glTexSubImage2D - specify a two-dimensional texture subimage

glTexSubImage2D
	glTexSubImage2D(target, level, xoffset, yoffset, width, height, format, type, pixels) -> None
glTexSubImage2Db
	glTexSubImage2Db(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Df
	glTexSubImage2Df(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Di
	glTexSubImage2Di(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Ds
	glTexSubImage2Ds(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Dub
	glTexSubImage2Dub(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Dui
	glTexSubImage2Dui(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None
glTexSubImage2Dus
	glTexSubImage2Dus(target, level, xoffset, yoffset, format, type, pixels[][] | pixels[][][]) -> None

void glTexSubImage2D(	GLenum target,
                      GLint level,
                      GLint xoffset,
                      GLint yoffset,
                      GLsizei	width,
                      GLsizei	height,
                      GLenum format,
                      GLenum type,
                      const GLvoid *pixels )

target   Specifies the target	texture.  Must be
         GL_TEXTURE_2D.

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

xoffset  Specifies a texel offset in the x direction within
         the texture array.

yoffset  Specifies a texel offset in the y direction within
         the texture array.

width	   Specifies the width of the texture subimage.

height   Specifies the height	of the texture subimage.

format   Specifies the format	of the pixel data.  The
         following symbolic values are accepted:
         GL_COLOR_INDEX, GL_RED, GL_GREEN, GL_BLUE,
         GL_ALPHA, GL_RGB, GL_RGBA, GL_LUMINANCE, and
         GL_LUMINANCE_ALPHA.

type	   Specifies the data type of the pixel	data.  The
         following symbolic values are accepted:
         GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP,
         GL_UNSIGNED_SHORT, GL_SHORT,	GL_UNSIGNED_INT,
         GL_INT, and GL_FLOAT.

pixels   Specifies a pointer to the image data in memory.

Texturing maps a portion of a	specified texture image	onto
each graphical primitive for which texturing is enabled.  To
enable and disable two-dimensional texturing,	call glEnable
and glDisable	with argument GL_TEXTURE_2D.

glTexSubImage2D redefines a contiguous subregion of an
existing two-dimensional texture image.  The texels
referenced by	pixels replace the portion of the existing
texture array	with x indices xoffset and
xoffset + width - 1, inclusive, and y	indices	yoffset	and
yoffset + height - 1,	inclusive. This	region may not include
any texels outside the range of the texture array as it was
originally specified.	 It is not an error to specify a
subtexture with zero width or	height,	but such a
specification	has no effect.

glTexSubImage2D 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_2D.

GL_INVALID_OPERATION is generated if the texture array has
not been defined by a	previous glTexImage2D operation.

GL_INVALID_VALUE is generated	if level is less than 0.

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

GL_INVALID_VALUE is generated	if xoffset <  -b,
(xoffset + width) > (w - b), yoffset <  -b, or
(yoffset + height) > (h - b).	 Where w is the
GL_TEXTURE_WIDTH, h is the GL_TEXTURE_HEIGHT,	and b is the
border width of the texture image being modified.  Note that
w and	h include twice	the border width.

GL_INVALID_VALUE is generated	if width or height is less
than 0.

GL_INVALID_ENUM is generated if format is not	an accepted
format constant.

GL_INVALID_ENUM is generated if type is not a	type constant.

GL_INVALID_ENUM is generated if type is GL_BITMAP and	format
is not GL_COLOR_INDEX.

GL_INVALID_OPERATION is generated if glTexSubImage2D is
executed between the execution of glBegin and	the
corresponding	execution of glEnd.

glGetTexImage
glIsEnabled with argument GL_TEXTURE_2D

glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D,
glCopyTexSubImage2D, glDrawPixels, glPixelStore,
glPixelTransfer, glTexEnv, glTexGen, glTexImage1D,
glTexImage2D,	glTexSubImage1D, glTexParameter