GLGETTEXIMAGE()GLGETTEXIMAGE()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 and
GL_TEXTURE_2D 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 format for the returned data. The supported
formats are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB,
GL_RGBA, 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, and GL_FLOAT.
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) or by glTexImage2D (GL_TEXTURE_2D). level specifies
the level-of-detail number of the desired image. format and type spec‐
ify 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 of glReadPixels 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 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 GL_PACK_ALIGNMENT.
NOTES
If an error is generated, no change is made to the contents of pixels.
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.
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_COMPONENTS
glGet with arguments GL_PACK_ALIGNMENT and others
SEE ALSO
glDrawPixels, glReadPixels, glTexEnv, glTexGen, glTexImage1D, glTexIm‐
age2D, glTexSubImage1D, glTexSubImage2D, glTexParameter
GLGETTEXIMAGE()
