95 lines
3.0 KiB
C
95 lines
3.0 KiB
C
/*
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* The MIT License (MIT)
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*
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* Copyright (c) 2016 B. Stultiens
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to
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* deal in the Software without restriction, including without limitation the
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* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#include "hsv2rgb.h"
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void hsv2rgb_8b(int16_t h, uint8_t s, uint8_t v, uint8_t *r, uint8_t *g , uint8_t *b)
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{
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uint8_t sextant;
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uint8_t bb;
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uint16_t ww;
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uint8_t h_fraction;
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if (!(s)) {
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*(r) = *(g) = *(b) = (v);
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return;
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}
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sextant = h >> 8;
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HSV_SEXTANT_TEST(sextant); // Optional: Limit hue sextants to defined space
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HSV_POINTER_SWAP(sextant, r, g, b); // Swap pointers depending which sextant we are in
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*g = v; // Top level
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// Perform actual calculations
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/*
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* Bottom level: v * (1.0 - s)
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* --> (v * (255 - s) + error_corr) / 256
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*/
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bb = ~s;
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ww = v * bb;
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ww += 1; // Error correction
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ww += ww >> 8; // Error correction
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*b = ww >> 8;
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h_fraction = h & 0xff; // 0...255
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if(!(sextant & 1)) {
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// *r = ...slope_up...;
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/*
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* Slope up: v * (1.0 - s * (1.0 - h))
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* --> (v * (255 - (s * (256 - h) + error_corr1) / 256) + error_corr2) / 256
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*/
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ww = !h_fraction ? ((uint16_t)s << 8) : (s * (uint8_t)(-h_fraction));
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ww += ww >> 8; // Error correction 1
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bb = ww >> 8;
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bb = ~bb;
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ww = v * bb;
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ww += v >> 1; // Error correction 2
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*r = ww >> 8;
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} else {
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// *r = ...slope_down...;
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/*
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* Slope down: v * (1.0 - s * h)
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* --> (v * (255 - (s * h + error_corr1) / 256) + error_corr2) / 256
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*/
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ww = s * h_fraction;
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ww += ww >> 8; // Error correction 1
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bb = ww >> 8;
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bb = ~bb;
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ww = v * bb;
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ww += v >> 1; // Error correction 2
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*r = ww >> 8;
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/*
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* A perfect match for h_fraction == 0 implies:
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* *r = (ww >> 8) + (h_fraction ? 0 : 1)
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* However, this is an extra calculation that may not be required.
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*/
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}
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}
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