GLGETTEXIMAGE(3G)GLGETTEXIMAGE(3G)NAMEglGetTexImage - return a texture image
C SPECIFICATION
void glGetTexImage( GLenum target,
GLint level,
GLenum format,
GLenum type,
GLvoid *pixels )
delim $$
PARAMETERS
target Specifies which texture is to be obtained. GL_TEXTURE_1D,
GL_TEXTURE_2D, and GL_TEXTURE_3D are accepted.
level Specifies the level-of-detail number of the desired image.
Level 0 is the base image level. Level $n$ is the $n$th mipmap
reduction image.
format Specifies a pixel for the returned data. The supported formats
are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_BGR,
GL_RGBA, GL_BGRA, 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, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, and GL_UNSIGNED_INT_2_10_10_10_REV.
pixels Returns the texture image. Should be a pointer to an array of
the type specified by type.
DESCRIPTIONglGetTexImage 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 glTexImage3D
(GL_TEXTURE_3D). 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
parameters, 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 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, 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 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 GL_PACK_ALIGNMENT.
NOTES
If an error is generated, no change is made to the contents of pixels.
When the GL_ARB_multitexture extension is supported, glGetTexImage
returns the texture image for the active texture unit.
The types GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, GL_UNSIGNED_INT_2_10_10_10_REV, and the
formats GL_BGR, and GL_BGRA are available only if the GL version is 1.2
or greater.
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 0.
GL_INVALID_VALUE may be generated if level is greater than $log sub 2
max$, where $max$ is the returned value of GL_MAX_TEXTURE_SIZE.
GL_INVALID_OPERATION is generated if glGetTexImage is executed between
the execution of glBegin and the corresponding execution of glEnd.
GL_INVALID_OPERATION is returned if type is one of
GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, or GL_UNSIGNED_SHORT_5_6_5_REV and format is
not GL_RGB.
GL_INVALID_OPERATION is returned if type is one of
GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV, and
format is neither GL_RGBA or GL_BGRA.
ASSOCIATED GETS
glGetTexLevelParameter with argument GL_TEXTURE_WIDTH
glGetTexLevelParameter with argument GL_TEXTURE_HEIGHT
glGetTexLevelParameter with argument GL_TEXTURE_BORDER
glGetTexLevelParameter with argument GL_TEXTURE_INTERNALFORMAT
glGet with arguments GL_PACK_ALIGNMENT and others
SEE ALSOglActiveTextureARB(3G), glDrawPixels(3G), glReadPixels(3G),
glTexEnv(3G), glTexGen(3G), glTexImage1D(3G), glTexImage2D(3G),
glTexImage3D(3G), glTexSubImage1D(3G), glTexSubImage2D(3G),
glTexSubImage3D(3G), glTexParameter(3G)
March 1, 2011
