WM_PAINT with PROGRESS_CLASS

Question

I'm creating Win32 control:

m_progress = CreateWindowExW(0, PROGRESS_CLASSW, L"ProgressBar", WS_VISIBLE | WS_CHILD | WS_TABSTOP, 153, 339, 135, 33, m_window, (HMENU)0, m_instance, 0);
SendMessageW(m_progress, WM_SETFONT, (WPARAM)m_fontBold, TRUE);
SendMessageW(m_progress, PBM_SETRANGE, 0, MAKELPARAM(0, 100));

It's working, but I also want to draw text with percentage on it So I've subclassed progress control like this:

m_progressPrevProc = (WNDPROC)SetWindowLongPtrW(m_progress, GWLP_WNDPROC, (LONG_PTR)ProgressMsgProcessor);
...
static LRESULT CALLBACK ProgressMsgProcessor(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    if (msg == WM_PAINT)
    {
        PAINTSTRUCT ps;
        RECT rc = { 5, 5, 135, 33 };
        //HDC hdc = BeginPaint(hwnd, &ps);
        //SelectObject(hdc, g_App.m_fontBold);
        //DrawTextA(hdc, "100 %", -1, &rc, DT_SINGLELINE | DT_CENTER | DT_VCENTER);
        //EndPaint(hwnd, &ps);
    }

    return CallWindowProcW((WNDPROC)PrevWndProcProzess, hwnd, msg, wparam, lparam);
}

But if uncomment atleast "HDC hdc = BeginPaint(hwnd, &ps);" then text appears, but default control absolutely disappears (like it's not drawn) How can I fix it to show default windows control with text on it, because I don't need to draw custom control, only add overlay text? Thank you

One someone's called `BeginPaint()/EndPaint()` the dirty region is validated and calling it again will return an empty region. The proper way to do this is to call `CallWindowProc` first, to allow the control to perform it's default painting, and then call `GetDC() / ReleaseDC()` to get a DC to draw into over the top. — Jonathan Potter, May 31 '18 at 12:05

score 2 · Accepted Answer · answered May 31 '18 at 12:06

The problem here is that you cleared the update region with your BeginPaint and EndPaint calls, so the progress bar doesn't think it has to draw anything. It's a weakness of the way WM_PAINT works that you can't paint over an existing control in this way. Instead, you have to do something like this:

static LRESULT CALLBACK ProgressMsgProcessor(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    if (msg == WM_PAINT)
    {
        // Paint the control first
        CallWindowProcW ((WNDPROC)PrevWndProcProzess, hwnd, msg, wparam, lparam);

        // Then draw over it
        HDC hDC = GetDC (hwnd);
        HFONT hOldFont = (HFONT) SelectObject(hDC, g_App.m_fontBold);

        // Draw your own stuff into hDC

        SelectObject (hDC, hOldFont);
        ReleaseDC (hwnd, hDC);
        return 0;
    }

    return CallWindowProcW ((WNDPROC)PrevWndProcProgress, hwnd, msg, wparam, lparam);
}

Other notes:

Your code as posted is drawing under the control, not over it (!). My code fixes that.
If you select and object into a DC, you should select the old one back in when you are done. Again, my code shows how to do this.

Just nitpicking, but in this example, you don't need to call `CallWindowProcW()` conditionally. I would move it above the `if` statement and save its return value to a local variable, and then `return` that variable after the `if` block is done, eg: `LRESULT lRes = CallWindowProcW((WNDPROC)PrevWndProcProzess, hwnd, msg, wparam, lparam); if (msg == WM_PAINT) { ... } return lRes;` — Remy Lebeau, May 31 '18 at 16:49
@RemyLebeau Yes, that would be neater here but (a) I was striving for clarity primarily, and (b) in the more general case calling `CallWindowProc` before doing anything else might not work for all type of message that `ProgressMsgProcessor` wants to handle (or might, in the future, want to handle). — Paul Sanders, May 31 '18 at 16:58
This is a great solution, many thanks. I've been stumbled on this for quite a while. Now the only issue remains the text being overdrawn each time you draw, for some reason the previous text always remains there. — Mecanik, Apr 20 '21 at 09:03

WM_PAINT with PROGRESS_CLASS

1 Answers1