HP b2600 Reference Manual page 329

If true, bits are ordered within a byte from least significant to most significant;
otherwise, the first bit in each byte is the most significant one. This parameter is
significant for bitmap data only.
GL_PACK_ROW_LENGTH
If greater than 0, GL_PACK_ROW_LENGTH defines the number of pixels in a row. If
the first pixel of a row is placed at location p in memory, then the location of the first
pixel of the next row is obtained by skipping
components or indices, where n is the number of components or indices in a pixel, l is
the number of pixels in a row (GL_PACK_ROW_LENGTH if it is greater than 0, the
width argument to the pixel routine otherwise), a is the value of
GL_PACK_ALIGNMENT, and s is the size, in bytes, of a single component (if a<s, then it
is as if a=s). In the case of 1-bit values, the location of the next row is obtained by
skipping
The word component in this description refers to the non-index values red, green, blue,
alpha, and depth. Storage format GL_RGB, for example, has three components per pixel:
first red, then green, and finally blue.
GL_PACK_SKIP_PIXELS and GL_PACK_SKIP_ROWS
These values are provided as a convenience to the programmer; they provide no
functionality that cannot be duplicated simply by incrementing the pointer passed to
glReadPixels. Setting GL_PACK_SKIP_PIXELS to i is equivalent to incrementing the
pointer by in components or indices, where n is the number of components or indices in
each pixel. Setting GL_PACK_SKIP_ROWS to j is equivalent to incrementing the
pointer by jk components or indices, where k is the number of components or indices per
row, as just computed in the GL_PACK_ROW_LENGTH section.
GL_PACK_ALIGNMENT
Specifies the alignment requirements for the start of each pixel row in memory. The
allowable values are 1 (byte-alignment), 2 (rows aligned to even-numbered bytes), 4
(word-alignment), and 8 (rows start on double-word boundaries).
The other six of the twelve storage parameters affect how pixel data is read from client
memory. These values are significant for glDrawPixels, glTexImage1D, glTexImage2D,
glTexSubImage1D, glTexSubImage2D, glBitmap, and glPolygonStipple. They are as
follows:
GL_UNPACK_SWAP_BYTES
Chapter 14
nl
s a
k = ----- - if ---------- -
a
snl s a
-- -
-------- -
s
a
8a nl
k =
----- -
8a
glPixelStore
components or indices.
P
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