Reset cursor in WM_SETCURSOR handler properly

Question

INTRODUCTION AND RELEVANT INFORMATION:

I have made an application that needs to change the look of a cursor into hand when mouse hovers above the static control, but resets it to a normal cursor otherwise.

My initial application was in full screen mode, but recently terms have changed and it must have a resizable window.

This means that my handler for WM_SETCURSOR must be rewritten to reflect newly introduced changes.

Cursors are loaded in WM_CREATE, and I have defined class cursor, like this:

   // cursors 
   case WM_CREATE:
      hCursorHand = LoadCursor( NULL, IDC_HAND );
      hCursorArrow = LoadCursor( NULL, IDC_ARROW );
      // other stuff

In my class:

   WNDCLASSEX wc;
   // ...
   wc.hCursor = hCursorArrow;
   //...

This is my old WM_CURSOR handler ( code is simplified for clarity purposes ):

   case WM_SETCURSOR:
        if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
             SetCursor(hCursorHand);
        else
             SetCursor(hCursorArrow);
        return TRUE;

If cursor hovers above static control, then my handler changes it to hand, else sets it to default cursor ( arrow ).

Bellow is the picture I have sketched in Paint that displays the desired look of the cursor when it hovers above static control, it is on the client area, and when user resizes window.

If additional code snippets are required, ask and I will edit my post, but for now, they are omitted to keep the post short and concise.

I work on Windows XP, using MS Visual Studio C++ and pure Win32 API.

MY EFFORTS TO SOLVE PROBLEM:

Bellow are the code snippets that I have tried, but they all failed:

First snippet:

   case WM_SETCURSOR:
        if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
        {
             SetCursor(hCursorHand); 
             return TRUE; 
        }
        else
             return DefWindowProc( hWnd, msg, lParam, wParam );

Second Snippet:

   case WM_SETCURSOR:
        if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
        {
             SetCursor(hCursorHand); 
             return TRUE; 
        }
        break; // based on MSDN example

Third snippet:

   case WM_SETCURSOR:
        if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
        {
             SetCursor(hCursorHand); 
             return TRUE; 
        }
        else
             return FALSE;

These set cursor to hand no matter where it is.

If I leave my WM_SETCURSOR handler unchanged, the only problem I get is that instead of sizing arrows, I get regular arrow ( as the cursor’s look ) when I hover over the border, but window can be sized.

If I comment out my WM_SETCURSOR handler, sizing arrows and cursor arrow appear properly, but cursor doesn’t change into hand when hovers above static control ( which is logical, since there is no WM_SETCURSOR handler to change it ).

I have browsed through SO archive, looked on MSDN, CodeProject , DaniWeb, Cprogramming and CodeGuru, but had no success.

Looking through those, I have found an example where people compare low word of the lParam against hit test code.

Looking through MSDN I have found link for hit test values ( http://msdn.microsoft.com/en-us/library/windows/desktop/ms645618%28v=vs.85%29.aspx ) and I have found link for cursor types (http://msdn.microsoft.com/en-us/library/windows/desktop/ms648391%28v=vs.85%29.aspx ).

Currently I am reading them, because I think that I will have to load additional cursor resources, take several comparisons of hit test values, and then use those resources to set cursor look accordingly.

QUESTION:

I really would like my WM_SETCURSOR handler to look like this:

   case WM_SETCURSOR:
        if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
        {
             SetCursor(hCursorHand); 
             return TRUE;
        }
        else
             // reset cursor's look to default

so I ask the community to instruct me on how to do this.

If this isn’t possible, then I will consider using multiple if statements to check the hit test code, and set cursor’s look accordingly.

Of course, if there is better solution for my problem, please suggest it, I will consider it as well.

Thank you.

Regards.

Answer 1

In general, if you handle the WM_SETCURSOR message you must either

• Call SetCursor() to set the cursor, and return TRUE, or
• If the message came from a child window, return FALSE for default processing, or
• If the message is from your own window, pass the message through to DefWindowProc()

I think the last two points aren't made quite clear by the MSDN docs.

The window under the mouse pointer gets the first WM_SETCURSOR message. If it handles it and returns at that point, nothing else happens. If however it calls DefWindowProc(), then DWP forwards the message to the window's parent to handle. If the parent chooses not to handle it, it can return FALSE and the DefWindowProc processing will continue.

But this only applies if the message came from a previous call to DWP. If the message originated with the window itself, rather than a child, returning TRUE or FALSE without setting the cursor means the cursor won't be set at all.

