#include "Precomp.h"
#include "OpenGLContext.h"
#include <CommCtrl.h>
#include <stdexcept>

#ifdef WIN32

#define WGL_CONTEXT_MAJOR_VERSION_ARB           0x2091
#define WGL_CONTEXT_MINOR_VERSION_ARB           0x2092
#define WGL_CONTEXT_LAYER_PLANE_ARB             0x2093
#define WGL_CONTEXT_FLAGS_ARB                   0x2094
#define WGL_CONTEXT_DEBUG_BIT_ARB               0x0001
#define WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB  0x0002
#define ERROR_INVALID_VERSION_ARB               0x2095

#define WGL_NUMBER_CL_PIXEL_FORMATS             0x2000
#define WGL_DRAW_TO_WINDOW                   0x2001
#define WGL_DRAW_TO_BITMAP                   0x2002
#define WGL_ACCELERATION                     0x2003
#define WGL_NEED_PALETTE                     0x2004
#define WGL_NEED_SYSTEM_PALETTE              0x2005
#define WGL_SWAP_LAYER_BUFFERS               0x2006
#define WGL_SWAP_METHOD                      0x2007
#define WGL_NUMBER_OVERLAYS                  0x2008
#define WGL_NUMBER_UNDERLAYS                 0x2009
#define WGL_TRANSPARENT                      0x200A
#define WGL_TRANSPARENT_VALUE                0x200B
#define WGL_SHARE_DEPTH                      0x200C
#define WGL_SHARE_STENCIL                    0x200D
#define WGL_SHARE_ACCUM                      0x200E
#define WGL_SUPPORT_GDI                      0x200F
#define WGL_SUPPORT_OPENGL                   0x2010
#define WGL_DOUBLE_BUFFER                    0x2011
#define WGL_STEREO                           0x2012
#define WGL_PIXEL_TYPE                       0x2013
#define WGL_COLOR_BITS                       0x2014
#define WGL_RED_BITS                         0x2015
#define WGL_RED_SHIFT                        0x2016
#define WGL_GREEN_BITS                       0x2017
#define WGL_GREEN_SHIFT                      0x2018
#define WGL_BLUE_BITS                        0x2019
#define WGL_BLUE_SHIFT                       0x201A
#define WGL_ALPHA_BITS                       0x201B
#define WGL_ALPHA_SHIFT                      0x201C
#define WGL_ACCUM_BITS                       0x201D
#define WGL_ACCUM_RED_BITS                   0x201E
#define WGL_ACCUM_GREEN_BITS                 0x201F
#define WGL_ACCUM_BLUE_BITS                  0x2020
#define WGL_ACCUM_ALPHA_BITS                 0x2021
#define WGL_DEPTH_BITS                       0x2022
#define WGL_STENCIL_BITS                     0x2023
#define WGL_AUX_BUFFERS                      0x2024
#define WGL_NO_ACCELERATION                  0x2025
#define WGL_GENERIC_ACCELERATION             0x2026
#define WGL_FULL_ACCELERATION                0x2027
#define WGL_SWAP_EXCHANGE                    0x2028
#define WGL_SWAP_COPY                        0x2029
#define WGL_SWAP_UNDEFINED                   0x202A
#define WGL_TYPE_RGBA                        0x202B
#define WGL_TYPE_COLORINDEX                  0x202C
#define WGL_SAMPLE_BUFFERS                   0x2041
#define WGL_SAMPLES                          0x2042

/////////////////////////////////////////////////////////////////////////////

class OpenGLLoadFunctions
{
public:
	OpenGLLoadFunctions() { ogl_LoadFunctions(); }
};

/////////////////////////////////////////////////////////////////////////////

OpenGLContext::OpenGLContext(void* windowptr) : window((HWND)windowptr)
{
	dc = GetDC(window);
	OpenGLCreationHelper helper(window);
	context = helper.CreateContext(dc, 3, 2);
	if (context)
	{
		Begin();
		static OpenGLLoadFunctions loadFunctions;
		End();
	}
}

