OPENGL: Resolve OpenGL functions on run-time.

Formerly we relied on static linkage. However, in the presense of modern
OpenGL (ES) implementations it is not easily identifable which library to link
against. For example, on Linux amd64 with nVidia drivers and SDL2 setup to
create a GLES 1.1 context one would need to link against libGL.so. However,
traditionally GLES 1.1 required to link against libGLESv1_CM.so. To prevent a
huge mess we simply resolve the OpenGL functions on run-time now and stop
linking against a static library (in most cases).

GLES support needs to be enabled manually on configure time for now.

Tizen changes have NOT been tested.

9 files changed, 400 insertions, 101 deletions

diff --git a/backends/graphics/opengl/extensions.cpp b/backends/graphics/opengl/context.cpp
index c76f8d7ca6..c4869c2ae6 100644
--- a/backends/graphics/opengl/extensions.cpp
+++ b/backends/graphics/opengl/context.cpp
@@ -20,7 +20,6 @@
  *
  */
 
-#include "backends/graphics/opengl/extensions.h"
 #include "backends/graphics/opengl/opengl-sys.h"
 #include "backends/graphics/opengl/opengl-graphics.h"
 
@@ -28,24 +27,41 @@
 
 namespace OpenGL {
 
-void ExtensionsDesc::reset() {
+void Context::reset() {
 	NPOTSupported = false;
 }
 
-ExtensionsDesc g_extensions;
-
-void OpenGLGraphicsManager::initializeGLExtensions() {
-	const char *extString = (const char *)glGetString(GL_EXTENSIONS);
+Context g_context;
 
+void OpenGLGraphicsManager::initializeGLContext() {
 	// Initialize default state.
-	g_extensions.reset();
+	g_context.reset();
+
+	// Load all functions.
+	// We use horrible trickery to silence C++ compilers.
+	// See backends/plugins/sdl/sdl-provider.cpp for more information.
+	assert(sizeof(void (*)()) == sizeof(void *));
+	void *fn = nullptr;
+#define GL_EXT_FUNC_DEF(ret, name, param) \
+	fn = getProcAddress(#name); \
+	memcpy(&g_context.name, &fn, sizeof(fn))
+#ifdef USE_BUILTIN_OPENGL
+#define GL_FUNC_DEF(ret, name, param) g_context.name = &name
+#else
+#define GL_FUNC_DEF GL_EXT_FUNC_DEF
+#endif
+#include "backends/graphics/opengl/opengl-func.h"
+#undef GL_EXT_FUNC_DEF
+#undef GL_FUNC_DEF
+
+	const char *extString = (const char *)g_context.glGetString(GL_EXTENSIONS);
 
 	Common::StringTokenizer tokenizer(extString, " ");
 	while (!tokenizer.empty()) {
 		Common::String token = tokenizer.nextToken();
 
 		if (token == "GL_ARB_texture_non_power_of_two") {
-			g_extensions.NPOTSupported = true;
+			g_context.NPOTSupported = true;
 		}
 	}
 }
diff --git a/backends/graphics/opengl/debug.cpp b/backends/graphics/opengl/debug.cpp
index d5d73fb5ec..c4319f5e36 100644
--- a/backends/graphics/opengl/debug.cpp
+++ b/backends/graphics/opengl/debug.cpp
@@ -54,7 +54,7 @@ Common::String getGLErrStr(GLenum error) {
 void checkGLError(const char *expr, const char *file, int line) {
 	GLenum error;
 
