glGetTexImage(3G)

NAME
     glGetTexImage - return a texture image


C SPECIFICATION
     void glGetTexImage( GLenum target,
                         GLint level,
                         GLenum format,
                         GLenum type,
                         GLvoid *pixels )


PARAMETERS
     target  Specifies which texture is to be obtained.  GL_TEXTURE_1D,
             GL_TEXTURE_2D, GL_DETAIL_TEXTURE_2D_SGIS, and GL_TEXTURE_3D_EXT
             are accepted.

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

     format  Specifies a pixel format for the returned data.  The supported
             formats are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA,
             GL_ABGR_EXT, GL_LUMINANCE, and GL_LUMINANCE_ALPHA.

     type    Specifies a pixel type for the returned data.  The supported
             types are GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT,
             GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2_EXT,
             GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
             GL_UNSIGNED_INT_8_8_8_8_EXT, and GL_UNSIGNED_INT_10_10_10_2_EXT.

     pixels  Returns the texture image.  Should be a pointer to an array of
             the type specified by type.


DESCRIPTION
     glGetTexImage returns a texture image into pixels.  target specifies
     whether the desired texture image is one specified by glTexImage1D
     (GL_TEXTURE_1D), glTexImage2D (GL_TEXTURE_2D or
     GL_DETAIL_TEXTURE_2D_SGIS), or by glTexImage3DEXT (GL_TEXTURE_3D_EXT).
     level specifies the level-of-detail number of the desired image.  format
     and type specify the format and type of the desired image array.  Please
     see the reference pages glTexImage1D and glDrawPixels for a description
     of the acceptable values for the format and type parameters,
     respectively.

     Operation of glGetTexImage is best understood by considering the selected
     internal four-component texture image to be an RGBA color buffer the size
     of the image.  The semantics of glGetTexImage are then identical to those
     of glReadPixels called with the same format and type, with x and y set to
     zero, width set to the width of the texture image (including border if
     one was specified), and height set to one for 1-D images, or to the
     height of the texture image (including border if one was specified) for
     2-D images.  (Similar considerations apply to 3D images, though there is
     no direct analogy with glReadPixels.)  Because the internal texture image
     is an RGBA image, pixel formats GL_COLOR_INDEX, GL_STENCIL_INDEX, and
     GL_DEPTH_COMPONENT are not accepted, and pixel type GL_BITMAP is not
     accepted.

     If the selected texture image does not contain four components, the
     following mappings are applied.  Single-component textures are treated as
     RGBA buffers with red set to the single-component value, and green, blue,
     and alpha set to zero.  Two-component textures are treated as RGBA
     buffers with red set to the value of component zero, alpha set to the
     value of component one, and green and blue set to zero.  Finally, three-
     component textures are treated as RGBA buffers with red set to component
     zero, green set to component one, blue set to component two, and alpha
     set to zero.

     To determine the required size of pixels, use glGetTexLevelParameter to
     ascertain the dimensions of the internal texture image, then scale the
     required number of pixels by the storage required for each pixel, based
     on format and type.  Be sure to take the pixel storage parameters into
     account, especially GL_PACK_ALIGNMENT.

NOTES
     If an error is generated, no change is made to the contents of pixels.

     If type is set to GL_UNSIGNED_BYTE_3_3_2_EXT,
     GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
     GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and the
     EXT_packed_pixels extension is not supported then a GL_INVALID_ENUM error
     is generated.

     GL_ABGR_EXT is part of the EXT_abgr extension and
     GL_DETAIL_TEXTURE_2D_SGIS is part of the SGIS_detail_texture extension.

     See glIntro for more information on using extensions.

ERRORS
     GL_INVALID_ENUM is generated if target, format, or type is not an
     accepted value.

     GL_INVALID_VALUE is generated if level is less than zero or greater than
     log max, where max is the returned value of GL_MAX_TEXTURE_SIZE.
        2

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

ASSOCIATED GETS
     glGetTexLevelParameter with argument GL_TEXTURE_WIDTH
     glGetTexLevelParameter with argument GL_TEXTURE_HEIGHT
     glGetTexLevelParameter with argument GL_TEXTURE_DEPTH_EXT
     glGetTexLevelParameter with argument GL_TEXTURE_BORDER
     glGetTexLevelParameter with argument GL_TEXTURE_COMPONENTS
     glGet with arguments GL_PACK_ALIGNMENT and others


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 do not support convolving
     texture images as they are retrieved from texture memory.

     The EXT_packed_pixels extension is not supported on RealityEngine,
     RealityEngine2, and VTX systems.


SEE ALSO
     glDrawPixels, glReadPixels, glTexImage1D, glTexImage2D, glTexImage3DEXT