xref: /plan9/sys/src/cmd/gs/src/gxblend.c (revision 593dc095aefb2a85c828727bbfa9da139a49bdf4)

/*
  Copyright (C) 2001 artofcode LLC.

  This software is provided AS-IS with no warranty, either express or
  implied.

  This software is distributed under license and may not be copied,
  modified or distributed except as expressly authorized under the terms
  of the license contained in the file LICENSE in this distribution.

  For more information about licensing, please refer to
  http://www.ghostscript.com/licensing/. For information on
  commercial licensing, go to http://www.artifex.com/licensing/ or
  contact Artifex Software, Inc., 101 Lucas Valley Road #110,
  San Rafael, CA  94903, U.S.A., +1(415)492-9861.

  Author: Raph Levien <raph@artofcode.com>
*/
/* $Id: gxblend.c,v 1.6 2004/08/18 04:48:56 dan Exp $ */
/* PDF 1.4 blending functions */

#include "memory_.h"
#include "gx.h"
#include "gstparam.h"
#include "gxblend.h"

typedef int art_s32;

static void
art_blend_luminosity_rgb_8(byte *dst, const byte *backdrop,
			   const byte *src)
{
    int rb = backdrop[0], gb = backdrop[1], bb = backdrop[2];
    int rs = src[0], gs = src[1], bs = src[2];
    int delta_y;
    int r, g, b;

    /*
     * From section 7.4 of the PDF 1.5 specification, for RGB, the luminosity
     * is:  Y = 0.30 R + 0.59 G + 0.11 B)
     */
    delta_y = ((rs - rb) * 77 + (gs - gb) * 151 + (bs - bb) * 28 + 0x80) >> 8;
    r = rb + delta_y;
    g = gb + delta_y;
    b = bb + delta_y;
    if ((r | g | b) & 0x100) {
	int y;
	int scale;

	y = (rs * 77 + gs * 151 + bs * 28 + 0x80) >> 8;
	if (delta_y > 0) {
	    int max;

	    max = r > g ? r : g;
	    max = b > max ? b : max;
	    scale = ((255 - y) << 16) / (max - y);
	} else {
	    int min;

	    min = r < g ? r : g;
	    min = b < min ? b : min;
	    scale = (y << 16) / (y - min);
	}
	r = y + (((r - y) * scale + 0x8000) >> 16);
	g = y + (((g - y) * scale + 0x8000) >> 16);
	b = y + (((b - y) * scale + 0x8000) >> 16);
    }
    dst[0] = r;
    dst[1] = g;
    dst[2] = b;
}

/*
 * The PDF 1.4 spec. does not give the details of the math involved in the
 * luminosity blending.  All we are given is:
 *   "Creates a color with the luminance of the source color and the hue
 *    and saturation of the backdrop color. This produces an inverse
 *    effect to that of the Color mode."
 * From section 7.4 of the PDF 1.5 specification, which is duscussing soft
 * masks, we are given that, for CMYK, the luminosity is:
 *    Y = 0.30 (1 - C)(1 - K) + 0.59 (1 - M)(1 - K) + 0.11 (1 - Y)(1 - K)
 * However the results of this equation do not match the results seen from
 * Illustrator CS.  Very different results are obtained if process gray
 * (.5, .5, .5, 0) is blended over pure cyan, versus gray (0, 0, 0, .5) over
 * the same pure cyan.  The first gives a medium cyan while the later gives a
 * medium gray.  This routine seems to match Illustrator's actions.  C, M and Y
 * are treated similar to RGB in the previous routine and black is treated
 * separately.
 *
 * Our component values have already been complemented, i.e. (1 - X).
 */
static void
art_blend_luminosity_cmyk_8(byte *dst, const byte *backdrop,
			   const byte *src)
{
    /* Treat CMY the same as RGB. */
    art_blend_luminosity_rgb_8(dst, backdrop, src);
    dst[3] = src[3];
}

static void
art_blend_saturation_rgb_8(byte *dst, const byte *backdrop,
			   const byte *src)
{
    int rb = backdrop[0], gb = backdrop[1], bb = backdrop[2];
    int rs = src[0], gs = src[1], bs = src[2];
    int minb, maxb;
    int mins, maxs;
    int y;
    int scale;
    int r, g, b;

    minb = rb < gb ? rb : gb;
    minb = minb < bb ? minb : bb;
    maxb = rb > gb ? rb : gb;
    maxb = maxb > bb ? maxb : bb;
    if (minb == maxb) {
	/* backdrop has zero saturation, avoid divide by 0 */
	dst[0] = gb;
	dst[1] = gb;
	dst[2] = gb;
	return;
    }

    mins = rs < gs ? rs : gs;
    mins = mins < bs ? mins : bs;
    maxs = rs > gs ? rs : gs;
    maxs = maxs > bs ? maxs : bs;

    scale = ((maxs - mins) << 16) / (maxb - minb);
    y = (rb * 77 + gb * 151 + bb * 28 + 0x80) >> 8;
    r = y + ((((rb - y) * scale) + 0x8000) >> 16);
    g = y + ((((gb - y) * scale) + 0x8000) >> 16);
    b = y + ((((bb - y) * scale) + 0x8000) >> 16);