-	while ((error = glGetError()) != GL_NO_ERROR) {
+	while ((error = g_context.glGetError()) != GL_NO_ERROR) {
 		// We cannot use error here because we do not know whether we have a
 		// working screen or not.
 		warning("GL ERROR: %s on %s (%s:%d)", getGLErrStr(error).c_str(), expr, file, line);
diff --git a/backends/graphics/opengl/extensions.h b/backends/graphics/opengl/extensions.h
deleted file mode 100644
index 5b9eb538d9..0000000000
--- a/backends/graphics/opengl/extensions.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/* ScummVM - Graphic Adventure Engine
- *
- * ScummVM is the legal property of its developers, whose names
- * are too numerous to list here. Please refer to the COPYRIGHT
- * file distributed with this source distribution.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- *
- */
-
-#ifndef BACKENDS_GRAPHICS_OPENGL_EXTENSIONS_H
-#define BACKENDS_GRAPHICS_OPENGL_EXTENSIONS_H
-
-namespace OpenGL {
-
-/**
- * Description structure of all available extensions.
- *
- * This includes information whether extensions we are interested in is
- * available or not. If extensions we are interested in add additional
- * functions, we keep function pointers around in here too.
- */
-struct ExtensionsDesc {
-	/**
-	 * Reset extension state.
-	 *
-	 * This marks all extensions as unavailable.
-	 */
-	void reset();
-
-	/** Whether GL_ARB_texture_non_power_of_two is available or not. */
-	bool NPOTSupported;
-};
-
-/**
- * Description of all available extensions.
- */
-extern ExtensionsDesc g_extensions;
-
-} // End of namespace OpenGL
-
-#endif
diff --git a/backends/graphics/opengl/opengl-defs.h b/backends/graphics/opengl/opengl-defs.h
new file mode 100644
index 0000000000..4b82d7edd7
--- /dev/null
+++ b/backends/graphics/opengl/opengl-defs.h
@@ -0,0 +1,219 @@
+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+/* This file is based on Mesa 3-D's gl.h and GLES/gl.h from Khronos Registry.
+ *
+ * Mesa 3-D's gl.h file is distributed under the following license:
+ * Mesa 3-D graphics library
+ *
+ * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
+ * Copyright (C) 2009  VMware, Inc.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ *
+ * GLES/gl.h from Khronos Registry is distributed under the following license:
+ * This document is licensed under the SGI Free Software B License Version
+ * 2.0. For details, see http://oss.sgi.com/projects/FreeB/ .
+ */
+
+#ifndef BACKENDS_GRAPHICS_OPENGL_OPENGL_DEFS_H
+#define BACKENDS_GRAPHICS_OPENGL_OPENGL_DEFS_H
+
+#include "common/scummsys.h"
+
+/*
+ * Datatypes
+ */
+typedef uint   GLenum;
+typedef uint8  GLboolean;
+typedef uint   GLbitfield;
+typedef void   GLvoid;
+typedef int8   GLbyte;   /* 1-byte signed */
+typedef int16  GLshort;  /* 2-byte signed */
+typedef int32  GLint;    /* 4-byte signed */
+typedef uint8  GLubyte;  /* 1-byte unsigned */
+typedef uint16 GLushort; /* 2-byte unsigned */
+typedef uint32 GLuint;   /* 4-byte unsigned */
+typedef int32  GLsizei;  /* 4-byte signed */
+typedef float  GLfloat;  /* single precision float */
+typedef float  GLclampf; /* single precision float in [0,1] */
+typedef double GLdouble; /* double precision float */
+typedef double GLclampd; /* double precision float in [0,1] */
+
+/*
+ * Constants
+ */
+
+/* StringName */
+#define GL_VENDOR                         0x1F00
+#define GL_RENDERER                       0x1F01
+#define GL_VERSION                        0x1F02
+#define GL_EXTENSIONS                     0x1F03
+
+/* ErrorCode */
+#define GL_NO_ERROR                       0
+#define GL_INVALID_ENUM                   0x0500
+#define GL_INVALID_VALUE                  0x0501
+#define GL_INVALID_OPERATION              0x0502
+#define GL_STACK_OVERFLOW                 0x0503
+#define GL_STACK_UNDERFLOW                0x0504
+#define GL_OUT_OF_MEMORY                  0x0505
+
+/* ClearBufferMask */
+#define GL_DEPTH_BUFFER_BIT               0x00000100
+#define GL_STENCIL_BUFFER_BIT             0x00000400
+#define GL_COLOR_BUFFER_BIT               0x00004000
+
