How do I implement double buffering and real-time drawing in GDI+?

Question

How do I implement double buffering and real-time drawing in GDI+?

thebluetropics 1,046

I've tried to repainting the window when there is no message left to process, like this:

while (true) {
    if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE)) {
        if (msg.message == WM_QUIT) break;

        TranslateMessage(&msg);
        DispatchMessageW(&msg);
    } else {
        PaintWindow(hwnd);
    }
}

And here is my PaintWindow() function:

bool PaintWindow(HWND _phwnd) {
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(_phwnd, &ps);

    RECT clientRect;
    GetClientRect(_phwnd, &clientRect);

    Gdiplus::SolidBrush defaultBrush(Gdiplus::Color(255, 23, 0, 0));
    Gdiplus::FontFamily fontFamily(L"Noto Sans");
    Gdiplus::Font font(&fontFamily, 14, Gdiplus::FontStyleRegular, Gdiplus::UnitPixel);

    Gdiplus::Graphics graphics(hdc);
    graphics.SetPixelOffsetMode(Gdiplus::PixelOffsetModeHalf);

    std::string str = std::to_string(number);
    std::wstring wstr(str.begin(), str.end());

    graphics.DrawString(wstr.c_str(), -1, &font, Gdiplus::PointF(0, 0), &defaultBrush);

    EndPaint(_phwnd, &ps);

    number++;

    return true;
}

I don't know why the window doesn't repaint everytime the PaintWindow() is called outside of the WM_PAINT.

I've tried moving the window a bit further outside the display's region, and yeah, it's updated when I drag the window back.

Note that PaintWindow() is called, I tested by adding the number.

And, how do I implement double buffering in GDI+? In Direct2D, it's done automatically. I have no clue of how to do that in GDI+.

David Lowndes 4,726 Reputation points

2023-03-18T09:13:21.15+00:00

Has anything invalidated the client area such that BeginPaint won't exclude everything?
See the remarks section of the BeginPaint documentation that notes:

The BeginPaint function automatically sets the clipping region of the device context to exclude any area outside the update region. The update region is set by the InvalidateRect or InvalidateRgn function and by the system after sizing, moving, creating, scrolling, or any other operation that affects the client area.
thebluetropics 1,046 Reputation points

2023-03-18T09:32:03.0366667+00:00

Hi @David Lowndes , thank you for the response.

I don't call InvalidateRect, nor InvalidateRgn. I thought it's just send a WM_PAINT message to my window.
David Lowndes 4,726 Reputation points

2023-03-18T09:43:42.08+00:00

If you want to draw at any time, have a look at using GetDC
Castorix31 90,681 Reputation points

2023-03-18T11:59:16.6633333+00:00

I don't know why the window doesn't repaint everytime the PaintWindow() is called outside of the WM_PAINT.

As David Lowndes pointed, see MSDN :

An application should not call BeginPaint except in response to a WM_PAINT message

from https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-beginpaint
thebluetropics 1,046 Reputation points

2023-03-18T13:57:56.74+00:00

I see, the reason why it doesn't work is that because I call BeginPaint() outside of the WM_PAINT message. However, I can achieve the same result as handling BeginPaint() on WM_PAINT using GetDC?
David Lowndes 4,726 Reputation points

2023-03-18T14:04:31.82+00:00

If that's what you want to do, yes. Give it a go and see.

thebluetropics 1,046

Thank you, it now works as expected:

bool PaintWindow(HWND _phwnd, HDC hdc) {
    RECT clientRect;
    GetClientRect(_phwnd, &clientRect);

    HDC hdcMemory = CreateCompatibleDC(hdc);
    HBITMAP hbitmapMemory = CreateCompatibleBitmap(hdc, clientRect.right, clientRect.bottom);
    HBITMAP hbitmapOld = static_cast<HBITMAP>(SelectObject(hdcMemory, hbitmapMemory));
    // Draw begin
    