    if ((r | g | b) & 0x100) {
	int scalemin, scalemax;
	int min, max;

	min = r < g ? r : g;
	min = min < b ? min : b;
	max = r > g ? r : g;
	max = max > b ? max : b;

	if (min < 0)
	    scalemin = (y << 16) / (y - min);
	else
	    scalemin = 0x10000;

	if (max > 255)
	    scalemax = ((255 - y) << 16) / (max - y);
	else
	    scalemax = 0x10000;

	scale = scalemin < scalemax ? scalemin : scalemax;
	r = y + (((r - y) * scale + 0x8000) >> 16);
	g = y + (((g - y) * scale + 0x8000) >> 16);
	b = y + (((b - y) * scale + 0x8000) >> 16);
    }

    dst[0] = r;
    dst[1] = g;
    dst[2] = b;
}

/* Our component values have already been complemented, i.e. (1 - X). */
static void
art_blend_saturation_cmyk_8(byte *dst, const byte *backdrop,
			   const byte *src)
{
    /* Treat CMY the same as RGB */
    art_blend_saturation_rgb_8(dst, backdrop, src);
    dst[3] = backdrop[3];
}

/* This array consists of floor ((x - x * x / 255.0) * 65536 / 255 +
   0.5) for x in [0..255]. */
const unsigned int art_blend_sq_diff_8[256] = {
    0, 256, 510, 762, 1012, 1260, 1506, 1750, 1992, 2231, 2469, 2705,
    2939, 3171, 3401, 3628, 3854, 4078, 4300, 4519, 4737, 4953, 5166,
    5378, 5588, 5795, 6001, 6204, 6406, 6606, 6803, 6999, 7192, 7384,
    7573, 7761, 7946, 8129, 8311, 8490, 8668, 8843, 9016, 9188, 9357,
    9524, 9690, 9853, 10014, 10173, 10331, 10486, 10639, 10790, 10939,
    11086, 11232, 11375, 11516, 11655, 11792, 11927, 12060, 12191, 12320,
    12447, 12572, 12695, 12816, 12935, 13052, 13167, 13280, 13390, 13499,
    13606, 13711, 13814, 13914, 14013, 14110, 14205, 14297, 14388, 14477,
    14564, 14648, 14731, 14811, 14890, 14967, 15041, 15114, 15184, 15253,
    15319, 15384, 15446, 15507, 15565, 15622, 15676, 15729, 15779, 15827,
    15874, 15918, 15960, 16001, 16039, 16075, 16110, 16142, 16172, 16200,
    16227, 16251, 16273, 16293, 16311, 16327, 16341, 16354, 16364, 16372,
    16378, 16382, 16384, 16384, 16382, 16378, 16372, 16364, 16354, 16341,
    16327, 16311, 16293, 16273, 16251, 16227, 16200, 16172, 16142, 16110,
    16075, 16039, 16001, 15960, 15918, 15874, 15827, 15779, 15729, 15676,
    15622, 15565, 15507, 15446, 15384, 15319, 15253, 15184, 15114, 15041,
    14967, 14890, 14811, 14731, 14648, 14564, 14477, 14388, 14297, 14205,
    14110, 14013, 13914, 13814, 13711, 13606, 13499, 13390, 13280, 13167,
    13052, 12935, 12816, 12695, 12572, 12447, 12320, 12191, 12060, 11927,
    11792, 11655, 11516, 11375, 11232, 11086, 10939, 10790, 10639, 10486,
    10331, 10173, 10014, 9853, 9690, 9524, 9357, 9188, 9016, 8843, 8668,
    8490, 8311, 8129, 7946, 7761, 7573, 7384, 7192, 6999, 6803, 6606,
    6406, 6204, 6001, 5795, 5588, 5378, 5166, 4953, 4737, 4519, 4300,
    4078, 3854, 3628, 3401, 3171, 2939, 2705, 2469, 2231, 1992, 1750,
    1506, 1260, 1012, 762, 510, 256, 0
};

/* This array consists of SoftLight (x, 255) - x, for values of x in
   the range [0..255] (normalized to [0..255 range). The original
   values were directly sampled from Adobe Illustrator 9. I've fit a
   quadratic spline to the SoftLight (x, 1) function as follows
   (normalized to [0..1] range):

   Anchor point (0, 0)
   Control point (0.0755, 0.302)
   Anchor point (0.18, 0.4245)
   Control point (0.4263, 0.7131)
   Anchor point (1, 1)

