232 lines
6.2 KiB
C
232 lines
6.2 KiB
C
/*
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* Copyright 2012 Michael Drake <tlsa@netsurf-browser.org>
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*
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* This file is part of libnsfb, http://www.netsurf-browser.org/
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* Licenced under the MIT License,
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* http://www.opensource.org/licenses/mit-license.php
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*
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* This is the *internal* interface for the cursor.
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*/
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#ifndef PALETTE_H
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#define PALETTE_H 1
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#include <stdint.h>
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#include <limits.h>
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#include "libnsfb.h"
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#include "libnsfb_plot.h"
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enum nsfb_palette_type_e {
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NSFB_PALETTE_EMPTY, /**< empty palette object */
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NSFB_PALETTE_NSFB_8BPP, /**< libnsfb's own 8bpp palette */
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NSFB_PALETTE_OTHER /**< any other palette */
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};
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struct nsfb_palette_s {
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enum nsfb_palette_type_e type; /**< Palette type */
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uint8_t last; /**< Last used palette index */
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nsfb_colour_t data[256]; /**< Palette for index modes */
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bool dither; /**< Whether to use error diffusion */
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struct {
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int width; /**< Length of error value buffer ring*/
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int current; /**< Current pos in ring buffer*/
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int *data; /**< Ring buffer error values */
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int data_len; /**< Max size of ring */
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} dither_ctx;
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};
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/** Create an empty palette object. */
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bool nsfb_palette_new(struct nsfb_palette_s **palette, int width);
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/** Free a palette object. */
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void nsfb_palette_free(struct nsfb_palette_s *palette);
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/** Init error diffusion for a plot. */
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void nsfb_palette_dither_init(struct nsfb_palette_s *palette, int width);
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/** Finalise error diffusion after a plot. */
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void nsfb_palette_dither_fini(struct nsfb_palette_s *palette);
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/** Generate libnsfb 8bpp default palette. */
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void nsfb_palette_generate_nsfb_8bpp(struct nsfb_palette_s *palette);
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/** Find best palette match for given colour. */
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static inline uint8_t nsfb_palette_best_match(struct nsfb_palette_s *palette,
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nsfb_colour_t c, int *r_error, int *g_error, int *b_error)
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{
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uint8_t best_col = 0;
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nsfb_colour_t palent;
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int col;
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int dr, dg, db; /* delta red, green blue values */
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int cur_distance;
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int best_distance = INT_MAX;
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switch (palette->type) {
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case NSFB_PALETTE_NSFB_8BPP:
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/* Index into colour cube part */
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dr = ((( c & 0xFF) * 5) + 128) / 256;
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dg = ((((c >> 8) & 0xFF) * 7) + 128) / 256;
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db = ((((c >> 16) & 0xFF) * 4) + 128) / 256;
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col = 40 * dr + 5 * dg + db;
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palent = palette->data[col];
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dr = ( c & 0xFF) - ( palent & 0xFF);
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dg = ((c >> 8) & 0xFF) - ((palent >> 8 ) & 0xFF);
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db = ((c >> 16) & 0xFF) - ((palent >> 16) & 0xFF);
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cur_distance = (dr * dr) + (dg * dg) + (db * db);
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best_col = col;
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best_distance = cur_distance;
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*r_error = dr;
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*g_error = dg;
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*b_error = db;
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/* Index into grayscale part */
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col = (( c & 0xFF) +
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((c >> 8) & 0xFF) +
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((c >> 16) & 0xFF) + (45 / 2)) / (15 * 3) - 1 + 240;
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palent = palette->data[col];
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dr = ( c & 0xFF) - ( palent & 0xFF);
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dg = ((c >> 8) & 0xFF) - ((palent >> 8) & 0xFF);
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db = ((c >> 16) & 0xFF) - ((palent >> 16) & 0xFF);
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cur_distance = (dr * dr) + (dg * dg) + (db * db);
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if (cur_distance < best_distance) {
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best_distance = cur_distance;
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best_col = col;
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*r_error = dr;
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*g_error = dg;
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*b_error = db;
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}
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break;
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case NSFB_PALETTE_OTHER:
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/* Try all colours in palette */
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for (col = 0; col <= palette->last; col++) {
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palent = palette->data[col];
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dr = ( c & 0xFF) - ( palent & 0xFF);
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dg = ((c >> 8) & 0xFF) - ((palent >> 8) & 0xFF);
