+/* extension #defines, types and entries, avoiding a dependency on additional
+ libraries like GLEW or the GL/glext.h header */
+#ifndef GL_ARRAY_BUFFER
+#define GL_ARRAY_BUFFER 0x8892
+#endif
+
+#ifndef GL_STATIC_DRAW
+#define GL_STATIC_DRAW 0x88E4
+#endif
+
+#ifndef GL_FRAGMENT_SHADER
+#define GL_FRAGMENT_SHADER 0x8B30
+#endif
+
+#ifndef GL_VERTEX_SHADER
+#define GL_VERTEX_SHADER 0x8B31
+#endif
+
+#ifndef GL_SHADING_LANGUAGE_VERSION
+#define GL_SHADING_LANGUAGE_VERSION 0x8B8C
+#endif
+
+#ifndef GL_COMPILE_STATUS
+#define GL_COMPILE_STATUS 0x8B81
+#endif
+
+#ifndef GL_LINK_STATUS
+#define GL_LINK_STATUS 0x8B82
+#endif
+
+#ifndef GL_INFO_LOG_LENGTH
+#define GL_INFO_LOG_LENGTH 0x8B84
+#endif
+
+typedef ptrdiff_t ourGLsizeiptr;
+typedef char ourGLchar;
+
+#ifndef APIENTRY
+#define APIENTRY
+#endif
+
+typedef void (APIENTRY *PFNGLGENBUFFERSPROC) (GLsizei n, GLuint *buffers);
+typedef void (APIENTRY *PFNGLBINDBUFFERPROC) (GLenum target, GLuint buffer);
+typedef void (APIENTRY *PFNGLBUFFERDATAPROC) (GLenum target, ourGLsizeiptr size, const GLvoid *data, GLenum usage);
+typedef GLuint (APIENTRY *PFNGLCREATESHADERPROC) (GLenum type);
+typedef void (APIENTRY *PFNGLSHADERSOURCEPROC) (GLuint shader, GLsizei count, const ourGLchar **string, const GLint *length);
+typedef void (APIENTRY *PFNGLCOMPILESHADERPROC) (GLuint shader);
+typedef GLuint (APIENTRY *PFNGLCREATEPROGRAMPROC) (void);
+typedef void (APIENTRY *PFNGLATTACHSHADERPROC) (GLuint program, GLuint shader);
+typedef void (APIENTRY *PFNGLLINKPROGRAMPROC) (GLuint program);
+typedef void (APIENTRY *PFNGLUSEPROGRAMPROC) (GLuint program);
+typedef void (APIENTRY *PFNGLGETSHADERIVPROC) (GLuint shader, GLenum pname, GLint *params);
+typedef void (APIENTRY *PFNGLGETSHADERINFOLOGPROC) (GLuint shader, GLsizei bufSize, GLsizei *length, ourGLchar *infoLog);
+typedef void (APIENTRY *PFNGLGETPROGRAMIVPROC) (GLenum target, GLenum pname, GLint *params);
+typedef void (APIENTRY *PFNGLGETPROGRAMINFOLOGPROC) (GLuint program, GLsizei bufSize, GLsizei *length, ourGLchar *infoLog);
+typedef GLint (APIENTRY *PFNGLGETATTRIBLOCATIONPROC) (GLuint program, const ourGLchar *name);
+typedef void (APIENTRY *PFNGLVERTEXATTRIBPOINTERPROC) (GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid *pointer);
+typedef void (APIENTRY *PFNGLENABLEVERTEXATTRIBARRAYPROC) (GLuint index);
+typedef GLint (APIENTRY *PFNGLGETUNIFORMLOCATIONPROC) (GLuint program, const ourGLchar *name);
+typedef void (APIENTRY *PFNGLUNIFORMMATRIX4FVPROC) (GLint location, GLsizei count, GLboolean transpose, const GLfloat *value);
+
+PFNGLGENBUFFERSPROC gl_GenBuffers;
+PFNGLBINDBUFFERPROC gl_BindBuffer;
+PFNGLBUFFERDATAPROC gl_BufferData;
+PFNGLCREATESHADERPROC gl_CreateShader;
+PFNGLSHADERSOURCEPROC gl_ShaderSource;
+PFNGLCOMPILESHADERPROC gl_CompileShader;
+PFNGLCREATEPROGRAMPROC gl_CreateProgram;
+PFNGLATTACHSHADERPROC gl_AttachShader;
+PFNGLLINKPROGRAMPROC gl_LinkProgram;
+PFNGLUSEPROGRAMPROC gl_UseProgram;
+PFNGLGETSHADERIVPROC gl_GetShaderiv;
+PFNGLGETSHADERINFOLOGPROC gl_GetShaderInfoLog;
+PFNGLGETPROGRAMIVPROC gl_GetProgramiv;
+PFNGLGETPROGRAMINFOLOGPROC gl_GetProgramInfoLog;
+PFNGLGETATTRIBLOCATIONPROC gl_GetAttribLocation;
+PFNGLVERTEXATTRIBPOINTERPROC gl_VertexAttribPointer;
+PFNGLENABLEVERTEXATTRIBARRAYPROC gl_EnableVertexAttribArray;
+PFNGLGETUNIFORMLOCATIONPROC gl_GetUniformLocation;
+PFNGLUNIFORMMATRIX4FVPROC gl_UniformMatrix4fv;