+/* Scissor box */
+#define GL_SCISSOR_BOX                    0x0C10
+#define GL_SCISSOR_TEST                   0x0C11
+
+/* MatrixMode */
+#define GL_MATRIX_MODE                    0x0BA0
+#define GL_MODELVIEW                      0x1700
+#define GL_PROJECTION                     0x1701
+#define GL_TEXTURE                        0x1702
+
+/* EnableCap */
+#define GL_FOG                            0x0B60
+#define GL_LIGHTING                       0x0B50
+#define GL_TEXTURE_2D                     0x0DE1
+#define GL_CULL_FACE                      0x0B44
+#define GL_ALPHA_TEST                     0x0BC0
+#define GL_BLEND                          0x0BE2
+#define GL_DITHER                         0x0BD0
+#define GL_DEPTH_TEST                     0x0B71
+#define GL_VERTEX_ARRAY                   0x8074
+#define GL_COLOR_ARRAY                    0x8076
+#define GL_TEXTURE_COORD_ARRAY            0x8078
+
+/* ShadingModel */
+#define GL_FLAT                           0x1D00
+#define GL_SMOOTH                         0x1D01
+
+/* HintMode */
+#define GL_DONT_CARE                      0x1100
+#define GL_FASTEST                        0x1101
+#define GL_NICEST                         0x1102
+
+/* HintTarget */
+#define GL_PERSPECTIVE_CORRECTION_HINT    0x0C50
+#define GL_POINT_SMOOTH_HINT              0x0C51
+#define GL_LINE_SMOOTH_HINT               0x0C52
+#define GL_FOG_HINT                       0x0C54
+#define GL_GENERATE_MIPMAP_HINT           0x8192
+
+/* BlendingFactorDest */
+#define GL_ZERO                           0
+#define GL_ONE                            1
+#define GL_SRC_COLOR                      0x0300
+#define GL_ONE_MINUS_SRC_COLOR            0x0301
+#define GL_SRC_ALPHA                      0x0302
+#define GL_ONE_MINUS_SRC_ALPHA            0x0303
+#define GL_DST_ALPHA                      0x0304
+#define GL_ONE_MINUS_DST_ALPHA            0x0305
+
+/* BlendingFactorSrc */
+/*      GL_ZERO */
+/*      GL_ONE */
+#define GL_DST_COLOR                      0x0306
+#define GL_ONE_MINUS_DST_COLOR            0x0307
+#define GL_SRC_ALPHA_SATURATE             0x0308
+/*      GL_SRC_ALPHA */
+/*      GL_ONE_MINUS_SRC_ALPHA */
+/*      GL_DST_ALPHA */
+/*      GL_ONE_MINUS_DST_ALPHA */
+
+/* PixelFormat */
+#define GL_ALPHA                          0x1906
+#define GL_RGB                            0x1907
+#define GL_RGBA                           0x1908
+#define GL_BGR                            0x80E0
+#define GL_BGRA                           0x80E1
+
+/* PixelStoreParameter */
+#define GL_UNPACK_ALIGNMENT               0x0CF5
+#define GL_PACK_ALIGNMENT                 0x0D05
+
+/* DataType */
+#define GL_BYTE                           0x1400
+#define GL_UNSIGNED_BYTE                  0x1401
+#define GL_SHORT                          0x1402
+#define GL_UNSIGNED_SHORT                 0x1403
+#define GL_FLOAT                          0x1406
+#define GL_FIXED                          0x140C
+
+/* PixelType */
+/*      GL_UNSIGNED_BYTE */
+#define GL_UNSIGNED_SHORT_4_4_4_4         0x8033
+#define GL_UNSIGNED_SHORT_5_5_5_1         0x8034
+#define GL_UNSIGNED_SHORT_5_6_5           0x8363
+
+#define GL_UNSIGNED_SHORT_4_4_4_4_REV     0x8365
+#define GL_UNSIGNED_SHORT_1_5_5_5_REV     0x8366
+#define GL_UNSIGNED_INT_8_8_8_8           0x8035
+#define GL_UNSIGNED_INT_8_8_8_8_REV       0x8367
+
+/* Implementation limits */
+#define GL_MAX_TEXTURE_SIZE               0x0D33
+
+/* TextureMagFilter */
+#define GL_NEAREST                        0x2600
+#define GL_LINEAR                         0x2601
+
+/* TextureParameterName */
+#define GL_TEXTURE_MAG_FILTER             0x2800
+#define GL_TEXTURE_MIN_FILTER             0x2801
+#define GL_TEXTURE_WRAP_S                 0x2802
+#define GL_TEXTURE_WRAP_T                 0x2803
+
+/* TextureWrapMode */
+#define GL_REPEAT                         0x2901
+#define GL_CLAMP_TO_EDGE                  0x812F
+
+/* BeginMode */
+#define GL_POINTS                         0x0000
+#define GL_LINES                          0x0001