OpenGLContext::~OpenGLContext()
{
	if (context)
		wglDeleteContext(context);
	if (dc)
		ReleaseDC(window, dc);
}

void OpenGLContext::Begin()
{
	refcount++;
	if (refcount == 1)
		wglMakeCurrent(dc, context);
}

void OpenGLContext::End()
{
	refcount--;
	if (refcount == 0)
		wglMakeCurrent(0, 0);
}

void OpenGLContext::SwapBuffers()
{
	Begin();
	::SwapBuffers(dc);
	End();
}

int OpenGLContext::GetWidth() const
{
	RECT box = { 0 };
	GetClientRect(window, &box);
	return box.right - box.left;
}

int OpenGLContext::GetHeight() const
{
	RECT box = { 0 };
	GetClientRect(window, &box);
	return box.bottom - box.top;
}

/////////////////////////////////////////////////////////////////////////////

OpenGLCreationHelper::OpenGLCreationHelper(HWND window) : window(window)
{
	WINDOWINFO window_info;
	memset(&window_info, 0, sizeof(WINDOWINFO));
	window_info.cbSize = sizeof(WINDOWINFO);
	GetWindowInfo(window, &window_info);

	query_window = CreateWindowEx(
		0,
		WC_STATIC,
		TEXT(""),
		WS_CHILD,
		window_info.rcWindow.left,
		window_info.rcWindow.top,
		window_info.rcWindow.right - window_info.rcWindow.left,
		window_info.rcWindow.bottom - window_info.rcWindow.top,
		window, 0, GetModuleHandle(0), 0);
	if (query_window == 0)
		return;

	query_dc = GetDC(query_window);
	if (query_dc == 0)
	{
		DestroyWindow(query_window);
		query_window = 0;
		return;
	}

	PIXELFORMATDESCRIPTOR pfd;
	memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
	pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL;
	pfd.iPixelType = PFD_TYPE_RGBA;
	pfd.cColorBits = 24;

	int pixelformat = ChoosePixelFormat(query_dc, &pfd);
	SetPixelFormat(query_dc, pixelformat, &pfd);

	query_context = wglCreateContext(query_dc);
	if (query_context == 0)
	{
		DeleteDC(query_dc);
		DestroyWindow(query_window);
		query_dc = 0;
		query_window = 0;
	}
}

OpenGLCreationHelper::~OpenGLCreationHelper()
{
	wglDeleteContext(query_context);
	DeleteDC(query_dc);
	DestroyWindow(query_window);
}

HGLRC OpenGLCreationHelper::CreateContext(HDC hdc, int major_version, int minor_version, HGLRC share_context)
{
	if (query_context == 0)
		return 0;

	PIXELFORMATDESCRIPTOR pfd;
	memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
	pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
	pfd.nVersion = 1;
	pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
	pfd.iPixelType = PFD_TYPE_RGBA;
	pfd.cColorBits = 24;
	pfd.cRedBits = 8;
	pfd.cGreenBits = 8;
	pfd.cBlueBits = 8;
	pfd.cAlphaBits = 8;
	pfd.cDepthBits = 24;
	pfd.cStencilBits = 8;
	int pixelformat = ChoosePixelFormat(hdc, &pfd);
	SetPixelFormat(hdc, pixelformat, &pfd);

	wglMakeCurrent(query_dc, query_context);

	ptr_wglCreateContextAttribsARB wglCreateContextAttribsARB = (ptr_wglCreateContextAttribsARB)wglGetProcAddress("wglCreateContextAttribsARB");