   I don't believe this is _exactly_ the function that Adobe uses,
   but it really should be close enough for all practical purposes.  */
const byte art_blend_soft_light_8[256] = {
    0, 3, 6, 9, 11, 14, 16, 19, 21, 23, 26, 28, 30, 32, 33, 35, 37, 39,
    40, 42, 43, 45, 46, 47, 48, 49, 51, 52, 53, 53, 54, 55, 56, 57, 57,
    58, 58, 59, 60, 60, 60, 61, 61, 62, 62, 62, 62, 63, 63, 63, 63, 63,
    63, 63, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 62, 62, 62,
    62, 62, 62, 62, 61, 61, 61, 61, 61, 61, 60, 60, 60, 60, 60, 59, 59,
    59, 59, 59, 58, 58, 58, 58, 57, 57, 57, 57, 56, 56, 56, 56, 55, 55,
    55, 55, 54, 54, 54, 54, 53, 53, 53, 52, 52, 52, 51, 51, 51, 51, 50,
    50, 50, 49, 49, 49, 48, 48, 48, 47, 47, 47, 46, 46, 46, 45, 45, 45,
    44, 44, 43, 43, 43, 42, 42, 42, 41, 41, 40, 40, 40, 39, 39, 39, 38,
    38, 37, 37, 37, 36, 36, 35, 35, 35, 34, 34, 33, 33, 33, 32, 32, 31,
    31, 31, 30, 30, 29, 29, 28, 28, 28, 27, 27, 26, 26, 25, 25, 25, 24,
    24, 23, 23, 22, 22, 21, 21, 21, 20, 20, 19, 19, 18, 18, 17, 17, 16,
    16, 15, 15, 15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10, 9, 9, 8, 8, 7,
    7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0
};

void
art_blend_pixel_8(byte *dst, const byte *backdrop,
		  const byte *src, int n_chan, gs_blend_mode_t blend_mode)
{
    int i;
    byte b, s;
    bits32 t;

    switch (blend_mode) {
	case BLEND_MODE_Normal:
	case BLEND_MODE_Compatible:	/* todo */
	    memcpy(dst, src, n_chan);
	    break;
	case BLEND_MODE_Multiply:
	    for (i = 0; i < n_chan; i++) {
		t = ((bits32) backdrop[i]) * ((bits32) src[i]);
		t += 0x80;
		t += (t >> 8);
		dst[i] = t >> 8;
	    }
	    break;
	case BLEND_MODE_Screen:
	    for (i = 0; i < n_chan; i++) {
		t =
		    ((bits32) (0xff - backdrop[i])) *
		    ((bits32) (0xff - src[i]));
		t += 0x80;
		t += (t >> 8);
		dst[i] = 0xff - (t >> 8);
	    }
	    break;
	case BLEND_MODE_Overlay:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (b < 0x80)
		    t = 2 * ((bits32) b) * ((bits32) s);
		else
		    t = 0xfe01 -
			2 * ((bits32) (0xff - b)) * ((bits32) (0xff - s));
		t += 0x80;
		t += (t >> 8);
		dst[i] = t >> 8;
	    }
	    break;
	case BLEND_MODE_SoftLight:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (s < 0x80) {
		    t = (0xff - (s << 1)) * art_blend_sq_diff_8[b];
		    t += 0x8000;
		    dst[i] = b - (t >> 16);
		} else {
		    t =
			((s << 1) -
			 0xff) * ((bits32) (art_blend_soft_light_8[b]));
		    t += 0x80;
		    t += (t >> 8);
		    dst[i] = b + (t >> 8);
		}
	    }
	    break;
	case BLEND_MODE_HardLight:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (s < 0x80)
		    t = 2 * ((bits32) b) * ((bits32) s);
		else
		    t = 0xfe01 -
			2 * ((bits32) (0xff - b)) * ((bits32) (0xff - s));
		t += 0x80;
		t += (t >> 8);
		dst[i] = t >> 8;
	    }
	    break;
	case BLEND_MODE_ColorDodge:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = 0xff - src[i];
		if (b == 0)
		    dst[i] = 0;
		else if (b >= s)
		    dst[i] = 0xff;
		else
		    dst[i] = (0x1fe * b + s) / (s << 1);
	    }
	    break;
	case BLEND_MODE_ColorBurn:
	    for (i = 0; i < n_chan; i++) {
		b = 0xff - backdrop[i];
		s = src[i];
		if (b == 0)
		    dst[i] = 0xff;
		else if (b >= s)
		    dst[i] = 0;
		else
		    dst[i] = 0xff - (0x1fe * b + s) / (s << 1);
	    }
	    break;
	case BLEND_MODE_Darken:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		dst[i] = b < s ? b : s;
	    }
	    break;
	case BLEND_MODE_Lighten:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		dst[i] = b > s ? b : s;
	    }
	    break;
	case BLEND_MODE_Difference:
	    for (i = 0; i < n_chan; i++) {
		art_s32 tmp;

