HP c3700 - Workstation, Справочное руководство, Страница: 330 / 486

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glPixelStore
Chapter 14
330
If true, byte ordering for multibyte color components, depth components, color indices, or
stencil indices is reversed. That is, if a four-byte component consists of bytes b
0
, b
1
, b
2
,
b
3
, it is taken from memory as b
3
, b
2
, b
1
, b
0
if GL_UNPACK_SWAP_BYTES is true.
GL_UNPACK_SWAP_BYTES has no effect on the memory order of components within a
pixel, only on the order of bytes within components or indices. For example, the three
components of a GL_RGB format pixel are always stored with red first, green second,
and blue third, regardless of the value of GL_UNPACK_SWAP_BYTES.
GL_UNPACK_LSB_FIRST
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 is relevant only for
bitmap data.
GL_UNPACK_ROW_LENGTH
If greater than 0, GL_UNPACK_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_UNPACK_ROW_LENGTH if it is greater than 0, the
width argument to the pixel routine otherwise), a is the value of
GL_UNPACK_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
components or indices.
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_UNPACK_SKIP_PIXELS and GL_UNPACK_SKIP_ROWS
These values are provided as a convenience to the programmer; they provide no
functionality that cannot be duplicated by incrementing the pointer passed to
glDrawPixels, glTexImage1D, glTexImage2D, glTexSubImage1D, glTexSubImage2D,
glBitmap, or glPolygonStipple. Setting GL_UNPACK_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_UNPACK_SKIP_ROWS to j is
k
nl
a
s
---
------
snl
a
---------
if
s a
≥
s a
<
-----------





=
k
nl
a
s
---
------
snl
a
---------
if
s a
≥
s a
<
-----------
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=