	HGLRC opengl3_context = 0;
	if (wglCreateContextAttribsARB)
	{
		std::vector<int> int_attributes;

		int_attributes.push_back(WGL_CONTEXT_MAJOR_VERSION_ARB);
		int_attributes.push_back(major_version);
		int_attributes.push_back(WGL_CONTEXT_MINOR_VERSION_ARB);
		int_attributes.push_back(minor_version);

		int_attributes.push_back(0x2094); // WGL_CONTEXT_FLAGS_ARB
		int_attributes.push_back(0x2); // WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB

		int_attributes.push_back(0x9126); // WGL_CONTEXT_PROFILE_MASK_ARB
		int_attributes.push_back(0x1); // WGL_CONTEXT_CORE_PROFILE_BIT_ARB

		int_attributes.push_back(0);

		opengl3_context = wglCreateContextAttribsARB(hdc, share_context, int_attributes.data());
	}

	wglMakeCurrent(0, 0);

	return opengl3_context;
}

#else

#include <cstdio>

#define GL_USE_DLOPEN // Using dlopen for linux by default

#ifdef GL_USE_DLOPEN
#define GL_OPENGL_LIBRARY "libGL.so.1"
#include <dlfcn.h>
#endif

#ifdef GL_USE_DLOPEN
#define GL_LOAD_GLFUNC(x) dlsym(opengl_lib_handle, # x)
#else
#define GL_LOAD_GLFUNC(x) &x
#endif

OpenGLContext::OpenGLContext(void* display, void* window) : disp((::Display*)display), window((::Window)window)
{
	try
	{
		CreateContext();
	}
	catch (const std::exception& e)
	{
		// to do: maybe provide a way to query what the creation error was
	}
}

OpenGLContext::~OpenGLContext()
{
	if (opengl_visual_info)
	{
		XFree(opengl_visual_info);
		opengl_visual_info = nullptr;
	}

	if (opengl_context)
	{
		if (glx.glXGetCurrentContext() == opengl_context)
			OpenGL::set_active(nullptr);

		if (disp)
			glx.glXDestroyContext(disp, opengl_context);

		opengl_context = nullptr;
	}
}

void OpenGLContext::Begin()
{
	refcount++;
	if (refcount == 1)
		glx.glXMakeCurrent(disp, window, opengl_context);
}

void OpenGLContext::End()
{
	refcount--;
	if (refcount == 0)
		glx.glXMakeCurrent(0, 0, opengl_context);
}

void OpenGLContext::SwapBuffers()
{
	Begin();
	glx.glXSwapBuffers(disp, window);
	End();
}

int OpenGLContext::GetWidth() const
{
	::Window root_window;
	int x, y;
	unsigned int width, height, border_width, border_height, depth;
	Status result = XGetGeometry(disp, window, &root_window, &x, &y, &width, &height, &border_width, &border_height, &depth);
	return (result != 0) ? width: 0;
}

int OpenGLContext::GetHeight() const
{
	::Window root_window;
	int x, y;
	unsigned int width, height, border_width, border_height, depth;
	Status result = XGetGeometry(disp, window, &root_window, &x, &y, &width, &height, &border_width, &border_height, &depth);
	return (result != 0) ? height : 0;
}

ProcAddress* OpenGLContext::get_proc_address(const char *function_name) const
{
	if (glx.glXGetProcAddressARB)
		return glx.glXGetProcAddressARB((GLubyte*)function_name);
	else if (glx.glXGetProcAddress)
		return glx.glXGetProcAddress((GLubyte*)function_name);
	else
		return nullptr;
}

void OpenGLContext::CreateContext()
{
#ifdef GL_USE_DLOPEN
	opengl_lib_handle = dlopen(GL_OPENGL_LIBRARY, RTLD_NOW | RTLD_GLOBAL);
	if (!opengl_lib_handle)
		throw std::runtime_error(std::string("Cannot open opengl library: ") + GL_OPENGL_LIBRARY);
#endif

