glCopyTexSubImage2D(3G)

NAME
     glCopyTexSubImage2D - copy a two-dimensional texture subimage


C SPECIFICATION
     void glCopyTexSubImage2D( GLenum target,
                               GLint level,
                               GLint xoffset,
                               GLint yoffset,
                               GLint x,
                               GLint y,
                               GLsizei width,
                               GLsizei height )


PARAMETERS
     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.

     x, y     Specify the window coordinates of the lower left corner of the
              rectangular region of pixels to be copied.

     width    Specifies the width of the texture subimage.

     height   Specifies the height of the texture subimage.

DESCRIPTION
     glCopyTexSubImage2D replaces a rectangular portion of a two-dimensional
     texture image with pixels from the current GL_READ_BUFFER (rather than
     from main memory, as is the case for glTexSubImage2D).

     The screen-aligned pixel rectangle with lower left corner at (x, y) and
     with width width and height height replaces the portion of the texture
     array with x indices xoffset through xoffset + width - 1, inclusive, and
     y indices yoffset through yoffset + height - 1, inclusive, at the mipmap
     level specified by level.

     The pixels in the rectangle 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
     array.

     The destination rectangle in the texture array may not include any texels
     outside 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.

     If any of the pixels within the specified rectangle 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, height, or border
     parameters of the specified texture array or to texel values outside the
     specified subregion.

NOTES
     glCopyTexSubImage2D 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.

     When the GL_ARB_imaging extension is supported, the RGBA components read
     from the framebuffer may be processed by the imaging pipeline.  See
     glTexImage1D for specific details.

ERRORS
     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 or glCopyTexImage2D operation.

     GL_INVALID_VALUE is generated if level is less than 0.

     GL_INVALID_VALUE may be generated if level is greater than log max, where
                                                                   2
     max is the returned value of GL_MAX_TEXTURE_SIZE.

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

     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 GL_TEXTURE_BORDER of the texture image
     being modified.  Note that w and h include twice the border width.

     GL_INVALID_OPERATION is generated if glCopyTexSubImage2D is executed
     between the execution of glBegin and the corresponding execution of
     glEnd.

ASSOCIATED GETS
     glGetTexImage
     glIsEnabled with argument GL_TEXTURE_2D


MACHINE DEPENDENCIES
     RealityEngine, RealityEngine2, and VTX systems do not support color
     matrix transformations on images as they are loaded to or read back from
     texture memory.

     RealityEngine, RealityEngine2, and VTX systems support
     glCopyTexSubImage2D and glCopyTexSubImage2DEXT with the following
     restrictions:

          1.  Only level 0 is supported; other levels result in a
              GL_INVALID_VALUE error.

          2.  The texel offsets and the dimensions of the subimage must be
              multiples of 32; otherwise a GL_INVALID_VALUE error is
              generated.

          3.  If glCopyTexSubImage2D or glCopyTexSubImage2DEXT is used when a
              GLX video source is the read drawable (see
              glXMakeCurrentReadSGI), the X offset and Y offset must both be 0
              and the subimage width must be 768; otherwise a GL_INVALID_VALUE
              error is generated.

          4.  GL_INTERLACE_SGIX is not supported (see glEnable).

     On InfiniteReality systems, there is a performance benefit when the width
     of the image to be transferred to texture memory is a multiple of 8.

     Texture borders are not supported on InfiniteReality systems.
     Applications should use borderless textures and GL_CLAMP_TO_EDGE_SGIS
     wrap mode.

     On High Impact and Maximum Impact systems, if the right side of the image
     to be transferred to texture memory is not the right side of the texture,
     then its index must be a multiple of 32, where index = xoffset+width.
     Otherwise it will generate a GL_INVALID_VALUE error.

     The SGIX_interlace extension is supported only on InfiniteReality
     systems, on RealityEngine, RealityEngine2, and VTX systems, on Octane2
     VPro systems, and on O2 systems.

     The INGR_interlace_read extension is supported only on Octane2 VPro
     systems, and on O2 systems.

     On O2 systems, when the current read drawable is a DM pbuffer, using
     glCopyTexSubImage2D or glCopyTexSubImage2DEXT to copy into a full texture
     image whose dimensions and format match those of the pbuffer causes a
     copy-by-reference.  This has performance advantages, especially for
     video-generated DMbuffers, because it provides a DMA path for updating
     textures.  Following the copy, rendering to the pbuffer or otherwise
     modifying the DMbuffer, will directly affect texture memory.  However,
     this behavior is essentially an unspecified side-effect of the
     implementation on O2, and cannot be used on other systems.


SEE ALSO
     glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D,
     glCopyTexSubImage3D, glPixelStore, glPixelTransfer, glReadBuffer,
     glTexEnv, glTexGen, glTexImage1D, glTexImage2D, glTexImage3D,
     glTexParameter, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D