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This commit is contained in:
Paul Peavyhouse 2019-10-19 05:17:22 -07:00
parent 649e438f0d
commit 8694b3889b
1 changed files with 27 additions and 2 deletions
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29
src/lv_misc/lv_color.h
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@ -304,8 +304,33 @@ static inline uint32_t lv_color_to32(lv_color_t color)
return ret.full;
#elif LV_COLOR_DEPTH == 16
/**
* Per https://docs.google.com/spreadsheets/d/1PppX8FJpddauAPasHwlNgIPGIuPGPNvRbhilIQ8w-7g/edit#gid=0
*/
* The floating point math for conversion is:
* valueto = valuefrom * ( (2^bitsto - 1) / (float)(2^bitsfrom - 1) )
* The faster integer math for conversion is:
* valueto = ( valuefrom * multiplier + adder ) >> divisor
* multiplier = FLOOR( ( (2^bitsto - 1) << divisor ) / (float)(2^bitsfrom - 1) )
*
* Find the smallest divisor where min and max valuefrom convert.
*
* 5-bit to 8-bit: ( 31 * multiplier + adder ) >> divisor = 255
* divisor multiplier adder min (0) max (31)
* 0 8 7 7 255
* 1 16 14 7 255
* 2 32 28 7 255
* 3 65 25 3 255
* 4 131 19 1 255
* 5 263 7 0 255
*
* 6-bit to 8-bit: 255 = ( 63 * multiplier + adder ) >> divisor
* divisor multiplier adder min (0) max (63)
* 0 4 3 3 255
* 1 8 6 3 255
* 2 16 12 3 255
* 3 32 24 3 255
* 4 64 48 3 255
* 5 129 33 1 255
* 6 259 3 0 255
*/
lv_color32_t ret;
ret.ch.red = ( color.ch.red * 263 + 7 ) >> 5;
#if LV_COLOR_16_SWAP == 0