What posts the WM_QUIT message? - c++

Question

I have just started on NeHe's OpenGl tutorials and I have written all the code from the first tutorial.
The program didn't run how i wanted it to run so i started to debug it and found out that a WM_QUIT message was posted somewhere.
I didn't post it anywhere exept from "case close:"(which never happens, I don't get that far).
So i just wondered, what could possibly post a WM_QUIT message. I am not that familiar with c++, but i have done a lot of java before.
Thanks in advance and sorry about my bad English.
Code:
#include <Windows.h>
#include <gl\GL.h>
#include <gl\GLU.h>
#include <glaux.h>
#include <iostream>
// Window/Rendering vars
HGLRC hRC = NULL; // Handle to the rendering context
HDC hDC = NULL; // Handle to Device context
HWND hWnd = NULL; // Handle to the Window
HINSTANCE hInstance = NULL; // Handle to a instance of the application
bool active = true; // Is window active
bool fullscreen = true; // Is window fullscreen
bool keys[256]; // Array for keypresses
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // Declaration of the window procedure
GLvoid ResizeGLScene(GLsizei width, GLsizei height) //resize and initialize GL window
{
if(height == 0)
{
height = 1;
}
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION); // Code after this will affect the projection matrix
glLoadIdentity(); // Reset the current matrix(projection)
gluPerspective(45.0f, width/height, 0.1f, 100.0f); // setting the perspective and calculating aspect ratio
glMatrixMode(GL_MODELVIEW); // Code after this will affect the modelview matrix
glLoadIdentity(); // Reset the current matrix(modelview)
}
int InitGL(GLvoid) //Setup and initialize openGL
{
glShadeModel(GL_SMOOTH); //Set shademodel to smooth shading
glClearColor(1.0f, 0.5f, 0.5f, 0.0f); //set the screen default color rgb
glClearDepth(1.0f); // set default depth to 1 and setup
glEnable(GL_DEPTH_TEST); // Enables depth test
glDepthFunc(GL_LEQUAL); // indicates the type of depth test
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // nicest perspective calculations
return true;
}
int DrawGLScene(GLvoid) //DRAWING
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // set the screen to the clear color and clears the depth buffer
glLoadIdentity();
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(100, 200);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex2f(200, 200);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex2f(200, 100);
glColor3f(0.0f, 0.0f, 0.0f);
glVertex2f(100, 100);
glEnd();
return true;
}
GLvoid KillGLWindow(GLvoid)
{
if(fullscreen) // is fuulscreen active
{
ChangeDisplaySettings(NULL, 0); // use default displaysetting(no fullscreen)
ShowCursor(true);
}
if(hRC) // is a rendering context present?
{
if(!wglMakeCurrent(NULL, NULL)) // can device context and rendering context be released?
{
MessageBox(NULL, "Couldn't Release DC And RC", "Shutdown Error", MB_OK | MB_ICONINFORMATION);
}
if(!wglDeleteContext(hRC)) // can rendering context be deleted
{
MessageBox(NULL, "Couldn't Release DC And RC", "Shutdown Error", MB_OK | MB_ICONINFORMATION);MessageBox(NULL, "Couldn't Delete Rendering Context", "Shutdown Error", MB_OK | MB_ICONINFORMATION);
}
hRC = NULL;
}
if(hDC && !ReleaseDC(hWnd, hDC)) // Can device context be released
{
MessageBox(NULL, "Couldn't Release Device Context", "Shutdown Error", MB_OK | MB_ICONINFORMATION);
}
if(hWnd && !DestroyWindow(hWnd)) // can window be destroyed
{
MessageBox(NULL, "Couldn't destroy window handle", "Shutdown Error", MB_OK | MB_ICONINFORMATION);
hWnd = NULL;
}
if(!UnregisterClass("OpenGL", hInstance))
{
MessageBox(NULL, "Couldn't Unregister Class", "Shutdown Error", MB_OK | MB_ICONINFORMATION);
hInstance = NULL;
}
}
BOOL CreateGLWindow(char* title, int width, int height, int bits, bool fullscreenflag)
{
GLuint PixelFormat;
WNDCLASS wc;
DWORD dwExStyle; //Window Extended Style
DWORD dwStyle; //Window Style
RECT WindowRect;
WindowRect.left = 0;
WindowRect.right = width;
WindowRect.top = 0;
WindowRect.bottom = height;
fullscreen = fullscreenflag;
hInstance = GetModuleHandle(NULL);
wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
wc.lpfnWndProc = (WNDPROC) WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL, IDI_WINLOGO);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = NULL;
wc.lpszMenuName = NULL;
wc.lpszClassName = "OpenGL";
if(!RegisterClass(&wc))
{
MessageBox(NULL, "Couldn't Register The Window Class", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
if(fullscreen)
{
DEVMODE dmScreenSettings; //Device Mode
memset(&dmScreenSettings, 0, sizeof(dmScreenSettings));
dmScreenSettings.dmSize = sizeof(dmScreenSettings);
dmScreenSettings.dmPelsHeight = width;
