must also reset the position of the thumb by using the SetScrollPos function.