    // draws to `hdcMemory` using GDI+
    
    // Draw end
    BitBlt(hdc, 0, 0, clientRect.right, clientRect.bottom, hdcMemory, 0, 0, SRCCOPY);
    SelectObject(hdcMemory, hbitmapOld);
    DeleteDC(hdcMemory);
    DeleteObject(hbitmapMemory);

    number++;

    return true;
}

case WM_PAINT: {
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(_phwnd, &ps);

    if (!PaintWindow(_phwnd, hdc)) return 1;

    EndPaint(_phwnd, &ps);
    return 0;
}

while (true) {
    if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE)) {
        if (msg.message == WM_QUIT) break;

        TranslateMessage(&msg);
        DispatchMessageW(&msg);
    } else {
        HDC hdc = GetDC(hwnd);
        if (!PaintWindow(hwnd, hdc)) break;
    }
}

However, I found that the window is not updating when I start dragging the window or when the window has a message to process. I know this behavior is because of PeekMessageW().

My only solution is to call PaintWindow() after every message, and limiting the drawing to only happens 60 times a second (matching my monitor refresh rate).

If there is another better solution to this, please let me know.

Thank you both of you, I have finally reached here since I was first learning Desktop Development on C++.

thebluetropics 1,046 Reputation points

2023-03-18T16:37:07.4666667+00:00
My only solution is to call PaintWindow() after every message, and limiting the drawing to only happens 60 times a second (matching my monitor refresh rate).

Wait, it doesn't work. The window doesn't repaint when the window is being dragged:

while (true) { if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message == WM_QUIT) break; TranslateMessage(&msg); DispatchMessageW(&msg); } HDC hdc = GetDC(hwnd); if (!PaintWindow(hwnd, hdc)) break; ReleaseDC(hwnd, hdc); }
thebluetropics 1,046 Reputation points

2023-03-18T16:48:39.38+00:00
Update: It seems that calling InvalidateRect() in the end of WM_PAINT does the job.

case WM_PAINT: { PAINTSTRUCT ps; HDC hdc = BeginPaint(_phwnd, &ps); if (!PaintWindow(_phwnd, hdc)) return 1; EndPaint(_phwnd, &ps); InvalidateRect(_phwnd, NULL, FALSE); return 0; }

I also don't need to call PaintWindow() after every message. The problem is that when the user drags the window, it does repaint, but, it's flickering. I don't know what causes it's to flicker. I uses the back-buffering method above, and it works. It's flicker only when I drag the window.

1 answer

Your answer

David Lowndes 4,726 Reputation points

2023-03-18T09:13:21.15+00:00

Has anything invalidated the client area such that BeginPaint won't exclude everything?
See the remarks section of the BeginPaint documentation that notes:

The BeginPaint function automatically sets the clipping region of the device context to exclude any area outside the update region. The update region is set by the InvalidateRect or InvalidateRgn function and by the system after sizing, moving, creating, scrolling, or any other operation that affects the client area.
thebluetropics 1,046 Reputation points

2023-03-18T09:32:03.0366667+00:00

Hi @David Lowndes , thank you for the response.

I don't call InvalidateRect, nor InvalidateRgn. I thought it's just send a WM_PAINT message to my window.
David Lowndes 4,726 Reputation points

2023-03-18T09:43:42.08+00:00

If you want to draw at any time, have a look at using GetDC
Castorix31 90,681 Reputation points

2023-03-18T11:59:16.6633333+00:00

I don't know why the window doesn't repaint everytime the PaintWindow() is called outside of the WM_PAINT.

