Create a DC OpenGL for multiple cards

gistfile1.txt

#include <string.h>
#include <windows.h>
#include <gl/gl.h>
#include "glext.h"
#include "wglext.h"
 
 
HWND WINAPI window_from_dc_replacement(HDC dc)
{
	static HWND wnd = NULL;
 
	if (dc == NULL)
		return NULL;
 
	if (wnd == NULL) {
		WNDCLASSA wc;
		memset(&amp;wc, 0, sizeof(wc));
		wc.lpfnWndProc = DefWindowProc;
		wc.hInstance = GetModuleHandleA(NULL);
		wc.lpszClassName = "_dummy_window_class_";
		RegisterClassA(&amp;wc);
		wnd = CreateWindowA(wc.lpszClassName, NULL, WS_POPUP, 0, 0, 32, 32, NULL, NULL, wc.hInstance, NULL);
	}
 
	return wnd;
}
 
void patch_window_from_dc()
{
	DWORD old_prot;
	unsigned __int64 wfdc = (unsigned __int64)GetProcAddress(GetModuleHandleA("user32.dll"), "WindowFromDC");
 
	VirtualProtect((void *)wfdc, 14, PAGE_EXECUTE_WRITECOPY, &amp;old_prot);
 
	// jmp [eip + 0]
	*(char *)(wfdc + 0) = 0xFF;
	*(char *)(wfdc + 1) = 0x25;
	*(unsigned *)(wfdc + 2) = 0x00000000;
	*(unsigned __int64 *)(wfdc + 6) = (unsigned __int64)&amp;window_from_dc_replacement;
}
 
 
unsigned char buf[4*256*256];
 
void test_pbuffer()
{
	PIXELFORMATDESCRIPTOR pfd;
	int pfi;
 
	PFNWGLCHOOSEPIXELFORMATARBPROC wglChoosePixelFormatARB;
	PFNWGLCREATEPBUFFERARBPROC wglCreatePbufferARB;
	PFNWGLGETPBUFFERDCARBPROC wglGetPbufferDCARB;
	PFNWGLRELEASEPBUFFERDCARBPROC wglReleasePbufferDCARB;
	PFNWGLDESTROYPBUFFERARBPROC wglDestroyPbufferARB;
 
	int attribs[] = {
		WGL_ACCELERATION_ARB, WGL_FULL_ACCELERATION_ARB,
		WGL_DRAW_TO_PBUFFER_ARB, 1,
		WGL_COLOR_BITS_ARB, 24,
		0 };
	int pbf, n;
	HPBUFFERARB pb;
	HDC pbdc;
 
	const char *vendor;
	HGLRC glrc;
	HDC dc = CreateDCA("\\\\.\\DISPLAY3", "\\\\.\\DISPLAY3", NULL, NULL);
	memset(&amp;pfd, 0, sizeof(pfd));
	pfd.nSize = sizeof(pfd);
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_SUPPORT_OPENGL|PFD_DRAW_TO_WINDOW|PFD_DOUBLEBUFFER_DONTCARE|PFD_STEREO_DONTCARE|PFD_DEPTH_DONTCARE;
	pfd.iPixelType = PFD_TYPE_RGBA;
	pfi = ChoosePixelFormat(dc, &amp;pfd);
	SetPixelFormat(dc, pfi, &amp;pfd);
	glrc = wglCreateContext(dc);
	wglMakeCurrent(dc, glrc);
 
	vendor = glGetString(GL_VENDOR);
	wglChoosePixelFormatARB = (PFNWGLCHOOSEPIXELFORMATARBPROC)wglGetProcAddress("wglChoosePixelFormatARB");
	wglCreatePbufferARB = (PFNWGLCREATEPBUFFERARBPROC)wglGetProcAddress("wglCreatePbufferARB");
	wglGetPbufferDCARB = (PFNWGLGETPBUFFERDCARBPROC)wglGetProcAddress("wglGetPbufferDCARB");
	wglReleasePbufferDCARB = (PFNWGLRELEASEPBUFFERDCARBPROC)wglGetProcAddress("wglReleasePbufferDCARB");
	wglDestroyPbufferARB = (PFNWGLDESTROYPBUFFERARBPROC)wglGetProcAddress("wglDestroyPbufferARB");
 
