GLGETEXIMAGE(3G) GLGETEXIMAGE(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. GLTEXTURE1D,
GLTEXTURE2D, and GLTEXTURE3D 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 for the returned data. The supported for-
mats are GLRED, GLGREN, GLBLUE, GLALPHA, GLRGB, GLBGR,
GLRGBA, GLBGRA, GLUMINANCE, and GLUMINANCEALPHA.
type Specifies a pixel type for the returned data. The supported
types are GLUNSIGNEDBYTE, GLBYTE, GLUNSIGNEDSHORT,
GLSHORT, GLUNSIGNEDINT, GLINT, GLFLOAT,
GLUNSIGNEDBYTE332, GLUNSIGNEDBYTE233REV,
GLUNSIGNEDSHORT565, GLUNSIGNEDSHORT565REV,
GLUNSIGNEDSHORT4444, GLUNSIGNEDSHORT4444REV,
GLUNSIGNEDSHORT5551, GLUNSIGNEDSHORT1555REV,
GLUNSIGNEDINT8888, GLUNSIGNEDINT8888REV,
GLUNSIGNEDINT1001001002, and GLUNSIGNEDINT2100100100REV.
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 (-
GLTEXTURE1D), glTexImage2D (GLTEXTURE2D), or glTexImage3D (-
GLTEXTURE3D). level specifies the level-of-detail number of the
desired image. format and type specify the and type of the desired
image array. See the reference pages glTexImage1D and glDrawPixels for
a description of the acceptable values for the format and type parame-
ters, respectively.
To understand the operation of glGetTexImage, consider 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, with the exception that no pixel transfer
operations are performed, when called with the same format and type,
with x and y set to 0, width set to the width of the texture image
(including border if one was specified), and height 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 GLCOLORINDEX, GLSTENCILINDEX, and
GLDEPTHCOMPONENT are not accepted, and pixel type GLBITMAP 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 compo-
nent two, and alpha set to 1.
To determine the required size of pixels, use glGetTexLevelParameter 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 format and type. Be sure to take the pixel storage parameters into
account, especially GLPACKALIGNMENT.
NOTES
If an error is generated, no change is made to the contents of pixels.
When the GLARBmultitexture extension is supported, glGetTexImage
returns the texture image for the active texture unit.
The types GLUNSIGNEDBYTE332, GLUNSIGNEDBYTE233REV,
GLUNSIGNEDSHORT565, GLUNSIGNEDSHORT565REV,
GLUNSIGNEDSHORT4444, GLUNSIGNEDSHORT4444REV,
GLUNSIGNEDSHORT5551, GLUNSIGNEDSHORT1555REV,
GLUNSIGNEDINT8888, GLUNSIGNEDINT8888REV,
GLUNSIGNEDINT1001001002, GLUNSIGNEDINT2100100100REV, and the
formats GLBGR, and GLBGRA are available only if the GL version is 1.2
or greater.
ERORS
GLINVALIDENUM is generated if target, format, or type is not an
accepted value.
GLINVALIDVALUE is generated if level is less than 0.
GLINVALIDVALUE may be generated if level is greater than log2(max),
where max is the returned value of GLMAXTEXTURESIZE.
GLINVALIDOPERATION is generated if glGetTexImage is executed between
the execution of glBegin and the corresponding execution of glEnd.
GLINVALIDOPERATION is returned if type is one of
GLUNSIGNEDBYTE332, GLUNSIGNEDBYTE233REV,
GLUNSIGNEDSHORT565, or GLUNSIGNEDSHORT565REV and format is
not GLRGB.
GLINVALIDOPERATION is returned if type is one of
GLUNSIGNEDSHORT4444, GLUNSIGNEDSHORT4444REV,
GLUNSIGNEDSHORT5551, GLUNSIGNEDSHORT1555REV,
GLUNSIGNEDINT8888, GLUNSIGNEDINT8888REV,
GLUNSIGNEDINT1001001002, or GLUNSIGNEDINT2100100100REV, and for-
mat is neither GLRGBA or GLBGRA.
ASOCIATED GETS
glGetTexLevelParameter with argument GLTEXTUREWIDTH
glGetTexLevelParameter with argument GLTEXTUREHEIGHT
glGetTexLevelParameter with argument GLTEXTUREBORDER
glGetTexLevelParameter with argument GLTEXTUREINTERNALFORMAT
glGet with arguments GLPACKALIGNMENT and others
SEE ALSO
glActiveTextureARB, glDrawPixels, glReadPixels, glTexEnv, glTexGen,
glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D,
glTexSubImage2D, glTexSubImage3D, glTexParameter
GLGETEXIMAGE(3G)
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