shithub: tinygl

ref: c58a9a045fd18630b95033f1414a09eaf3544558
dir: /src/zdither.c/

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/*
 * Highly optimised dithering 16 bits -> 8 bits.
 * The formulas were taken in Mesa (Bob Mercier mercier@hollywood.cinenet.net).
 */

#include "../include/zbuffer.h"
#include <assert.h>
//#include <stdio.h>
#include <stdlib.h>

#if defined(TGL_FEATURE_8_BITS)

#define _R 5
#define _G 9
#define _B 5
#define _DX 4
#define _DY 4
#define _D (_DX * _DY)
#define _MIX(r, g, b) (((g) << 6) | ((b) << 3) | (r))

#define DITHER_TABLE_SIZE (1 << 15)

#define DITHER_INDEX(r, g, b) ((b) + (g)*_B + (r) * (_B * _G))

#define MAXC 256
static GLint kernel8[_DY * _DX] = {
	0 * MAXC, 8 * MAXC,  2 * MAXC, 10 * MAXC, 12 * MAXC, 4 * MAXC, 14 * MAXC, 6 * MAXC,
	3 * MAXC, 11 * MAXC, 1 * MAXC, 9 * MAXC,  15 * MAXC, 7 * MAXC, 13 * MAXC, 5 * MAXC,
};

/* we build the color table and the lookup table */

void ZB_initDither(ZBuffer* zb, GLint nb_colors, GLubyte* color_indexes, GLint* color_table) {
	GLint c, r, g, b, i, index, r1, g1, b1;

	if (nb_colors < (_R * _G * _B)) {
		//		tgl_fixme("zdither: not enough colors\n");
		exit(1);
	}

	for (i = 0; i < nb_colors; i++)
		color_table[i] = 0;

	zb->nb_colors = nb_colors;
	zb->ctable = gl_malloc(nb_colors * sizeof(GLint));

	for (r = 0; r < _R; r++) {
		for (g = 0; g < _G; g++) {
			for (b = 0; b < _B; b++) {
				r1 = (r * 255) / (_R - 1);
				g1 = (g * 255) / (_G - 1);
				b1 = (b * 255) / (_B - 1);
				index = DITHER_INDEX(r, g, b);
				c = (r1 << 16) | (g1 << 8) | b1;
				zb->ctable[index] = c;
				color_table[index] = c;
			}
		}
	}

	zb->dctable = gl_malloc(DITHER_TABLE_SIZE);

	for (i = 0; i < DITHER_TABLE_SIZE; i++) {
		r = (i >> 12) & 0x7;
		g = (i >> 8) & 0xF;
		b = (i >> 3) & 0x7;
		index = DITHER_INDEX(r, g, b);
		zb->dctable[i] = color_indexes[index];
	}
}

void ZB_closeDither(ZBuffer* zb) {
	gl_free(zb->ctable);
	gl_free(zb->dctable);
}

#if 0
int ZDither_lookupColor(GLint r,GLint g,GLint b)
{
  GLubyte *ctable=zdither_color_table;
  return ctable[_MIX(_DITH0(_R, r), _DITH0(_G, g),_DITH0(_B, b))];
}
#endif

#define DITHER_PIXEL2(a)                                                                                                                                       \
	{                                                                                                                                                          \
		register GLint v, t, r, g, c;                                                                                                                          \
		v = *(GLuint*)(pp + (a));                                                                                                                              \
		g = (v & 0x07DF07DF) + g_d;                                                                                                                            \
		r = (((v & 0xF800F800) >> 2) + r_d) & 0x70007000;                                                                                                      \
		t = r | g;                                                                                                                                             \
		c = ctable[t & 0xFFFF] | (ctable[t >> 16] << 8);                                                                                                       \
		*(GLushort*)(dest + (a)) = c;                                                                                                                          \
	}

/* NOTE: all the memory access are 16 bit aligned, so if buf or
   linesize are not multiple of 2, it cannot work efficiently (or
   hang!) */

void ZB_ditherFrameBuffer(ZBuffer* zb, GLubyte* buf, GLint linesize) {
	GLint xk, yk, x, y, c1, c2;
	GLubyte* dest1;
	GLushort* pp1;
	GLint r_d, g_d, b_d;
	GLubyte* ctable = zb->dctable;
	register GLubyte* dest;
	register GLushort* pp;

	assert(((long)buf & 1) == 0 && (linesize & 1) == 0);

	for (yk = 0; yk < 4; yk++) {
		for (xk = 0; xk < 4; xk += 2) {
#if BYTE_ORDER == BIG_ENDIAN
			c1 = kernel8[yk * 4 + xk + 1];
			c2 = kernel8[yk * 4 + xk];
#else
			c1 = kernel8[yk * 4 + xk];
			c2 = kernel8[yk * 4 + xk + 1];
#endif
			r_d = ((c1 << 2) & 0xF800) >> 2;
			g_d = (c1 >> 4) & 0x07C0;
			b_d = (c1 >> 9) & 0x001F;

			r_d |= (((c2 << 2) & 0xF800) >> 2) << 16;
			g_d |= ((c2 >> 4) & 0x07C0) << 16;
			b_d |= ((c2 >> 9) & 0x001F) << 16;
			g_d = b_d | g_d;

			dest1 = buf + (yk * linesize) + xk;
			// NOTE BY GEK: The following line was modified to fix a compiler warning,
			// casting zb->pbuf to GLushort*
			pp1 = (GLushort*)(zb->pbuf) + (yk * zb->xsize) + xk;

			for (y = yk; y < zb->ysize; y += 4) {
				dest = dest1;
				pp = pp1;
				for (x = xk; x < zb->xsize; x += 16) {

					DITHER_PIXEL2(0);
					DITHER_PIXEL2(1 * 4);
					DITHER_PIXEL2(2 * 4);
					DITHER_PIXEL2(3 * 4);

					pp += 16;
					dest += 16;
				}
				dest1 += linesize * 4;
				pp1 += zb->xsize * 4;
			}
		}
	}
}

#endif