	wglChoosePixelFormatARB(dc, attribs, NULL, 1, &amp;pbf, &amp;n);
	pb = wglCreatePbufferARB(dc, pbf, 256, 256, NULL);
	pbdc = wglGetPbufferDCARB(pb);
	wglMakeCurrent(pbdc, glrc);
 
	glClearColor(0.5f, 0, 1, 0);		
	glClear(GL_COLOR_BUFFER_BIT);
	glScissor(64, 64, 128, 128);
	glEnable(GL_SCISSOR_TEST);		
	glClearColor(0, 1, 0.5f, 0);		
	glClear(GL_COLOR_BUFFER_BIT);
	glReadPixels(0, 0, 256,256, GL_RGBA, GL_UNSIGNED_BYTE, buf);
}
 
 
void test_fbo()
{
	PIXELFORMATDESCRIPTOR pfd;
	int pfi;
 
	void (_stdcall *glGenRenderbuffers)(GLsizei n, GLuint *renderbuffers);
	void (_stdcall *glBindRenderbuffer)(GLenum target, GLuint renderbuffer);
	void (_stdcall *glRenderbufferStorage)(GLenum target, GLenum internalformat, GLsizei width, GLsizei height);
	void (_stdcall *glGenFramebuffers)(GLsizei n, GLuint *framebuffers);
	void (_stdcall *glBindFramebuffer)(GLenum target, GLuint framebuffer);
	void (_stdcall *glFramebufferRenderbuffer)(GLenum target, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer);
	GLenum (_stdcall *glCheckFramebufferStatus)(GLenum target);
 
	const char *vendor;
	GLuint cb, fb;
	GLenum res;
 
	HGLRC glrc;
	HDC dc = CreateDCA("\\\\.\\DISPLAY1", "\\\\.\\DISPLAY1", NULL, NULL);
	memset(&amp;pfd, 0, sizeof(pfd));
	pfd.nSize = sizeof(pfd);
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_SUPPORT_OPENGL|PFD_DRAW_TO_WINDOW|PFD_DOUBLEBUFFER_DONTCARE|PFD_STEREO_DONTCARE|PFD_DEPTH_DONTCARE;
	pfd.iPixelType = PFD_TYPE_RGBA;
	pfi = ChoosePixelFormat(dc, &amp;pfd);
	SetPixelFormat(dc, pfi, &amp;pfd);
	glrc = wglCreateContext(dc);
	wglMakeCurrent(dc, glrc);
 
	vendor = glGetString(GL_VENDOR);
	*(PROC *)&amp;glGenRenderbuffers = wglGetProcAddress("glGenRenderbuffers");
	*(PROC *)&amp;glBindRenderbuffer = wglGetProcAddress("glBindRenderbuffer");
	*(PROC *)&amp;glRenderbufferStorage = wglGetProcAddress("glRenderbufferStorage");
	*(PROC *)&amp;glGenFramebuffers = wglGetProcAddress("glGenFramebuffers");
	*(PROC *)&amp;glBindFramebuffer = wglGetProcAddress("glBindFramebuffer");
	*(PROC *)&amp;glFramebufferRenderbuffer = wglGetProcAddress("glFramebufferRenderbuffer");
	*(PROC *)&amp;glCheckFramebufferStatus = wglGetProcAddress("glCheckFramebufferStatus");
 
	glGenRenderbuffers(1, &amp;cb);
	glBindRenderbuffer(GL_RENDERBUFFER, cb);
	glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA, 256, 256);
 
	glGenFramebuffers(1, &amp;fb);
	glBindFramebuffer(GL_FRAMEBUFFER, fb);
	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, cb);
 
	res = glCheckFramebufferStatus(GL_FRAMEBUFFER);
//	if (res != GL_FRAMEBUFFER_COMPLETE) _asm int 3
 
	glClearColor(0.5f, 0, 1, 0);
	glClear(GL_COLOR_BUFFER_BIT);
	glReadPixels(0, 0, 256,256, GL_RGBA, GL_UNSIGNED_BYTE, buf);
}
 
 
int WINAPI WinMain(HINSTANCE i, HINSTANCE pi, LPSTR cl, int s)
{
	patch_window_from_dc();
 
	if (0) {
		DISPLAY_DEVICEA dev;
		int k = 0;
		dev.cb = sizeof(dev);
		while (EnumDisplayDevicesA(NULL, k, &amp;dev, 0))
			k += 1;
	}
 
	test_fbo();
	//test_pbuffer();
 
	return 0;
}