extern void (GLAPIENTRY *qglCopyTexSubImage1D)(GLenum target, GLint level, GLint xoffset, GLint x, GLint y, GLsizei width);
extern void (GLAPIENTRY *qglCopyTexSubImage2D)(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height);
extern void (GLAPIENTRY *qglCopyTexSubImage1D)(GLenum target, GLint level, GLint xoffset, GLint x, GLint y, GLsizei width);
extern void (GLAPIENTRY *qglCopyTexSubImage2D)(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height);