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## Creating an OpenGL context on Windows with Glew.

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### #1Tocs  Members

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Posted 26 June 2014 - 11:57 AM

Something weird has happened. I had context creation working just fine. It worked on my desktop and my laptop and I was happily plugging along doing graphics programming. One day I attempt to build my code on my laptop again, suddenly context creation starts to fail. I don't know what has changed.

My original context creation code looks like this

https://gist.github.com/LordTocs/f227528a729986df9643

It's sloppy and has next to no error handling but it at least worked. It still works on my desktop and fails on my laptop.

Specifically wglCreateContextAttribsARB fails.

I started to modify the code in an attempt to figure out what was wrong. I added some "GetLastError()" print outs in hopes I was doing something silly and it would tell me what was wrong. Using "FormatMessage()" to change error code into readable stings.

Instead of a usable error I was greeted with GetLastError() returning 3221692565. Which FormatMessage() had no idea what to do with. A quick cursory internet search lead me to a single result on the opengl forums. Which didn't yield any results

After some reading I was told not to create a forward compatible context. And that I should use wglChoosePixelFormatARB to get the appropriate pixel format. Thinking this was the issue, I tried to use this function, it didn't help.

So now I'm left with this code that doesn't work and I'm very confused.

void DisplayWindowsError()
{
LPVOID lpMsgBuf;
DWORD dw = GetLastError();

FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&lpMsgBuf,
0, NULL);

if (lpMsgBuf)
{
std::cout << "Windows Error:" << dw << ": " << (char *)lpMsgBuf << std::endl;
LocalFree(lpMsgBuf);
}
else
{
std::cout << "Windows Error:" << dw << ": unknown" <<  std::endl;
}
}

GraphicsContext::GraphicsContext(ContextTarget &target)
: Target (target)
{
PIXELFORMATDESCRIPTOR pfd =			// pfd Tells Windows How We Want Things To Be
{
sizeof(PIXELFORMATDESCRIPTOR),	// Size Of This Pixel Format Descriptor
1,								// Version Number
PFD_DRAW_TO_WINDOW |			// Format Must Support Window
PFD_SUPPORT_OPENGL |			// Format Must Support OpenGL
PFD_DOUBLEBUFFER,				// Must Support Double Buffering
PFD_TYPE_RGBA,					// Request An RGBA Format
32,								// Select Our Color Depth
0, 0, 0, 0, 0, 0,				// Color Bits Ignored
0,								// No Alpha Buffer
0,								// Shift Bit Ignored
0,								// No Accumulation Buffer
0, 0, 0, 0,						// Accumulation Bits Ignored
24,								// 32Bit Z-Buffer (Depth Buffer)
8,								// No Stencil Buffer
0,								// No Auxiliary Buffer
PFD_MAIN_PLANE,					// Main Drawing Layer
0,								// Reserved
0, 0, 0								// Layer Masks Ignored
};
PixelFormat = 1;
if (!(PixelFormat = ChoosePixelFormat (target.GetHDC (), &pfd)))
{
DisplayWindowsError();
cout << "Failed to choose pixel format." << endl;
}

if (!SetPixelFormat(target.GetHDC(),PixelFormat, &pfd))
{
//DestroyGameWindow (); //Insert Error
DisplayWindowsError();
cout << "Failed to set pixel format." << endl;
}

HGLRC temp;
temp = wglCreateContext(target.GetHDC());
if (!temp)
{
//DestroyGameWindow (); //Insert Error
cout << "Failed to create context" << endl;

}
DisplayWindowsError();
if (!wglMakeCurrent(target.GetHDC (), temp))
{
//DestroyGameWindow ();
cout << "Failed to make current." << endl;
GLErrorCheck();
}
DisplayWindowsError();

