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/*
* ordered dither rotines
*
* stolen from The GIMP and trimmed for speed
*
*/
#include <stdlib.h>
#include "dither.h"
#define DITHER_LEVEL 8
void (*dither_line)(unsigned char *, unsigned char *, int, int);
static long red_mult, green_mult;
static long red_dither[256];
static long green_dither[256];
static long blue_dither[256];
static long gray_dither[256];
typedef unsigned long vector[DITHER_LEVEL];
typedef vector matrix[DITHER_LEVEL];
#if DITHER_LEVEL == 8
#define DITHER_MASK 7
static matrix DM =
{
{0, 32, 8, 40, 2, 34, 10, 42},
{48, 16, 56, 24, 50, 18, 58, 26},
{12, 44, 4, 36, 14, 46, 6, 38},
{60, 28, 52, 20, 62, 30, 54, 22},
{3, 35, 11, 43, 1, 33, 9, 41},
{51, 19, 59, 27, 49, 17, 57, 25},
{15, 47, 7, 39, 13, 45, 5, 37},
{63, 31, 55, 23, 61, 29, 53, 21}
};
#endif
#if DITHER_LEVEL == 4
#define DITHER_MASK 3
static matrix DM =
{
{0, 8, 2, 10},
{12, 4, 14, 6},
{3, 11, 1, 9},
{15, 7, 13, 5}
};
#endif
void
init_dither(int shades_r, int shades_g, int shades_b, int shades_gray)
{
int i, j;
unsigned char low_shade, high_shade;
unsigned short index;
float red_colors_per_shade;
float green_colors_per_shade;
float blue_colors_per_shade;
float gray_colors_per_shade;
red_mult = shades_g * shades_b;
green_mult = shades_b;
red_colors_per_shade = 256.0 / (shades_r - 1);
green_colors_per_shade = 256.0 / (shades_g - 1);
blue_colors_per_shade = 256.0 / (shades_b - 1);
gray_colors_per_shade = 256.0 / (shades_gray - 1);
/* this avoids a shift when checking these values */
for (i = 0; i < DITHER_LEVEL; i++)
for (j = 0; j < DITHER_LEVEL; j++)
DM[i][j] *= 0x10000;
/* setup arrays containing three bytes of information for red, green, & blue */
/* the arrays contain :
* 1st byte: low end shade value
* 2nd byte: high end shade value
* 3rd & 4th bytes: ordered dither matrix index
*/
for (i = 0; i < 256; i++) {
/* setup the red information */
{
low_shade = (unsigned char) (i / red_colors_per_shade);
high_shade = low_shade + 1;
index = (unsigned short)
(((i - low_shade * red_colors_per_shade) / red_colors_per_shade) *
(DITHER_LEVEL * DITHER_LEVEL + 1));
low_shade *= red_mult;
high_shade *= red_mult;
red_dither[i] = (index << 16) + (high_shade << 8) + (low_shade);
}
/* setup the green information */
{
low_shade = (unsigned char) (i / green_colors_per_shade);
high_shade = low_shade + 1;
index = (unsigned short)
(((i - low_shade * green_colors_per_shade) / green_colors_per_shade) *
(DITHER_LEVEL * DITHER_LEVEL + 1));
low_shade *= green_mult;
high_shade *= green_mult;
green_dither[i] = (index << 16) + (high_shade << 8) + (low_shade);
}
/* setup the blue information */
{
low_shade = (unsigned char) (i / blue_colors_per_shade);
high_shade = low_shade + 1;
index = (unsigned short)
(((i - low_shade * blue_colors_per_shade) / blue_colors_per_shade) *
(DITHER_LEVEL * DITHER_LEVEL + 1));
blue_dither[i] = (index << 16) + (high_shade << 8) + (low_shade);
}
/* setup the gray information */
{
low_shade = (unsigned char) (i / gray_colors_per_shade);
high_shade = low_shade + 1;
index = (unsigned short)
(((i - low_shade * gray_colors_per_shade) / gray_colors_per_shade) *
(DITHER_LEVEL * DITHER_LEVEL + 1));
gray_dither[i] = (index << 16) + (high_shade << 8) + (low_shade);
}
}
}
void
dither_line_color(unsigned char *src, unsigned char *dest, int y, int width)
{
register long a, b;
long *ymod, xmod;
ymod = DM[y & DITHER_MASK];
while (width--) {
xmod = width & DITHER_MASK;
b = red_dither[*(src++)];
if (ymod[xmod] < b)
b >>= 8;
a = green_dither[*(src++)];
if (ymod[xmod] < a)
a >>= 8;
b += a;
a = blue_dither[*(src++)];
if (ymod[xmod] < a)
a >>= 8;
b += a;
*(dest++) = b & 0xff;
}
}
void
dither_line_gray(unsigned char *src, unsigned char *dest, int y, int width)
{
long *ymod, xmod;
register long a,g;
ymod = DM[y & DITHER_MASK];
while (width--) {
xmod = width & DITHER_MASK;
#if 1
g = (src[0]*3 + src[1]*6 + src[2]) / 10;
a = gray_dither[g];
src += 3;
#else
a = gray_dither[*(src++)];
#endif
if (ymod[xmod] < a)
a >>= 8;
*(dest++) = a & 0xff;
}
}
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