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commit 5a09bd55e0ab64565d12d30ef583d9572d66d6be Author: Tomas Gavenciak gavento@ucw.cz Date: Fri Dec 21 00:23:25 2012 +0100

Reformulate part of codegen docs

diff --git a/doc/gen.txt b/doc/gen.txt index 949f585..1cdf906 100644 --- a/doc/gen.txt +++ b/doc/gen.txt @@ -24,29 +24,45 @@ class PixelSize(object):

self.suffix = suffix

- self.bit_endian = bit_endian - - def needs_bit_endian(self): + self.bit_endian = bit_endian ... - + -------------------------------------------------------------------------------

The Pixel Size object represents pixel as a continous block of data.

-The 'size' is size in bits and is sometimes called bpp which stands for bits -per pixel. It also contains suffix that is a string used as a suffix for -functions that manipulates with this pixel size. +The 'size' is size in bits and is sometimes called bpp which stands for "bits +per pixel". This number includes padding bits, if any. + +The 'suffix' is a string used as a suffix for functions, macros and other +identifiers that operate with this pixel size. + +The 'bit_endian' determines the ordering of pixel bits within a byte in bitmaps +and graymaps. This is significant in pixel types with pixel boundaries +within a byte, i.e. 1 bpp, 4 bpp or 17 bpp. + +It can be either 'BE' or 'LE' (i.e. most significant bit left or right in the bitmap). +Usually, the bitmap is ordered with left bits earlier in the memory, but the +earlier/later relationship is important. +This is defined in terms of natural pixel ordering within the memory. + +'BE' means that the earlier (usually left-most) pixels use the higher ("big") +bits of the byte. I.e. in 1 bpp, the first pixel would have value 128, the second 64 +and so on. + +'LE' means that the earlier (usually left-most) pixels use the lower ("little") +bits of the byte. I.e. in 1 bpp, the first pixel would have value 1, the second 2, +the eight'th 128 and so on.

-The 'bit_endian' determines direction of bits in bitmaps and graymaps (i.e. -most significant bit left or right). It can be either 'BE' or 'LE'. To avoid -confusion following two figures describes bits layout in 1 bit and 2 bits +The following two figures describe bit layout in 1 bpp and 2 bpp grayscale bitmaps. The rectangles in the figures represents bytes as they are -in the buffer. The start of the image (i.e. topleft corner and coodinate 0,0) -is on the left side. The numbers describes position of the bit in the byte (as -seen by shifts and bitmask from within C language implementation). +in the bitmap memory. The start of the image (i.e. topleft corner +and coodinates (0,0)) is on the left side. +The numbers describe position of the bit in the byte, 'i' representing +value '1<<i', that is 7-th bit representing value 128 and 0-th bit value 1.

BE -~~ +++

["graphviz", "bit-endian-be-1bit.png"] ------------------------------------------------------------------------------ @@ -87,7 +103,7 @@ digraph bit_endian { ------------------------------------------------------------------------------

LE -~~ +++

["graphviz", "bit-endian-le-1bit.png"] ------------------------------------------------------------------------------ @@ -115,9 +131,9 @@ digraph bit_endian { rankdir = LR;

node0 [label = "<e> ..."]; - node1 [label = "{0 1 | 2 3 | 4 5 | <e> 6 7}"]; - node2 [label = "{<b> 0 1 | 2 3 | 4 5 | <e> 6 7}"]; - node3 [label = "{<b> 0 1 | 2 3 | 4 5 | <e> 6 7}"]; + node1 [label = "{1 0 | 3 2 | 5 4 | <e> 7 6}"]; + node2 [label = "{<b> 1 0 | 3 2 | 5 4 | <e> 7 6}"]; + node3 [label = "{<b> 1 0 | 3 2 | 5 4 | <e> 7 6}"]; node4 [label = "{<b> ...}"];

node0:e -> node1:b; @@ -127,9 +143,10 @@ digraph bit_endian { } ------------------------------------------------------------------------------

-NOTE: Different pixels can share the same pixel size as for certain types - of operations the function doesn't depend on actual arrangements of the - color channels in pixel (i.e. Get/Put Pixel, Rotate buffer 90 degrees, etc...). +NOTE: Different pixel types (i.e. RGB888 and BGR888) can share the same pixel + size, since certain types of operations do not depend on the actual + arrangement of the color channels in a pixel + (i.e. get/put pixel, rotate buffer 90 degrees, etc.).

TODO: Rename size to bpp?

-----------------------------------------------------------------------

Summary of changes: doc/gen.txt | 59 ++++++++++++++++++++++++++++++++++++++--------------------- 1 files changed, 38 insertions(+), 21 deletions(-)

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