GLenum err = glewInit();

if (err != GLEW_OK)
{
char *error = (char *)glewGetErrorString(err);
cout << "GLEW INIT FAIL: " << error << endl;
}

int contextattribs [] =
{
WGL_CONTEXT_MAJOR_VERSION_ARB, 4,
WGL_CONTEXT_MINOR_VERSION_ARB, 2,
#ifdef _DEBUG
WGL_CONTEXT_FLAGS_ARB,  WGL_CONTEXT_DEBUG_BIT_ARB,
#endif
0
};

int pfattribs[] =
{
WGL_DRAW_TO_WINDOW_ARB, GL_TRUE,
WGL_SUPPORT_OPENGL_ARB, GL_TRUE,
WGL_DOUBLE_BUFFER_ARB, GL_TRUE,
WGL_PIXEL_TYPE_ARB, WGL_TYPE_RGBA_ARB,
WGL_COLOR_BITS_ARB, 32,
WGL_DEPTH_BITS_ARB, 24,
WGL_STENCIL_BITS_ARB, 8,
0
};

if (wglewIsSupported ("WGL_ARB_create_context") == 1)
{
unsigned int formatcount;

if (!wglChoosePixelFormatARB(target.GetHDC(), pfattribs, nullptr, 1, (int *)&PixelFormat, &formatcount))
{
std::cout << "Failed to find a matching pixel format" << std::endl;
DisplayWindowsError();
}

if (!SetPixelFormat(target.GetHDC(), PixelFormat, &pfd))
{
DisplayWindowsError();
std::cout << "Failed to set pixelformat" << std::endl;
}

hRC = wglCreateContextAttribsARB(Target.GetHDC(), nullptr, contextattribs);
if (!hRC)
{
DisplayWindowsError();
std::cout << "Failed to create context." << std::endl;
}
wglMakeCurrent(nullptr, nullptr);
DisplayWindowsError();
wglDeleteContext(temp);
DisplayWindowsError();
GLErrorCheck();
MakeCurrent ();

}
else
{
cout << "Failed to create context again..." << endl;
}

#ifdef _DEBUG
glEnable(GL_DEBUG_OUTPUT);
glDebugMessageCallback(dbgcallback, nullptr);
#endif

//GLErrorCheck;
char *version = (char *)glGetString(GL_VERSION);
//GLErrorCheck;
std::cout << "Version: " << version << std::endl << "Shading Version: " << shadeversion << std::endl;

glViewport (0,0,Target.GetWidth (), Target.GetHeight ());
GLErrorCheck ();

SetClearColor (Color(0,0,0,0));
SetClearDepth(1000.0f);
//EnableDepthBuffering ();
//DisableDepthTest ();
NormalBlending ();

glHint(GL_POLYGON_SMOOTH_HINT, GL_NICEST); //Doesn't get Abstracted
GLErrorCheck();

}


If anyone knows what I'm doing wrong I'd love to know.

Thanks.

### #2NumberXaero  Prime Members

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Posted 26 June 2014 - 01:15 PM

int attribs [] =
{
WGL_CONTEXT_MAJOR_VERSION_ARB, 4,
WGL_CONTEXT_MINOR_VERSION_ARB, 2,
#ifdef _DEBUG
WGL_CONTEXT_FLAGS_ARBWGL_CONTEXT_FORWARD_COMPATIBLE_BIT | WGL_CONTEXT_DEBUG_BIT_ARB,
#else
WGL_CONTEXT_FLAGS_ARBWGL_CONTEXT_FORWARD_COMPATIBLE_BIT,
#endif
0
};

I think "WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB," is needed for versions greater then 3.2

### #3Tocs  Members

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Posted 26 June 2014 - 01:39 PM

Hmm I placed it into the "contextattribs []" array in the new code. Still getting the same result. Thanks for the help.

### #4ProtectedMode  Members

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Posted 26 June 2014 - 01:41 PM

Is there any reason you can't use something like GLFW?

### #5Tocs  Members

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Posted 26 June 2014 - 01:56 PM

I suppose there isn't really a great reason to not use GLFW. Other than I do my own window creation as well. I have a little UI framework that the context creation hooks into as well. I suppose I could fiddle with GLFW to get it all to work in harmony. But I've been using my own context creation for like a year now, it only recently decided to die on my laptop. Is there any reason I can't use my own context creation? It's part "not invented here" syndrome and part curiosity as to what I'm doing wrong. Perhaps I'll look at GLFW's source for hints.

### #6Tocs  Members

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Posted 26 June 2014 - 02:19 PM

I noticed 3221692565 is 0xC0072095. According to the NVidia create context spec 0x2095 is ERROR_INVALID_VERSION_ARB. So I bumped the version down to 3.3 and it successfully creates a context. Which raises more questions because I should be able to create a 4.2 context. I need a 4.2 context because of shader_storage_buffers and other things.