Another thing: although your question didn't specify, I'm assuming from your use of GetDlgItem() that your top-level window is a dialog. If that's true, you can't just return TRUE or FALSE for a message - you need to return the value using SetWindowLongPtr() and store the return value in DWLP_MSGRESULT. Returning FALSE from a dialog procedure indicates that you didn't handle the message at all - this is equivalent to passing a message through to DefWindowProc().

So I think the proper handling for your situation is, in your top-level window:

case WM_SETCURSOR:
    if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
    {
        SetCursor(hCursorHand); 
        SetWindowLongPtr(hwnd, DWLP_MSGRESULT, TRUE);
        return TRUE;
    }
    return FALSE;

If your top-level window isn't in fact a dialog, you would do this:

case WM_SETCURSOR:
    if( (HWND)wParam == GetDlgItem( hwnd, 4000 ) ) 
    {
        SetCursor(hCursorHand); 
        return TRUE;
    }
    return DefWindowProc(hwnd, uMsg, wParam, lParam);

Answer 2

Here's my first example, if cursor go to menubar, cursor changes to cursor hand:

HCURSOR cursorHand = LoadCursor(NULL, IDC_HAND);
case WM_SETCURSOR:
    if(LOWORD(lParam) == HTMENU)
    {
          SetCursor(cursorHand);
    }
 break;

Here's my second example, if cursor goes to button, cursor changes to cursorHand:

HCURSOR cursorHand =  LoadCursor(NULL, IDC_HAND);

case WM_SETCURSOR:
      if(LOWORD(lParam) == buttonId)//declare you
      {
            SetCursor(cursorHand);
       }
   break;

Warning:menubar and button is not created! Create you and please, check my answer example.

Answer 3

The question as I understand it is, given a parent window with one more more child windows (one of which is a static control) how do you set the cursor to the hand when the cursor is over the static control, and the arrow when the cursor is over the client area of the parent window, and let default processing take place when the cursor is over a non-client area of the parent window.

To check things out, I wrote a simple program with a top-level window with a static control as a child window. My first attempt was the following:

1) Set the class cursor of the top-level window to LoadCursor(NULL, IDC_ARROW). This allows the default processing to set the cursor to the arrow when appropriate.

2) Keep track of the position of the mouse cursor by handling the WM_MOUSEMOVE message by calling my HandleWMMouseMove function as follows:

case WM_MOUSEMOVE:
    HandleWMMouseMove(lParam);
    break;

//ptCurrMousePos is a global variable of type POINT
static void     HandleWMMouseMove(LPARAM mousepos)
{
    ptCurrMousePos.x = (int)(short)(LOWORD(mousepos));
    ptCurrMousePos.y = (int)(short)(HIWORD(mousepos));
}

3) and then all I had to do was handle the WM_SETCURSOR message by calling my HandleWMSetCursor function as follows:

    case WM_SETCURSOR:
        if (HandleWMSetCursor())
            return TRUE;
        break;

//hwndFrame is a handle to the top-level window.
//hwndStatic is a handle to the static control.
static BOOL     HandleWMSetCursor(void)
{
    if (ChildWindowFromPoint(hwndFrame, ptCurrMousePos)==hwndStatic) {
        SetCursor(hCursorHand);
        return TRUE;
    }

    return FALSE;
}

this worked fine but I couldn't understand how the code posted in the question was working even partially. So I asked the questioner whether the child window was really a static control. The answer was yes but it was created with the SS_NOTIFY style. So I created my child window with this style and my code stopped working, but the code posted with the question started to work. With the help of the Spy++ program distributed with Visual Studio I learned the following.

Static controls are normally transparent (not in the visual sense, but meaning that even when the mouse is over the transparent window, Windows will consider the mouse to be over the window underneath the transparent window).

When you create a static control with SS_NOTIFY the control is no longer transparent (i.e. it starts to receive an process mouse messages (like WM_MOUSEMOVE), so my code stopped working because it never received WM_MOUSE messages when the cursor was over the static control. On the other hand the code in the question did not work when the static control was created without SS_NOTIFY because without this style the static control was transparent, which meant that the WARAM in the WM_SETCURSOR message was never equal to the static control (in other words Windows never considered the mouse to be over the static control because it was transparent).

It is possible to combine the two approaches by changing the WM_SETCURSOR handler function to the following:

//hwndFrame is a handle to the top-level window.
//hwndStatic is a handle to the static control.
static BOOL     HandleWMSetCursor(WPARAM wParam)
{
    if (((HWND)wParam == hwndStatic) || (ChildWindowFromPoint(hwndFrame, ptCurrMousePos)==hwndStatic)) {
        SetCursor(hCursorHand);
        return TRUE;
    }

    return FALSE;
}