glCopyTexSubImage1D -	copy a one-dimensional texture

	  void glCopyTexSubImage1D( GLenum target,
				    GLint level,
				    GLint xoffset,
				    GLint x,
				    GLint y,
				    GLsizei width )

	  target   Specifies the target	texture.  Must be

	  level	   Specifies the level-of-detail number.  Level	0 is
		   the base image level.  Level	n is the nth mipmap
		   reduction image.

	  xoffset  Specifies the texel offset within the texture

	  x, y	   Specify the window coordinates of the left corner
		   of the row of pixels	to be copied.

	  width	   Specifies the width of the texture subimage.

	  glCopyTexSubImage1D replaces a portion of a one-dimensional
	  texture image	with pixels from the current GL_READ_BUFFER
	  (rather than from main memory, as is the case	for

	  The screen-aligned pixel row with left corner	at (x, y), and
	  with length width replaces the portion of the	texture	array
	  with x indices xoffset through xoffset + width - 1,
	  inclusive. The destination in	the texture array may not
	  include any texels outside the texture array as it was
	  originally specified.

	  The pixels in	the row	are processed exactly as if
	  glCopyPixels had been	called,	but the	process	stops just
	  before final conversion.  At this point all pixel component
	  values are clamped to	the range [0, 1] and then converted to
	  the texture's	internal format	for storage in the texel

	  It is	not an error to	specify	a subtexture with zero width,
	  but such a specification has no effect.  If any of the
	  pixels within	the specified row of the current
	  GL_READ_BUFFER are outside the read window associated	with
	  the current rendering	context, then the values obtained for
	  those	pixels are undefined.

	  No change is made to the internalformat, width, or border
	  parameters of	the specified texture array or to texel	values
	  outside the specified	subregion.

	  glCopyTexSubImage1D is available only	if the GL version is
	  1.1 or greater.

	  Texturing has	no effect in color index mode.

	  glPixelStore and glPixelTransfer modes affect	texture	images
	  in exactly the way they affect glDrawPixels.

	  GL_INVALID_ENUM is generated if target is not	GL_TEXTURE_1D.

	  GL_INVALID_OPERATION is generated if the texture array has
	  not been defined by a	previous glTexImage1D or
	  glCopyTexImage1D operation.

	  GL_INVALID_VALUE is generated	if level is less than 0.

	  GL_INVALID_VALUE may be generated if level>log  max, where
	  max is the returned value of GL_MAX_TEXTURE_SIZE.

	  GL_INVALID_VALUE is generated	if y <	-b or if width <  -b,
	  where	b is the border	width of the texture array.

	  GL_INVALID_VALUE is generated	if xoffset <  -b, or
	  (xoffset + width) > (w-b), where w is	the GL_TEXTURE_WIDTH,
	  and b	is the GL_TEXTURE_BORDER of the	texture	image being
	  modified.  Note that w includes twice	the border width.

	  glIsEnabled with argument GL_TEXTURE_1D

	  glCopyPixels,	glCopyTexImage1D, glCopyTexImage2D,
	  glCopyTexSubImage2D, glPixelStore, glPixelTransfer,
	  glTexEnv, glTexGen, glTexImage1D, glTexImage2D,
	  glTexParameter, glTexSubImage1D, glTexSubImage2D