### #7swiftcoder  Senior Moderators

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Posted 26 June 2014 - 03:41 PM

Your driver reports OpenGL 4.3, *not* 4.2. Try creating a 4.3 context and see what happens.

OpenGL drivers are notoriously picky about version specifications - on my MacBook the drivers require I specify the exact version supported by the driver, not any previous major/minor version.

Edited by swiftcoder, 26 June 2014 - 03:41 PM.

Tristam MacDonald - Software Engineer @ Amazon - [swiftcoding] [GitHub]

### #8Tocs  Members

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Posted 26 June 2014 - 05:11 PM

Interesting thought. Alas, 4.3 fails as well.

Here's where the code's at now.


void DisplayWindowsError()
{
LPVOID lpMsgBuf;
DWORD dw = GetLastError();

FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&lpMsgBuf,
0, NULL);

if (lpMsgBuf)
{
std::cout << "Windows Error:" << dw << ": " << (char *)lpMsgBuf << std::endl;
LocalFree(lpMsgBuf);
}
else
{
std::cout << "Windows Error:" << dw << ": unknown " << std::hex << dw <<  std::endl;
}
}

GraphicsContext::GraphicsContext(ContextTarget &target)
: Target (target)
{
PIXELFORMATDESCRIPTOR pfd =			// pfd Tells Windows How We Want Things To Be
{
sizeof(PIXELFORMATDESCRIPTOR),	// Size Of This Pixel Format Descriptor
1,								// Version Number
PFD_DRAW_TO_WINDOW |			// Format Must Support Window
PFD_SUPPORT_OPENGL |			// Format Must Support OpenGL
PFD_DOUBLEBUFFER,				// Must Support Double Buffering
PFD_TYPE_RGBA,					// Request An RGBA Format
32,								// Select Our Color Depth
0, 0, 0, 0, 0, 0,				// Color Bits Ignored
0,								// No Alpha Buffer
0,								// Shift Bit Ignored
0,								// No Accumulation Buffer
0, 0, 0, 0,						// Accumulation Bits Ignored
24,								// 32Bit Z-Buffer (Depth Buffer)
8,								// No Stencil Buffer
0,								// No Auxiliary Buffer
PFD_MAIN_PLANE,					// Main Drawing Layer
0,								// Reserved
0, 0, 0								// Layer Masks Ignored
};
PixelFormat = 1;
if (!(PixelFormat = ChoosePixelFormat (target.GetHDC (), &pfd)))
{
DisplayWindowsError();
cout << "Failed to choose pixel format." << endl;
}

if (!SetPixelFormat(target.GetHDC(),PixelFormat, &pfd))
{
//DestroyGameWindow (); //Insert Error
DisplayWindowsError();
cout << "Failed to set pixel format." << endl;
}

HGLRC temp;
temp = wglCreateContext(target.GetHDC());
if (!temp)
{
//DestroyGameWindow (); //Insert Error
cout << "Failed to create context" << endl;

}
DisplayWindowsError();
if (!wglMakeCurrent(target.GetHDC (), temp))
{
//DestroyGameWindow ();
cout << "Failed to make current." << endl;
GLErrorCheck();
}
DisplayWindowsError();

GLenum err = glewInit();

if (err != GLEW_OK)
{
char *error = (char *)glewGetErrorString(err);
cout << "GLEW INIT FAIL: " << error << endl;
}

int contextattribs [] =
{
WGL_CONTEXT_MAJOR_VERSION_ARB, 4,
WGL_CONTEXT_MINOR_VERSION_ARB, 3,
#ifdef _DEBUG
WGL_CONTEXT_FLAGS_ARB, WGL_CONTEXT_DEBUG_BIT_ARB,
#endif
0
};

int pfattribs[] =
{
WGL_DRAW_TO_WINDOW_ARB, GL_TRUE,
WGL_SUPPORT_OPENGL_ARB, GL_TRUE,
WGL_DOUBLE_BUFFER_ARB, GL_TRUE,
WGL_PIXEL_TYPE_ARB, WGL_TYPE_RGBA_ARB,
WGL_COLOR_BITS_ARB, 32,
WGL_DEPTH_BITS_ARB, 24,
WGL_STENCIL_BITS_ARB, 8,
0
};

if (wglewIsSupported ("WGL_ARB_create_context") == 1)
{
unsigned int formatcount;