	glx.glXChooseVisual = (GL_GLXFunctions::ptr_glXChooseVisual) GL_LOAD_GLFUNC(glXChooseVisual);
	glx.glXCopyContext = (GL_GLXFunctions::ptr_glXCopyContext) GL_LOAD_GLFUNC(glXCopyContext);
	glx.glXCreateContext = (GL_GLXFunctions::ptr_glXCreateContext) GL_LOAD_GLFUNC(glXCreateContext);
	glx.glXCreateGLXPixmap = (GL_GLXFunctions::ptr_glXCreateGLXPixmap) GL_LOAD_GLFUNC(glXCreateGLXPixmap);
	glx.glXDestroyContext = (GL_GLXFunctions::ptr_glXDestroyContext) GL_LOAD_GLFUNC(glXDestroyContext);
	glx.glXDestroyGLXPixmap = (GL_GLXFunctions::ptr_glXDestroyGLXPixmap) GL_LOAD_GLFUNC(glXDestroyGLXPixmap);
	glx.glXGetConfig = (GL_GLXFunctions::ptr_glXGetConfig) GL_LOAD_GLFUNC(glXGetConfig);
	glx.glXGetCurrentContext = (GL_GLXFunctions::ptr_glXGetCurrentContext) GL_LOAD_GLFUNC(glXGetCurrentContext);
	glx.glXGetCurrentDrawable = (GL_GLXFunctions::ptr_glXGetCurrentDrawable) GL_LOAD_GLFUNC(glXGetCurrentDrawable);
	glx.glXIsDirect = (GL_GLXFunctions::ptr_glXIsDirect) GL_LOAD_GLFUNC(glXIsDirect);
	glx.glXMakeCurrent = (GL_GLXFunctions::ptr_glXMakeCurrent) GL_LOAD_GLFUNC(glXMakeCurrent);
	glx.glXQueryExtension = (GL_GLXFunctions::ptr_glXQueryExtension) GL_LOAD_GLFUNC(glXQueryExtension);
	glx.glXQueryVersion = (GL_GLXFunctions::ptr_glXQueryVersion) GL_LOAD_GLFUNC(glXQueryVersion);
	glx.glXSwapBuffers = (GL_GLXFunctions::ptr_glXSwapBuffers) GL_LOAD_GLFUNC(glXSwapBuffers);
	glx.glXUseXFont = (GL_GLXFunctions::ptr_glXUseXFont) GL_LOAD_GLFUNC(glXUseXFont);
	glx.glXWaitGL = (GL_GLXFunctions::ptr_glXWaitGL) GL_LOAD_GLFUNC(glXWaitGL);
	glx.glXWaitX = (GL_GLXFunctions::ptr_glXWaitX) GL_LOAD_GLFUNC(glXWaitX);
	glx.glXGetClientString = (GL_GLXFunctions::ptr_glXGetClientString) GL_LOAD_GLFUNC(glXGetClientString);
	glx.glXQueryServerString = (GL_GLXFunctions::ptr_glXQueryServerString) GL_LOAD_GLFUNC(glXQueryServerString);
	glx.glXQueryExtensionsString = (GL_GLXFunctions::ptr_glXQueryExtensionsString) GL_LOAD_GLFUNC(glXQueryExtensionsString);
	glx.glXGetCurrentDisplay = (GL_GLXFunctions::ptr_glXGetCurrentDisplay) GL_LOAD_GLFUNC(glXGetCurrentDisplay);
	glx.glXChooseFBConfig = (GL_GLXFunctions::ptr_glXChooseFBConfig) GL_LOAD_GLFUNC(glXChooseFBConfig);
	glx.glXCreateNewContext = (GL_GLXFunctions::ptr_glXCreateNewContext) GL_LOAD_GLFUNC(glXCreateNewContext);
	glx.glXCreatePbuffer = (GL_GLXFunctions::ptr_glXCreatePbuffer) GL_LOAD_GLFUNC(glXCreatePbuffer);
	glx.glXCreatePixmap = (GL_GLXFunctions::ptr_glXCreatePixmap) GL_LOAD_GLFUNC(glXCreatePixmap);
	glx.glXCreateWindow = (GL_GLXFunctions::ptr_glXCreateWindow) GL_LOAD_GLFUNC(glXCreateWindow);
	glx.glXDestroyPbuffer = (GL_GLXFunctions::ptr_glXDestroyPbuffer) GL_LOAD_GLFUNC(glXDestroyPbuffer);
	glx.glXDestroyPixmap = (GL_GLXFunctions::ptr_glXDestroyPixmap) GL_LOAD_GLFUNC(glXDestroyPixmap);
	glx.glXDestroyWindow = (GL_GLXFunctions::ptr_glXDestroyWindow) GL_LOAD_GLFUNC(glXDestroyWindow);
	glx.glXGetCurrentReadDrawable = (GL_GLXFunctions::ptr_glXGetCurrentReadDrawable) GL_LOAD_GLFUNC(glXGetCurrentReadDrawable);
	glx.glXGetFBConfigAttrib = (GL_GLXFunctions::ptr_glXGetFBConfigAttrib) GL_LOAD_GLFUNC(glXGetFBConfigAttrib);
	glx.glXGetFBConfigs = (GL_GLXFunctions::ptr_glXGetFBConfigs) GL_LOAD_GLFUNC(glXGetFBConfigs);
	glx.glXGetSelectedEvent = (GL_GLXFunctions::ptr_glXGetSelectedEvent) GL_LOAD_GLFUNC(glXGetSelectedEvent);
	glx.glXGetVisualFromFBConfig = (GL_GLXFunctions::ptr_glXGetVisualFromFBConfig) GL_LOAD_GLFUNC(glXGetVisualFromFBConfig);
	glx.glXMakeContextCurrent = (GL_GLXFunctions::ptr_glXMakeContextCurrent) GL_LOAD_GLFUNC(glXMakeContextCurrent);
	glx.glXQueryContext = (GL_GLXFunctions::ptr_glXQueryContext) GL_LOAD_GLFUNC(glXQueryContext);
	glx.glXQueryDrawable = (GL_GLXFunctions::ptr_glXQueryDrawable) GL_LOAD_GLFUNC(glXQueryDrawable);
	glx.glXSelectEvent = (GL_GLXFunctions::ptr_glXSelectEvent) GL_LOAD_GLFUNC(glXSelectEvent);

