I have been reading in my book for a while and I tried writing a simple windows program from scratch. I have been scrutinizing the code for quite some time. It even got to the point where I had to open the book back up again and compare my code (which I unsuccessfully tried writing almost totally by myself) with the code from the book. I still cannot find my error. The code compiles, but doesn''t execute. If you can help me, I will love you for all eternity. The code is not documented.

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h>
#include <gl/glaux.h>

HDC g_hDc;

void SetupPixelFormat(HDC hDc) {
	int nPixelFormat;
	static PIXELFORMATDESCRIPTOR pfd = { 
			sizeof(PIXELFORMATDESCRIPTOR),
			1,
			PFD_DRAW_TO_WINDOW |
			PFD_SUPPORT_OPENGL |
			PFD_DOUBLEBUFFER,
			PFD_TYPE_RGBA,
			32,
			0,0,0,0,0,0,
			0,
			0,
			0,
			0,0,0,0,
			16,
			0,
			0,
			PFD_MAIN_PLANE,
			0,
			0,0,0
	};
	nPixelFormat = ChoosePixelFormat(hDc, &pfd);
	SetPixelFormat(hDc, nPixelFormat, &pfd);

}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
static HGLRC hRc;
static HDC hDc;
int width, height;
switch(message) {
case WM_CREATE:
	hDc = GetDC(hwnd);
	g_hDc = hDc;
	SetupPixelFormat(hDc);
	wglCreateContext(hDc);
	wglMakeCurrent(hDc, hRc);
	
case WM_CLOSE:
	wglMakeCurrent(hDc, NULL);
	wglDeleteContext(hRc);

	DestroyWindow(hwnd);		////////This was suggested by someone else, not from the book!

	PostQuitMessage(0);

	return 0;
	break;

case WM_PAINT:
	height = HIWORD(lParam);
	width = LOWORD(lParam);
	if(height == 0) 
		height = 1;

	glViewport(0, 0, width, height);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	gluPerspective(45.0f, (GLfloat)width/(GLfloat)height, 1.0f, 1000.0f);

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	
	return 0;
	break;


default:
	break;
	}

return (DefWindowProc(hwnd, message, wParam, lParam));
}

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) {
	WNDCLASSEX WindowClass;
	HWND hwnd;
	MSG msg;
	bool done;
	WindowClass.cbSize = sizeof(WNDCLASSEX);
	WindowClass.style = CS_HREDRAW | CS_VREDRAW;
	WindowClass.lpfnWndProc = WndProc;
	WindowClass.cbClsExtra = 0;
	WindowClass.cbWndExtra = 0;
	WindowClass.hInstance = hInstance;
	WindowClass.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
	WindowClass.hCursor = LoadCursor(hInstance, IDC_CROSS);
	WindowClass.hbrBackground = NULL;
	WindowClass.hIconSm = LoadIcon(NULL, IDI_WINLOGO);
	WindowClass.lpszClassName = "My class";
	WindowClass.lpszMenuName = "My windows application";	

	if(!RegisterClassEx(&WindowClass))
		return 0;

		hwnd = CreateWindowEx(NULL,
		"My class",
		"My window",
		WS_OVERLAPPEDWINDOW | WS_VISIBLE | WS_SYSMENU | WS_CLIPCHILDREN |
		WS_CLIPSIBLINGS,
		0, 0, 
		512, 512,
		NULL,
		NULL,
		hInstance,
		NULL);
		
		if(!hwnd)
			return 0;

		done = false;

		ShowWindow(hwnd, SW_SHOW);
		UpdateWindow(hwnd);

		while(!done) {
			PeekMessage(&msg, hwnd, NULL, NULL, PM_REMOVE);
			if(msg.message == WM_CLOSE)
				done = true;

			else {
				glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
				glLoadIdentity();
				glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
				glColor3f(0.0f, 1.0f, 0.0f);
				glBegin(GL_LINES);
					glVertex3f(0.0f, 0.0f, -1.0f);
					glVertex3f(1.0f, 1.0f, -1.0f);
				glEnd();

				SwapBuffers(g_hDc);
				TranslateMessage(&msg);
				DispatchMessage(&msg);

			}
		}
		return msg.wParam;
}
 

Like I said, I don''t get any errors or warnings, but for some reason nothing shows up.

hum i notice somehting but i dont if it really isnthe problem.. the msg.message.. change to msg.wParam.. also the last return would work fine with return 0.... other thing.. the wglCreateContext (hDc) to what ?? tri this hRc = wglCreateContext (hDc) ... and make both wglCreateContext and wglMakeCurrent (hDc,hRc) inside the other funcion called setuuppixelformat.. if i''m not mistake .. strange the gl/ should not work it''s gl\whatever.h ...