		tmp = ((art_s32) backdrop[i]) - ((art_s32) src[i]);
		dst[i] = tmp < 0 ? -tmp : tmp;
	    }
	    break;
	case BLEND_MODE_Exclusion:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		t = ((bits32) (0xff - b)) * ((bits32) s) +
		    ((bits32) b) * ((bits32) (0xff - s));
		t += 0x80;
		t += (t >> 8);
		dst[i] = t >> 8;
	    }
	    break;
	case BLEND_MODE_Luminosity:
	    switch (n_chan) {
		case 1:			/* DeviceGray */
	    	    dlprintf(
			"art_blend_pixel_8: DeviceGray luminosity blend mode not implemented\n");
		    break;
		case 3:			/* DeviceRGB */
	    	    art_blend_luminosity_rgb_8(dst, backdrop, src);
		    break;
		case 4:			/* DeviceCMYK */
	    	    art_blend_luminosity_cmyk_8(dst, backdrop, src);
		    break;
		default:		/* Should not happen */
		    break;
	    }
	    break;
	case BLEND_MODE_Color:
	    switch (n_chan) {
		case 1:			/* DeviceGray */
	    	    dlprintf(
			"art_blend_pixel_8: DeviceGray color blend mode not implemented\n");
		    break;
		case 3:			/* DeviceRGB */
		    art_blend_luminosity_rgb_8(dst, src, backdrop);
		    break;
		case 4:			/* DeviceCMYK */
		    art_blend_luminosity_cmyk_8(dst, src, backdrop);
		    break;
		default:		/* Should not happen */
		    break;
	    }
	    break;
	case BLEND_MODE_Saturation:
	    switch (n_chan) {
		case 1:			/* DeviceGray */
	    	    dlprintf(
			"art_blend_pixel_8: DeviceGray saturation blend mode not implemented\n");
		    break;
		case 3:			/* DeviceRGB */
	    	    art_blend_saturation_rgb_8(dst, backdrop, src);
		    break;
		case 4:			/* DeviceCMYK */
	    	    art_blend_saturation_cmyk_8(dst, backdrop, src);
		    break;
		default:		/* Should not happen */
		    break;
	    }
	    break;
	case BLEND_MODE_Hue:
	    {
		byte tmp[4];

	        switch (n_chan) {
		    case 1:		/* DeviceGray */
	    		dlprintf(
			    "art_blend_pixel_8: DeviceGray hue blend mode not implemented\n");
		        break;
		    case 3:		/* DeviceRGB */
			art_blend_luminosity_rgb_8(tmp, src, backdrop);
			art_blend_saturation_rgb_8(dst, tmp, backdrop);
		        break;
		    case 4:		/* DeviceCMYK */
		        art_blend_luminosity_cmyk_8(tmp, src, backdrop);
			art_blend_saturation_cmyk_8(dst, tmp, backdrop);
		        break;
		    default:		/* Should not happen */
		        break;
	        }
	    }
	    break;
	default:
	    dlprintf1("art_blend_pixel_8: blend mode %d not implemented\n",
		      blend_mode);
	    memcpy(dst, src, n_chan);
	    break;
    }
}

void
art_blend_pixel(ArtPixMaxDepth* dst, const ArtPixMaxDepth *backdrop,
		const ArtPixMaxDepth* src, int n_chan,
		gs_blend_mode_t blend_mode)
{
    int i;
    ArtPixMaxDepth b, s;
    bits32 t;

    switch (blend_mode) {
	case BLEND_MODE_Normal:
	case BLEND_MODE_Compatible:	/* todo */
	    memcpy(dst, src, n_chan * sizeof(ArtPixMaxDepth));
	    break;
	case BLEND_MODE_Multiply:
	    for (i = 0; i < n_chan; i++) {
		t = ((bits32) backdrop[i]) * ((bits32) src[i]);
		t += 0x8000;
		t += (t >> 16);
		dst[i] = t >> 16;
	    }
	    break;
	case BLEND_MODE_Screen:
	    for (i = 0; i < n_chan; i++) {
		t =
		    ((bits32) (0xffff - backdrop[i])) *
		    ((bits32) (0xffff - src[i]));
		t += 0x8000;
		t += (t >> 16);
		dst[i] = 0xffff - (t >> 16);
	    }
	    break;
	case BLEND_MODE_Overlay:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (b < 0x8000)
		    t = 2 * ((bits32) b) * ((bits32) s);
		else
		    t = 0xfffe0001u -
			2 * ((bits32) (0xffff - b)) * ((bits32) (0xffff - s));
		t += 0x8000;
		t += (t >> 16);
		dst[i] = t >> 16;
	    }
	    break;
	case BLEND_MODE_HardLight:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (s < 0x8000)
		    t = 2 * ((bits32) b) * ((bits32) s);
		else
		    t = 0xfffe0001u -
			2 * ((bits32) (0xffff - b)) * ((bits32) (0xffff - s));
		t += 0x8000;
		t += (t >> 16);
		dst[i] = t >> 16;
	    }
	    break;
	case BLEND_MODE_ColorDodge:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		if (b == 0)
		    dst[i] = 0;
		else if (s >= b)
		    dst[i] = 0xffff;
		else
		    dst[i] = (0x1fffe * s + b) / (b << 1);
	    }
	    break;
	case BLEND_MODE_ColorBurn:
	    for (i = 0; i < n_chan; i++) {
		b = 0xffff - backdrop[i];
		s = src[i];
		if (b == 0)
		    dst[i] = 0xffff;
		else if (b >= s)
		    dst[i] = 0;
		else
		    dst[i] = 0xffff - (0x1fffe * b + s) / (s << 1);
	    }
	case BLEND_MODE_Darken:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		dst[i] = b < s ? b : s;
	    }
	    break;
	case BLEND_MODE_Lighten:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		dst[i] = b > s ? b : s;
	    }
	    break;
	case BLEND_MODE_Difference:
	    for (i = 0; i < n_chan; i++) {
		art_s32 tmp;

