wglCreateContext fails with error "The pixel format is invalid" - c

Question

I'm trying to access the entire screen with the context.
Here's my current code (currently only this file):
#include <stdio.h>
#include <Windows.h>
#include <GL/gl.h>
#include <gl/glu.h>
#include <GL/glext.h>
int main(int argc, char *argv[]) {
HDC hdc = GetDC(NULL);
HGLRC hglrc;
hglrc = wglCreateContext(hdc);
// Handle errors
if (hglrc == NULL) {
DWORD errorCode = GetLastError();
LPVOID lpMsgBuf;
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
errorCode,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&lpMsgBuf,
0, NULL );
printf("Failed with error %d: %s", errorCode, lpMsgBuf);
LocalFree(lpMsgBuf);
ExitProcess(errorCode);
}
wglMakeCurrent(hdc, hglrc);
printf("%s\n", (char) glGetString(GL_VENDOR));
wglMakeCurrent(NULL, NULL);
wglDeleteContext(hglrc);
return 0;
}
The problem is in this code at the start:
HDC hdc = GetDC(NULL);
HGLRC hglrc;
hglrc = wglCreateContext(hdc);
and the program's output (printed in the error handling if statement) is
Failed with error 2000: The pixel format is invalid.
Calling GetDC(NULL) is specified as retrieving the DC of the entire screen, so I'm not sure what is going wrong here. How do I fix this?
EDIT: added more information

Answer 1

You didn't set the pixel format.
Have a look at the documentation here.
You should declare a pixel format descriptor, for example:
PIXELFORMATDESCRIPTOR pfd =
{
sizeof(PIXELFORMATDESCRIPTOR),
1,
PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER, // Flags
PFD_TYPE_RGBA, // The kind of framebuffer. RGBA or palette.
32, // Colordepth of the framebuffer.
0, 0, 0, 0, 0, 0,
0,
0,
0,
0, 0, 0, 0,
24, // Number of bits for the depthbuffer
8, // Number of bits for the stencilbuffer
0, // Number of Aux buffers in the framebuffer.
PFD_MAIN_PLANE,
0,
0, 0, 0
};
Then use the ChoosePixelFormat to obtain the pixel format number, e.g.:
int iPixelFormat = ChoosePixelFormat(hdc, &pfd);
and finally call the SetPixelFormat function to set the correct pixel format, e.g.:
SetPixelFormat(hdc, iPixelFormat, &pfd);
Only then, you can call the wglCreateContext function.
UPDATE
As pointed out by user Chris Becke one can not call SetPixelFormat on the screen hDC (obtained with GetDC(NULL) as per the OP code). This is reported also in the khronos wiki here.
Therefore, you must also create your own Window, obtain its DC and then use it to set the pixel format and create the GL context. If you want to render "fullscreen" you simply have to create a borderless window with the same size of the screen. I suggest to have a look at the answers to this old question here on SO about this matter.