	glx.glXGetProcAddressARB = (GL_GLXFunctions::ptr_glXGetProcAddressARB) GL_LOAD_GLFUNC(glXGetProcAddressARB);
	glx.glXGetProcAddress = (GL_GLXFunctions::ptr_glXGetProcAddress) GL_LOAD_GLFUNC(glXGetProcAddress);

	if ((glx.glXDestroyContext == nullptr) ||
		(glx.glXMakeCurrent == nullptr) ||
		(glx.glXGetCurrentContext == nullptr) ||
		(glx.glXChooseVisual == nullptr) ||
		(glx.glXIsDirect == nullptr) ||
		(glx.glXGetConfig == nullptr) ||
		(glx.glXQueryExtensionsString == nullptr) ||
		(glx.glXQueryVersion == nullptr) ||
		(glx.glXGetVisualFromFBConfig == nullptr) ||
		(glx.glXCreateNewContext == nullptr) ||
		(glx.glXCreateContext == nullptr))
	{
		throw std::runtime_error("Cannot obtain required OpenGL GLX functions");
	}

	if ((glx.glXGetProcAddressARB == nullptr) && (glx.glXGetProcAddress == nullptr))
	{
		throw std::runtime_error("Cannot obtain required OpenGL GLX functions");
	}

	// FBConfigs were added in GLX version 1.3.
	int glx_major, glx_minor;
	if (!glx.glXQueryVersion(disp, &glx_major, &glx_minor) || ((glx_major == 1) && (glx_minor < 3)) || (glx_major < 1))
		throw std::runtime_error("GLX 1.3 or better is required");

	create_glx_1_3(disp);

