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I have four windows, which are one parent window and three child windows. I want to make two of those child windows to draw stuff. The first child window is using OpenGL, and the second child window is using GDI. If I just draw some stuff on my OpenGL window and everything works fine, but when I try to draw(or just try to process WM_PAINT message) something else on my GDI window, those child windows become weird. Firstly, some parts(like buttons, statics, title bar) of my third child window will be missing. Secondly, if I try to resize any of those windows, one or two child windows will be missing. But once I click those windows they will be back. Thirdly, PeekMessage does not work anymore, it always return a FALSE, MessageBox seems not to work properly(I cannot see the popup window, but I can hear the sound), either.

My third child window just created. enter image description here

After I click it. enter image description here

I thought there might be something wrong with the message processing, but I cannot figure out what is actually happening. Is here anyone has any suggestions?

Message Loop:

MSG msg;


DWORD dwLast;
DWORD dwCurrent;
DWORD dwInterval = 20;//50 FPS 1000 / 50
dwLast = GetTickCount();

while (1) {

    while (PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE) == FALSE)
    {
        dwCurrent = GetTickCount();
        if (dwCurrent - dwLast < dwInterval)
            continue;

        SendMessage(Handle_Child_Demo, WM_PAINT, 0, 0);

        dwLast = dwCurrent;
    }
    if (GetMessage(&msg, NULL, 0, 0) != TRUE) {
        break;
    }
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

I am not using MDI to create my child windows, I just used CreateWindow to create all my child windows, and I think that must be something wrong with it, what else do I need to do to make sure those child windows work properly?

markable
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  • different window is different thread ... So you have to have separate OpenGL context for each GL window and use `wglMakeCurrent` to switch between contexts properly (on Activate and on Exit events). Also GDI and visual WinAPI calls MUST BE CALLED FROM MAIN THREAD OF TARGETED WINDOW (WndProc) otherwise weird things will happen even in unrelated code ... like random exception gfx errors crashes ... BTW you can combine GDI and GL in the same window without any problems ... just make sure updates are not forcing repainting in the wrong time. – Spektre Jul 25 '16 at 06:29
  • The real problems get started when you got older Intel gfx cards/drivers see [What is the proper OpenGL initialisation on Intel HD 3000?](http://stackoverflow.com/q/19099162/2521214) – Spektre Jul 25 '16 at 06:35
  • I have only one GL window, and the whole program is using only one thread. I use wglMakeCurrent(DC,GL) when it starts drawing, and use wglMakeCurrent(NULL,NULL) when it stopped. – markable Jul 25 '16 at 06:38
  • @Spektre BTW I am not using Intel gfx cards. – markable Jul 25 '16 at 06:40
  • You got 4 windows each call to its own WndProc callback you can consider as separate thread. If you access GDI or winapi calls between windows then you got a problem. – Spektre Jul 25 '16 at 06:40
  • You mean I have to use wglMakeCurrent in every WndProc? Or I just use it when it is the GL window? – markable Jul 25 '16 at 06:44
  • Only for GL windows ... on enter you have to set actual renedring context handle and on exit/close you should set it to NULL. Your problems could also be wrongly handled resize and repaint events ... – Spektre Jul 25 '16 at 06:45
  • I just cannot understand why everything works fine without adding a handler to WM_PAINT for GDI window, and my only GL window resize code here glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(45.0f, (GLfloat)width / (GLfloat)height, 0.1f, 100.0f); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); – markable Jul 25 '16 at 07:03
  • Please show your code. – andlabs Jul 25 '16 at 11:53
  • Show the message loop for main window (that's usually in `WinMain` with `GetMessage/PeekMessage`). Also show the message loop for other OpenGL windows if any. – Barmak Shemirani Jul 26 '16 at 04:04
  • You can see the main window loop(the only one message loop) in my question now. – markable Jul 26 '16 at 05:59
  • I am not using MDI to create my child windows, I just used CreateWindow to create all my child windows, and I think that must be something wrong with it, what else do I need to do to make sure those child windows work properly? – markable Jul 26 '16 at 07:07

1 Answers1

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MUST USE MDI to create child windows, just remember, USE MDI!!!! Or there will be something really weird, this is bacese those messages are not processed properly, and MDI will help us to do it.

markable
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