		tmp = ((art_s32) backdrop[i]) - ((art_s32) src[i]);
		dst[i] = tmp < 0 ? -tmp : tmp;
	    }
	    break;
	case BLEND_MODE_Exclusion:
	    for (i = 0; i < n_chan; i++) {
		b = backdrop[i];
		s = src[i];
		t = ((bits32) (0xffff - b)) * ((bits32) s) +
		    ((bits32) b) * ((bits32) (0xffff - s));
		t += 0x8000;
		t += (t >> 16);
		dst[i] = t >> 16;
	    }
	    break;
	default:
	    dlprintf1("art_blend_pixel: blend mode %d not implemented\n",
		      blend_mode);
	    memcpy(dst, src, n_chan);
	    break;
    }
}

byte
art_pdf_union_8(byte alpha1, byte alpha2)
{
    int tmp;

    tmp = (0xff - alpha1) * (0xff - alpha2) + 0x80;
    return 0xff - ((tmp + (tmp >> 8)) >> 8);
}

byte
art_pdf_union_mul_8(byte alpha1, byte alpha2, byte alpha_mask)
{
    int tmp;

    if (alpha_mask == 0xff) {
	tmp = (0xff - alpha1) * (0xff - alpha2) + 0x80;
	return 0xff - ((tmp + (tmp >> 8)) >> 8);
    } else {
	tmp = alpha2 * alpha_mask + 0x80;
	tmp = (tmp + (tmp >> 8)) >> 8;
	tmp = (0xff - alpha1) * (0xff - tmp) + 0x80;
	return 0xff - ((tmp + (tmp >> 8)) >> 8);
    }
}

void
art_pdf_composite_pixel_alpha_8(byte *dst, const byte *src, int n_chan,
				gs_blend_mode_t blend_mode)
{
    byte a_b, a_s;
    unsigned int a_r;
    int tmp;
    int src_scale;
    int c_b, c_s;
    int i;

    a_s = src[n_chan];
    if (a_s == 0) {
	/* source alpha is zero, avoid all computations and possible
	   divide by zero errors. */
	return;
    }

    a_b = dst[n_chan];
    if (a_b == 0) {
	/* backdrop alpha is zero, just copy source pixels and avoid
	   computation. */

	/* this idiom is faster than memcpy (dst, src, n_chan + 1); for
	   expected small values of n_chan. */
	for (i = 0; i <= n_chan >> 2; i++) {
	    ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
	}

	return;
    }

    /* Result alpha is Union of backdrop and source alpha */
    tmp = (0xff - a_b) * (0xff - a_s) + 0x80;
    a_r = 0xff - (((tmp >> 8) + tmp) >> 8);
    /* todo: verify that a_r is nonzero in all cases */

    /* Compute a_s / a_r in 16.16 format */
    src_scale = ((a_s << 16) + (a_r >> 1)) / a_r;

    if (blend_mode == BLEND_MODE_Normal) {
	/* Do simple compositing of source over backdrop */
	for (i = 0; i < n_chan; i++) {
	    c_s = src[i];
	    c_b = dst[i];
	    tmp = (c_b << 16) + src_scale * (c_s - c_b) + 0x8000;
	    dst[i] = tmp >> 16;
	}
    } else {
	/* Do compositing with blending */
	byte blend[ART_MAX_CHAN];

	art_blend_pixel_8(blend, dst, src, n_chan, blend_mode);
	for (i = 0; i < n_chan; i++) {
	    int c_bl;		/* Result of blend function */
	    int c_mix;		/* Blend result mixed with source color */

	    c_s = src[i];
	    c_b = dst[i];
	    c_bl = blend[i];
	    tmp = a_b * (c_bl - ((int)c_s)) + 0x80;
	    c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
	    tmp = (c_b << 16) + src_scale * (c_mix - c_b) + 0x8000;
	    dst[i] = tmp >> 16;
	}
    }
    dst[n_chan] = a_r;
}

#if 0
/**
 * art_pdf_composite_pixel_knockout_8: Composite two pixels with knockout.
 * @dst: Where to store resulting pixel, also immediate backdrop.
 * @backdrop: Initial backdrop color.
 * @src: Source pixel color.
 * @n_chan: Number of channels.
 * @blend_mode: Blend mode.
 *
 * Composites two pixels using the compositing operation specialized
 * for knockout groups (Section 5.5). A few things to keep in mind:
 *
 * 1. This is a reference implementation, not a high-performance one.
 *
 * 2. All pixels are assumed to have a single alpha channel.
 *
 * 3. Zero is black, one is white.
 *
 * Also note that src and dst are expected to be allocated aligned to
 * 32 bit boundaries, ie bytes from [0] to [(n_chan + 3) & -4] may
 * be accessed.
 *
 * All pixel values have both alpha and shape channels, ie with those
 * included the total number of channels is @n_chan + 2.
 *
 * An invariant: shape >= alpha.
 **/
void
art_pdf_composite_pixel_knockout_8(byte *dst,
				   const byte *backdrop, const byte *src,
				   int n_chan, gs_blend_mode_t blend_mode)
{
    int i;
    byte ct[ART_MAX_CHAN + 1];
    byte src_shape;
    byte backdrop_alpha;
    byte dst_alpha;
    bits32 src_opacity;
    bits32 backdrop_weight, t_weight;
    int tmp;