	//if (!glx.glXIsDirect(disp, opengl_context))
	//	printf("No hardware acceleration available. I hope you got a really fast machine.\n");
}

void OpenGLContext::create_glx_1_3(::Display* disp)
{
	if (glx.glXChooseFBConfig == nullptr)
		throw std::runtime_error("Cannot find the glXChooseFBConfig function");

	// Setup OpenGL:
	int gl_attribs_single[] =
	{
		GLX_X_RENDERABLE, True,
		GLX_RENDER_TYPE, GLX_RGBA_BIT,
		GLX_DEPTH_SIZE, 16,
		GLX_STENCIL_SIZE, 8,
		GLX_BUFFER_SIZE, 24,
		None
	};

	std::vector<int> gl_attribs;
	gl_attribs.reserve(64);

	gl_attribs.push_back(GLX_X_RENDERABLE);
	gl_attribs.push_back(True);
	gl_attribs.push_back(GLX_DRAWABLE_TYPE);
	gl_attribs.push_back(GLX_WINDOW_BIT);
	gl_attribs.push_back(GLX_RENDER_TYPE);
	gl_attribs.push_back(GLX_RGBA_BIT);
	gl_attribs.push_back(GLX_X_VISUAL_TYPE);
	gl_attribs.push_back(GLX_TRUE_COLOR);
	gl_attribs.push_back(GLX_RED_SIZE);
	gl_attribs.push_back(8);
	gl_attribs.push_back(GLX_GREEN_SIZE);
	gl_attribs.push_back(8);
	gl_attribs.push_back(GLX_BLUE_SIZE);
	gl_attribs.push_back(8);
	gl_attribs.push_back(GLX_ALPHA_SIZE);
	gl_attribs.push_back(8);
	gl_attribs.push_back(GLX_DEPTH_SIZE);
	gl_attribs.push_back(24);
	gl_attribs.push_back(GLX_STENCIL_SIZE);
	gl_attribs.push_back(8);
	gl_attribs.push_back(GLX_DOUBLEBUFFER);
	gl_attribs.push_back(True);
	gl_attribs.push_back(GLX_STEREO);
	gl_attribs.push_back(False);
	gl_attribs.push_back(None);

	// get an appropriate visual
	int fb_count;
	GLXFBConfig* fbc = glx.glXChooseFBConfig(disp, DefaultScreen(disp), &gl_attribs[0], &fb_count);
	if (!fbc)
	{
		printf("Requested visual not supported by your OpenGL implementation. Falling back on singlebuffered Visual!\n");
		fbc = glx.glXChooseFBConfig(disp, DefaultScreen(disp), gl_attribs_single, &fb_count);
		if (!fbc)
			throw std::runtime_error(" glxChooseFBConfig failed");
		fbconfig = fbc[0];
	}
	else
	{
		if (!glx.glXGetFBConfigAttrib)
			throw std::runtime_error("Cannot find function glXGetFBConfigAttrib");

		int required_samples = 1; // desc.multisampling();
		int desired_config = 0;
		int max_sample_buffers = 0;
		int max_samples = 0;
		// Find the best fitting multisampling option
		for (int i = 0; i < fb_count; i++)
		{
			int samp_buf, samples;
			glx.glXGetFBConfigAttrib(disp, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);
			glx.glXGetFBConfigAttrib(disp, fbc[i], GLX_SAMPLES, &samples);

			// Samples are most important, because they are variable
			if (max_samples < required_samples)
			{
				if (samples > max_samples)
				{
					max_samples = samples;
					desired_config = i;
				}
			}

			// Use the maximum sample buffer
			if (max_samples == samples)	// Only check if the sample is valid
			{
				if (max_sample_buffers < samp_buf)
				{
					max_sample_buffers = samp_buf;
					desired_config = i;
				}
			}
		}
		fbconfig = fbc[desired_config];
	}

	XFree(fbc);

	if (opengl_visual_info) XFree(opengl_visual_info);
	opengl_visual_info = glx.glXGetVisualFromFBConfig(disp, fbconfig);
	if (opengl_visual_info == nullptr)
	{
		throw std::runtime_error("glXGetVisualFromFBConfig failed");
	}