As David Lowndes pointed, see MSDN :

An application should not call BeginPaint except in response to a WM_PAINT message

from https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-beginpaint
thebluetropics 1,046 Reputation points

2023-03-18T13:57:56.74+00:00

I see, the reason why it doesn't work is that because I call BeginPaint() outside of the WM_PAINT message. However, I can achieve the same result as handling BeginPaint() on WM_PAINT using GetDC?
David Lowndes 4,726 Reputation points

2023-03-18T14:04:31.82+00:00

If that's what you want to do, yes. Give it a go and see.
thebluetropics 1,046 Reputation points

2023-03-18T15:47:02.7633333+00:00

Thank you, it now works as expected:

bool PaintWindow(HWND _phwnd, HDC hdc) { RECT clientRect; GetClientRect(_phwnd, &clientRect); HDC hdcMemory = CreateCompatibleDC(hdc); HBITMAP hbitmapMemory = CreateCompatibleBitmap(hdc, clientRect.right, clientRect.bottom); HBITMAP hbitmapOld = static_cast<HBITMAP>(SelectObject(hdcMemory, hbitmapMemory)); // Draw begin // draws to `hdcMemory` using GDI+ // Draw end BitBlt(hdc, 0, 0, clientRect.right, clientRect.bottom, hdcMemory, 0, 0, SRCCOPY); SelectObject(hdcMemory, hbitmapOld); DeleteDC(hdcMemory); DeleteObject(hbitmapMemory); number++; return true; }

case WM_PAINT: { PAINTSTRUCT ps; HDC hdc = BeginPaint(_phwnd, &ps); if (!PaintWindow(_phwnd, hdc)) return 1; EndPaint(_phwnd, &ps); return 0; }

while (true) { if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message == WM_QUIT) break; TranslateMessage(&msg); DispatchMessageW(&msg); } else { HDC hdc = GetDC(hwnd); if (!PaintWindow(hwnd, hdc)) break; } }

However, I found that the window is not updating when I start dragging the window or when the window has a message to process. I know this behavior is because of PeekMessageW().

My only solution is to call PaintWindow() after every message, and limiting the drawing to only happens 60 times a second (matching my monitor refresh rate).

If there is another better solution to this, please let me know.

Thank you both of you, I have finally reached here since I was first learning Desktop Development on C++.
thebluetropics 1,046 Reputation points

2023-03-18T16:37:07.4666667+00:00

My only solution is to call PaintWindow() after every message, and limiting the drawing to only happens 60 times a second (matching my monitor refresh rate).

Wait, it doesn't work. The window doesn't repaint when the window is being dragged:

while (true) { if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message == WM_QUIT) break; TranslateMessage(&msg); DispatchMessageW(&msg); } HDC hdc = GetDC(hwnd); if (!PaintWindow(hwnd, hdc)) break; ReleaseDC(hwnd, hdc); }
thebluetropics 1,046 Reputation points

2023-03-18T16:48:39.38+00:00

Update: It seems that calling InvalidateRect() in the end of WM_PAINT does the job.

case WM_PAINT: { PAINTSTRUCT ps; HDC hdc = BeginPaint(_phwnd, &ps); if (!PaintWindow(_phwnd, hdc)) return 1; EndPaint(_phwnd, &ps); InvalidateRect(_phwnd, NULL, FALSE); return 0; }

I also don't need to call PaintWindow() after every message. The problem is that when the user drags the window, it does repaint, but, it's flickering. I don't know what causes it's to flicker. I uses the back-buffering method above, and it works. It's flicker only when I drag the window.

Answer 1

Xiaopo Yang - MSFT 12,731 Microsoft External Staff

Hello @thebluetropics,

Try to use Off-Screen DC for Flicker-Free. See Flicker-Free Displays Using an Off-Screen DC. Also see When to Draw in a Window. And as far as Double Buffering concerned, the back buffer should be rendered in the background.

Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2023-03-23T05:26:49.5633333+00:00

What you're using is Off-Screen DC but lack of WM_ERASEBKGND, compared to Flicker-Free Displays Using an Off-Screen DC. The default handling for the WM_ERASEBKGND message is to fill the area with the current window background color, which could cause the flicker. Have you tried the double buffering sample? @thebluetropics
Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2023-03-29T08:26:44.32+00:00

Hello @thebluetropics, Any update?

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How do I implement double buffering and real-time drawing in GDI+?

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