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Add a practical description of endian-independent RGB/BGR coding
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@17681 b3059339-0415-0410-9bf9-f77b7e298cf2
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@ -135,3 +135,24 @@ that you actually get:
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Depending upon the CPU being little- or big-endian, different 'in memory' and
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'in register' formats will be equal (LE -> BGRA == BGR32 / BE -> ARGB == BGR32)
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Practical coding guide:
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The 4, 8, 15, and 16 bit formats are defined so that the portable way to
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access them is to load the pixel into an integer and use bitmasks.
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The 24 bit formats are defined so that the portable way to access them is
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to address the 3 components as separate bytes, as in ((uint8_t *)pixel)[0],
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((uint8_t *)pixel)[1], ((uint8_t *)pixel)[2].
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When a 32-bit format is identified by the four characters A, R, G, and B in
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some order, the portable way to access it is by addressing the 4 components
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as separate bytes.
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When a 32-bit format is identified by the 3 characters R, G, and B in some
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order followed by the number 32, the portable way to access it is to load
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the pixel into an integer and use bitmasks.
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When the above portable access methods are not used, you will need to write
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2 versions of your code, and use #ifdef WORDS_BIGENDIAN to choose the correct
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one.
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