OpenGL man pages
glGetTexImage - return a texture image
void glGetTexImage( GLenum target,
GLvoid *pixels )
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 nth mipmap reduction
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.
glGetTexImage 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 specify the
format and type of the desired image array. Please see the reference pages
glTexImage1D and glDrawPixels for a description of the acceptable values
for the format and type parameters, respectively.
Operation of glGetTexImage is best understood by considering 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
zero, width set to the width of the texture image (including border if one
was specified), and height set to one for 1-D images, or to the height of
the texture image (including border if one was specified) for 2-D 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, and green, blue,
and alpha set to zero. 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 zero. 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 zero.
To determine the required size of pixels, use glGetTexLevelParameter to
ascertain 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.
GL_INVALID_ENUM is generated if target, format, or type is not an accepted
GL_INVALID_VALUE is generated if level is less than zero or greater than
log 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.
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
glDrawPixels, glReadPixels, glTexImage1D, glTexImage2D
Fri Dec 6 11:18:03 EST 1996
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