    if (src[n_chan] == 0)
	return;
    if (src[n_chan + 1] == 255 && blend_mode == BLEND_MODE_Normal ||
	dst[n_chan] == 0) {
	/* this idiom is faster than memcpy (dst, src, n_chan + 2); for
	   expected small values of n_chan. */
	for (i = 0; i <= (n_chan + 1) >> 2; i++) {
	    ((bits32 *) dst)[i] = ((const bits32 *)src[i]);
	}

	return;
    }


    src_shape = src[n_chan + 1];	/* $fs_i$ */
    src_opacity = (255 * src[n_chan] + 0x80) / src_shape;	/* $qs_i$ */
#if 0
    for (i = 0; i < (n_chan + 3) >> 2; i++) {
	((bits32 *) src_tmp)[i] = ((const bits32 *)src[i]);
    }
    src_tmp[n_chan] = src_opacity;

    for (i = 0; i <= n_chan >> 2; i++) {
	((bits32 *) tmp)[i] = ((bits32 *) backdrop[i]);
    }
#endif

    backdrop_scale = if (blend_mode == BLEND_MODE_Normal) {
	/* Do simple compositing of source over backdrop */
	for (i = 0; i < n_chan; i++) {
	    c_s = src[i];
	    c_b = dst[i];
	    tmp = (c_b << 16) + ct_scale * (c_s - c_b) + 0x8000;
	    ct[i] = tmp >> 16;
	}
    } else {
	/* Do compositing with blending */
	byte blend[ART_MAX_CHAN];

	art_blend_pixel_8(blend, backdrop, src, n_chan, blend_mode);
	for (i = 0; i < n_chan; i++) {
	    int c_bl;		/* Result of blend function */
	    int c_mix;		/* Blend result mixed with source color */

	    c_s = src[i];
	    c_b = dst[i];
	    c_bl = blend[i];
	    tmp = a_b * (((int)c_bl) - ((int)c_s)) + 0x80;
	    c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
	    tmp = (c_b << 16) + ct_scale * (c_mix - c_b) + 0x8000;
	    ct[i] = tmp >> 16;
	}
    }

    /* do weighted average of $Ct$ using relative alpha contribution as weight */
    backdrop_alpha = backdrop[n_chan];
    tmp = (0xff - blend_alpha) * (0xff - backdrop_alpha) + 0x80;
    dst_alpha = 0xff - (((tmp >> 8) + tmp) >> 8);
    dst[n_chan] = dst_alpha;
    t_weight = ((blend_alpha << 16) + 0x8000) / dst_alpha;
    for (i = 0; i < n_chan; i++) {

    }
}
#endif

void
art_pdf_uncomposite_group_8(byte *dst,
			    const byte *backdrop,
			    const byte *src, byte src_alpha_g, int n_chan)
{
    byte backdrop_alpha = backdrop[n_chan];
    int i;
    int tmp;
    int scale;

    dst[n_chan] = src_alpha_g;

    if (src_alpha_g == 0)
	return;

    scale = (backdrop_alpha * 255 * 2 + src_alpha_g) / (src_alpha_g << 1) -
	backdrop_alpha;
    for (i = 0; i < n_chan; i++) {
	int si, di;

	si = src[i];
	di = backdrop[i];
	tmp = (si - di) * scale + 0x80;
	tmp = si + ((tmp + (tmp >> 8)) >> 8);

	/* todo: it should be possible to optimize these cond branches */
	if (tmp < 0)
	    tmp = 0;
	if (tmp > 255)
	    tmp = 255;
	dst[i] = tmp;
    }

}

void
art_pdf_recomposite_group_8(byte *dst, byte *dst_alpha_g,
			    const byte *src, byte src_alpha_g,
			    int n_chan,
			    byte alpha, gs_blend_mode_t blend_mode)
{
    byte dst_alpha;
    int i;
    int tmp;
    int scale;

    if (src_alpha_g == 0)
	return;

    if (blend_mode == BLEND_MODE_Normal && alpha == 255) {
	/* In this case, uncompositing and recompositing cancel each
	   other out. Note: if the reason that alpha == 255 is that
	   there is no constant mask and no soft mask, then this
	   operation should be optimized away at a higher level. */
	for (i = 0; i <= n_chan >> 2; i++)
	    ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
	if (dst_alpha_g != NULL) {
	    tmp = (255 - *dst_alpha_g) * (255 - src_alpha_g) + 0x80;
	    *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
	return;
    } else {
	/* "interesting" blend mode */
	byte ca[ART_MAX_CHAN + 1];	/* $C, \alpha$ */

	dst_alpha = dst[n_chan];
	if (src_alpha_g == 255 || dst_alpha == 0) {
	    for (i = 0; i < (n_chan + 3) >> 2; i++)
		((bits32 *) ca)[i] = ((const bits32 *)src)[i];
	} else {
	    /* Uncomposite the color. In other words, solve
	       "src = (ca, src_alpha_g) over dst" for ca */