if (!wglChoosePixelFormatARB(target.GetHDC(), pfattribs, nullptr, 1, (int *)&PixelFormat, &formatcount))
{
std::cout << "Failed to find a matching pixel format" << std::endl;
DisplayWindowsError();
}

if (!SetPixelFormat(target.GetHDC(), PixelFormat, &pfd))
{
DisplayWindowsError();
std::cout << "Failed to set pixelformat" << std::endl;
}

hRC = wglCreateContextAttribsARB(Target.GetHDC(), nullptr, contextattribs);
if (!hRC)
{
DisplayWindowsError();
std::cout << "Failed to create context." << std::endl;
}
wglMakeCurrent(nullptr, nullptr);
DisplayWindowsError();
wglDeleteContext(temp);
DisplayWindowsError();
GLErrorCheck();
MakeCurrent ();

}
else
{
cout << "Failed to create context again..." << endl;
}

#ifdef _DEBUG
glEnable(GL_DEBUG_OUTPUT);
glDebugMessageCallback(dbgcallback, nullptr);
#endif

//GLErrorCheck;
char *version = (char *)glGetString(GL_VERSION);
//GLErrorCheck;
std::cout << "Version: " << version << std::endl << "Shading Version: " << shadeversion << std::endl;

glViewport (0,0,Target.GetWidth (), Target.GetHeight ());
GLErrorCheck ();

SetClearColor (Color(0,0,0,0));
SetClearDepth(1000.0f);
//EnableDepthBuffering ();
//DisableDepthTest ();
NormalBlending ();

glHint(GL_POLYGON_SMOOTH_HINT, GL_NICEST); //Doesn't get Abstracted
GLErrorCheck();

}


Outputs:
Windows Error:0: The operation completed successfully.
Windows Error:0: The operation completed successfully.
Windows Error:3221692565: unknown c0072095
Failed to create context.

Maybe my drivers need updating or something...

### #9cgrant  Members

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Posted 27 June 2014 - 12:49 PM

Setting the major version to 1 and the minor version to 0 in the context attrbute list gives you the latest/highest version supported by the driver at least for compatibility profile context.

After some reading I was told not to create a forward compatible context. And that I should use wglChoosePixelFormatARB to get the appropriate pixel format. Thinking this was the issue, I tried to use this function, it didn't help.

Told by whom. The only thing to be aware of with creating compatiblity context is deprecation, and even if the driver supported a core context, the deprecated functionality is still present in the driver, just not accessible from the core profile context. Feel free to use whatever context that suits you taste. In general its always good to stay away from deprecated functionality in whatever software library you are using, and OpenGL shouldn't be any different in that regards.

### #10cgrant  Members

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Posted 27 June 2014 - 12:50 PM

Just for clarification, my question in regards to the quote is only for the first sentence.

### #11Tocs  Members

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Posted 27 June 2014 - 05:46 PM

The wiki says "A forward compatible context must fully remove deprecated features in the version that it returns; you should never actually use this." It's actually bolded on wiki so I took it at face value. Perhaps the wiki is overzealous. It seems like it would be a good idea to not include deprecated features, however I suppose if somewhere down the line features I'm using became deprecated and I asked for the latest context without deprecated features I would suddenly break my program. That seems like a far out case though.

Interestingly enough if I set major to 1 and minor to 0. I get a 3.3 context. I tried updating the drivers, same results.

### #12swiftcoder  Senior Moderators

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Posted 27 June 2014 - 05:54 PM

The wiki says "A forward compatible context must fully remove deprecated features in the version that it returns;you should never actually use this." It's actually bolded on wiki so I took it at face value. Perhaps the wiki is overzealous. It seems like it would be a good idea to not include deprecated features, however I suppose if somewhere down the line features I'm using became deprecated and I asked for the latest context without deprecated features I would suddenly break my program. That seems like a far out case though.

They are just paraphrasing NVidia's guidelines there. You would expect a Core context to be more efficient, given that all deprecated functionality can be removed, but in some cases a single driver implements both Core and non-Core contexts, and in the Core case, it may have to add a bunch of extra error checking to make sure you don't call non-Core functionality.

I generally recommend that you use a Core context for development, and if you feel it necessary, switch to a non-Core context for release.

Tristam MacDonald - Software Engineer @ Amazon - [swiftcoding] [GitHub]

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