+#define GL_LINE_LOOP                      0x0002
+#define GL_LINE_STRIP                     0x0003
+#define GL_TRIANGLES                      0x0004
+#define GL_TRIANGLE_STRIP                 0x0005
+#define GL_TRIANGLE_FAN                   0x0006
+
+#endif
diff --git a/backends/graphics/opengl/opengl-func.h b/backends/graphics/opengl/opengl-func.h
new file mode 100644
index 0000000000..75bc0b4e81
--- /dev/null
+++ b/backends/graphics/opengl/opengl-func.h
@@ -0,0 +1,97 @@
+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+/* This file is based on Mesa 3-D's gl.h and GLES/gl.h from Khronos Registry.
+ *
+ * Mesa 3-D's gl.h file is distributed under the following license:
+ * Mesa 3-D graphics library
+ *
+ * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
+ * Copyright (C) 2009  VMware, Inc.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ *
+ * GLES/gl.h from Khronos Registry is distributed under the following license:
+ * This document is licensed under the SGI Free Software B License Version
+ * 2.0. For details, see http://oss.sgi.com/projects/FreeB/ .
+ */
+
+/*
+ * This file is a template file to be used inside specific locations in the
+ * OpenGL graphics code. It is not to be included otherwise. It intentionally
+ * does not contain include guards because it can be required to include it
+ * multiple times in a source file.
+ *
+ * Functions are defined by two different user supplied macros:
+ * GL_FUNC_DEF: Define a (builtin) OpenGL (ES) function.
+ * GL_EXT_FUNC_DEF: Define an OpenGL (ES) extension function.
+ */
+
+GL_FUNC_DEF(void, glEnable, (GLenum cap));
+GL_FUNC_DEF(void, glDisable, (GLenum cap));
+GL_FUNC_DEF(void, glClear, (GLbitfield mask));
+GL_FUNC_DEF(void, glColor4f, (GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha));
+GL_FUNC_DEF(void, glViewport, (GLint x, GLint y, GLsizei width, GLsizei height));
+GL_FUNC_DEF(void, glMatrixMode, (GLenum mode));
+GL_FUNC_DEF(void, glLoadIdentity, ());
+#ifdef USE_GLES
+GL_FUNC_DEF(void, glOrthof, (GLfloat left, GLfloat right, GLfloat bottom, GLfloat top, GLfloat zNear, GLfloat zFar));
+#else
+GL_FUNC_DEF(void, glOrtho, (GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near_val, GLdouble far_val));
+#endif
+GL_FUNC_DEF(void, glShadeModel, (GLenum mode));
+GL_FUNC_DEF(void, glHint, (GLenum target, GLenum mode));
+GL_FUNC_DEF(void, glClearColor, (GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha));
+GL_FUNC_DEF(void, glBlendFunc, (GLenum sfactor, GLenum dfactor));
+GL_FUNC_DEF(void, glEnableClientState, (GLenum array));
+GL_FUNC_DEF(void, glPixelStorei, (GLenum pname, GLint param));
+GL_FUNC_DEF(void, glScissor, (GLint x, GLint y, GLsizei width, GLsizei height));
+GL_FUNC_DEF(void, glReadPixels, (GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid *pixels));
+GL_FUNC_DEF(void, glGetIntegerv, (GLenum pname, GLint *params));
+GL_FUNC_DEF(void, glDeleteTextures, (GLsizei n, const GLuint *textures));
+GL_FUNC_DEF(void, glGenTextures, (GLsizei n, GLuint *textures));
+GL_FUNC_DEF(void, glBindTexture, (GLenum target, GLuint texture));
+GL_FUNC_DEF(void, glTexParameteri, (GLenum target, GLenum pname, GLint param));
+GL_FUNC_DEF(void, glTexImage2D, (GLenum target, GLint level, GLint internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid *pixels));
+GL_FUNC_DEF(void, glTexCoordPointer, (GLint size, GLenum type, GLsizei stride, const GLvoid *pointer));
+GL_FUNC_DEF(void, glVertexPointer, (GLint size, GLenum type, GLsizei stride, const GLvoid *pointer));
+GL_FUNC_DEF(void, glDrawArrays, (GLenum mode, GLint first, GLsizei count));
+GL_FUNC_DEF(void, glTexSubImage2D, (GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type, const GLvoid *pixels));
+GL_FUNC_DEF(const GLubyte *, glGetString, (GLenum name));
+GL_FUNC_DEF(GLenum, glGetError, ());
diff --git a/backends/graphics/opengl/opengl-graphics.cpp b/backends/graphics/opengl/opengl-graphics.cpp
index 54c4906413..2af7da5f1f 100644
--- a/backends/graphics/opengl/opengl-graphics.cpp
+++ b/backends/graphics/opengl/opengl-graphics.cpp
@@ -23,7 +23,6 @@
 