	// create a GLX context
	opengl_context = create_context_glx_1_3(nullptr);
}

bool OpenGLContext::is_glx_extension_supported(const char* ext_name)
{
	const char* ext_string = glx.glXQueryExtensionsString(disp, opengl_visual_info->screen);
	if (ext_string)
	{
		const char* start;
		const char* where, * terminator;

		// Extension names should not have spaces.
		where = strchr(ext_name, ' ');
		if (where || *ext_name == '\0')
			return false;

		int ext_len = strlen(ext_name);

		// It takes a bit of care to be fool-proof about parsing the OpenGL extensions string. Don't be fooled by sub-strings, etc.
		for (start = ext_string; ; )
		{
			where = strstr(start, ext_name);

			if (!where)
				break;

			terminator = where + ext_len;

			if (where == start || *(where - 1) == ' ')
				if (*terminator == ' ' || *terminator == '\0')
					return true;

			start = terminator;
		}
	}
	return false;
}

static bool cl_ctxErrorOccurred = false;
static int cl_ctxErrorHandler(::Display* dpy, XErrorEvent* ev)
{
	cl_ctxErrorOccurred = true;
	return 0;
}

GLXContext OpenGLContext::create_context_glx_1_3(GLXContext shared_context)
{
	GLXContext context;

	context = glx.glXCreateNewContext(disp, fbconfig, GLX_RGBA_TYPE, shared_context, True);
	if (context == nullptr)
		throw std::runtime_error("glXCreateContext failed");

	ptr_glXCreateContextAttribs glXCreateContextAttribs = nullptr;

	if (is_glx_extension_supported("GLX_ARB_create_context"))
	{
		if (glx.glXGetProcAddressARB)
			glXCreateContextAttribs = (ptr_glXCreateContextAttribs)glx.glXGetProcAddressARB((GLubyte*) "glXCreateContextAttribsARB");
		if (glx.glXGetProcAddress)
			glXCreateContextAttribs = (ptr_glXCreateContextAttribs)glx.glXGetProcAddress((GLubyte*) "glXCreateContextAttribsARB");
	}

	if (glXCreateContextAttribs)
	{
		// Install an X error handler so the application won't exit if GL 3.0 context allocation fails.
		//
		// Note this error handler is global.  All display connections in all threads
		// of a process use the same error handler, so be sure to guard against other
		// threads issuing X commands while this code is running.
		int (*oldHandler)(::Display*, XErrorEvent*) = XSetErrorHandler(&cl_ctxErrorHandler);

		std::vector<int> int_attributes;

		int_attributes.push_back(0x2091);	// GLX_CONTEXT_MAJOR_VERSION_ARB
		int_attributes.push_back(major_version);
		int_attributes.push_back(0x2092);	// GLX_CONTEXT_MINOR_VERSION_ARB
		int_attributes.push_back(minor_version);

		int_attributes.push_back(0x2094);	// GLX_CONTEXT_FLAGS_ARB
		int_attributes.push_back(0x2);		// GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB

		int_attributes.push_back(0x9126);	// GLX_CONTEXT_PROFILE_MASK_ARB
		int_attributes.push_back(0x1);		// GLX_CONTEXT_CORE_PROFILE_BIT_ARB

		int_attributes.push_back(None);

		cl_ctxErrorOccurred = false;

		GLXContext context_gl3 = glXCreateContextAttribs(disp, fbconfig, shared_context, True, &int_attributes[0]);

		if (cl_ctxErrorOccurred)
		{
			if (context_gl3)
			{
				glx.glXDestroyContext(disp, context_gl3);
				context_gl3 = nullptr;
			}
		}

		// Restore the original error handler
		XSetErrorHandler(oldHandler);

		if (context_gl3)
		{
			glx.glXDestroyContext(disp, context);
			context = context_gl3;
		}
	}
	return context;
}

#endif