+
+#if TARGET_HOST_POSIX_X11
+#ifndef GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB
+#define GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB 0x20B2
+#endif
+
+#ifndef GLX_CONTEXT_MAJOR_VERSION_ARB
+#define GLX_CONTEXT_MAJOR_VERSION_ARB 0x2091
+#endif
+
+#ifndef GLX_CONTEXT_MINOR_VERSION_ARB
+#define GLX_CONTEXT_MINOR_VERSION_ARB 0x2092
+#endif
+
+#ifndef GLX_CONTEXT_FLAGS_ARB
+#define GLX_CONTEXT_FLAGS_ARB 0x2094
+#endif
+
+#ifndef GLX_CONTEXT_PROFILE_MASK_ARB
+#define GLX_CONTEXT_PROFILE_MASK_ARB 0x9126
+#endif
+
+#ifndef GLX_CONTEXT_DEBUG_BIT_ARB
+#define GLX_CONTEXT_DEBUG_BIT_ARB 0x0001
+#endif
+
+#ifndef GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB
+#define GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB 0x0002
+#endif
+
+#ifndef GLX_CONTEXT_CORE_PROFILE_BIT_ARB
+#define GLX_CONTEXT_CORE_PROFILE_BIT_ARB 0x00000001
+#endif
+
+#ifndef GLX_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB
+#define GLX_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB 0x00000002
+#endif
+
+#ifndef GLX_RGBA_FLOAT_TYPE
+#define GLX_RGBA_FLOAT_TYPE 0x20B9
+#endif
+
+#ifndef GLX_RGBA_FLOAT_BIT
+#define GLX_RGBA_FLOAT_BIT 0x00000004
+#endif
+#endif /* TARGET_HOST_POSIX_X11 */
+
+
+#if TARGET_HOST_MS_WINDOWS
+/* The following include file is available from SGI but is not standard:
+ * #include <GL/wglext.h>
+ * So we copy the necessary parts out of it.
+ * XXX: should local definitions for extensions be put in a separate include file?
+ */
+typedef const char * (WINAPI * PFNWGLGETEXTENSIONSSTRINGARBPROC) (HDC hdc);
+
+typedef BOOL (WINAPI * PFNWGLCHOOSEPIXELFORMATARBPROC) (HDC hdc, const int *piAttribIList, const FLOAT *pfAttribFList, UINT nMaxFormats, int *piFormats, UINT *nNumFormats);
+
+#define WGL_DRAW_TO_WINDOW_ARB 0x2001
+#define WGL_ACCELERATION_ARB 0x2003
+#define WGL_SUPPORT_OPENGL_ARB 0x2010
+#define WGL_DOUBLE_BUFFER_ARB 0x2011
+#define WGL_COLOR_BITS_ARB 0x2014
+#define WGL_ALPHA_BITS_ARB 0x201B
+#define WGL_DEPTH_BITS_ARB 0x2022
+#define WGL_STENCIL_BITS_ARB 0x2023
+#define WGL_FULL_ACCELERATION_ARB 0x2027
+
+#define WGL_SAMPLE_BUFFERS_ARB 0x2041
+#define WGL_SAMPLES_ARB 0x2042
+
+#define WGL_TYPE_RGBA_FLOAT_ARB 0x21A0
+
+#define WGL_FRAMEBUFFER_SRGB_CAPABLE_ARB 0x20A9
+
+#ifndef WGL_ARB_create_context
+#define WGL_ARB_create_context 1
+#ifdef WGL_WGLEXT_PROTOTYPES
+extern HGLRC WINAPI wglCreateContextAttribsARB (HDC, HGLRC, const int *);
+#endif /* WGL_WGLEXT_PROTOTYPES */
+typedef HGLRC (WINAPI * PFNWGLCREATECONTEXTATTRIBSARBPROC) (HDC hDC, HGLRC hShareContext, const int *attribList);
+
+#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_PROFILE_MASK_ARB 0x9126
+
+#define WGL_CONTEXT_DEBUG_BIT_ARB 0x0001
+#define WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB 0x0002
+
+#define WGL_CONTEXT_CORE_PROFILE_BIT_ARB 0x00000001
+#define WGL_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB 0x00000002
+
+#define ERROR_INVALID_VERSION_ARB 0x2095
+#define ERROR_INVALID_PROFILE_ARB 0x2096
+#endif
+
+#endif /* TARGET_HOST_MS_WINDOWS */
+
+
+/* pushing attribute/value pairs into an array */
+#define ATTRIB(a) attributes[where++]=(a)
+#define ATTRIB_VAL(a,v) {ATTRIB(a); ATTRIB(v);}