Which messages can be passed to a low-level mouse hook callback function?

Question

So, I was reading the WinApi documentation for the callback function of a low-level mouse hook and I got confused about the WPARAM parameter passed to this function.

From the Documentation about the callback function:

wParam [in]
Type: WPARAM

The identifier of the mouse message. This parameter can be one of the following messages: WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_MOUSEHWHEEL, WM_RBUTTONDOWN, or WM_RBUTTONUP.

This only mentions WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_MOUSEHWHEEL, WM_RBUTTONDOWN and WM_RBUTTONUP.

But in the Documentation about the MSLLHOOKSTRUCT structure (used with low-level mouse hooks), other messages are also mentioned:

mouseData

Type: DWORD

If the message is WM_MOUSEWHEEL, the high-order word of this member is the wheel delta. The low-order word is reserved. A positive value indicates that the wheel was rotated forward, away from the user; a negative value indicates that the wheel was rotated backward, toward the user. One wheel click is defined as WHEEL_DELTA, which is 120.

If the message is WM_XBUTTONDOWN, WM_XBUTTONUP, WM_XBUTTONDBLCLK, WM_NCXBUTTONDOWN, WM_NCXBUTTONUP, or WM_NCXBUTTONDBLCLK, the high-order word specifies which X button was pressed or released, and the low-order word is reserved. This value can be one or more of the following values. Otherwise, mouseData is not used.

Are those messages also passed in the WPARAM parameter?

I've never even worked out what an 'X' button is :) But I imagine everything between `WM_MOUSEFIRST` and `WM_MOUSELAST` would go to the hook. — Jonathan Potter, Jul 15 '19 at 23:59
@JonathanPotter "*I've never even worked out what an 'X' button is*" - see [XBUTTONs](https://learn.microsoft.com/en-us/windows/win32/inputdev/about-mouse-input#xbuttons) on MSDN — Remy Lebeau, Jul 16 '19 at 01:07

score 2 · Accepted Answer · answered Jul 16 '19 at 06:56

2

Are those messages also passed in the WPARAM parameter?

Yes.

For example, if you want to handle the X button messages, they are posted to your application using WM_XBUTTONDOWN and WM_XBUTTONUP. The low-order word of wParam indicates which X button is down (if any).

In addition, please refer Responding to Mouse Clicks

The WM_XBUTTONDOWN and WM_XBUTTONUP window messages apply to both XBUTTON1 and XBUTTON2. The wParam parameter indicates which button was clicked.

UINT button = GET_XBUTTON_WPARAM(wParam);  
if (button == XBUTTON1)
{
    // XBUTTON1 was clicked.
}
else if (button == XBUTTON2)
{
    // XBUTTON2 was clicked.
}

answered Jul 16 '19 at 06:56

Strive Sun

5,988
1
9
26

@thebear8 hi, please tell me if my answer can help you. If you have any questions, please let me know at any time. – Strive Sun Aug 12 '19 at 02:29
Sorry, I completely forgot to accept your answer, it's quite a while ago, but I just noticed. – thebear8 May 30 '20 at 15:10

Which messages can be passed to a low-level mouse hook callback function?

1 Answers1