dmScreenSettings.dmPelsHeight = height;
dmScreenSettings.dmBitsPerPel = bits;
dmScreenSettings.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;
if(ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN) != DISP_CHANGE_SUCCESSFUL)
{
if(MessageBox(NULL, "Fullscreen mode not supported by Graphics Card. Do you want to use windowed mode?", "OpenGL", MB_YESNO | MB_ICONEXCLAMATION) == IDYES)
{
fullscreen = false;
}
else
{
MessageBox(NULL, "Program is closing.", "CLOSING", MB_OK | MB_ICONSTOP);
return false;
}
}
}
if(fullscreen)
{
dwExStyle = WS_EX_APPWINDOW;
dwStyle = WS_POPUP;
ShowCursor(false);
}
else
{
dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;
dwStyle = WS_OVERLAPPEDWINDOW;
}
AdjustWindowRectEx(&WindowRect, dwStyle, false, dwExStyle);
if(!(hWnd = CreateWindowEx(dwExStyle,
"OpenGL",
title,
WS_CLIPSIBLINGS |
WS_CLIPCHILDREN |
dwStyle,
0, 0,
WindowRect.right - WindowRect.left,
WindowRect.bottom - WindowRect.top,
NULL,
NULL,
hInstance,
NULL)))
{
KillGLWindow();
MessageBox(NULL, "Window creation error", "Error", MB_OK | MB_ICONEXCLAMATION);
return false;
}
static PIXELFORMATDESCRIPTOR pfd =
{
sizeof(PIXELFORMATDESCRIPTOR),
1,
PFD_DRAW_TO_WINDOW |
PFD_SUPPORT_OPENGL |
PFD_DOUBLEBUFFER,
PFD_TYPE_RGBA,
bits,
0, 0, 0, 0, 0, 0,
0,
0,
0,
0, 0, 0, 0,
16,
0,
0,
PFD_MAIN_PLANE,
0,
0, 0, 0
};
if(!(hDC = GetDC(hWnd)))
{
KillGLWindow();
MessageBox(NULL, "Can't create a Gl Device Context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
if(!(PixelFormat = ChoosePixelFormat(hDC, &pfd)))
{
KillGLWindow();
MessageBox(NULL, "Couldn't find the rigth pixelformat", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
if(!SetPixelFormat(hDC, PixelFormat, &pfd))
{
KillGLWindow();
MessageBox(NULL, "Couldn't set pixelformat", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
if(!(hRC = wglCreateContext(hDC)))
{
KillGLWindow();
MessageBox(NULL, "Can't create a Gl rendering Context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
if(!wglMakeCurrent(hDC, hRC))
{
KillGLWindow();
MessageBox(NULL, "Can't activate a Gl rendering Context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
ShowWindow(hWnd, SW_SHOW);
SetForegroundWindow(hWnd);
SetFocus(hWnd);
ResizeGLScene(width, height);
if(!InitGL())
{
KillGLWindow();
MessageBox(NULL, "GL Initialization Failed", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return false;
}
return true;
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch(uMsg)
{
case WM_ACTIVATE:
{
if(!HIWORD(wParam))
{
active = true;
}
else
{
active = false;
}
return 0;
}
case WM_SYSCOMMAND:
{
switch(wParam)
{
case SC_SCREENSAVE:
case SC_MONITORPOWER:
return 0;
}
break;
}
case WM_CLOSE:
{
std::cout << "Close" << std::endl;
PostQuitMessage(0);
return 0;
}
case WM_KEYDOWN:
{
keys[wParam] = true;
return 0;
}
case WM_KEYUP:
{
keys[wParam] = false;
return 0;
}
case WM_SIZE:
{
ResizeGLScene(LOWORD(lParam), HIWORD(lParam));
return 0;
}
}
return DefWindowProc(hWnd, uMsg, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
MSG msg;
bool done = false;
if(MessageBox(NULL, "Run application in fullscreen mode?", "Initate Fullscreen", MB_YESNO | MB_ICONQUESTION) == IDNO)
{
fullscreen = false;
}
if(!CreateGLWindow("NeHe's OpenGl Framework", 800, 600, 16, fullscreen))
{
MessageBox(NULL, "framwork failed", "ERROR", MB_OK | MB_ICONEXCLAMATION);
return 0;
}
while(!done)
{
if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
if(msg.message = WM_QUIT)
{
std::cout << "EXIT" << std::endl;
done = false;
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
std::cout << "Translate and Dispatch Msg" << std::endl;
}
}
else
{
if(active)
{
if(keys[VK_ESCAPE])
{
done = true;
}
else
{
DrawGLScene();
SwapBuffers(hDC);
}
}
if(keys[VK_F1])
{
keys[VK_F1] = false;
KillGLWindow();
fullscreen =! fullscreen;
if(!CreateGLWindow("NeHe's OpenGL Framework", 800, 600, 16, fullscreen))
{
return 0;
}
}
}
}
KillGLWindow();
return (msg.wParam);
}

Answer 1

In the case of this program the thing that's setting the message to WM_QUIT is this:
if(msg.message = WM_QUIT)
You've accidentally set the message to WM_QUIT instead of testing for the value by using ==, and because the result of the operation is a non-zero value it always evaluates the true section. In other words it terminates as soon as it receives even a single message rather than pumping the message loop.
If you change the line to:
if(msg.message == WM_QUIT)
Then it tests, instead of assigning the value, and should work correctly.
In general, compiling with full warnings will point this one out.

Answer 2

From the MSDN docs:
WM_QUIT message
Indicates a request to terminate an application, and is generated when the application calls the PostQuitMessage function. This message causes the GetMessage function to return zero.