Metal Typhoon

case WM_CREATE:
hDc = GetDC(hwnd);
g_hDc = hDc;
SetupPixelFormat(hDc);
wglCreateContext(hDc);
wglMakeCurrent(hDc, hRc);
return 0 ;

AND

while(!done) {
if(PeekMessage(&msg, 0, NULL, NULL, PM_REMOVE)){
if(msg.message == WM_QUIT)
done = true;

TranslateMessage(&msg);
DispatchMessage(&msg);
}
else {
...
}
}

Also, yeah. You''ll want to store the rendering context and so you can actually draw.

Peace,
ZE.


//email me.//zealouselixir software.//msdn.//n00biez.//
miscellaneous links

I see where I should''ve assigned the wglCreateContext(hDc) to something. I changed that in my WM_CREATE: case in my wndproc (the only place it seems that should be changed) and the code does not run.

case WM_CREATE:	hDc = GetDC(hwnd);	g_hDc = hDc;	hRc = wglCreateContext(hDc);	SetupPixelFormat(hDc);	wglMakeCurrent(hDc, hRc); 

That is what it looks like, is that correct?

A few more things:

*[EDIT] DON'TUse NULL instead of 0 unless you defined NULL yourself.
*Don't use globals, ever.
*Don't set your background to NULL/0. If you're having trouble with an explicit cast error, then explicitly cast! (e.g. hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH))
*return 0 from all the messages you process (there might be exceptions to that sometimes)
*Don't use glaux. All you might need it for is bitmap loading, and you can write your own.
*I would strongly advise you to set up your perspective stuff within WM_SIZE, rather than WM_PAINT.
*Only process messages when you get them. That is, PeekMessage will return true if you have received a message from the queue, and only then do you need to check for a WM_QUIT (not WM_CLOSE) and dispatch it.
*I'd advise that you add CS_OWNDC to your class styles
*When loading icons and cursors that are already defined (e.g. IDI_WINLOGO, IDC_ARROW, IDC_CROSS), don't set the hInstance to the hInstance of your application. Rather, set it to NULL/0 unless you are loading the icon from a file or a resource

That's about it.

[edited by - zealouselixir on August 12, 2002 10:34:51 PM]

You need to return 0 in the WM_CREATE handler

Developer Tutorials

Tilch is right- you need to return from WM_CREATE, otherwise execution proceeds to your code under WM_CLOSE, where you call DestroyWindow.
this is useful if you want do the same thing for two or more different messages:

case WM_KEYDOWN:
case WM_LBUTTONDOWN:
//do something here
return 0;

whatever you put in between WM_LBUTTONDOWN will execute in the case of a keydown or a left mouse button click.
This same concept is your problem because you are calling DestroyWindow directly after WM_CREATE, so you never even show it before it''s destruction...and you probably dont want to destroy it until you close your application. That may be your problem as far as getting the window to show up. You should add more error handling, like checking the return of the API functions you call. By the way i am by no means an expert, I''m a beginner. these are just some things i''ve learned from my own mistakes.
one other thing- it is redundant to call break after return because return ends the function, whereas break just exits the switch. this is not an error that would cause problems, but i hope you can better understand what is going on in your code.

Hey guys, you have been MORE than helpful. I have saved just about everything in this post in text files. I don't really know how to learn this freakin API...I just read OpenGL game programming, I take notes, I write down what Winmain and wndproc are supposed to accomplish and then I try to write the program on my own. A lot of the stuff you guys suggested goes against what i learned in ogl game programming (e.g the global variables) but then again they have made plenty of mistakes in that book.

Also, do you guys have any suggestions for learning the OpenGL api. I mean are there any special rituals you guys have when reading or coding or whatnot? Thanks again for helping me and being cool.

[edited by - Shadow1234567890 on August 13, 2002 10:15:15 AM]

One more error I have encountered...when I am doing something wrong I get this error: cannot open Debug/Opengl3.exe for writing.

This means that I can''t compile it, and I can''t shut down my program (it runs in the background and uses 99% of my processor). I have to restart my computer and if i am lucky I will be able to compile. Any special reason why this is happening?

Now I must go restart