<HTML>
<BODY>
<PRE>
<STRONG>NAME</STRONG>
<STRONG>glGetTexImage</STRONG> - return a texture image
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glGetTexImage</STRONG>( GLenum <EM>target</EM>,
GLint <EM>level</EM>,
GLenum <EM>format</EM>,
GLenum <EM>type</EM>,
GLvoid *<EM>pixels</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>target</EM> Specifies which texture is to be obtained.
<STRONG>GL_TEXTURE_1D</STRONG> and <STRONG>GL_TEXTURE_2D</STRONG> are accepted.
<EM>level</EM> 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.
<EM>format</EM> Specifies a pixel format for the returned data. The
supported formats are <STRONG>GL_RED</STRONG>, <STRONG>GL_GREEN</STRONG>, <STRONG>GL_BLUE</STRONG>,
<STRONG>GL_ALPHA</STRONG>, <STRONG>GL_RGB</STRONG>, <STRONG>GL_RGBA</STRONG>, <STRONG>GL_LUMINANCE</STRONG>, and
<STRONG>GL_LUMINANCE_ALPHA</STRONG>.
<EM>type</EM> Specifies a pixel type for the returned data. The
supported types are <STRONG>GL_UNSIGNED_BYTE</STRONG>, <STRONG>GL_BYTE</STRONG>,
<STRONG>GL_UNSIGNED_SHORT</STRONG>, <STRONG>GL_SHORT</STRONG>, <STRONG>GL_UNSIGNED_INT</STRONG>,
<STRONG>GL_INT</STRONG>, and <STRONG>GL_FLOAT</STRONG>.
<EM>pixels</EM> Returns the texture image. Should be a pointer to
an array of the type specified by <EM>type</EM>.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glGetTexImage</STRONG> returns a texture image into <EM>pixels</EM>. <EM>target</EM>
specifies whether the desired texture image is one specified
by <STRONG>glTexImage1D</STRONG> (<STRONG>GL_TEXTURE_1D</STRONG>) or by <STRONG>glTexImage2D</STRONG>
(<STRONG>GL_TEXTURE_2D</STRONG>). <EM>level</EM> specifies the level-of-detail number
of the desired image. <EM>format</EM> and <EM>type</EM> specify the format
and type of the desired image array. See the reference
pages <STRONG>glTexImage1D</STRONG> and <STRONG>glDrawPixels</STRONG> for a description of the
acceptable values for the <EM>format</EM> and <EM>type</EM> parameters,
respectively.
To understand the operation of <STRONG>glGetTexImage</STRONG>, consider the
selected internal four-component texture image to be an RGBA
color buffer the size of the image. The semantics of
<STRONG>glGetTexImage</STRONG> are then identical to those of <STRONG>glReadPixels</STRONG>
called with the same <EM>format</EM> and <EM>type</EM>, with <EM>x</EM> and <EM>y</EM> set to 0,
<EM>width</EM> set to the width of the texture image (including
border if one was specified), and <EM>height</EM> set to 1 for 1D
images, or to the height of the texture image (including
border if one was specified) for 2D images. Because the
internal texture image is an RGBA image, pixel formats
<STRONG>GL_COLOR_INDEX</STRONG>, <STRONG>GL_STENCIL_INDEX</STRONG>, and <STRONG>GL_DEPTH_COMPONENT</STRONG> are
not accepted, and pixel type <STRONG>GL_BITMAP</STRONG> 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, green set to 0, blue set to
0, and alpha set to 1. 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 0. 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
1.
To determine the required size of <EM>pixels</EM>, use
<STRONG>glGetTexLevelParameter</STRONG> to determine the dimensions of the
internal texture image, then scale the required number of
pixels by the storage required for each pixel, based on
<EM>format</EM> and <EM>type</EM>. Be sure to take the pixel storage
parameters into account, especially <STRONG>GL_PACK_ALIGNMENT</STRONG>.
<STRONG>NOTES</STRONG>
If an error is generated, no change is made to the contents
of <EM>pixels</EM>.
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>target</EM>, <EM>format</EM>, or <EM>type</EM> is
not an accepted value.
<STRONG>GL_INVALID_VALUE</STRONG> is generated if <EM>level</EM> is less than 0.
<STRONG>GL_INVALID_VALUE</STRONG> may be generated if <EM>level</EM> is greater than
log max, where max is the returned value of
<STRONG>GL_MAX_TEXTURE_SIZE</STRONG>.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glGetTexImage</STRONG> is
executed between the execution of <STRONG>glBegin</STRONG> and the
corresponding execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGetTexLevelParameter</STRONG> with argument <STRONG>GL_TEXTURE_WIDTH</STRONG>
<STRONG>glGetTexLevelParameter</STRONG> with argument <STRONG>GL_TEXTURE_HEIGHT</STRONG>
<STRONG>glGetTexLevelParameter</STRONG> with argument <STRONG>GL_TEXTURE_BORDER</STRONG>
<STRONG>glGetTexLevelParameter</STRONG> with argument <STRONG>GL_TEXTURE_COMPONENTS</STRONG>
<STRONG>glGet</STRONG> with arguments <STRONG>GL_PACK_ALIGNMENT</STRONG> and others
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glDrawPixels</STRONG>, <STRONG>glReadPixels</STRONG>, <STRONG>glTexEnv</STRONG>, <STRONG>glTexGen</STRONG>,
<STRONG>glTexImage1D</STRONG>, <STRONG>glTexImage2D</STRONG>, <STRONG>glTexSubImage1D</STRONG>,
<STRONG>glTexSubImage2D</STRONG>, <STRONG>glTexParameter</STRONG>
</PRE>
</BODY>
</HTML>
