glGetTexImage(3G) OpenGL Reference glGetTexImage(3G)
glGetTexImage - return a texture image
void glGetTexImage( GLenum target,
GLint level,
GLenum format,
GLenum type,
GLvoid *pixels )
target Specifies which texture is to be obtained. GL_TEXTURE_1D,
GL_TEXTURE_2D, GL_DETAIL_TEXTURE_2D_SGIS, 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 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_BGR,
GL_RGBA, GL_BGRA, 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,
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.
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 glTexImage3D (GL_TEXTURE_3D). level
specifies the level-of-detail number of the desired image. format and
type specify the format 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
Page 1
glGetTexImage(3G) OpenGL Reference glGetTexImage(3G)
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.
(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, 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.
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.
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.
GL_INVALID_ENUM is generated if target, format, or type is not an
accepted value.
Page 2
glGetTexImage(3G) OpenGL Reference glGetTexImage(3G)
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_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 not GL_RGBA, GL_BGRA or GL_ABGR_EXT.
GL_INVALID_OPERATION is generated when the SGIX_subsample extension is
supported, and the pixel storage mode GL_PACK_SUBSAMPLE_RATE_SGIX is not
GL_PIXEL_SUBSAMPLE_4444_SGIX, and the width of the texture image is not a
multiple of 2, or format is not a 3 or 4 component format, or type is a
packed pixels type.
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_INTERNALFORMAT
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.
The SGIX_subsample and SGIX_resample extensions are supported only on
Octane2 VPro systems. Applying the GL_PIXEL_SUBSAMPLE_2424_SGIX
subsample rate is accelerated for direct immmediate mode transfers when
the format is GL_RGB or GL_RGBA, and the type is GL_UNSIGNED_BYTE or
GL_UNSIGNED_SHORT.
Page 3
glGetTexImage(3G) OpenGL Reference glGetTexImage(3G)
glDrawPixels, glReadPixels, glTexEnv, glTexGen, glTexImage1D,
glTexImage2D, glTexImage3D, glTexSubImage1D, glTexSubImage2D,
glTexSubImage3D, glTexParameter
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