	    /* todo (maybe?): replace this code with call to
	       art_pdf_uncomposite_group_8() to reduce code
	       duplication. */

	    scale = (dst_alpha * 255 * 2 + src_alpha_g) / (src_alpha_g << 1) -
		dst_alpha;
	    for (i = 0; i < n_chan; i++) {
		int si, di;

		si = src[i];
		di = dst[i];
		tmp = (si - di) * scale + 0x80;
		tmp = si + ((tmp + (tmp >> 8)) >> 8);

		/* todo: it should be possible to optimize these cond branches */
		if (tmp < 0)
		    tmp = 0;
		if (tmp > 255)
		    tmp = 255;
		ca[i] = tmp;
	    }
	}

	tmp = src_alpha_g * alpha + 0x80;
	tmp = (tmp + (tmp >> 8)) >> 8;
	ca[n_chan] = tmp;
	if (dst_alpha_g != NULL) {
	    tmp = (255 - *dst_alpha_g) * (255 - tmp) + 0x80;
	    *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
	art_pdf_composite_pixel_alpha_8(dst, ca, n_chan, blend_mode);
    }
    /* todo: optimize BLEND_MODE_Normal buf alpha != 255 case */
}

void
art_pdf_composite_group_8(byte *dst, byte *dst_alpha_g,
			  const byte *src,
			  int n_chan, byte alpha, gs_blend_mode_t blend_mode)
{
    byte src_alpha;		/* $\alpha g_n$ */
    byte src_tmp[ART_MAX_CHAN + 1];
    int i;
    int tmp;

    if (alpha == 255) {
	art_pdf_composite_pixel_alpha_8(dst, src, n_chan, blend_mode);
	if (dst_alpha_g != NULL) {
	    tmp = (255 - *dst_alpha_g) * (255 - src[n_chan]) + 0x80;
	    *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
    } else {
	src_alpha = src[n_chan];
	if (src_alpha == 0)
	    return;
	for (i = 0; i < (n_chan + 3) >> 2; i++)
	    ((bits32 *) src_tmp)[i] = ((const bits32 *)src)[i];
	tmp = src_alpha * alpha + 0x80;
	src_tmp[n_chan] = (tmp + (tmp >> 8)) >> 8;
	art_pdf_composite_pixel_alpha_8(dst, src_tmp, n_chan, blend_mode);
	if (dst_alpha_g != NULL) {
	    tmp = (255 - *dst_alpha_g) * (255 - src_tmp[n_chan]) + 0x80;
	    *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
    }
}

void
art_pdf_composite_knockout_simple_8(byte *dst,
				    byte *dst_shape,
				    const byte *src,
				    int n_chan, byte opacity)
{
    byte src_shape = src[n_chan];
    int i;

    if (src_shape == 0)
	return;
    else if (src_shape == 255) {
	for (i = 0; i < (n_chan + 3) >> 2; i++)
	    ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
	dst[n_chan] = opacity;
	if (dst_shape != NULL)
	    *dst_shape = 255;
    } else {
	/* Use src_shape to interpolate (in premultiplied alpha space)
	   between dst and (src, opacity). */
	int dst_alpha = dst[n_chan];
	byte result_alpha;
	int tmp;

	tmp = (opacity - dst_alpha) * src_shape + 0x80;
	result_alpha = dst_alpha + ((tmp + (tmp >> 8)) >> 8);

	if (result_alpha != 0)
	    for (i = 0; i < n_chan; i++) {
		/* todo: optimize this - can strength-reduce so that
		   inner loop is a single interpolation */
		tmp = dst[i] * dst_alpha * (255 - src_shape) +
		    ((int)src[i]) * opacity * src_shape + (result_alpha << 7);
		dst[i] = tmp / (result_alpha * 255);
	    }
	dst[n_chan] = result_alpha;

	/* union in dst_shape if non-null */
	if (dst_shape != NULL) {
	    tmp = (255 - *dst_shape) * (255 - src_shape) + 0x80;
	    *dst_shape = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
    }
}

void
art_pdf_composite_knockout_isolated_8(byte *dst,
				      byte *dst_shape,
				      const byte *src,
				      int n_chan,
				      byte shape,
				      byte alpha_mask, byte shape_mask)
{
    int tmp;
    int i;

    if (shape == 0)
	return;
    else if ((shape & shape_mask) == 255) {
	for (i = 0; i < (n_chan + 3) >> 2; i++)
	    ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
	tmp = src[n_chan] * alpha_mask + 0x80;
	dst[n_chan] = (tmp + (tmp >> 8)) >> 8;
	if (dst_shape != NULL)
	    *dst_shape = 255;
    } else {
	/* Use src_shape to interpolate (in premultiplied alpha space)
	   between dst and (src, opacity). */
	byte src_shape, src_alpha;
	int dst_alpha = dst[n_chan];
	byte result_alpha;
	int tmp;

	tmp = shape * shape_mask + 0x80;
	src_shape = (tmp + (tmp >> 8)) >> 8;

	tmp = src[n_chan] * alpha_mask + 0x80;
	src_alpha = (tmp + (tmp >> 8)) >> 8;

	tmp = (src_alpha - dst_alpha) * src_shape + 0x80;
	result_alpha = dst_alpha + ((tmp + (tmp >> 8)) >> 8);

	if (result_alpha != 0)
	    for (i = 0; i < n_chan; i++) {
		/* todo: optimize this - can strength-reduce so that
		   inner loop is a single interpolation */
		tmp = dst[i] * dst_alpha * (255 - src_shape) +
		    ((int)src[i]) * src_alpha * src_shape +
		    (result_alpha << 7);
		dst[i] = tmp / (result_alpha * 255);
	    }
	dst[n_chan] = result_alpha;

