Windows PBuffer without a window

If I understand you right, you want to create a PBuffer without creating a window. Here is a standard code to create a PBuffer:

	HDC hDC = wglGetCurrentDC();	

	// Get ready to query for a suitable pixel format that meets our minimum requirements.

	int iAttributes[2*MAX_ATTRIBS];
	float fAttributes[2*MAX_ATTRIBS];
	int nfAttribs = 0;
	int niAttribs = 0;
	// Attribute arrays must be "0" terminated - for simplicity, first

	// just zero-out the array then fill from left to right.	

	for (i=0; i<2*MAX_ATTRIBS; i++ ){
		iAttributes[i] = 0;
		fAttributes[i] = 0;
	}
	// Since we are trying to create a pbuffer, the pixel format we

	//request (and subsequently use) must be "p-buffer capable".

	iAttributes[2*niAttribs]=WGL_DRAW_TO_PBUFFER_ARB;
	iAttributes[2*niAttribs+1]=true;
	niAttribs++;
	// We require a minimum of 24-bit depth.

	iAttributes[2*niAttribs ]=WGL_DEPTH_BITS_ARB;
	iAttributes[2*niAttribs+1]=24;
	niAttribs++;
	// We require a minimum of 8-bits for each R, G, B, and A.

	iAttributes[2*niAttribs]=WGL_RED_BITS_ARB;
	iAttributes[2*niAttribs+1]=8;
	niAttribs++;
	iAttributes[2*niAttribs]=WGL_GREEN_BITS_ARB;
	iAttributes[2*niAttribs+1]=8;
	niAttribs++;
	iAttributes[2*niAttribs]=WGL_BLUE_BITS_ARB;
	iAttributes[2*niAttribs+1]=8;
	niAttribs++;
	iAttributes[2*niAttribs]=WGL_ALPHA_BITS_ARB;
	iAttributes[2*niAttribs+1]=8;
	niAttribs++;
	// Now obtain a list of pixel formats that meet these minimum requirements.

	int pformat;
	unsigned int nformats;
	if(!wglChoosePixelFormatARB( hDC, iAttributes, fAttributes, 1, &pformat, &nformats)){
		printf("pbuffer creation error: Couldn't find a suitable pixel format.\n" );
		return false;
	}

	for (i=0; i<2*MAX_ATTRIBS; i++ )iAttributes[i] = 0;
		
	g_hPBuffer=wglCreatePbufferARB( hDC, pformat, PBUFFERSIZE, PBUFFERSIZE, iAttributes );
	g_hPBufDC=wglGetPbufferDCARB( g_hPBuffer );

	int w,h;
	wglQueryPbufferARB( g_hPBuffer, WGL_PBUFFER_WIDTH_ARB, &w );
	wglQueryPbufferARB( g_hPBuffer, WGL_PBUFFER_HEIGHT_ARB, &h );
	printf("PBuffer size: %d x %d\n",w,h);	

	g_hPBufRC=wglCreateContext(g_hPBufDC);	
	return true;

As you can see the most functions uses de current device context which is activated when you create an OpenGL window.
You could try to create a DC of the screen and use it. I'm not sure if that will work.

[edited by - dslprog on April 23, 2004 6:39:32 PM]

basicaly, as dslprog says, you need a device context which I belive needs to be setup for OpenGL.

The reason being, before that point OGL isnt setup and, on windows at least, you need OGL to be set up in order to get at the extra WGL functions for making pbuffers.

I know how to make a pbuffer. If I do the hidden window thing it works fine. I want to be able to create a pbuffer without making the hidden window. I can create a DC without error. I get a valid pixel format. When I set the format it returns true but sets GetLastError to INVALID_HANDLE. After that wglCreateContext returns a nonzero number but if I try to make the context current I get a error in the 3 billion range. I have looked at several posts that say it can be done but I have never seen any code that works. If someone can generate working code I would appreciate it a lot.

"... we should have such an empire for liberty as she has never surveyed since the creation ..."
Thomas Jefferson

how do you create the DC?

CreateDC with a device string from enumdisplaydevices.

"... we should have such an empire for liberty as she has never surveyed since the creation ..."
Thomas Jefferson