 #include "backends/graphics/opengl/opengl-graphics.h"
 #include "backends/graphics/opengl/texture.h"
-#include "backends/graphics/opengl/extensions.h"
 
 #include "common/textconsole.h"
 #include "common/translation.h"
@@ -57,7 +56,7 @@ OpenGLGraphicsManager::OpenGLGraphicsManager()
 #endif
     {
 	memset(_gamePalette, 0, sizeof(_gamePalette));
-	g_extensions.reset();
+	g_context.reset();
 }
 
 OpenGLGraphicsManager::~OpenGLGraphicsManager() {
@@ -836,8 +835,8 @@ void OpenGLGraphicsManager::setActualScreenSize(uint width, uint height) {
 }
 
 void OpenGLGraphicsManager::notifyContextCreate(const Graphics::PixelFormat &defaultFormat, const Graphics::PixelFormat &defaultFormatAlpha) {
-	// Initialize all extensions.
-	initializeGLExtensions();
+	// Initialize context for use.
+	initializeGLContext();
 
 	// Disable 3D properties.
 	GLCALL(glDisable(GL_CULL_FACE));
diff --git a/backends/graphics/opengl/opengl-graphics.h b/backends/graphics/opengl/opengl-graphics.h
index f83c9537ec..3d5f74b387 100644
--- a/backends/graphics/opengl/opengl-graphics.h
+++ b/backends/graphics/opengl/opengl-graphics.h
@@ -281,10 +281,9 @@ private:
 	//
 
 	/**
-	 * Checks for availability of extensions we want to use and initializes them
-	 * when available.
+	 * Initialize the active context for use.
 	 */
-	void initializeGLExtensions();
+	void initializeGLContext();
 
 protected:
 	/**
diff --git a/backends/graphics/opengl/opengl-sys.h b/backends/graphics/opengl/opengl-sys.h
index 8d8fecf5d6..08b3b4581c 100644
--- a/backends/graphics/opengl/opengl-sys.h
+++ b/backends/graphics/opengl/opengl-sys.h
@@ -23,45 +23,70 @@
 #ifndef BACKENDS_GRAPHICS_OPENGL_OPENGL_SYS_H
 #define BACKENDS_GRAPHICS_OPENGL_OPENGL_SYS_H
 
-// The purpose of this header is to include the OpenGL headers in an uniform
-// fashion. A notable example for a non standard port is the Tizen port.
-
 #include "common/scummsys.h"
 
 #include "backends/graphics/opengl/debug.h"
-
-#ifdef WIN32
-#if defined(ARRAYSIZE) && !defined(_WINDOWS_)
-#undef ARRAYSIZE
-#endif
-#define WIN32_LEAN_AND_MEAN
-#include <windows.h>
-#undef ARRAYSIZE
-#endif
-
-// HACK: In case common/util.h has been included already we need to make sure
-// to define ARRAYSIZE again in case of Windows.
-#if !defined(ARRAYSIZE) && defined(COMMON_UTIL_H)
-#define ARRAYSIZE(x) ((int)(sizeof(x) / sizeof(x[0])))
+#ifdef SDL_BACKEND
+#include "backends/platform/sdl/sdl-sys.h"
 #endif
 