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db = ((c >> 16) & 0xFF) - ((palent >> 16) & 0xFF);
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cur_distance = (dr * dr) + (dg * dg) + (db * db);
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if (cur_distance < best_distance) {
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best_distance = cur_distance;
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best_col = col;
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*r_error = dr;
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*g_error = dg;
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*b_error = db;
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}
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}
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break;
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default:
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break;
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}
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return best_col;
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}
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/** Find best palette match for given colour, with error diffusion. */
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static inline uint8_t nsfb_palette_best_match_dither(
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struct nsfb_palette_s *palette, nsfb_colour_t c)
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{
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int r, g, b;
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int current;
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int error;
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int width = palette->dither_ctx.width;
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uint8_t best_col_index;
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if (palette == NULL)
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return 0;
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if (palette->dither == false)
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return nsfb_palette_best_match(palette, c, &r, &g, &b);
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current = palette->dither_ctx.current;
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/* Get RGB components of colour, and apply error */
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r = ( c & 0xFF) + palette->dither_ctx.data[current ];
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g = ((c >> 8) & 0xFF) + palette->dither_ctx.data[current + 1];
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b = ((c >> 16) & 0xFF) + palette->dither_ctx.data[current + 2];
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/* Clamp new RGB components to range */
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if (r < 0) r = 0;
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if (r > 255) r = 255;
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if (g < 0) g = 0;
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if (g > 255) g = 255;
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if (b < 0) b = 0;
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if (b > 255) b = 255;
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/* Reset error diffusion slots to 0 */
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palette->dither_ctx.data[current ] = 0;
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palette->dither_ctx.data[current + 1] = 0;
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palette->dither_ctx.data[current + 2] = 0;
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/* Rebuild colour from modified components */
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c = r + (g << 8) + (b << 16);
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/* Get best match for pixel, and find errors for each component */
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best_col_index = nsfb_palette_best_match(palette, c, &r, &g, &b);
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/* Advance one set of error diffusion slots */
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current += 3;
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if (current >= width)
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current = 0;
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palette->dither_ctx.current = current;
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/* Save errors
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*
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* [*]-[N]
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* / | \
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* [l]-[m]-[r]
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*/
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error = current;
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/* Error for [N] (next) */
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if (error != 0) {
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/* The pixel exists */
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palette->dither_ctx.data[error ] += r * 7 / 16;
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palette->dither_ctx.data[error + 1] += g * 7 / 16;
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palette->dither_ctx.data[error + 2] += b * 7 / 16;
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}
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error += width - 2 * 3;
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if (error >= width)
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error -= width;
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/* Error for [l] (below, left) */
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if (error >= 0 && error != 3) {
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/* The pixel exists */
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palette->dither_ctx.data[error ] += r * 3 / 16;
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palette->dither_ctx.data[error + 1] += g * 3 / 16;
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palette->dither_ctx.data[error + 2] += b * 3 / 16;
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}
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error += 3;
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if (error >= width)
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error -= width;
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/* Error for [m] (below, middle) */
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palette->dither_ctx.data[error ] += r * 5 / 16;
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palette->dither_ctx.data[error + 1] += g * 5 / 16;
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palette->dither_ctx.data[error + 2] += b * 5 / 16;
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error += 3;
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if (error >= width)
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error -= width;
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/* Error for [r] (below, right) */
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if (error != 0) {
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/* The pixel exists */
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palette->dither_ctx.data[error ] += r / 16;
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palette->dither_ctx.data[error + 1] += g / 16;
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palette->dither_ctx.data[error + 2] += b / 16;
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}
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return best_col_index;
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}
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#endif /* PALETTE_H */
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