	/* union in dst_shape if non-null */
	if (dst_shape != NULL) {
	    tmp = (255 - *dst_shape) * (255 - src_shape) + 0x80;
	    *dst_shape = 255 - ((tmp + (tmp >> 8)) >> 8);
	}
    }
}

void
art_pdf_composite_knockout_8(byte *dst,
			     byte *dst_alpha_g,
			     const byte *backdrop,
			     const byte *src,
			     int n_chan,
			     byte shape,
			     byte alpha_mask,
			     byte shape_mask, gs_blend_mode_t blend_mode)
{
    /* This implementation follows the Adobe spec pretty closely, rather
       than trying to do anything clever. For example, in the case of a
       Normal blend_mode when the top group is non-isolated, uncompositing
       and recompositing is more work than needed. So be it. Right now,
       I'm more worried about manageability than raw performance. */
    byte alpha_t;
    byte src_alpha, src_shape;
    byte src_opacity;
    byte ct[ART_MAX_CHAN];
    byte backdrop_alpha;
    byte alpha_g_i_1, alpha_g_i, alpha_i;
    int tmp;
    int i;
    int scale_b;
    int scale_src;

    if (shape == 0 || shape_mask == 0)
	return;

    tmp = shape * shape_mask + 0x80;
    /* $f s_i$ */
    src_shape = (tmp + (tmp >> 8)) >> 8;

    tmp = src[n_chan] * alpha_mask + 0x80;
    src_alpha = (tmp + (tmp >> 8)) >> 8;

    /* $q s_i$ */
    src_opacity = (src_alpha * 510 + src_shape) / (2 * src_shape);

    /* $\alpha t$, \alpha g_b is always zero for knockout groups */
    alpha_t = src_opacity;

    /* $\alpha b$ */
    backdrop_alpha = backdrop[n_chan];

    tmp = (0xff - src_opacity) * backdrop_alpha;
    /* $(1 - q s_i) \cdot alpha_b$ scaled by 2^16 */
    scale_b = tmp + (tmp >> 7) + (tmp >> 14);

    /* $q s_i$ scaled by 2^16 */
    scale_src = (src_opacity << 8) + (src_opacity) + (src_opacity >> 7);

    /* Do simple compositing of source over backdrop */
    if (blend_mode == BLEND_MODE_Normal) {
	for (i = 0; i < n_chan; i++) {
	    int c_s;
	    int c_b;

	    c_s = src[i];
	    c_b = backdrop[i];
	    tmp = (c_b << 16) * scale_b + (c_s - c_b) + scale_src + 0x8000;
	    ct[i] = tmp >> 16;
	}
    } else {
	byte blend[ART_MAX_CHAN];

	art_blend_pixel_8(blend, backdrop, src, n_chan, blend_mode);
	for (i = 0; i < n_chan; i++) {
	    int c_s;
	    int c_b;
	    int c_bl;		/* Result of blend function */
	    int c_mix;		/* Blend result mixed with source color */

	    c_s = src[i];
	    c_b = backdrop[i];
	    c_bl = blend[i];
	    tmp = backdrop_alpha * (c_bl - ((int)c_s)) + 0x80;
	    c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
	    tmp = (c_b << 16) * scale_b + (c_mix - c_b) + scale_src + 0x8000;
	    ct[i] = tmp >> 16;
	}
    }

    /* $\alpha g_{i - 1}$ */
    alpha_g_i_1 = *dst_alpha_g;

    tmp = src_shape * (((int)alpha_t) - alpha_g_i_1) + 0x80;
    /* $\alpha g_i$ */
    alpha_g_i = alpha_g_i_1 + ((tmp + (tmp >> 8)) >> 8);

    tmp = (0xff - backdrop_alpha) * (0xff - alpha_g_i) + 0x80;
    /* $\alpha_i$ */
    alpha_i = 0xff - ((tmp + (tmp >> 8)) >> 8);

    if (alpha_i > 0) {
	int scale_dst;
	int scale_t;
	byte dst_alpha;

	/* $f s_i / \alpha_i$ scaled by 2^16 */
	scale_t = ((src_shape << 17) + alpha_i) / (2 * alpha_i);

	/* $\alpha_{i - 1}$ */
	dst_alpha = dst[n_chan];

	tmp = (1 - src_shape) * dst_alpha;
	tmp = (tmp << 9) + (tmp << 1) + (tmp >> 7) + alpha_i;
	scale_dst = tmp / (2 * alpha_i);

	for (i = 0; i < n_chan; i++) {
	    tmp = dst[i] * scale_dst + ct[i] * scale_t + 0x8000;
	    /* todo: clamp? */
	    dst[i] = tmp >> 16;
	}
    }
    dst[n_chan] = alpha_i;
    *dst_alpha_g = alpha_g_i;
}