+// On Tizen we include the toolchain's OpenGL file. This is something we
+// actually want to avoid. However, since Tizen uses eglGetProcAddress which
+// is not required to return valid function pointers to non OpenGL extension
+// functions, we need the system's definitions to resolve all OpenGL
+// functions.
+// TODO: See if there is an alternative which allows us to avoid including
+// Tizen's OpenGL header here.
 #if defined(TIZEN)
-#include <FGraphicsOpengl.h>
-using namespace Tizen::Graphics::Opengl;
-#elif defined(USE_GLES)
-#include <GLES/gl.h>
-#elif defined(SDL_BACKEND)
-#include <SDL_opengl.h>
+	#include <FGraphicsOpengl.h>
+	using namespace Tizen::Graphics::Opengl;
+	#define USE_BUILTIN_OPENGL
 #else
-#include <GL/gl.h>
+	#include "backends/graphics/opengl/opengl-defs.h"
 #endif
 
 #ifdef SDL_BACKEND
-#define GLCALLCONV APIENTRY
+	// Win32 needs OpenGL functions declared with APIENTRY.
+	// However, SDL does not define APIENTRY in it's SDL.h file on non-Windows
+	// targets, thus if it is not available, we just dummy define it.
+	#ifndef APIENTRY
+		#define APIENTRY
+	#endif
+	#define GL_CALL_CONV APIENTRY
 #else
-#define GLCALLCONV
+	#define GL_CALL_CONV
 #endif
 
-#define GLCALL(x) GL_WRAP_DEBUG(x, x)
+namespace OpenGL {
+
+/**
+ * Description structure of the OpenGL (ES) context.
+ */
+struct Context {
+	/**
+	 * Reset context.
+	 *
+	 * This marks all extensions as unavailable.
+	 */
+	void reset();
+
+	/** Whether GL_ARB_texture_non_power_of_two is available or not. */
+	bool NPOTSupported;
+
+#define GL_FUNC_DEF(ret, name, param) ret (GL_CALL_CONV *name)param
+#define GL_EXT_FUNC_DEF GL_FUNC_DEF
+#include "backends/graphics/opengl/opengl-func.h"
+#undef GL_EXT_FUNC_DEF
+#undef GL_FUNC_DEF
+};
+
+/**
+ * The (active) OpenGL context.
+ */
+extern Context g_context;
+
+} // End of namespace OpenGL
+
+#define GLCALL(x) GL_WRAP_DEBUG(g_context.x, x)
 
 #endif
diff --git a/backends/graphics/opengl/texture.cpp b/backends/graphics/opengl/texture.cpp
index 696e1e6252..bc255004e7 100644
--- a/backends/graphics/opengl/texture.cpp
+++ b/backends/graphics/opengl/texture.cpp
@@ -21,8 +21,6 @@
  */
 
 #include "backends/graphics/opengl/texture.h"
-#include "backends/graphics/opengl/extensions.h"
-#include "backends/graphics/opengl/opengl-graphics.h"
 
 #include "common/rect.h"
 #include "common/textconsole.h"
@@ -44,7 +42,7 @@ static GLuint nextHigher2(GLuint v) {
 GLint Texture::_maxTextureSize = 0;
 
 void Texture::queryTextureInformation() {
-	glGetIntegerv(GL_MAX_TEXTURE_SIZE, &_maxTextureSize);
+	GLCALL(glGetIntegerv(GL_MAX_TEXTURE_SIZE, &_maxTextureSize));
 	debug(5, "OpenGL maximum texture size: %d", _maxTextureSize);
 }
 
@@ -105,7 +103,7 @@ void Texture::enableLinearFiltering(bool enable) {
 
 void Texture::allocate(uint width, uint height) {
 	uint texWidth = width, texHeight = height;
-	if (!g_extensions.NPOTSupported) {
+	if (!g_context.NPOTSupported) {
 		texWidth  = nextHigher2(texWidth);
 		texHeight = nextHigher2(texHeight);
 	}